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  • An enzymatic method for precise oxygen affinity measurements over nanomolar-to-millimolar concentration regime
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2020-01-02
    Ria Sanyal, Ambika Bhagi-Damodaran

    Abstract Oxygen affinity is an important property of metalloproteins that helps elucidate their reactivity profile and mechanism. Heretofore, oxygen affinity values were determined either using flash photolysis and polarography techniques that require expensive instrumentation, or using oxygen titration methods which are erroneous at low nanomolar and at high millimolar oxygen concentrations. Here, we describe an inexpensive, easy-to-setup, and a one-pot method for oxygen affinity measurements that uses the enzyme chlorite dismutase (Cld) as a precise in situ oxygen source. Using this method, we measure thermodynamic and kinetic oxygen affinities (Kd and KM) of different classes of heme and non-heme metalloproteins involved in oxygen transport, sensing, and catalysis. The method enables oxygen affinity measurements over a wide concentration range from 10 nM to 5 mM which is unattainable by simply diluting oxygen-saturated buffers. In turn, we were able to precisely measure oxygen affinities of a model set of eight different metalloproteins with affinities ranging from 48 ± 3 nM to 1.18 ± 0.03 mM. Overall, the Cld method is easy and inexpensive to set up, requires significantly lower quantities of protein, enables precise oxygen affinity measurements, and is applicable for proteins exhibiting nanomolar-to-millimolar affinity values. Graphic abstract

  • SrnR from Streptomyces griseus is a nickel-binding transcriptional activator
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-12-18
    Ylenia Beniamino, Giulia Pesce, Annamaria Zannoni, Davide Roncarati, Barbara Zambelli

    Nickel ions are crucial components for the catalysis of biological reactions in prokaryotic organisms. As an uncontrolled nickel trafficking is toxic for living organisms, nickel-dependent bacteria have developed tightly regulated strategies to maintain the correct intracellular metal ion quota. These mechanisms require transcriptional regulator proteins that respond to nickel concentration, activating or repressing the expression of specific proteins related to Ni(II) metabolism. In Streptomyces griseus, a Gram-positive bacterium used for antibiotic production, SgSrnR and SgSrnQ regulate the nickel-dependent antagonistic expression of two superoxide dismutase (SOD) enzymes, a Ni-SOD and a FeZn-SOD. According to a previously proposed model, SgSrnR and SgSrnQ form a protein complex in which SgSrnR works as repressor, binding directly to the promoter of the gene coding for FeZn-SOD, while SgSrnQ is the Ni(II)-dependent co-repressor. The present work focuses on the determination of the biophysical and functional properties of SgSrnR. The protein was heterologously expressed and purified from Escherichia coli. The structural and metal-binding analysis, carried out by circular dichroism, light scattering, fluorescence and isothermal titration calorimetry, showed that the protein is a well-structured homodimer, able to bind nickel with moderate affinity. DNase I footprinting and β-galactosidase gene reporter assays revealed that apo-SgSrnR is able to bind its DNA operator and activates a transcriptional response. The structural and functional properties of this protein are discussed relatively to its role as a Ni(II)-dependent sensor.

  • Fluorescence detection of laccases activity by the photoinduced electron transfer (PET) process
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-12-12
    Mehdi Sheikh Arabi, Changiz Karami, Mohammad Ali Taher, Elahe Ahmadi

    Laccases play a vital role in some physiological processes, for example in morphogenesis, carbon cycle, and defense against parasitism. So, designing a high-sensitivity accurate method is essential for researchers. In this study, a simple fluorescence method based on the function of carbon nitride (g-C3N4) by dopamine is synthesized. For the design of this sensor, carbon nitride (g-C3N4) is initially synthesis by using a simple method, which is carried out by heating melamine at 550 °C for 3 h and modifying it with dopamine by a linker such as glutaraldehyde. However, the g-C3N4–Dopa produced by this method, with an excitation wavelength of 330 nm, has a fluorescence emission at 466 nm. When laccase and g-C3N4–Dopa were mixed, dopamine with redox property was oxidized to dopaquinone; this causes the phenomenon of photoinduced electron transfer (PET) process between g-C3N4 and the dopaquinone. Hence, fluorescence quenching occurs due to this phenomenon. As a result of these discussions, a sensor for the laccase activity was designed based on the fluorescence quenching degree, supporting a linear range of 0.0–400.0 U L−1 with the detection limit of 2.0 U L−1. Using this sensor, the activity of the laccase enzyme in the human serum samples is measured.

  • Mixed ligand complexes of Co(II), Ni(II) and Cu(II) with quercetin and diimine ligands: synthesis, characterization, anti-cancer and anti-oxidant activity
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-12-12
    Hasene Mutlu Gençkal, Merve Erkisa, Pınar Alper, Saliha Sahin, Engin Ulukaya, Ferda Ari

    In this work, mixed ligand complexes of Co(II) Ni(II) and Cu(II) were synthesized using quercetin and diimine (1,10-phenanthroline or 2,2′-bipyiridine) ligands. The obtained Ni(II) and Co(II) complexes are new and the Cu(II) complexes are synthesized by different method from the literature. The characterization of complexes was performed by elemental analysis, thermogravimetric analysis, ESI–MS, UV–visible and infrared spectral analyses, magnetic susceptibility and molar conductivity measurements. It was found that quercetin, diimine and metal(II) ion form 1:1:1 complexes. Resulting data supported octahedral geometry for Ni(II) and Co(II) complexes and square pyramidal geometry for Cu(II) complexes. The proposed compositions are [Co(queH-1)Cl(phen)(H2O)]∙2H2O (1, queH = quercetin, phen = 1,10-phenanthroline), [Ni(queH-1)Cl(phen)(H2O)]∙2H2O (2), [Cu(queH-1)Cl(phen)]∙2.5H2O (3) and [Cu(queH-1)Cl(bpy)]∙2H2O (4, bpy = 2,2′-bipyiridine). Antioxidant capacity and total phenolic content of complexes measured by Folin–Ciocalteu and ABTS methods. Anti-cancer effect of these compounds were tested against different cancer cells (A549, PC-3, HeLa and MCF-7). Apoptosis identified by the fluorescence imaging, caspase cleaved cytokeratin-18 and flow cytometry analysis (annexin V, caspase 3/7, mitochondria membrane potential and oxidative stress). As a result, Cu(II) complexes are more effective than the other compounds and Complex 3 is a promising anti-cancer compound against breast cancer MCF-7 and MDA-MB-231 cells (IC50 values are 2.4 and 5.4 µM for 48 h, respectively). Flow cytometry analysis exhibited that Complex 3 caused apoptosis in MCF-7 cells. These results support that Complex 3 has anticancer activity and can be a potential anticancer agent especially in breast cancer.

  • Spectroscopic and biochemical insight into an electron-bifurcating [FeFe] hydrogenase
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-12-10
    Nipa Chongdar, Krzysztof Pawlak, Olaf Rüdiger, Edward J. Reijerse, Patricia Rodríguez-Maciá, Wolfgang Lubitz, James A. Birrell, Hideaki Ogata

    The heterotrimeric electron-bifurcating [FeFe] hydrogenase (HydABC) from Thermotoga maritima (Tm) couples the endergonic reduction of protons (H+) by dihydronicotinamide adenine dinucleotide (NADH) (∆G0 ≈ 18 kJ mol−1) to the exergonic reduction of H+ by reduced ferredoxin (Fdred) (∆G0 ≈ − 16 kJ mol−1). The specific mechanism by which HydABC functions is not understood. In the current study, we describe the biochemical and spectroscopic characterization of TmHydABC recombinantly produced in Escherichia coli and artificially maturated with a synthetic diiron cofactor. We found that TmHydABC catalyzed the hydrogen (H2)-dependent reduction of nicotinamide adenine dinucleotide (NAD+) in the presence of oxidized ferredoxin (Fdox) at a rate of ≈17 μmol NADH min−1 mg−1. Our data suggest that only one flavin is present in the enzyme and is not likely to be the site of electron bifurcation. FTIR and EPR spectroscopy, as well as FTIR spectroelectrochemistry, demonstrated that the active site for H2 conversion, the H-cluster, in TmHydABC behaves essentially the same as in prototypical [FeFe] hydrogenases, and is most likely also not the site of electron bifurcation. The implications of these results are discussed with respect to the current hypotheses on the electron bifurcation mechanism of [FeFe] hydrogenases. Overall, the results provide insight into the electron-bifurcating mechanism and present a well-defined system for further investigations of this fascinating class of [FeFe] hydrogenases.

  • Correction to: Aluminium in human brain tissue: how much is too much?
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-20
    Christopher Exley, Matthew J. Mold

    The authors declare

  • Aluminium in human brain tissue: how much is too much?
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-08-29
    Christopher Exley, Matthew J. Mold

    A burgeoning body of research confirms and affirms the presence of aluminium in human brain tissue. Recently, the first data on aluminium content of brain tissue from donors with diagnoses of familial Alzheimer’s disease, autism spectrum disorder, multiple sclerosis and epilepsy have been published. Quantitative data are supported by aluminium-specific fluorescence microscopy identifying the locations of aluminium in human brain tissue. The challenge in the future will be to confirm or refute the role played by brain aluminium intoxication in human neurodegenerative disease.

  • Metal binding to the amyloid-β peptides in the presence of biomembranes: potential mechanisms of cell toxicity
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-09-27
    Sebastian K. T. S. Wärmländer, Nicklas Österlund, Cecilia Wallin, Jinming Wu, Jinghui Luo, Ann Tiiman, Jüri Jarvet, Astrid Gräslund

    The amyloid-β (Aβ) peptides are key molecules in Alzheimer’s disease (AD) pathology. They interact with cellular membranes, and can bind metal ions outside the membrane. Certain oligomeric Aβ aggregates are known to induce membrane perturbations and the structure of these oligomers—and their membrane-perturbing effects—can be modulated by metal ion binding. If the bound metal ions are redox active, as e.g., Cu and Fe ions are, they will generate harmful reactive oxygen species (ROS) just outside the membrane surface. Thus, the membrane damage incurred by toxic Aβ oligomers is likely aggravated when redox-active metal ions are present. The combined interactions between Aβ oligomers, metal ions, and biomembranes may be responsible for at least some of the neuronal death in AD patients.

  • Biometals as conformational modulators of α-synuclein photochemical crosslinking
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-14
    Dinendra L. Abeyawardhane, Alyson M. Curry, Ashley K. Forney, Joel W. Roberts, Heather R. Lucas

    Metal dyshomeostasis has long been linked to Parkinson’s disease (PD), and the amyloidogenic protein α-synuclein (αS) is universally recognized as a key player in PD pathology. Structural consequences upon coordination of copper and iron to αS have gained attention due to significant dyshomeostasis of both metals in the PD brain. Protein–metal association can navigate protein folding in distinctive pathways based on the identity of the bio-metal in question. In this work, we employed photo-chemical crosslinking of unmodified proteins (PICUP) to evaluate these potential metal ion-induced structural alterations in the folding dynamics of N-terminally acetylated αS (NAcαS) following metal coordination. Through fluorescence analysis and immunoblotting analyses following photoirradiation, we discovered that coordination of iron obstructs copper-promoted crosslinking. The absence of intra-molecular crosslinking upon iron association further supports its C-terminal coordination site and suggests a potential role for iron in mitigating nearby post-translational modification of tyrosine residues. Decreased fluorescence emission upon synergistic coordination of both copper and iron highlighted that although copper acts as a conformational promotor of NAcαS crosslinking, iron inhibits analogous conformational changes within the protein. The metal coordination preferences of NAcαS suggest that both competitive binding sites as well as dual metal coordination contribute to the changes in folding dynamics, unveiling unique structural orientations for NAcαS that have a direct and measureable influence on photoinitiated dityrosine crosslinks. Moreover, our findings have physiological implications in that iron overload, as is associated with PD-insulted brain tissue, may serve as a conformational block of copper-promoted protein oxidation.

  • Impact of pyridine-2-carboxaldehyde-derived aroylhydrazones on the copper-catalyzed oxidation of the M112A PrP 103–112 mutant fragment
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-08-10
    Daphne S. Cukierman, Nikolett Bodnár, Beatriz N. Evangelista, Lajos Nagy, Csilla Kállay, Nicolás A. Rey

    Misfolded prion protein (PrPSc) is known for its role in fatal neurodegenerative conditions, such as Creutzfeldt–Jakob disease. PrP fragments and their mutants represent important tools in the investigation of the neurotoxic mechanisms and in the evaluation of new compounds that can interfere with the processes involved in neuronal death. Metal-catalyzed oxidation of PrP has been implicated as a trigger for the conformational changes in protein structure, which, in turn, lead to misfolding. Targeting redox-active biometals copper and iron is relevant in the context of protection against the oxidation of biomolecules and the generation of oxidative stress, observed in several conditions and considered an event that might promote sporadic prion diseases as well as other neurodegenerative disorders. In this context, ortho-pyridine aroylhydrazones are of interest, as they can act as moderate tridentate ligands towards divalent metal ions such as copper(II). In the present work, we explore the potentiality of this chemical class as peptide protecting agents against the deleterious metal-catalyzed oxidation in the M112A mutant fragment of human PrP, which mimics relevant structural features that may play an important role in the neurotoxicity observed in prion pathologies. The compounds inhere studied, especially HPCFur, showed an improved stability in aqueous solution compared to our patented lead hydrazone INHHQ, displaying a very interesting protective effect toward the oxidation of methionine and histidine, processes that are related to both physiological and pathological aging.

  • Arsenic-induced neurotoxicity: a mechanistic appraisal
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-21
    Carla Garza-Lombó, Aglaia Pappa, Mihalis I. Panayiotidis, María E. Gonsebatt, Rodrigo Franco

    Arsenic is a metalloid found in groundwater as a byproduct of soil/rock erosion and industrial and agricultural processes. This xenobiotic elicits its toxicity through different mechanisms, and it has been identified as a toxicant that affects virtually every organ or tissue in the body. In the central nervous system, exposure to arsenic can induce cognitive dysfunction. Furthermore, iAs has been linked to several neurological disorders, including neurodevelopmental alterations, and is considered a risk factor for neurodegenerative disorders. However, the exact mechanisms involved are still unclear. In this review, we aim to appraise the neurotoxic effects of arsenic and the molecular mechanisms involved. First, we discuss the epidemiological studies reporting on the effects of arsenic in intellectual and cognitive function during development as well as studies showing the correlation between arsenic exposure and altered cognition and mental health in adults. The neurotoxic effects of arsenic and the potential mechanisms associated with neurodegeneration are also reviewed including data from experimental models supporting epidemiological evidence of arsenic as a neurotoxicant. Next, we focused on recent literature regarding arsenic metabolism and the molecular mechanisms that begin to explain how arsenic damages the central nervous system including, oxidative stress, energy failure and mitochondrial dysfunction, epigenetics, alterations in neurotransmitter homeostasis and synaptic transmission, cell death pathways, and inflammation. Outlining the specific mechanisms by which arsenic alters the cell function is key to understand the neurotoxic effects that convey cognitive dysfunction, neurodevelopmental alterations, and neurodegenerative disorders.

  • Rebalancing metal dyshomeostasis for Alzheimer’s disease therapy
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-09-05
    Guan‐Jun Yang, Hao Liu, Dik-Lung Ma, Chung-Hang Leung

    Alzheimer’s disease (AD) is a type of neurodegenerative malady that is associated with the accumulation of amyloid plaques. Metal ions are critical for the development and upkeep of brain activity, but metal dyshomeostasis can contribute to the development of neurodegenerative diseases, including AD. This review highlights the association between metal dyshomeostasis and AD pathology, the feasibility of rebalancing metal homeostasis as a therapeutic strategy for AD, and a survey of current drugs that action via rebalancing metal homeostasis. Finally, we discuss the challenges that should be overcome by researchers in the future to enable the practical use of metal homeostasis rebalancing agents for clinical application.

  • Is brain iron trafficking part of the physiology of the amyloid precursor protein?
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-10-01
    Danielle K. Bailey, Daniel J. Kosman

    The amyloid precursor protein is so named, because a proteolytic fragment of it was found associated with a neuropathic disorder now known as Alzheimer’s disease. This fragment, Aβ, along with tau makes up the plaques and tangles that are the hallmark of AD. Iron (and other first-row transition metals) is found associated with these proteinaceous deposits. Much research has focused on the relationship of the plaques and iron to the etiology of the disease. This commentary asks another question, one only more recently addressed namely, what is the physiologic function of the amyloid precursor protein (APP) and of its secretase-generated soluble species? Overall, the data make clear that APP and its products have neurotrophic functions and some data indicate one of these may be to modulate the trafficking of iron in the brain.

  • Active-site environment of Cu bound amyloid β and amylin peptides
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-10-16
    Ishita Pal, Madhuparna Roy, Somdatta Ghosh Dey

    Alzheimer’s disease (AD) and Type 2 Diabetes mellitus (T2Dm), two of the most common amyloidogenic diseases. They share a common pathological symptom, i.e., the formation of amyloid deposits comprised of amyloid β and amylin peptides, respectively. Autopsy of brains of AD-affected patients shows the presence of abnormally high concentrations of Cu in the deposited amyloid β plaques, while a significantly higher level of Cu is found in the serum of patients suffering from T2Dm. These invoke that Cu might play a crucial role in the onset of both AD and T2Dm. In fact, Cu is found to bind amyloid β as well as amylin relevant to AD and T2Dm, respectively. Cu–Aβ and Cu–amylin in their reduced states can generate partially reduced oxygen species (PROS) on reaction with O2 which leads to oxidative stress in the brain and in the pancreas, respectively. However, the pathway of O2 reduction is quite different for the two complexes. Moreover, the use of various spectroscopic techniques such as absorption, EPR, and CD involving native and site-directed mutants of the peptides show that their active-site environments are also dissimilar. Here, we have discussed the different aspects of Cu–Aβ and Cu–amylin complexes including their pH-dependent coordination environments and their reactivity towards O2 which may be responsible for the oxidative stress associated with the two diseases. This depicts the significance of the Cu bound peptide complexes in the context of AD and T2Dm.

  • Redox active metals in neurodegenerative diseases
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-10-24
    Karla Acevedo, Shashank Masaldan, Carlos M. Opazo, Ashley I. Bush

    Copper (Cu) and iron (Fe) are redox active metals essential for the regulation of cellular pathways that are fundamental for brain function, including neurotransmitter synthesis and release, neurotransmission, and protein turnover. Cu and Fe are tightly regulated by sophisticated homeostatic systems that tune the levels and localization of these redox active metals. The regulation of Cu and Fe necessitates their coordination to small organic molecules and metal chaperone proteins that restrict their reactions to specific protein centres, where Cu and Fe cycle between reduced (Fe2+, Cu+) and oxidised states (Fe3+, Cu2+). Perturbation of this regulation is evident in the brain affected by neurodegeneration. Here we review the evidence that links Cu and Fe dyshomeostasis to neurodegeneration as well as the promising preclinical and clinical studies reporting pharmacological intervention to remedy Cu and Fe abnormalities in the treatment of Alzheimer’s disease (AD), Parkinson’s disease (PD) and Amyotrophic lateral sclerosis (ALS).

  • Early-life Pb exposure as a potential risk factor for Alzheimer’s disease: are there hazards for the Mexican population?
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-26
    Miguel Chin-Chan, Luis Cobos-Puc, Isabel Alvarado-Cruz, Melike Bayar, Maria Ermolaeva

    Alzheimer’s disease (AD) is the main cause of dementia in elderly. Increasing life expectancy is behind the growing prevalence of AD worldwide with approximately 45 million cases currently documented and projection studies suggesting a triplication of this number by 2050. Mexico does not have an accurate AD registry, but 860,000 cases were reported in 2014 and the prediction reaches 3.5 million cases by 2050. Amyloid plaques and neurofibrillary tangles represent the main hallmarks of AD, being constituted of amyloid beta (Aβ) peptide and phosphorylated tau, respectively. The risk factors for AD include genetic mutations, lifestyle and environmental pollution. Particularly, lead (Pb) has attracted attention due to its ability to target multiple pathways involved in the pathophysiology of AD. Although the epidemiological data are limiting, animal and in vitro studies show growing evidence of causal effects of Pb exposure on AD-linked features including Aβ aggregation and tau phosphorylation. Interestingly, many Pb effects occur selectively following early-life exposure to the metal, suggesting an epigenetic mechanism. This hypothesis is supported by changes in DNA methylation and microRNA expression patterns inflicted by early-life Pb exposure. Pb pollution in Mexico represents a significant problem because past and current mining activities, historical use of Pb as fuel additive and culturally rooted use of Pb in glazed ceramics, contribute to high levels of Pb pollution in Mexico. In this review we will discuss potential risks of AD development in Mexican populations chronically exposed to Pb in their childhood.

  • Effects of Cu(II) on the aggregation of amyloid-β
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-10-10
    Martina G. M. Weibull, Signe Simonsen, Cecilie R. Oksbjerg, Manish K. Tiwari, Lars Hemmingsen

    Aberrant aggregation of the Aβ protein is a hallmark of Alzheimer’s disease (AD), but no complete characterization of the molecular level pathogenesis has been achieved. A promising hypothesis is that dysfunction of metal ion homeostasis, and consequently, the undesired interaction of metal ions with Aβ, may be central to the development of AD. Qualitatively, most data indicate that Cu(II) induces rapid self-assembly of both Aβ40 and Aβ42 during the initial phase of the aggregation, while at longer time scales fibrillation may occur, depending on the experimental conditions. For Aβ40 and Cu(II):Aβ ≤ 1, most data imply that low concentration of Aβ40 favors nucleation and rapid fibril elongation, while high concentration of Aβ40 favors formation of amorphous aggregates. However, there are conflicting reports on this issue. For Aβ42 and Cu(II):Aβ ≤ 1, there is consensus that the lag time is extended upon addition of Cu(II). For Cu(II):Aβ > 1, the lag time is increased upon interaction with Cu(II), and in most cases fibrillation is not observed, presumably because Cu(II) occupies a second more solvent-exposed binding site, which is more prone to form metal ion-bridged species and cause rapid formation of non-fibrillar aggregates. The interesting N-terminally truncated Aβ11–40 with high affinity for Cu(II), exhibits delay of fibrillation upon addition of 0.4 eq. Cu(II). In our view, there are still problems achieving reproducible results in this field, and we provide a shortlist of some of the pitfalls. Finally, we propose a consensus model for the effects of Cu(II) on the aggregation kinetics of Aβ.

  • Copper, dityrosine cross-links and amyloid-β aggregation
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-10-30
    Guillem Vázquez, Ana B. Caballero, Jakub Kokinda, Ana Hijano, Raimon Sabaté, Patrick Gamez

    Copper is involved in Alzheimer’s disease (AD) where it appears to affect the aggregation of amyloid-β (Aβ) and to catalyze the production of reactive oxygen species (ROS). Oxidative stress apparently produces Aβ dimers that are covalently linked through two tyrosine residues. Such dityrosine cross-links are considered as potential markers of the disease and seem to be implicated in the pathological disorder. In the present study, pure o,o′-dityrosine (diY) was prepared enzymatically (with horseradish peroxidase; HRP), which was subsequently used to construct calibration lines aimed at quantifying nanomolar amounts of diY in reaction mixtures by fluorescence spectroscopy. Hence, diY concentrations down to 67 nM could be determined, which allowed to find that ca. 3% of dityrosine-bridged dimers of Aβ(1–40) were produced after 3 days at 37 °C in the presence of copper and dihydrogen peroxide. These cross-linked dimers in the presence of copper(II) ions completely inhibit the typical aggregation of Aβ, since β sheets could not be detected applying the usual Thioflavin T (ThT) method. Furthermore, the use of a potent Cu(II) chelator, such as the ATCUN tripeptide, l-histidyl-l-alanyl-l-histidine (HAH), efficiently prevented the copper-mediated generation of ROS and the associated dityrosine-bridged Aβ dimers, suggesting that such metal chelators may find future applications in the field of anti-AD drug design.

  • Copper and the brain noradrenergic system
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-05
    Svetlana Lutsenko, Clorissa Washington-Hughes, Martina Ralle, Katharina Schmidt

    Copper (Cu) plays an essential role in the development and function of the brain. In humans, genetic disorders of Cu metabolism may cause either severe Cu deficiency (Menkes disease) or excessive Cu accumulation (Wilson disease) in the brain tissue. In either case, the loss of Cu homeostasis results in catecholamine misbalance, abnormal myelination of neurons, loss of normal brain architecture, and a spectrum of neurologic and/or psychiatric manifestations. Several metabolic processes have been identified as particularly sensitive to Cu dis-homeostasis. This review focuses on the role of Cu in noradrenergic neurons and summarizes the current knowledge of mechanisms that maintain Cu homeostasis in these cells. The impact of Cu misbalance on catecholamine metabolism and functioning of noradrenergic system is discussed.

  • Metal coordination and peripheral substitution modulate the activity of cyclic tetrapyrroles on αS aggregation: a structural and cell-based study
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-09-05
    Nazareno González, Iñaki Gentile, Hugo A. Garro, Susana Delgado-Ocaña, Carla F. Ramunno, Fiamma A. Buratti, Christian Griesinger, Claudio O. Fernández

    The discovery of aggregation inhibitors and the elucidation of their mechanism of action are key in the quest to mitigate the toxic consequences of amyloid formation. We have previously characterized the antiamyloidogenic mechanism of action of sodium phtalocyanine tetrasulfonate ([Na4(H2PcTS)]) on α-Synuclein (αS), demonstrating that specific aromatic interactions are fundamental for the inhibition of amyloid assembly. Here we studied the influence that metal preferential affinity and peripheral substituents may have on the activity of tetrapyrrolic compounds on αS aggregation. For the first time, our laboratory has extended the studies in the field of the bioinorganic chemistry and biophysics to cellular biology, using a well-established cell-based model to study αS aggregation. The interaction scenario described in our work revealed that both N- and C-terminal regions of αS represent binding interfaces for the studied compounds, a behavior that is mainly driven by the presence of negatively or positively charged substituents located at the periphery of the macrocycle. Binding modes of the tetrapyrrole ligands to αS are determined by the planarity and hydrophobicity of the aromatic ring system in the tetrapyrrolic molecule and/or the preferential affinity of the metal ion conjugated at the center of the macrocyclic ring. The different capability of phthalocyanines and meso-tetra (N-methyl-4-pyridyl) porphine tetrachloride ([H2PrTPCl4]) to modulate αS aggregation in vitro was reproduced in cell-based models of αS aggregation, demonstrating unequivocally that the modulation exerted by these compounds on amyloid assembly is a direct consequence of their interaction with the target protein.

  • Catalytic effect of riboflavin on electron transfer from NADH to aquacobalamin
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-26
    Ilia A. Dereven’kov, Luciana Hannibal, Sergei V. Makarov, Pavel A. Molodtsov

    Reduction of cobalamin by non-dedicated cellular reductases has been reported in earlier work, however, the sources of reducing power and the mechanisms are unknown. This study reports results of kinetic and mechanistic investigation of the reaction between aquacobalamin, H2OCbl, and reduced β-nicotinamide adenine dinucleotide, NADH. This interaction leads to the formation of one-electron reduced cobalamin, cob(II)alamin, and proceeds via water substitution on aquacobalamin by NADH and further decomposition of NADH–Co(III) complex to cob(II)alamin and NADH·+. Riboflavin catalyzes the reduction of aquacobalamin by NADH both in free form and with aquacobalamin bound to the cobalamin processing enzyme CblC. The rate-determining step of this catalytic reaction is the interaction between riboflavin and NADH to produce a charge transfer complex that reacts with aquacobalamin. Aquacobalamin quenches the fluorescence of NADH and riboflavin predominantly via a static mechanism.

  • Study of the role of Mg 2+ in dsRNA processing mechanism by bacterial RNase III through QM/MM simulations
    J. Biol. Inorg. Chem. (IF 3.632) Pub Date : 2019-11-21
    Salvador I. Drusin, Rodolfo M. Rasia, Diego M. Moreno

    The ribonuclease III (RNase III) cleaves dsRNA in specific positions generating mature RNAs. RNase III enzymes play important roles in RNA processing, post-transcriptional gene expression, and defense against viral infection. The enzyme’s active site contains Mg2+ ions bound by a network of acidic residues and water molecules, but there is a lack of information about their specific roles. In this work, multiple steered molecular dynamics simulations at QM/MM level were performed to explore the hydrolysis reaction carried out by the enzyme. Free energy profiles modifying the features of the active site are obtained and the role of Mg2+ ions, the solvent molecules and the residues of the active site are discussed in detail. Our results show that Mg2+ ions carry out different roles in the hydrolysis process positioning the substrate for the attack from a coordinated nucleophile and activating it to perform hydrolysis reaction, cleaving the dsRNA backbone in a SN2 substitution. In addition, water molecules present in the active site lower the energy barrier of the process.

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