Solution structure of the complex between CR2 SCR 1-2 and C3d of human complement: An X-ray scattering and sedimentation modelling study
Solution structure of the complex between CR2 SCR 1-2 and C3d of human complement: An X-ray scattering and sedimentation modelling study
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DOI：
10.1016/j.jmb.2004.12.006
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发表时间：
2005-02-25
影响因子：
5.6
通讯作者：
Perkins, SJ
中科院分区：
文献类型：
--
作者：
Gilbert, HE;Eaton, JT;Perkins, SJ
2 型补体受体（CR2、CD21）与 C3d（补体主要成分 C3 的片段）形成紧密复合物。先前的C3d-CR2 SCR 1-2复合物和游离CR2 SCR 1-2的晶体结构表明CR2的两个SCR域以闭合V形结构彼此接触。 SCR 1 和 SCR 2 通过异常长的八残基连接肽连接。通过 X 射线散射和分析超速离心确定 CR2 SCR 1-2、C3d 及其复合物的中等分辨率溶液结构。 CR2 SCR 1-2 是单体。对于 CR2 SCR 1-2，其回转半径 R-G 为 2.12(+/-0.05) nm，最大长度为 10 nm，沉降系数 s(20,w)(o) 为 1.40(+/-0.03) S 与晶体结构计算的结果不一致，而是表明其为开放结构。 CR2 SCR1-2 溶液结构的计算机建模基于连接 SCR 1 和 SCR 2 的八残基连接肽的结构随机化，以给出 9950 个试验模型。与 X 射线散射曲线的比较表明，两个 SCR 域最受青睐的排列对应于 SCR 域之间没有接触的开放 V 形结构。对于C3d，X射线散射和沉降速度实验表明它以单体-二聚体平衡形式存在，解离常数为40 μM。单体 C3d 的 X 射线散射曲线给出的 RG 值为 1.95 nm，这与其 3.17 S 的 s(20,w)(o) 值一起与 20 单体 C3d 晶体结构具有良好的一致性。 C3d 二聚体的建模与其散射和超速离心参数具有良好的一致性。对于复合物，散射和超速离心实验表明没有二聚化，表明C3d二聚化位点位于CR2 SCR 1-2结合位点附近。 2.44(+/-0.1)run的R-G值、9nm的长度和3.45(0.01)S的s(20,w)(o)值表明其结构20并不比C3d的结构拉长很多。对9950个CR2 SCR 1-2模型通过SCR 2与C3d结合的计算表明，SCR 1与SCR 2形成开放的V形结构，并且能够与C3d表面相互作用。我们得出的结论是，CR2 SCR 1-2 形成的开放 V 形结构，无论是游离状态还是与 C3d 结合时，都是与其配体 C3d 形成紧密双结构域相互作用的最佳选择。 (C) 2004 Elsevier Ltd. 保留所有权利。
Complement receptor type 2 (CR2, CD21) forms a tight complex with C3d, a fragment of C3, the major complement component. Previous crystal structures of the C3d-CR2 SCR 1-2 complex and free CR2 SCR 1-2 showed that the two SCR domains of CR2 form contact with each other in a closed V-shaped structure. SCR 1 and SCR 2 are connected by an unusually long eight-residue linker peptide. Medium-resolution solution structures for CR2 SCR 1-2, C3d, and their complex were determined by X-ray scattering and analytical ultracentrifugation. CR2 SCR 1-2 is monomeric. For CR2 SCR 1-2, its radius of gyration R-G of 2.12(+/-0.05) nm, its maximum length of 10 nm and its sedimentation coefficient s(20,w)(o) of 1.40(+/-0.03) S do not agree with those calculated from the crystal structures, and instead suggest an open structure. Computer modelling of the CR2 SCR1-2 solution structure was based on the structural randomisation of the eight-residue linker peptide joining SCR 1 and SCR 2 to give 9950 trial models. Comparisons with the X-ray scattering curve indicated that the most favoured arrangements for the two SCR domains corresponded to an open V-shaped structure with no contacts between the SCR domains. For C3d, X-ray scattering and sedimentation velocity experiments showed that it exists as a monomer-dimer equilibrium with a dissociation constant of 40 muM. The X-ray scattering curve for monomeric C3d gave an RG value of 1.95 nm, and this together with its s(20,w)(o) value of 3.17 S gave good agreement with the 20 monomeric C3d crystal structure. Modelling of the C3d dimer gave good agreements with its scattering and ultracentrifugation parameters. For the complex, scattering and ultracentrifugation experiments showed that there was no dimerisation, indicating that the C3d dimerisation site was located close to the CR2 SCR 1-2 binding site. The R-G value of 2.44(+/-0.1) run, its length of 9 nm and its s(20,w)(o) value of 3.45( 0.01) S showed that its structure 20 was not much more elongated than that of C3d. Calculations with 9950 models of CR2 SCR 1-2 bound to C3d through SCR 2 showed that SCR 1 formed an open V-shaped structure with SCR 2 and was capable of interacting with the surface of C3d. We conclude that the open V-shaped structures formed by CR2 SCR 1-2, both when free and when bound to C3d, are optimal for the formation of a tight two-domain interaction with its ligand C3d. (C) 2004 Elsevier Ltd. All rights reserved.