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  • Dispersion from C α or N H : 4D experiments for backbone resonance assignment of intrinsically disordered proteins
    J. Biomol. NMR (IF 2.319) Pub Date : 2020-01-13
    Helena Tossavainen, Santeri Salovaara, Maarit Hellman, Riikka Ihalin, Perttu Permi

    Resonance assignment of intrinsically disordered proteins is remarkably challenging due to scant chemical shift dispersion arising from conformational heterogeneity. The challenge is even greater if repeating segments are present in the amino acid sequence. To forward unambiguous resonance assignment of intrinsically disordered proteins, we present iHACANCO, HACACON and (HACA)CONCAHA, three Hα-detected 4D experiments with Cα as an additional dimension. In addition, we present (HACA)CON(CA)NH and (HACA)N(CA)CONH, new 4D Hα-start, HN-detect experiments which have two NH dimensions to enhance peak dispersion in a sequential walk through C′, NH and HN, and provide more accurate NH/HN chemical shifts than those that can be obtained from a crowded 1H, 15N-HSQC spectrum. Application of these 4D experiments is demonstrated using BilRI (165 aa), an outer-membrane intrinsically disordered protein from the opportunistic oral pathogen Aggregatibacter actinomycetemcomitans. BilRI amino acid sequence encompasses three very similar repeats with a 13-residue identical stretch in two of them.

    更新日期:2020-01-13
  • Two-dimensional NMR lineshape analysis of single, multiple, zero and double quantum correlation experiments
    J. Biomol. NMR (IF 2.319) Pub Date : 2020-01-08
    Christopher A. Waudby, Margaux Ouvry, Ben Davis, John Christodoulou

    NMR spectroscopy provides a powerful approach for the characterisation of chemical exchange and molecular interactions by analysis of series of experiments acquired over the course of a titration measurement. The appearance of NMR resonances undergoing chemical exchange depends on the frequency difference relative to the rate of exchange, and in the case of one-dimensional experiments chemical exchange regimes are well established and well known. However, two-dimensional experiments present additional complexity, as at least one additional frequency difference must be considered. Here we provide a systematic classification of chemical exchange regimes in two-dimensional NMR spectra. We highlight important differences between exchange in HSQC and HMQC experiments, that on a practical level result in more severe exchange broadening in HMQC spectra, but show that complementary alternatives to the HMQC are available in the form of HZQC and HDQC experiments. We present the longitudinal relaxation optimised SOFAST-H(Z/D)QC experiment for the simultaneous acquisition of sensitivity-enhanced HZQC and HDQC spectra, and the longitudinal and transverse relaxation optimised BEST-ZQ-TROSY for analysis of large molecular weight systems. We describe the application of these experiments to the characterisation of the interaction between the Hsp90 N-terminal domain and a small molecule ligand, and show that the independent analysis of HSQC, HMQC, HZQC and HDQC experiments provides improved confidence in the fitted dissociation constant and dissociation rate. Joint analysis of such data may provide improved sensitivity to detect and analyse more complex multi-state interaction mechanisms such as induced fit or conformational selection.

    更新日期:2020-01-08
  • Spectral editing of intra- and inter-chain methyl–methyl NOEs in protein complexes
    J. Biomol. NMR (IF 2.319) Pub Date : 2020-01-02
    Ricarda Törner, Rida Awad, Pierre Gans, Bernhard Brutscher, Jerome Boisbouvier

    Specific isotopic labeling of methyl groups in a perdeuterated protein background enables the detection of long range NOEs in proteins or high molecular weight complexes. We introduce here an approach, combining an optimized isotopic labeling scheme with a specifically tailored NMR pulse sequence, to distinguish between intramolecular and intermolecular NOE connectivities. In hetero-oligomeric complexes, this strategy enables sign encoding of intra-subunit and inter-subunit NOEs. For homo-oligomeric assemblies, our strategy allows the specific detection of intra-chain NOEs in high resolution 3D NOESY spectra. The general principles, possibilities and limitations of this approach are presented. Applications of this approach for the detection of intermolecular NOEs in a hetero-hexamer, and the assignment of methyl 1H and 13C resonances in a homo-tetrameric protein complex are shown.

    更新日期:2020-01-02
  • Simultaneous recording of intra- and inter-residue linking experiments for backbone assignments in proteins at MAS frequencies higher than 60 kHz
    J. Biomol. NMR (IF 2.319) Pub Date : 2020-01-01
    Kshama Sharma, P. K. Madhu, Vipin Agarwal, Kaustubh R. Mote

    Obtaining site-specific assignments for the NMR spectra of proteins in the solid state is a significant bottleneck in deciphering their biophysics. This is primarily due to the time-intensive nature of the experiments. Additionally, the low resolution in the \(^{1}{\text {H}}\)-dimension requires multiple complementary experiments to be recorded to lift degeneracies in assignments. We present here an approach, gleaned from the techniques used in multiple-acquisition experiments, which allows the recording of forward and backward residue-linking experiments in a single experimental block. Spectra from six additional pathways are also recovered from the same experimental block, without increasing the probe duty cycle. These experiments give intra- and inter residue connectivities for the backbone \(^{13}{\text {C}}_\alpha\), \(^{15}{\text {N}}\), \(^{1}{\text {H}}_{\text {N}}\) and \(^{1}{\text {H}}_\alpha\) resonances and should alone be sufficient to assign these nuclei in proteins at MAS frequencies > 60 kHz. The validity of this approach is tested with experiments on a standard tripeptide N-formyl methionyl-leucine-phenylalanine (f-MLF) at a MAS frequency of 62.5 kHz, which is also used as a test-case for determining the sensitivity of each of the experiments. We expect this approach to have an immediate impact on the way assignments are obtained at MAS frequencies \(> 60\text { kHz}\).

    更新日期:2020-01-01
  • Enhancing NMR derived ensembles with kinetics on multiple timescales
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-12-14
    Colin A. Smith, Adam Mazur, Ashok K. Rout, Stefan Becker, Donghan Lee, Bert L. de Groot, Christian Griesinger

    Nuclear magnetic resonance (NMR) has the unique advantage of elucidating the structure and dynamics of biomolecules in solution at physiological temperatures, where they are in constant movement on timescales from picoseconds to milliseconds. Such motions have been shown to be critical for enzyme catalysis, allosteric regulation, and molecular recognition. With NMR being particularly sensitive to these timescales, detailed information about the kinetics can be acquired. However, nearly all methods of NMR-based biomolecular structure determination neglect kinetics, which introduces a large approximation to the underlying physics, limiting both structural resolution and the ability to accurately determine molecular flexibility. Here we present the Kinetic Ensemble approach that uses a hierarchy of interconversion rates between a set of ensemble members to rigorously calculate Nuclear Overhauser Effect (NOE) intensities. It can be used to simultaneously refine both temporal and structural coordinates. By generalizing ideas from the extended model free approach, the method can analyze the amplitudes and kinetics of motions anywhere along the backbone or side chains. Furthermore, analysis of a large set of crystal structures suggests that NOE data contains a surprising amount of high-resolution information that is better modeled using our approach. The Kinetic Ensemble approach provides the means to unify numerous types of experiments under a single quantitative framework and more fully characterize and exploit kinetically distinct protein states. While we apply the approach here to the protein ubiquitin and cross validate it with previously derived datasets, the approach can be applied to any protein for which NOE data is available.

    更新日期:2019-12-17
  • Non-uniform sampling in quantitative assessment of heterogeneous solid-state NMR line shapes
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-12-13
    Ekaterina Burakova, Suresh K. Vasa, Alexander Klein, Rasmus Linser

    Non-uniform sampling has been successfully used for solution and solid-state NMR of homogeneous samples. In the solid state, protein samples are often dominated by inhomogeneous contributions to the homogeneous line widths. In spite of different technical strategies for peak reconstruction by different methods, we validate that NUS can generally be used also for such situations where spectra are made up of complex peak shapes rather than Lorentian lines. Using the RMSD between subsampled and reconstructed data and those spectra obtained with uniform sampling for a sample comprising a wide conformational distribution, we quantitatively evaluate the identity of inhomogeneous peak patterns. The evaluation comprises Iterative Soft Thresholding (hmsIST implementation) as a method explicitly not assuming Lorentian lineshapes, as well as Sparse Multidimensional Iterative Lineshape Enhanced (SMILE) algorithm and Signal Separation Algorithm (SSA) reconstruction, which do work on the basis of Lorentian lineshape models, with different sampling densities. Even though individual peculiarities are apparent, all methods turn out principally viable to reconstruct the heterogeneously broadened peak shapes.

    更新日期:2019-12-13
  • 2-Fluorotyrosine is a valuable but understudied amino acid for protein-observed 19 F NMR
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-11-23
    Peter D. Ycas, Nicole Wagner, Noelle M. Olsen, Riqiang Fu, William C. K. Pomerantz

    Incorporation of 19F into proteins allows for the study of their molecular interactions via NMR. The study of 19F labeled aromatic amino acids has largely focused on 4-,5-, or 6-fluorotryptophan, 4-fluorophenylalanine, (4,5, or 6FW) or 3-fluorotyrosine (3FY), whereas 2-fluorotyrosine (2FY) has remained largely understudied. Here we report a comparative analysis with different fluorinated amino acids. We first report the NMR chemical shift responsiveness of five aromatic amino acid mimics to changes in solvent polarity and find that the most responsive, a mimic of 3FY, has a 2.9-fold greater change in chemical shift compared to the other amino acid mimics in aprotic solvents including the 2FY mimic. We also probed the utility of 2FY for 19F NMR by measuring its NMR relaxation properties in solution and the chemical shift anisotropy (CSA) of a polycrystalline sample of the amino acid by magic angle spinning. Using protein-observed fluorine NMR (PrOF NMR), we compared the influence of 2FY and 3FY incorporation on stability and pKa perturbation when incorporated into the KIX domain of CBP/p300. Lastly, we investigated the 19F NMR response of both 2FY and 3FY-labeled proteins to a protein–protein interaction partner, MLL, and discovered that 2FY can report on allosteric interactions that are not observed with 3FY-labeling in this protein complex. The reduced perturbation to pKa and similar but reduced CSA of 2FY to 3FY supports 2FY as a suitable alternative amino acid for incorporation into large proteins for 19F NMR analysis.

    更新日期:2019-11-26
  • Backbone and methyl assignment of bacteriorhodopsin incorporated into nanodiscs
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-11-21
    Laurens Kooijman, Philipp Ansorge, Matthias Schuster, Christian Baumann, Frank Löhr, Simon Jurt, Peter Güntert, Oliver Zerbe

    Resonance assignments are challenging for membrane proteins due to the size of the lipid/detergent-protein complex and the presence of line-broadening from conformational exchange. As a consequence, many correlations are missing in the triple-resonance NMR experiments typically used for assignments. Herein, we present an approach in which correlations from these solution-state NMR experiments are supplemented by data from 13C unlabeling, single-amino acid type labeling, 4D NOESY data and proximity of moieties to lipids or water in combination with a structure of the protein. These additional data are used to edit the expected peaklists for the automated assignment protocol FLYA, a module of the program package CYANA. We demonstrate application of the protocol to the 262-residue proton pump from archaeal bacteriorhodopsin (bR) in lipid nanodiscs. The lipid-protein assembly is characterized by an overall correlation time of 44 ns. The protocol yielded assignments for 62% of all backbone (H, N, Cα, Cβ, C′) resonances of bR, corresponding to 74% of all observed backbone spin systems, and 60% of the Ala, Met, Ile (δ1), Leu and Val methyl groups, thus enabling to assign a large fraction of the protein without mutagenesis data. Most missing resonances stem from the extracellular half, likely due intermediate exchange line-broadening. Further analysis revealed that missing information of the amino acid type of the preceding residue is the largest problem, and that 4D NOESY experiments are particularly helpful to compensate for that information loss.

    更新日期:2019-11-21
  • XIPP: multi-dimensional NMR analysis software
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-11-20
    Daniel S. Garrett, Mengli Cai, G. Marius Clore

    Here we present the XIPP (eXtensible Interactive Peak Picker) NMR software for analyzing multidimensional NMR data of proteins, DNA, RNA and protein-nucleic acid complexes. XIPP organizes experiments into pre-defined studies and replaces our original PIPP software suite which is no longer supported. Default study types exist for backbone assignment, sidechain assignment, NOE assignment and several relaxation series experiments, used in solution NMR studies. XIPP is written in Java and Jython. The default study types are defined in Jython which can be modified and extended to create new types of studies.

    更新日期:2019-11-21
  • Using Deep Neural Networks to Reconstruct Non-uniformly Sampled NMR Spectra
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-10
    D. Flemming Hansen

    Non-uniform and sparse sampling of multi-dimensional NMR spectra has over the last decade become an important tool to allow for fast acquisition of multi-dimensional NMR spectra with high resolution. The success of non-uniform sampling NMR hinge on both the development of algorithms to accurately reconstruct the sparsely sampled spectra and the design of sampling schedules that maximise the information contained in the sampled data. Traditionally, the reconstruction tools and algorithms have aimed at reconstructing the full spectrum and thus ‘fill out the missing points’ in the time-domain spectrum, although other techniques are based on multi-dimensional decomposition and extraction of multi-dimensional shapes. Also over the last decade, machine learning, deep neural networks, and artificial intelligence have seen new applications in an enormous range of sciences, including analysis of MRI spectra. As a proof-of-principle, it is shown here that simple deep neural networks can be trained to reconstruct sparsely sampled NMR spectra. For the reconstruction of two-dimensional NMR spectra, reconstruction using a deep neural network performs as well, if not better than, the currently and widely used techniques. It is therefore anticipated that deep neural networks provide a very valuable tool for the reconstruction of sparsely sampled NMR spectra in the future to come.

    更新日期:2019-11-17
  • Investigation of the internal structure and dynamics of cellulose by 13 C-NMR relaxometry and 2DPASS-MAS-NMR measurements
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-14
    Manasi Ghosh, Naveen Kango, Krishna Kishor Dey

    Internal structure and dynamics of commercial and natural cellulose were studied by measuring chemical shift anisotropy (CSA) parameters, and spin–lattice relaxation rate (1/T1) at each and every chemically different carbon nuclear site. CSA parameters were measured by 13C two-dimensional phase adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) NMR experiment. Site specific spin–lattice relaxation time was measured by Torchia-CP method. Anisotropy parameters of C4 and C6 regions are higher than C1 and C235 regions and asymmetry of C4 line is lower than any other carbon site. The higher values of CSA parameters of C4 and C6 nuclei arise due to the rotation of O4–C4, C1–O4, O5–C5–C6–O6 and C4–C5–C6–O6 bonds at torsion angles ψ, Φ, χ and χ′ respectively and the influence of interchain and intrachain hydrogen bondings. Two distinct peaks are also observed for C4 and C6 resonance line position—one peak arises primarily due to the nuclei in amorphous region and another one arises due to the same nuclei resides in paracrystalline region. The spin–lattice relaxation time and the CSA parameters are different at these two distinct peak positions of C4 and C6 line. Molecular correlation time of each and every chemically different carbon site was calculated with the help of CSA parameters and spin–lattice relaxation time. The molecular correlation time of the amorphous region is one order of magnitude less than the crystalline region. The distinction between amorphous and paracrystalline regions of cellulose is more vividly portrayed by determining spin–lattice relaxation time, CSA parameters, and molecular correlation time at each and every chemically different carbon site. This type of study correlating the structure and dynamics of cellulose will illuminate the path of inventing biomimetic materials.

    更新日期:2019-11-17
  • Accelerating 2D NMR relaxation dispersion experiments using iterated maps
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-06
    Jared Rovny, Robert L. Blum, J. Patrick Loria, Sean E. Barrett

    NMR relaxation dispersion experiments play a central role in exploring molecular motion over an important range of timescales, and are an example of a broader class of multidimensional NMR experiments that probe important biomolecules. However, resolving the spectral features of these experiments using the Fourier transform requires sampling the full Nyquist grid of data, making these experiments very costly in time. Practitioners often reduce the experiment time by omitting 1D experiments in the indirectly observed dimensions, and reconstructing the spectra using one of a variety of post-processing algorithms. In prior work, we described a fast, Fourier-based reconstruction method using iterated maps according to the Difference Map algorithm of Veit Elser (DiffMap). Here we describe coDiffMap, a new reconstruction method that is based on DiffMap, but which exploits the strong correlations between 2D data slices in a pseudo-3D experiment. We apply coDiffMap to reconstruct dispersion curves from an \(R_2\) relaxation dispersion experiment, and demonstrate that the method provides fast reconstructions and accurate relaxation curves down to very low numbers of sparsely-sampled data points.

    更新日期:2019-11-17
  • Random coil shifts of posttranslationally modified amino acids
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-17
    Anne C. Conibear, K. Johan Rosengren, Christian F. W. Becker, Hanspeter Kaehlig

    Most eukaryotic proteins are modified during and/or after translation, regulating their structure, function and localisation. The role of posttranslational modifications (PTMs) in both normal cellular processes and in diseases is already well recognised and methods for detection of PTMs and generation of specifically modified proteins have developed rapidly over the last decade. However, structural consequences of PTMs and their specific effects on protein dynamics and function are not well understood. Furthermore, while random coil NMR chemical shifts of the 20 standard amino acids are available and widely used for residue assignment, dihedral angle predictions and identification of structural elements or propensity, they are not available for most posttranslationally modified amino acids. Here, we synthesised a set of random coil peptides containing common naturally occurring PTMs and determined their random coil NMR chemical shifts under standardised conditions. We highlight unique NMR signatures of posttranslationally modified residues and their effects on neighbouring residues. This comprehensive dataset complements established random coil shift datasets of the 20 standard amino acids and will facilitate identification and assignment of posttranslationally modified residues. The random coil shifts will also aid in determination of secondary structure elements and prediction of structural parameters of proteins and peptides containing PTMs.

    更新日期:2019-11-17
  • Feasibility of trifluoromethyl TROSY NMR at high magnetic fields
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-02
    Brittney A. Klein, Brian D. Sykes

    Insights into the structure and dynamics of large biological systems has been greatly improved by two concurrent NMR approaches: the application of transverse relaxation-optimized spectroscopy (TROSY) techniques in multi-dimensional NMR, especially the methyl-TROSY, and the resurgence of 19F NMR using trifluoromethyl (CF3) probes. Herein we investigate the feasibility of combining these approaches into a trifluoromethyl-TROSY experiment. Using a CF3-labelled parvalbumin, we have evaluated the natural abundance 13C-19F correlation spectra and find no indication of a CF3 TROSY at high magnetic fields.

    更新日期:2019-11-17
  • Improving the quality of oriented membrane protein spectra using heat-compensated separated local field experiments
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-28
    Songlin Wang, T. Gopinath, Gianluigi Veglia

    Oriented sample solid-state NMR (OS-ssNMR) spectroscopy is a powerful technique to determine the topology of membrane proteins in oriented lipid bilayers. Separated local field (SLF) experiments are central to this technique as they provide first-order orientational restraints, i.e., dipolar couplings and anisotropic chemical shifts. Despite the use of low-E (or E-free) probes, the heat generated during the execution of 2D and 3D SLF pulse sequences causes sizeable line-shape distortions. Here, we propose a new heat-compensated SE-SAMPI4 (hcSE-SAMPI4) pulse sequence that holds the temperature constant for the duration of the experiment. This modification of the SE-SAMPI4 results in sharper and more intense resonances without line-shape distortions. The spectral improvements are even more apparent when paramagnetic relaxation agents are used to speed up data collection. We tested the hcSE-SAMPI4 pulse sequence on a single-span membrane protein, sarcolipin (SLN), reconstituted in magnetically aligned lipid bicelles. In addition to eliminating peak distortions, the hcSE-SAMPI4 experiment increased the average signal-to-noise ratio by 20% with respect to the original SE-SAMPI4.

    更新日期:2019-11-17
  • CombLabel: rational design of optimized sequence-specific combinatorial labeling schemes. Application to backbone assignment of membrane proteins with low stability
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-08
    M. Yu. Myshkin, M. A. Dubinnyi, D. S. Kulbatskii, E. N. Lyukmanova, M. P. Kirpichnikov, Z. O. Shenkarev

    Assignment of backbone resonances is a necessary initial step in every protein NMR investigation. Standard assignment procedure is based on the set of 3D triple-resonance (1H–13C–15N) spectra and requires at least several days of experimental measurements. This limits its application to the proteins with low stability. To speed up the assignment procedure, combinatorial selective labeling (CSL) can be used. In this case, sequence-specific information is extracted from 2D spectra measured for several selectively 13C,15N-labeled samples, produced in accordance with a special CSL scheme. Here we review previous applications of the CSL approach and present novel deterministic ‘CombLabel’ algorithm, which generates CSL schemes minimizing the number of labeled samples and their price and maximizing assignment information that can be obtained for a given protein sequence. Theoretical calculations revealed that CombLabel software outperformed previously proposed stochastic algorithms. Current implementation of CombLabel robustly calculates CSL schemes containing up to six samples, which is sufficient for moderately sized (up to 200 residues) proteins. As a proof of concept, we calculated CSL scheme for the first voltage-sensing domain of human Nav1.4 channel, a 134 residue four helical transmembrane protein having extremely low stability in micellar solution (half-life ~ 24 h at 45 °C). Application of CSL doubled the extent of backbone resonance assignment, initially obtained by conventional approach. The obtained assignment coverage (~ 50%) is sufficient for ligand screening and mapping of binding interfaces.

    更新日期:2019-11-17
  • Assigning NMR spectra of RNA, peptides and small organic molecules using molecular network visualization software
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-19
    Jan Marchant, Michael F. Summers, Bruce A. Johnson

    NMR assignment typically involves analysis of peaks across multiple NMR spectra. Chemical shifts of peaks are measured before being assigned to atoms using a variety of methods. These approaches quickly become complicated by overlap, ambiguity, and the complexity of correlating assignments among multiple spectra. Here we propose an alternative approach in which a network of linked peak-boxes is generated at the predicted positions of peaks across all spectra. These peak-boxes correlate known relationships and can be matched to the observed spectra. The method is illustrated with RNA, but a variety of molecular types should be readily tractable with this approach.

    更新日期:2019-11-17
  • Reaching the sparse-sampling limit for reconstructing a single peak in a 2D NMR spectrum using iterated maps
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-07-10
    Robert L. Blum, Jared Rovny, J. Patrick Loria, Sean E. Barrett

    Many of the ubiquitous experiments of biomolecular NMR, including \(R_2\), \(R_{1\rho }\), and CEST, involve acquiring repeated 2D spectra under slightly different conditions. Such experiments are amenable to acceleration using non-uniform sampling spectral reconstruction methods that take advantage of prior information. We previously developed one such technique, an iterated maps method (DiffMap) that we successfully applied to 2D NMR spectra, including \(R_2\) relaxation dispersion data. In that prior work, we took a top-down approach to reconstructing the 2D spectrum with a minimal number of sparse samples, reaching an undersampling fraction that appeared to leave some room for improvement. In this study, we develop an in-depth understanding of the action of the DiffMap algorithm, identifying the factors that cause reconstruction errors for different undersampling fractions. This improved understanding allows us to formulate a bottom-up approach to finding the lowest number of sparse samples required to accurately reconstruct individual spectral features with DiffMap. We also discuss the difficulty of extending this method to reconstructing many peaks at once, and suggest a way forward.

    更新日期:2019-11-17
  • Intra-residue methyl–methyl correlations for valine and leucine residues in large proteins from a 3D-HMBC-HMQC experiment
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-11-12
    Lucas Siemons, Harold W. Mackenzie, Vaibhav Kumar Shukla, D. Flemming Hansen

    Methyl-TROSY based NMR experiments have over the last two decades become one of the most important means to characterise dynamics and functional mechanisms of large proteins and macromolecular machines in solution. The chemical shift assignment of methyl groups in large proteins is, however, still not trivial and it is typically performed using backbone-dependent experiments in a ‘divide and conquer’ approach, mutations, structure-based assignments or a combination of these. Structure-based assignment of methyl groups is an emerging strategy, which reduces the time and cost required as well as providing a method that is independent of a backbone assignment. One crucial step in available structure-based assignment protocols is linking the two prochiral methyl groups of leucine and valine residues. This has previously been achieved by recording NOESY spectra with short mixing times or by comparing NOESY spectra. Herein, we present a method based on through-bond scalar coupling transfers, a 3D-HMBC-HMQC experiment, to link the intra-residue methyl groups of leucine and valine. It is shown that the HMBC-HMQC method has several advantages over solely using NOESY spectra since a unique intra-residue cross-peak is observed. Moreover, overlap in the methyl-TROSY HMQC spectrum can easily be identified with the HMBC-HMQC experiment, thereby removing possible ambiguities in the assignment.

    更新日期:2019-11-13
  • A simple protocol for expression of isotope-labeled proteins in Escherichia coli grown in shaker flasks at high cell density
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-11-01
    Mengli Cai, Ying Huang, Robert Craigie, G. Marius Clore

    Protein expression in E. coli grown in shaker flasks is a routine and pivotal tool in many research laboratories. To maximize protein yields, cells are normally induced in the middle of the linear growth phase, typically at an OD600 of ≤ 1 for cells grown in Luria–Bertani (LB) medium at 37 °C. We recently showed that the E. coli linear growth phase can be extended to higher cell density when cells are cultured under less than optimal conditions such as in minimal medium and/or at lower temperatures. Maximizing the yield of protein per unit volume of culture is important for reducing the costs, especially when isotopically labeling is required. Here, we present a modified minimal medium and a simple protocol that can increase the protein yield up to fourfold in a pH-stabilized LB medium and up to sevenfold in a modified M9+ medium (M9++). When M9++ medium coupled with the high density (OD600 ~ 6) cell growth protocol are used to express uniformly 15N- or 15N/13C-labeled proteins, the amount of 15NH4Cl and 13C6-glucose for a given cell mass is reduced by 50% and ~ 65%, respectively, relative to the traditional low density (OD600 ~ 1) cell growth protocol with M9 medium; the inclusion of 0.1% LB in the minimal medium permits a reduction in the concentration of both the trace element solution and MgCl2, which can cause precipitation. Mass data indicate that inclusion of 0.1% LB does not significantly affect the isotope enrichment level.

    更新日期:2019-11-04
  • Investigation of backbone dynamics and local geometry of bio-molecules using calculated NMR chemical shifts and anisotropies
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-23
    Ulrich Sternberg, Raiker Witter

    Prerequisite for chemical shift (CS) and CS tensor calculations are highly refined structures defining the molecular surroundings of the nuclei under study. Here, we present geometry optimizations with 13C and 15N CS constraints for large bio-molecules like peptides and proteins. The method discussed here provides both, refined structures and chemical shift tensors. Furthermore, since the experimental resonances of aligned systems are related to CS tensors, they strongly depend on the orientation and motion of molecules, their fragments, functional groups and moieties. For efficient CS calculations we apply a semi-empirical approach—the bond polarization theory (BPT). The BPT relies on linear bond polarization parameters and we present a new set of parameters based on ab initio second-order Møller–Plesset perturbation theory calculations. The new parametrization extends the applicability of the BPT approach to a wide range of organic molecules and bio-polymers. Here, the method has been applied to the protein ubiquitin and the membrane-active peptide gramicidin A (dimer) in oriented bilayers. The calculated 13C and 15N CS values of best-refined structures published until now gave a large scatter with respect to the experiment. It will be shown that BPT CS optimizations can reduce these errors to values near the experimental uncertainty. In combination with molecular dynamics with orientational constraints it is possible to study motional dynamics and BPT calculations can provide residual chemical shift anisotropies.

    更新日期:2019-11-04
  • Revisiting 1 H N CPMG relaxation dispersion experiments: a simple modification can eliminate large artifacts
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-23
    Tairan Yuwen, Lewis E. Kay

    Carr–Purcell–Meiboom–Gill relaxation dispersion experiments are commonly used to probe biomolecular dynamics on the millisecond timescale. The simplest experiment involves using backbone 15N spins as probes of motion and pulse sequences are now available for providing accurate dispersion profiles in this case. In contrast, 1H-based experiments recorded on fully protonated samples are less common because of difficulties associated with homonuclear scalar couplings that can result in transfer of magnetization between coupled spins, leading to significant artifacts. Herein we examine a version of the 1HN CPMG experiment that has been used in our laboratory where a pair of CPMG pulse trains comprising non-selective, high power 1H refocusing pulses sandwich an amide selective pulse that serves to refocus scalar-coupled evolution by the end of the train. The origin of the artifacts in our original scheme is explained and a new, significantly improved sequence is presented. The utility of the new experiment is demonstrated by obtaining flat 1HN dispersion profiles in a protonated protein system that is not expected to undergo millisecond timescale dynamics, and subsequently by measuring profiles on a cavity mutant of T4 lysozyme that exchanges between a pair of distinct states, establishing that high quality data can be generated even for fully protonated samples.

    更新日期:2019-11-04
  • Perspective: the essential role of NMR in the discovery and characterization of intrinsically disordered proteins
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-15
    H. Jane Dyson, Peter E. Wright

    The 2019 ISMAR Prize recognized NMR studies of disordered proteins. Here we provide a highly personal perspective on the discovery of intrinsically disordered proteins and the development and application of NMR methods to characterize their conformational ensembles, dynamics, and interactions.

    更新日期:2019-11-04
  • Paramagnetic-iterative relaxation matrix approach: extracting PRE-restraints from NOESY spectra for 3D structure elucidation of biomolecules
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-12
    E. C. Cetiner, H. R. A. Jonker, C. Helmling, D. B. Gophane, C. Grünewald, S. Th. Sigurdsson, H. Schwalbe

    Paramagnetic relaxation enhancement (PRE) can be used to determine long-range distance restraints in biomolecules. The PREs are typically determined by analysis of intensity differences in HSQC experiments of paramagnetic and diamagnetic spin labels. However, this approach requires both isotope- and spin-labelling. Herein, we report a novel method to evaluate NOESY intensities in the presence of a paramagnetic moiety to determine PRE restraints. The advantage of our approach over HSQC-based approaches is the increased number of available signals without the need for isotope labelling. NOESY intensities affected by a paramagnetic center were evaluated during a structure calculation within the paramagnetic iterative relaxation matrix approach (P-IRMA). We applied P-IRMA to a 14-mer RNA with a known NMR solution structure, which allowed us to assess the quality of the PRE restraints. To this end, three different spin labels have been attached at different positions of the 14-mer to test the influence of flexibility on the structure calculation. Structural disturbances introduced by the spin label have been evaluated by chemical shift analysis. Furthermore, the impact of P-IRMA on the quality of the structure bundles were tested by intentionally leaving out available diamagnetic restraints. Our analyses show that P-IRMA is a powerful tool to refine RNA structures for systems that are insufficiently described by using only diamagnetic restraints.

    更新日期:2019-11-04
  • Random coil chemical shifts for serine, threonine and tyrosine phosphorylation over a broad pH range
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-09
    Ruth Hendus-Altenburger, Catarina B. Fernandes, Katrine Bugge, Micha B. A. Kunze, Wouter Boomsma, Birthe B. Kragelund

    Phosphorylation is one of the main regulators of cellular signaling typically occurring in flexible parts of folded proteins and in intrinsically disordered regions. It can have distinct effects on the chemical environment as well as on the structural properties near the modification site. Secondary chemical shift analysis is the main NMR method for detection of transiently formed secondary structure in intrinsically disordered proteins (IDPs) and the reliability of the analysis depends on an appropriate choice of random coil model. Random coil chemical shifts and sequence correction factors were previously determined for an Ac-QQXQQ-NH2-peptide series with X being any of the 20 common amino acids. However, a matching dataset on the phosphorylated states has so far only been incompletely determined or determined only at a single pH value. Here we extend the database by the addition of the random coil chemical shifts of the phosphorylated states of serine, threonine and tyrosine measured over a range of pH values covering the pKas of the phosphates and at several temperatures (www.bio.ku.dk/sbinlab/randomcoil). The combined results allow for accurate random coil chemical shift determination of phosphorylated regions at any pH and temperature, minimizing systematic biases of the secondary chemical shifts. Comparison of chemical shifts using random coil sets with and without inclusion of the phosphoryl group, revealed under/over estimations of helicity of up to 33%. The expanded set of random coil values will improve the reliability in detection and quantification of transient secondary structure in phosphorylation-modified IDPs.

    更新日期:2019-11-04
  • NMR-based fragment screening and lead discovery accelerated by principal component analysis
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-09-20
    Andrew T. Namanja, Jia Xu, Haihong Wu, Qi Sun, Anup K. Upadhyay, Chaohong Sun, Steven R. Van Doren, Andrew M. Petros

    Protein-based NMR spectroscopy has proven to be a very robust method for finding fragment leads to protein targets. However, one limitation of protein-based NMR is that the data acquisition and analysis can be time consuming. In order to streamline the scoring of protein-based NMR fragment screening data and the determination of ligand affinities using 2D NMR experiments we have developed a data analysis workflow based on principal component analysis (PCA) within the TREND NMR Pro software package. We illustrate this using four different proteins and sets of ligands which interact with these proteins over a range of affinities. Also, these PCA-based methods can be successfully applied even to systems where ligand binding to target proteins is in intermediate or even slow exchange on the NMR time scale. Finally, these methods will work for scoring of fragment binding data using protein spectra that are either highly overlapped or lower in resolution.

    更新日期:2019-11-04
  • Improved strategy for isoleucine 1 H/ 13 C methyl labeling in Pichia pastoris
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-09-20
    Rustam Ali, Lindsay D. Clark, Jacob A. Zahm, Andrew Lemoff, Karthik Ramesh, Daniel M. Rosenbaum, Michael K. Rosen

    Site specific methyl labeling combined with methyl TROSY offers a powerful NMR approach to study structure and dynamics of proteins and protein complexes of high molecular weight. Robust and cost-effective methods have been developed for site specific protein 1H/13C methyl labeling in an otherwise deuterated background in bacteria. However, bacterial systems are not suitable for expression and isotope labeling of many eukaryotic and membrane proteins. The yeast Pichia pastoris (P. pastoris) is a commonly used host for expression of eukaryotic proteins, and site-specific methyl labeling of perdeuterated eukaryotic proteins has recently been achieved with this system. However, the practical utility of methyl labeling and deuteration in P. pastoris is limited by high costs. Here, we describe an improved method for 1H/13C-labeling of the δ-methyl group of isoleucine residues in a perdeuterated background, which reduces the cost by ≥ 50% without compromising the efficiency of isotope enrichment. We have successfully implemented this method to label actin and a G-protein coupled receptor. Our approach will facilitate studies of the structure and dynamics of eukaryotic proteins by NMR spectroscopy.

    更新日期:2019-11-04
  • Fast MAS 1 H– 13 C correlation NMR for structural investigations of plant cell walls
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-09-18
    Pyae Phyo, Mei Hong

    Plant cell walls consist of a mixture of polysaccharides that render the cell wall a strong and dynamic material. Understanding the molecular structure and dynamics of wall polysaccharides is important for understanding and improving the properties of this energy-rich biomaterial. So far, solid-state NMR studies of cell wall structure and dynamics have solely relied on 13C chemical shifts measured from 2D and 3D correlation experiments. To increase the spectral resolution, sensitivity and upper limit of measurable distances, it is of interest to explore 1H chemical shifts and 1H-detected NMR experiments for analyzing cell walls. Here we demonstrate 2D and 3D 1H–13C correlation experiments at both moderate and fast MAS frequencies of 10–50 kHz to resolve and assign 1H chemical shifts of matrix polysaccharides in Arabidopsis primary cell walls. Both 13C-detected and 1H-detected experiments are implemented and are shown to provide useful and complementary information. Using the assigned 1H chemical shifts, we measured long-range correlations between matrix polysaccharides and cellulose using 1H–1H instead of 13C–13C spin diffusion, and the 2D experiments can be conducted with either 13C or 1H detection.

    更新日期:2019-11-04
  • MAS dependent sensitivity of different isotopomers in selectively methyl protonated protein samples in solid state NMR
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-09-12
    Kai Xue, Riddhiman Sarkar, Zdenek Tosner, Daniela Lalli, Carina Motz, Benita Koch, Guido Pintacuda, Bernd Reif

    Sensitivity and resolution together determine the quality of NMR spectra in biological solids. For high-resolution structure determination with solid-state NMR, proton-detection emerged as an attractive strategy in the last few years. Recent progress in probe technology has extended the range of available MAS frequencies up to above 100 kHz, enabling the detection of resolved resonances from sidechain protons, which are important reporters of structure. Here we characterise the interplay between MAS frequency in the newly available range of 70–110 kHz and proton content on the spectral quality obtainable on a 1 GHz spectrometer for methyl resonances. Variable degrees of proton densities are tested on microcrystalline samples of the α-spectrin SH3 domain with selectively protonated methyl isotopomers (CH3, CH2D, CHD2) in a perdeuterated matrix. The experimental results are supported by simulations that allow the prediction of the sensitivity outside this experimental frequency window. Our results facilitate the selection of the appropriate labelling scheme at a given MAS rotation frequency.

    更新日期:2019-11-04
  • Site-selective 1 H/ 2 H labeling enables artifact-free 1 H CPMG relaxation dispersion experiments in aromatic side chains
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-09-10
    Heiner N. Raum, Julia Schörghuber, Matthias Dreydoppel, Roman J. Lichtenecker, Ulrich Weininger

    Aromatic side chains are often key residues in enzyme active sites and protein binding sites, making them attractive probes of protein dynamics on the millisecond timescale. Such dynamic processes can be studied by aromatic 13C or 1H CPMG relaxation dispersion experiments. Aromatic 1H CPMG relaxation dispersion experiments in phenylalanine, tyrosine and the six-ring moiety of tryptophan, however, are affected by 3J 1H–1H couplings which are causing anomalous relaxation dispersion profiles. Here we show that this problem can be addressed by site-selective 1H/2H labeling of the aromatic side chains and that artifact-free relaxation dispersion profiles can be acquired. The method has been further validated by measuring folding–unfolding kinetics of the small protein GB1. The determined rate constants and populations agree well with previous results from 13C CPMG relaxation dispersion experiments. Furthermore, the CPMG-derived chemical shift differences between the folded and unfolded states are in excellent agreement with those obtained directly from the spectra. In summary, site-selective 1H/2H labeling enables artifact-free aromatic 1H CPMG relaxation dispersion experiments in phenylalanine and the six-ring moiety of tryptophan, thereby extending the available methods for studying millisecond dynamics in aromatic protein side chains.

    更新日期:2019-11-04
  • Tuning a timing device that regulates lateral root development in rice
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Lucila Andrea Acevedo, Nathan E. Korson, Justin M. Williams, Linda K. Nicholson

    Peptidyl Prolyl Isomerases (PPIases) accelerate cis–trans isomerization of prolyl peptide bonds. In rice, the PPIase LRT2 is essential for lateral root initiation. LRT2 displays in vitro isomerization of a highly conserved W–P peptide bond (104W–P105) in the natural substrate OsIAA11. OsIAA11 is a transcription repressor that, in response to the plant hormone auxin, is targeted to ubiquitin-mediated proteasomal degradation via specific recognition of the cis isomer of its 104W–P105 peptide bond. OsIAA11 controls transcription of specific genes, including its own, that are required for lateral root development. This auxin-responsive negative feedback circuit governs patterning and development of lateral roots along the primary root. The ability to tune LRT2 activity via mutagenesis is crucial for understanding and modeling the role of this bimodal switch in the auxin circuit and lateral root development. We present characterization of the thermal stability and isomerization rates of several LRT2 mutants acting on the OsIAA11 substrate. The thermally stable mutants display activities lower than that of wild-type (WT) LRT2. These include binding diminished but catalytically active P125K, binding incompetent W128A, and binding capable but catalytically incompetent H133Q mutations. Additionally, LRT2 homologs hCypA from human, TaCypA from Triticum aestivum (wheat) and PPIB from E. coli were shown to have 110, 50 and 60% of WT LRT2 activity on the OsIAA11 substrate. These studies identify several thermally stable LRT2 mutants with altered activities that will be useful for establishing relationships between cis–trans isomerization, auxin circuit dynamics, and lateral root development in rice.

    更新日期:2019-11-04
  • Artifacts can emerge in spectra recorded with even the simplest of pulse schemes: an HMQC case study
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-02-23
    Lewis E. Kay

    With the development of sophisticated pulsed field gradient- and phase cycling-approaches for suppressing certain coherence transfer pathways and selecting for others it is sometimes easy to forget that the process is not flawless. In some cases artifacts can emerge because unwanted transfers are immune to the phase cycle or the application of gradients. We consider here a simple 1H,13C HMQC pulse scheme and show that imperfections in the single 1H 180° refocusing pulse can give rise to small artifacts in methyl spectra that cannot be eliminated through extensive phase cycling or the use of gradients, but that are easily removed when the pulse is of the composite variety.

    更新日期:2019-11-04
  • Determination of methyl order parameters using solid state NMR under off magic angle spinning
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Kai Xue, Salvatore Mamone, Benita Koch, Riddhiman Sarkar, Bernd Reif

    Quantification of dipolar couplings in biological solids is important for the understanding of dynamic processes. Under Magic Angle Spinning (MAS), order parameters are normally obtained by recoupling of anisotropic interactions involving the application of radio frequency pulses. We have recently shown that amide backbone order parameters can be estimated accurately in a spin-echo experiment in case the rotor spinning angle is slightly mis-calibrated. In this work, we apply this method to determine methyl order parameters in a deuterated sample of the SH3 domain of chicken α-spectrin in which the methyl containing side chains valine and leucine are selectively protonated.

    更新日期:2019-11-04
  • Partial alignment, residual dipolar couplings and molecular symmetry in solution NMR
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Justin L. Lorieau

    Residual dipolar couplings (RDCs) and residual anisotropic chemical shifts (RACSs) are produced by the partial alignment of solution NMR samples. RDCs and RACSs yield high-resolution structural and dynamic information on the orientation of bonds and chemical groups in molecules. Many molecules form oligomers or have intrinsic symmetries, which may simplify the analysis of their partial alignment datasets. In this report, we explore the theory of partial alignment using an irreducible spherical representation, and we investigate the impact of molecular symmetry on the alignment of molecules. Though previous studies have reported simplified relationships on the partial alignment of molecules bearing different symmetry groups, we show that these simplified relationships may not be universal and only apply to a limited set of systems.

    更新日期:2019-11-04
  • Exchange saturation transfer and associated NMR techniques for studies of protein interactions involving high-molecular-weight systems
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Vitali Tugarinov, G. Marius Clore

    A brief overview of theoretical and experimental aspects of the Dark state Exchange Saturation Transfer (DEST) and lifetime line broadening (\(\Delta R_{2}^{{}}\)) NMR methodologies is presented from a physico-chemical perspective. We describe how the field-dependence of \(\Delta R_{2}^{{}}\) can be used for determining the exchange regime on the transverse spin relaxation time-scale. Some limitations of DEST/\(\Delta R_{2}^{{}}\) methodology in applications to molecular systems with intermediate molecular weights are discussed, and the means of overcoming these limitations via the use of closely related exchange NMR techniques is presented. Finally, several applications of DEST/\(\Delta R_{2}^{{}}\) methodology are described from a methodological viewpoint, with an emphasis on providing examples of how kinetic and relaxation parameters of exchange can be reliably extracted from the experimental data in each particular case.

    更新日期:2019-11-04
  • 19 F NMR relaxation studies of fluorosubstituted tryptophans
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-21
    Manman Lu, Rieko Ishima, Tatyana Polenova, Angela M. Gronenborn

    We present 19F longitudinal and transverse relaxation studies for four differently fluorosubstituted l-tryptophans, which carry single F atoms in the indole ring, both in the context of the free amino acid and when located in the cyclophilin A protein. For the free 4F-, 5F-, 6F-, 7F-l-Trp, satisfactory agreement between experimentally measured and calculated relaxation rates was obtained, suggesting that the parameters used for calculating the rates for the indole frame are sufficiently accurate. We also measured and calculated relaxation rates for four differently 19F-tryptophan labeled cyclophilin A proteins, transferring the parameters from the free amino acid to the protein-bound moiety. Our results suggest that 19F relaxation data of the large and rigid indole ring in Trp are only moderately affected by protein motions and provide critical reference points for evaluating fluorine NMR relaxation in the future, especially in fluorotryptophan labeled proteins.

    更新日期:2019-11-04
  • Importance of time-ordered non-uniform sampling of multi-dimensional NMR spectra of Aβ 1–42 peptide under aggregating conditions
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Jinfa Ying, C. Ashley Barnes, John M. Louis, Ad Bax

    Although the order of the time steps in which the non-uniform sampling (NUS) schedule is implemented when acquiring multi-dimensional NMR spectra is of limited importance when sample conditions remain unchanged over the course of the experiment, it is shown to have major impact when samples are unstable. In the latter case, time-ordering of the NUS data points by the normalized radial length yields a reduction of sampling artifacts, regardless of the spectral reconstruction algorithm. The disadvantage of time-ordered NUS sampling is that halting the experiment prior to its completion will result in lower spectral resolution, rather than a sparser data matrix. Alternatively, digitally correcting for sample decay prior to reconstruction of randomly ordered NUS data points can mitigate reconstruction artifacts, at the cost of somewhat lower sensitivity. Application of these sampling schemes to the Alzheimer’s amyloid beta (Aβ1–42) peptide at an elevated concentration, low temperature, and 3 kbar of pressure, where approximately 75% of the peptide reverts to an NMR-invisible state during the collection of a 3D 15N-separated NOESY spectrum, highlights the improvement in artifact suppression and reveals weak medium-range NOE contacts in several regions, including the C-terminal region of the peptide.

    更新日期:2019-11-04
  • Structural characterization of the human membrane protein VDAC2 in lipid bilayers by MAS NMR
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-12
    Matthew T. Eddy, Tsyr-Yan Yu, Gerhard Wagner, Robert G. Griffin

    The second isoform of the human voltage dependent anion channel (VDAC2) is a mitochondrial porin that translocates calcium and other metabolites across the outer mitochondrial membrane. VDAC2 has been implicated in cardioprotection and plays a critical role in a unique apoptotic pathway in tumor cells. Despite its medical importance, there have been few biophysical studies of VDAC2 in large part due to the difficulty of obtaining homogeneous preparations of the protein for spectroscopic characterization. Here we present high resolution magic angle spinning nuclear magnetic resonance (NMR) data obtained from homogeneous preparation of human VDAC2 in 2D crystalline lipid bilayers. The excellent resolution in the spectra permit several sequence-specific assignments of the signals for a large portion of the VDAC2 N-terminus and several other residues in two- and three-dimensional heteronuclear correlation experiments. The first 12 residues appear to be dynamic, are not visible in cross polarization experiments, and they are not sufficiently mobile on very fast timescales to be visible in 13C INEPT experiments. A comparison of the NMR spectra of VDAC2 and VDAC1 obtained from highly similar preparations demonstrates that the spectral quality, line shapes and peak dispersion exhibited by the two proteins are nearly identical. This suggests an overall similar dynamic behavior and conformational homogeneity, which is in contrast to two earlier reports that suggested an inherent conformational heterogeneity of VDAC2 in membranes. The current data suggest that the sample preparation and spectroscopic methods are likely applicable to studying other human membrane porins, including human VDAC3, which has not yet been structurally characterized.

    更新日期:2019-11-04
  • I-PINE web server: an integrative probabilistic NMR assignment system for proteins.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-06-06
    Woonghee Lee,Arash Bahrami,Hesam T Dashti,Hamid R Eghbalnia,Marco Tonelli,William M Westler,John L Markley

    Various methods for understanding the structural and dynamic properties of proteins rely on the analysis of their NMR chemical shifts. These methods require the initial assignment of NMR signals to particular atoms in the sequence of the protein, a step that can be very time-consuming. The probabilistic interaction network of evidence (PINE) algorithm for automated assignment of backbone and side chain chemical shifts utilizes a Bayesian probabilistic network model that analyzes sequence data and peak lists from multiple NMR experiments. PINE, which is one of the most popular and reliable automated chemical shift assignment algorithms, has been available to the protein NMR community for longer than a decade. We announce here a new web server version of PINE, called Integrative PINE (I-PINE), which supports more types of NMR experiments than PINE (including three-dimensional nuclear Overhauser enhancement and four-dimensional J-coupling experiments) along with more comprehensive visualization of chemical shift based analysis of protein structure and dynamics. The I-PINE server is freely accessible at http://i-pine.nmrfam.wisc.edu . Help pages and tutorial including browser capability are available at: http://i-pine.nmrfam.wisc.edu/instruction.html . Sample data that can be used for testing the web server are available at: http://i-pine.nmrfam.wisc.edu/examples.html .

    更新日期:2019-11-01
  • Solution structure of the N-terminal domain of the Staphylococcus aureus hibernation promoting factor.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-06-06
    Konstantin S Usachev,Shamil Z Validov,Iskander Sh Khusainov,Alexander A Varfolomeev,Vladimir V Klochkov,Albert V Aganov,Marat M Yusupov

    Staphylococcus aureus hibernation promoting factor (SaHPF) is a 22,2 kDa protein which plays a crucial role in 100S Staphylococcus aureus ribosome formation during stress. SaHPF consists of N-terminal domain (NTD) that prevents proteins synthesis by binding to the 30S subunit at the P- and A-sites, connected through a flexible linker with a C-terminal domain (CTD) that keeps ribosomes in 100S form via homodimerization. Recently obtained 100S ribosome structure of S. aureus by cryo-EM shown that SaHPF-NTD bound to the ribosome active sites, however due to the absence of SaHPF-NTD structure it was modeled by homology with the E. coli hibernation factors HPF and YfiA. In present paper we have determined the solution structure of SaHPF-NTD by high-resolution NMR spectroscopy which allows us to increase structural knowledge about HPF structure from S. aureus.

    更新日期:2019-11-01
  • Accurate measurement of dipole/dipole transverse cross-correlated relaxation [Formula: see text] in methylenes and primary amines of uniformly [Formula: see text]-labeled proteins.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-16
    Dmitry M Lesovoy,Maxim A Dubinnyi,Svetlana B Nolde,Eduard V Bocharov,Alexander S Arseniev

    Side chains possess a broader conformational space (compared to the backbone) and are directly affected by intra- and intermolecular interactions, hence their dynamics and the corresponding NMR relaxation data are more sensitive and informative. Nevertheless, transverse relaxation in [Formula: see text] ([Formula: see text] or [Formula: see text]) spin systems is predominantly non-measurable in uniformly [Formula: see text]-labeled proteins due to cross-correlation effects. In the present publication, we propose a number of pulse sequences for accurate and precise measurement of the dipole-dipole transverse cross-correlated relaxation rate [Formula: see text], which, similarly to [Formula: see text] measurements, provides information about the amplitudes of intramolecular dynamics. The suggested approach has allowed us to circumvent a number of obstacles that were limiting earlier applications of [Formula: see text]: (1) impossibility of transmission of the central component of the triplet of [Formula: see text] group to [Formula: see text]-acquisition via INEPT has been solved by transmission of the averaged signal of "inner" and "outer" components of the triplet; (2) direct recording of the entire triplets resulting in substantial overlap of side chain signals has been replaced by recording of individual singlets with the use of [Formula: see text]-modulated approach and constant-time evolution; (3) low sensitivity has been enhanced via proton acquisition which required special attention to a zero-quantum coherence evolution. The proposed method expands the set of "dynamics sensors" covering protein side chains and substantially improves the quality and the level of detail of experimental data describing dynamic processes in proteins and protein complexes.

    更新日期:2019-11-01
  • NMRlib: user-friendly pulse sequence tools for Bruker NMR spectrometers.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-12
    Adrien Favier,Bernhard Brutscher

    We present NMRlib, a suite of jython-based tools designed for Bruker spectrometers (TopSpin versions 3.2-4.0) that allow easy setup, management, and exchange of NMR experiments. A NMR experiment can be set up and executed in a few clicks by navigating through the NMRlib GUI tree structure, without any further parameter adjustment. NMRlib is magnetic-field independent, and thus particularly helpful for laboratories operating multiple NMR spectrometers. NMRlib is easily personalized by adding, deleting, or reorganizing experiments. Additional tools are provided for data processing, visualization, and analysis. In particular, NMRlib contains all the polarization-enhanced fast-pulsing NMR experiments (SOFAST, BEST, HADAMAC,…) developed in our laboratory over the last decade. We also discuss some specific features that have been implemented to make these experiments most efficient and user friendly.

    更新日期:2019-11-01
  • Validation of protein backbone structures calculated from NMR angular restraints using Rosetta.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-12
    Joel Lapin,Alexander A Nevzorov

    Multidimensional solid-state NMR spectra of oriented membrane proteins can be used to infer the backbone torsion angles and hence the overall protein fold by measuring dipolar couplings and chemical shift anisotropies, which depend on the orientation of each peptide plane with respect to the external magnetic field. However, multiple peptide plane orientations can be consistent with a given set of angular restraints. This ambiguity is further exacerbated by experimental uncertainty in obtaining and interpreting such restraints. The previously developed algorithms for structure calculations using angular restraints typically involve a sequential walkthrough along the backbone to find the torsion angles between the consecutive peptide plane orientations that are consistent with the experimental data. This method is sensitive to experimental uncertainty in interpreting the peak positions of as low as ± 10 Hz, often yielding high structural RMSDs for the calculated structures. Here we present a significantly improved version of the algorithm which includes the fitting of several peptide planes at once in order to prevent propagation of error along the backbone. In addition, a protocol has been devised for filtering the structural solutions using Rosetta scoring functions in order to find the structures that both fit the spectrum and satisfy bioinformatics restraints. The robustness of the new algorithm has been tested using synthetic angular restraints generated from the known structures for two proteins: a soluble protein 2gb1 (56 residues), chosen for its diverse secondary structure elements, i.e. an alpha-helix and two beta-sheets, and a membrane protein 4a2n, from which the first two transmembrane helices (having a total of 64 residues) have been used. Extensive simulations have been performed by varying the number of fitted planes, experimental error, and the number of NMR dimensions. It has been found that simultaneously fitting two peptide planes always shifted the distribution of the calculated structures toward lower structural RMSD values as compared to fitting a single torsion-angle pair. For each protein, irrespective of the simulation parameters, Rosetta was able to distinguish the most plausible structures, often having structural RMSDs lower than 2 Å with respect to the original structure. This study establishes a framework for de-novo protein structure prediction using a combination of solid-state NMR angular restraints and bioinformatics.

    更新日期:2019-11-01
  • Detection of chemical exchange in methyl groups of macromolecules.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-14
    Michelle L Gill,Andrew Hsu,Arthur G Palmer

    The zero- and double-quantum methyl TROSY Hahn-echo and the methyl 1H-1H dipole-dipole cross-correlation nuclear magnetic resonance experiments enable estimation of multiple quantum chemical exchange broadening in methyl groups in proteins. The two relaxation rate constants are established to be linearly dependent using molecular dynamics simulations and empirical analysis of experimental data. This relationship allows chemical exchange broadening to be recognized as an increase in the Hahn-echo relaxation rate constant. The approach is illustrated by analyzing relaxation data collected at three temperatures for E. coli ribonuclease HI and by analyzing relaxation data collected for different cofactor and substrate complexes of E. coli AlkB.

    更新日期:2019-11-01
  • Erratum to: Pitfalls in compressed sensing reconstruction and how to avoid them.
    J. Biomol. NMR (IF 2.319) Pub Date : 2017-06-24
    Alexandra Shchukina,Paweł Kasprzak,Rupashree Dass,Michał Nowakowski,Krzysztof Kazimierczuk

    更新日期:2019-11-01
  • Erratum to: CcpNmr AnalysisAssign: a flexible platform for integrated NMR analysis.
    J. Biomol. NMR (IF 2.319) Pub Date : 2017-04-20
    Simon P Skinner,Rasmus H Fogh,Wayne Boucher,Timothy J Ragan,Luca G Mureddu,Geerten W Vuister

    更新日期:2019-11-01
  • Conformational flexibility of adenine riboswitch aptamer in apo and bound states using NMR and an X-ray free electron laser.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-10-14
    Jienv Ding,Monalisa Swain,Ping Yu,Jason R Stagno,Yun-Xing Wang

    Riboswitches are structured cis-regulators mainly found in the untranslated regions of messenger RNA. The aptamer domain of a riboswitch serves as a sensor for its ligand, the binding of which triggers conformational changes that regulate the behavior of its expression platform. As a model system for understanding riboswitch structures and functions, the add adenine riboswitch has been studied extensively. However, there is a need for further investigation of the conformational dynamics of the aptamer in light of the recent real-time crystallographic study at room temperature (RT) using an X-ray free electron laser (XFEL) and femtosecond X-ray crystallography (SFX). Herein, we investigate the conformational motions of the add adenine riboswitch aptamer domain, in the presence or absence of adenine, using nuclear magnetic resonance relaxation measurements and analysis of RT atomic displacement factors (B-factors). In the absence of ligand, the P1 duplex undergoes a fast exchange where the overall molecule exhibits a motion at kex ~ 319 s-1, based on imino signals. In the presence of ligand, the P1 duplex adopts a highly ordered conformation, with kex~ 83 s-1, similar to the global motion of the molecule, excluding the loops and binding pocket, at 84 s-1. The µs-ms motions in both the apo and bound states are consistent with RT B-factors. Reduced spatial atomic fluctuation, ~ 50%, in P1 upon ligand binding coincides with significantly attenuated temporal dynamic exchanges. The binding pocket is structured in the absence or presence of ligand, as evidenced by relatively low and similar RT B-factors. Therefore, despite the dramatic rearrangement of the binding pocket, those residues exhibit similar spatial thermal fluctuation before and after binding.

    更新日期:2019-11-01
  • Time-domain signal modelling in multidimensional NMR experiments for estimation of relaxation parameters.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-06
    Yevgen Matviychuk,Mark J Bostock,Daniel Nietlispach,Daniel J Holland

    We present a model-based method for estimation of relaxation parameters from time-domain NMR data specifically suitable for processing data in popular 2D phase-sensitive experiments. Our model is formulated in terms of commutative bicomplex algebra, which allows us to use the complete information available in an NMR signal acquired with principles of quadrature detection without disregarding any of its dimensions. Compared to the traditional intensity-analysis method, our model-based approach offers an important advantage for the analysis of overlapping peaks and is robust over a wide range of signal-to-noise ratios. We assess its performance with simulated experiments and then apply it for determination of [Formula: see text], [Formula: see text], and [Formula: see text] relaxation rates in datasets of a protein with more than 100 cross peaks.

    更新日期:2019-11-01
  • Maximizing accuracy of RNA structure in refinement against residual dipolar couplings.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-03
    Christina Bergonzo,Alexander Grishaev

    Structural information about ribonucleic acid (RNA) is lagging behind that of proteins, in part due to its high charge and conformational variability. Molecular dynamics (MD) has played an important role in describing RNA structure, complementing information from both nuclear magnetic resonance (NMR), or X-ray crystallography. We examine the impact of the choice of the empirical force field for RNA structure refinement using cross-validation against residual dipolar couplings (RDCs) as structural accuracy reporter. Four force fields, representing both the state-of-the art in RNA simulation and the most popular selections in NMR structure determination, are compared for a prototypical A-RNA helix. RNA structural accuracy is also evaluated as a function of both density and nature of input NMR data including RDCs, anisotropic chemical shifts, and distance restraints. Our results show a complex interplay between the experimental restraints and the force fields indicating two best-performing choices: high-fidelity refinement in explicit solvent, and the conformational database-derived potentials. Accuracy of RNA models closely tracks the density of 1-bond C-H RDCs, with other data types having beneficial, but smaller effects. At lower RDC density, or when refining against NOEs only, the two selected force fields are capable of accurately describing RNA helices with little or no experimental RDC data, making them available for the higher order structure assembly or better quantification of the intramolecular dynamics. Unrestrained simulations of simple RNA motifs with state-of-the art MD force fields appear to capture the flexibility inherent in nucleic acids while also maintaining a good agreement with the experimental observables.

    更新日期:2019-11-01
  • Improving the sensitivity of FT-NMR spectroscopy by apodization weighted sampling.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-03
    Bernd Simon,Herbert Köstler

    Apodization weighted acquisition is a simple approach to enhance the sensitivity of multidimensional NMR spectra by scaling the number of scans during acquisition of the indirect dimension(s). The signal content of the resulting spectra is identical to conventionally sampled data, yet the spectra show improved signal-to-noise ratios. There are no special requirements for data acquisition and processing: the time-domain data can be transformed with the same schemes used for conventionally recorded spectra, including Fourier transformation. The method is of general use in multidimensional liquid and solid state NMR experiments if the number of recorded transients per sampling point is bigger than the minimum required phase cycle of the pulse sequence.

    更新日期:2019-11-01
  • Measurement of residual dipolar couplings in methyl groups via carbon detection.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-02
    Robert V Williams,Jeong-Yeh Yang,Kelley W Moremen,I Jonathan Amster,James H Prestegard

    Residual dipolar couplings (RDCs) provide both structural and dynamical information useful in the characterization of biological macromolecules. While most data come from the interaction of simple pairs of directly bonded spin-1/2 nuclei (1H-15N, 1H-13C, 1H-1H), it is possible to acquire data from interactions among the multiple spins of 13C-labeled methyl groups (1H3-13C). This is especially important because of the advantages that observation of 13C-labeled methyl groups offers in working with very large molecules. Here we consider some of the options for measurement of methyl RDCs in large and often fully protonated proteins and arrive at a pulse sequence that exploits both J-modulation and direct detection of 13C. Its utility is illustrated by application to a fully protonated two domain fragment from the mammalian glycoprotein, Robo1, 13C-methyl-labeled in all valines.

    更新日期:2019-11-01
  • Super resolution NOESY spectra of proteins.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-02
    Charles F DeLisle,H Bhagya Mendis,Justin L Lorieau

    Spectral resolution remains one of the most significant limitations in the NMR study of biomolecules. We present the srNOESY (super resolution nuclear overhauser effect spectroscopy) experiment, which enhances the resolution of NOESY cross-peaks at the expense of the diagonal peak line-width. We studied two proteins, ubiquitin and the influenza hemagglutinin fusion peptide in bicelles, and we achieved average resolution enhancements of 21-47% and individual peak enhancements as large as ca. 450%. New peaks were observed over the conventional NOESY experiment in both proteins as a result of these improvements, and the final structures generated from the calculated restraints matched published models. We discuss the impact of the experimental parameters, spin diffusion and the information content of the srNOESY lineshape.

    更新日期:2019-11-01
  • Selective isotope labeling for NMR structure determination of proteins in complex with unlabeled ligands.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-05-02
    Konstantinos Tripsianes,Ulrike Schütz,Leonidas Emmanouilidis,Gerd Gemmecker,Michael Sattler

    The physiological role of proteins is frequently linked to interactions with non-protein ligands or posttranslational modifications. Structural characterization of these complexes or modified proteins by NMR may be difficult as the ligands are usually not available in an isotope-labeled form and NMR spectra may suffer from signal overlap. Here, we present an optimized approach that uses specific NMR isotope-labeling schemes for overcoming both hurdles. This approach enabled the high-resolution structure determination of the farnesylated C-terminal domain of the peroxisomal protein PEX19. The approach combines specific 13C, 15N and 2H isotope labeling with tailored NMR experiments to (i) unambiguously identify the NMR frequencies and the stereochemistry of the unlabeled 15-carbon isoprenoid, (ii) resolve the NMR signals of protein methyl groups that contact the farnesyl moiety and (iii) enable the unambiguous assignment of a large number of protein-farnesyl NOEs. Protein deuteration was combined with selective isotope-labeling and protonation of amino acids and methyl groups to resolve ambiguities for key residues that contact the farnesyl group. Sidechain-labeling of leucines, isoleucines, methionines, and phenylalanines, reduced spectral overlap, facilitated assignments and yielded high quality NOE correlations to the unlabeled farnesyl. This approach was crucial to enable the first NMR structure of a farnesylated protein. The approach is readily applicable for NMR structural analysis of a wide range of protein-ligand complexes, where isotope-labeling of ligands is not well feasible.

    更新日期:2019-11-01
  • 19F-substituted amino acids as an alternative to fluorophore labels: monitoring of degradation and cellular uptake of analogues of penetratin by 19F NMR.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-03-20
    Malene V Christensen,Kenneth T Kongstad,Teis Esben Sondergaard,Dan Staerk,Hanne M Nielsen,Henrik Franzyk,Reinhard Wimmer

    Current methods for assessment of cellular uptake of cell-penetrating peptides (CPPs) often rely on detection of fluorophore-labeled CPPs. However, introduction of the fluorescent probe often confers changed physicochemical properties, so that the fluorophore-CPP conjugate may exhibit cytotoxic effects and membrane damage not exerted by the native CPP. In the present study, introduction of fluorine probes was investigated as an alternative to fluorophore labeling of a CPP, since this only confers minor changes to its overall physicochemical properties. The high sensitivity of 19F NMR spectroscopy and the absence of background signals from naturally occurring fluorine enabled detection of internalized CPP. Also, degradation of fluorine-labeled peptides during exposure to Caco-2 cells could be followed by using 19F NMR spectroscopy. In total, five fluorinated analogues of the model CPP penetratin were synthesized by using commercially available fluorinated amino acids as labels, including one analogue also carrying an N-terminal fluorophore. The apparent cellular uptake was considerably higher for the fluorophore-penetratin conjugate indicating that the fluorophore moiety promoted uptake of the peptide. The use of 19F NMR spectroscopy enabled monitoring of the fate of the CPPs over time by establishing molar balances, and by verifying CPP integrity upon uptake. Thus, the NMR-based method offers several advantages over currently widespread methods relying on fluorescence detection. The present findings provide guidelines for improved labeling strategies for CPPs, thereby expanding the repertoire of analytical techniques available for studying degradation and uptake of CPPs.

    更新日期:2019-11-01
  • Hybridization of TEDOR and NCX MAS solid-state NMR experiments for simultaneous acquisition of heteronuclear correlation spectra and distance measurements.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-02-26
    T Gopinath,Songlin Wang,John Lee,Hideki Aihara,Gianluigi Veglia

    Magic angle spinning (MAS) solid-state NMR (ssNMR) spectroscopy is a major technique for the characterization of the structural dynamics of biopolymers at atomic resolution. However, the intrinsic low sensitivity of this technique poses significant limitations to its routine application in structural biology. Here we achieve substantial savings in experimental time using a new subclass of Polarization Optimized Experiments (POEs) that concatenate TEDOR and SPECIFIC-CP transfers into a single pulse sequence. Specifically, we designed new 2D and 3D experiments (2D TEDOR-NCX, 3D TEDOR-NCOCX, and 3D TEDOR-NCACX) to obtain distance measurements and heteronuclear chemical shift correlations for resonance assignments using only one experiment. We successfully tested these experiments on N-Acetyl-Val-Leu dipeptide, microcrystalline U-13C,15N ubiquitin, and single- and multi-span membrane proteins reconstituted in lipid membranes. These pulse sequences can be implemented on any ssNMR spectrometer equipped with standard solid-state hardware using only one receiver. Since these new POEs speed up data acquisition considerably, we anticipate their broad application to fibrillar, microcrystalline, and membrane-bound proteins.

    更新日期:2019-11-01
  • Accounting for the temperature dependence of 13C spin-lattice relaxation of methyl groups in the glycyl-alanyl-leucine model system under MAS with spin diffusion.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-14
    Van C Phan,Elizabeth A Fry,Kurt W Zilm

    The difficulties in quantitatively modeling the temperature dependence of spin-lattice relaxation in a model isotope-enriched peptide are explored as a prelude to obtaining dynamics parameters for motions in proteins from such measurements. The degree to which this can be handled by adding spin diffusion to a bath in standard rate matrix relaxation theory is studied using a small tri-peptide model system, glycyl-alanyl-leucine (GAL). We observe in this molecule that the relaxation of backbone carbons CO and Cα is not dominated by local fluctuations of the 13C-1H dipolar couplings, but rather by 13C-13C spin diffusion to nearby methyl relaxation sinks. A treatment of the methyl relaxation itself, which ignores 13C-13C spin diffusion effects back to the otherwise slowly relaxing bath, provides poor agreement between theory and experimental data obtained for the temperature dependence of the methyl relaxation rates. Closed form approximate spectral densities and relaxation rates for a methyl group during magic angle spinning are obtained to compute the needed transition rates. These average computed rates, in conjunction with an extended form of the Solomon equations, are found to adequately model the temperature dependence of the methyl relaxation rates when spin diffusion is included. The barrier to rotation for the alanine methyl in GAL is determined to be 3.5 kcal mol-1.

    更新日期:2019-11-01
  • Editorial.
    J. Biomol. NMR (IF 2.319) Pub Date : 2019-08-20
    Darón I Freedberg,Lewis E Kay

    更新日期:2019-11-01
  • Solution structure of monomeric human FAM96A.
    J. Biomol. NMR (IF 2.319) Pub Date : 2013-06-25
    Bingjie Ouyang,Lei Wang,Shuo Wan,Yang Luo,Lu Wang,Jian Lin,Bin Xia

    更新日期:2019-11-01
  • Segmental isotopic labeling of HIV-1 capsid protein assemblies for solid state NMR.
    J. Biomol. NMR (IF 2.319) Pub Date : 2018-02-22
    Sebanti Gupta,Robert Tycko

    Recent studies of noncrystalline HIV-1 capsid protein (CA) assemblies by our laboratory and by Polenova and coworkers (Protein Sci 19:716-730, 2010; J Mol Biol 426:1109-1127, 2014; J Biol Chem 291:13098-13112, 2016; J Am Chem Soc 138:8538-8546, 2016; J Am Chem Soc 138:12029-12032, 2016; J Am Chem Soc 134:6455-6466, 2012; J Am Chem Soc 132:1976-1987, 2010; J Am Chem Soc 135:17793-17803, 2013; Proc Natl Acad Sci USA 112:14617-14622, 2015; J Am Chem Soc 138:14066-14075, 2016) have established the capability of solid state nuclear magnetic resonance (NMR) measurements to provide site-specific structural and dynamical information that is not available from other types of measurements. Nonetheless, the relatively high molecular weight of HIV-1 CA leads to congestion of solid state NMR spectra of fully isotopically labeled assemblies that has been an impediment to further progress. Here we describe an efficient protocol for production of segmentally labeled HIV-1 CA samples in which either the N-terminal domain (NTD) or the C-terminal domain (CTD) is uniformly 15N,13C-labeled. Segmental labeling is achieved by trans-splicing, using the DnaE split intein. Comparisons of two-dimensional solid state NMR spectra of fully labeled and segmentally labeled tubular CA assemblies show substantial improvements in spectral resolution. The molecular structure of HIV-1 assemblies is not significantly perturbed by the single Ser-to-Cys substitution that we introduce between NTD and CTD segments, as required for trans-splicing.

    更新日期:2019-11-01
  • Solvent saturation transfer to proteins (SSTP) for structural and functional characterization of proteins.
    J. Biomol. NMR (IF 2.319) Pub Date : 2017-12-01
    Pushpa Mishra,C Ashley Barnes,Madeleine Strickland,Nico Tjandra

    Protein structure determination using NMR is dependent on experimentally acquired distance restraints. Often, however, an insufficient number of these restraints are available for determining a protein's correct fold, much less its detailed three-dimensional structure. In consideration of this problem, we propose a simple means to acquire supplemental structural restraints from protein surface accessibilities using solvent saturation transfer to proteins (SSTP), based on the principles of paramagnetic chemical-exchange saturation transfer. Here, we demonstrate the utility of SSTP in structure calculations of two proteins, TSG101 and ubiquitin. The observed SSTP was found to be directly proportional to solvent accessibility. Since SSTP does not involve the direct excitation of water, which compromises the analysis of protein protons entangled in the breadth of the water resonance, it has an advantage over conventional water-based magnetization transfers. Inclusion of structural restraints derived from SSTP improved both the precision and accuracy of the final protein structures in comparison to those determined by traditional approaches, when using minimal amounts of additional structural data. Furthermore, we show that SSTP can detect weak protein-protein interactions which are unobservable by chemical shift perturbations.

    更新日期:2019-11-01
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