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首页> 外文期刊>Journal of Molecular Biology >Folded-back solution structure of monomeric factor H of human complement by synchrotron X-ray and neutron scattering, analytical ultracentrifugation and constrained molecular modelling
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Folded-back solution structure of monomeric factor H of human complement by synchrotron X-ray and neutron scattering, analytical ultracentrifugation and constrained molecular modelling

机译：人体X射线和中子散射，分析超速离心和约束分子建模的人类补体单体因子H折返溶液结构

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Factor H (FH) is a regulatory cofactor for the protease factor I in the breakdown of C3b in the complement system of immune defence, and binds to heparin and other polyanionic substrates. FH is composed of 20 short consensus/complement repeat (SCR) domains, for which the overall arrangement in solution is unknown. As previous studies had shown that FH can form monomeric or dimeric structures, X-ray and neutron scattering was accordingly performed with FH in the concentration range bet-M een 0.7 and 14 mg ml(-1) The radius of gyration of FH was determined to be 11.1-11.3 nm by both methods, and the radii of gyration of the cross-section were 4.4 nm and 1.7 nm. The distance distribution function P(r) showed that the overall length of FH was 38 nm. The neutron data showed that FH was monomeric with a molecular mass of 165,000(+/- 17,000) Da. Analytical ultracentrifugation data confirmed this, where sedimentation equilibrium curve fits gave a mean molecular mass of 155,000(+/-3,000) Da. Sedimentation velocity experiments using the g*(s) derivative method showed that FH was monodisperse and had a sedimentation coefficient of 5.3(+/-0.1) S. In order to construct a full model of FH for scattering curve and sedimentation coefficient fits, homology models were constructed for 17 of the 20 SCR domains using knowledge of the NMR structures for FH SCR-5, SCR-15 and SCR-16, and vaccinia coat protein SCR-3 and SCR-4. Molecular dynamics simulations were used to generate a large conformational library for each of the 19 SCR-SCR linker peptides. Peptides from these libraries were combined with the 20 SCR structures in order to generate stereochemically complete models for the FH structure. Using an automated constrained fit procedure, the analysis of 16,752 possible FH models showed that only those models in which the 20 SCR domains were bent back upon themselves were able to account for the scattering and sedimentation data. The best-fit models showed that FH had an overall length of 38 nm and is flexible. This length is significantly less than a predicted length of 73 nm if the 20 SCR structures had been arranged in an extended arrangement. This outcome is attributed to several long linker sequences. These bent-back domain structures may correspond to conformational flexibility in FH and enable the multiple FH binding sites for C3 and heparin to come into close proximity. (C) 2001 Academic Press. [References: 68]
机译：因子H（FH）是免疫防御补体系统中C3b分解中蛋白酶因子I的调节辅助因子，并与肝素和其他聚阴离子底物结合。 FH由20个较短的共有/互补重复（SCR）域组成，对于这些域，解决方案的总体排列是未知的。如先前的研究表明FH可以形成单体或二聚体结构，因此在浓度范围为0.7和14 mg ml（-1）范围内用FH进行了X射线和中子散射，确定了FH的回转半径两种方法都为11.1-11.3nm，截面的回转半径为4.4nm和1.7nm。距离分布函数P（r）显示FH的总长度为38 nm。中子数据显示，FH是单体的，分子量为165,000（+/- 17,000）Da。超离心分析数据证实了这一点，其中沉降平衡曲线拟合得出的平均分子量为155,000（+/- 3,000）Da。用g *（s）导数法进行的沉降速度实验表明，FH是单分散的，沉降系数为5.3（+/- 0.1）S。为了建立一个完整的FH模型，用于散射曲线和沉降系数的拟合，需要同源性利用FH SCR-5，SCR-15和SCR-16以及牛痘外壳蛋白SCR-3和SCR-4的NMR结构知识，为20个SCR域中的17个构建了模型。使用分子动力学模拟为19个SCR-SCR接头肽的每一个生成一个大的构象文库。将这些文库中的肽与20个SCR结构结合，以生成FH结构的立体化学完整模型。使用自动约束拟合程序，对16,752种可能的FH模型进行的分析表明，只有那些将20个SCR域向后弯曲的模型才能解释散射和沉降数据。最佳拟合模型表明，FH的总长度为38 nm，并且很灵活。如果将20个SCR结构安排在扩展排列中，则该长度显着小于73 nm的预期长度。该结果归因于几个长的接头序列。这些弯曲的结构域结构可能对应于FH的构象灵活性，并使C3和肝素的多个FH结合位点紧密接近。 （C）2001学术出版社。 [参考：68]

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