Solution Structure of the Detergent-Photosystem II Core Complex Investigated by Small-Angle Scattering Techniques.,The Journal of Physical Chemistry B

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Solution Structure of the Detergent-Photosystem II Core Complex Investigated by Small-Angle Scattering Techniques.
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-08-20 , DOI: 10.1021/acs.jpcb.0c07169
Maksym Golub ₁ , Rana Hussein ₂ , Mohamed Ibrahim ₂ , Max Hecht ₁ , Dietmar Christian Florian Wieland ₃ , Anne Martel ₄ , Barbara Machado ₅ , Athina Zouni ₂ , Jörg Pieper ₁

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Albeit achieving the X-ray diffraction structure of dimeric photosystem II core complexes (dPSIIcc) at the atomic resolution, the nature of the detergent belt surrounding dPSIIcc remains ambiguous. Therefore, the solution structure of the whole detergent–protein complex of dPSIIcc of Thermosynechococcus elongatus (T. elongatus) solubilized in n-dodecyl-ß-d-maltoside (ßDM) was investigated by a combination of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) with contrast variation. First, the structure of dPSIIcc was studied separately in SANS experiments using a contrast of 5% D₂O. Guinier analysis reveals that the dPSIIcc solution is virtually free of aggregation in the studied concentration range of 2–10 mg/mL dPSIIcc, and characterized by a radius of gyration of 62 Å. A structure reconstitution shows that dPSIIcc in buffer solution widely retains the crystal structure reported by X-ray free electron laser studies at room temperature with a slight expansion of the entire protein. Additional SANS experiments on dPSIIcc samples in a buffer solution containing 75% D₂O provide information about the size and shape of the whole detergent–dPSIIcc. The maximum position of P(r) function increases to 68 Å, i.e., it is about 6 Å larger than that of dPSIIcc only, thus indicating the presence of an additional structure. Thus, it can be concluded that dPSIIcc is surrounded by a monomolecular belt of detergent molecules under appropriate solubilization conditions. The homogeneity of the ßDM–dPSIIcc solutions was also verified using dynamic light scattering. Complementary SAXS experiments indicate the presence of unbound detergent micelles by a separate peak consistent with a spherical shape possessing a radius of about 40 Å. The latter structure also contributes to the SANS data but rather broadens the SANS curve artificially. Without the simultaneous inspection of SANS and SAXS data, this effect may lead to an apparent underestimation of the size of the PS II–detergent complex. The formation of larger unbound detergent aggregates in solution prior to crystallization may have a significant effect on the crystal formation or quality of the ßDM–dPSIIcc.

中文翻译：

用小角度散射技术研究了洗涤剂-光系统II核心配合物的溶液结构。

尽管在原子分辨率上获得了二聚光系统II核心配合物（dPSIIcc）的X射线衍射结构，但围绕dPSIIcc的去污剂带的性质仍然不明确。因此，整个洗涤剂-蛋白质复合物的dPSIIcc的溶液结构细长嗜热（T.细长）中溶解Ñ十二烷基-SS- d -maltoside（SSDM）通过小角X射线散射的组合（调查SAXS）和具有对比度变化的小角中子散射（SANS）。首先，在SANS实验中分别使用5％D ₂的对比研究dPSIIcc的结构O. Guinier分析表明，在研究的2-10 mg / mL dPSIIcc浓度范围内，dPSIIcc溶液几乎没有聚集，并且其回转半径为62Å。结构重建表明，缓冲溶液中的dPSIIcc在室温下广泛保留了X射线自由电子激光研究报告的晶体结构，整个蛋白质略有膨胀。在含有75％D ₂的缓冲溶液中对dPSIIcc样品进行的其他SANS实验O提供有关整个洗涤剂dPSIIcc的大小和形状的信息。P（r）函数的最大位置增加到68，即，仅比dPSIIcc的最大位置大约6，因此表明存在其他结构。因此，可以得出结论，在适当的增溶条件下，dPSIIcc被洗涤剂分子的单分子带包围。ßDM–dPSIIcc溶液的均匀性也使用动态光散射进行了验证。补充SAXS实验表明，未结合的洗涤剂胶束的存在是通过一个单独的峰实现的，该峰与半径约为40的球形一致。后一种结构也有助于SANS数据，但人为地扩大了SANS曲线。如果不同时检查SANS和SAXS数据，这种影响可能导致对PS II洗涤剂体系的大小的明显低估。结晶前溶液中较大的未结合洗涤剂聚集物的形成可能对ßDM–dPSIIcc的晶体形成或质量产生重大影响。

更新日期：2020-10-02

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