Solution Structure of the Detergent-Photosystem II Core Complex Investigated by Small-Angle Scattering Techniques
Solution Structure of the Detergent-Photosystem II Core Complex Investigated by Small-Angle Scattering Techniques
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DOI：
10.1021/acs.jpcb.0c07169
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发表时间：
2020-10-01
影响因子：
3.3
通讯作者：
Pieper, Jorg
中科院分区：
文献类型：
--
作者：
Golub, Maksym;Hussein, Rana;Pieper, Jorg
尽管实现了X射线衍射结构的二聚体光系统II核心复合物（dPSIIcc）在原子分辨率，洗涤剂带周围dPSIIcc的性质仍然是模糊的。因此，对细长热聚球藻（Thermosynechococcuselongatus）dPSIIcc的整个洗涤剂-蛋白质复合物的溶液结构进行了研究。用小角X射线散射（SAXS）和小角中子散射（SANS）相结合的方法研究了β-D-麦芽糖苷（β-DM）增溶的葡萄糖（β-D-DM）对葡萄糖（β-D-DM）的增溶作用。首先，在SANS实验中使用5%D_2O的对比分别研究了dPSIIcc的结构。Guinier分析表明，dPSIIcc溶液在2-10 mg/mL dPSIIcc的研究浓度范围内几乎没有聚集，其特征在于回转半径为62埃。结构重建表明，在缓冲溶液中的dPSIIcc广泛地保留了晶体结构报告的X-射线自由电子激光研究在室温下与整个蛋白质的轻微膨胀。在含有75%D2O的缓冲溶液中对dPSIIcc样品进行的附加SANS实验提供了关于整个洗涤剂-dPSIIcc的尺寸和形状的信息。P（r）函数的最大位置增加到68埃，即，它仅比dPSIIcc大约6埃，因此表明存在另外的结构。因此，可以得出结论，dPSIIcc在适当的增溶条件下被洗涤剂分子的单分子带包围。还使用动态光散射验证了β DM-dPSIIcc溶液的均匀性。互补的SAXS实验通过与具有约40埃半径的球形一致的单独峰指示未结合的洗涤剂胶束的存在。后一种结构也有助于SANS数据，但人为地加宽了SANS曲线。如果不同时检查SANS和SAXS数据，这种效应可能导致PS II-去污剂复合物的大小明显低估。在结晶之前在溶液中形成较大的未结合的去污剂聚集体可能对β DM-dPSIIcc的晶体形成或质量具有显著影响。
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-beta-d-maltoside (beta DM) 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 angstrom. 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 angstrom, i.e., it is about 6 angstrom 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 beta DM-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 angstrom. 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 beta DM-dPSIIcc.