Crystal structure of the MACPF domain of human complement protein C8α in complex with the C8γ subunit
Crystal structure of the MACPF domain of human complement protein C8α in complex with the C8γ subunit
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DOI：
10.1016/j.jmb.2008.03.061
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发表时间：
2008-05-29
影响因子：
5.6
通讯作者：
Sodetz, James M.
中科院分区：
文献类型：
--
作者：
Slade, Daniel J.;Lovelace, Leslie L.;Sodetz, James M.
人C8是在细菌膜上组装以形成称为“膜攻击复合物”（MAC）的孔样结构的五种补体组分（C5 b、C6、C7、C8和C9）之一。C8含有三个遗传上不同的亚基（C8 α、C8 β、C8 γ），排列为与C8 β非共价结合的二硫键连接的C8 α-γ二聚体。C6、C7、C8 α、C8 β和C9是同源的。所有包含N-和C-末端模块和一个插入的40-kDa片段称为膜攻击复合物/穿孔素（MACPF）域。C8 γ亚基是不相关的，属于脂质运载蛋白家族，其显示β-桶折叠并通常结合小的疏水配体。基于序列相似性，已经鉴定了数百种具有MACPF结构域的蛋白质;然而，大多数的结构和功能是未知的。最近报道了分泌的细菌蛋白Plu-MACPF和人C8 α MACPF结构域的晶体结构，它们都显示出与细菌成孔胆固醇依赖性溶细胞素（CDC）相似的折叠。在本研究中，我们以2.15埃的分辨率确定了与C8 γ（α MACPF-γ）二硫键连接的人C8（x MACPF结构域）的晶体结构。α MACPF部分具有预测的CDC样折叠，并显示与C8 γ相互作用的两个区域。一个是在先前表征的C8 α中的19个残基插入（indel）中，并填充推定的C8 γ配体结合位点的入口。第二个是疏水口袋，与C8 γ β-桶侧面的残基接触。后一种相互作用诱导α MACPF的构象变化，这可能对C8功能很重要。还观察到α MACPF和Plu-MACPF中MACPF特征基序Y/W-G-T/S-H-F/Y-X-6-G-G的结构保守性，以及已知对于CDC的重折叠和孔形成重要的几个关键甘氨酸残基的保守性。(C)2008爱思唯尔有限公司版权所有。
Human C8 is one of five complement components (C5b, C6, C7, C8, and C9) that assemble on bacterial membranes to form a porelike structure referred to as the "membrane attack complex" (MAC). C8 contains three genetically distinct subunits (C8 alpha, C8 beta, C8 gamma) arranged as a disulfide-linked C8 alpha-gamma dimer that is noncovalently associated with C8 beta. C6, C7 C8 alpha, C8 beta, and C9 are homologous. All contain N- and C-terminal modules and an intervening 40-kDa segment referred to as the membrane attack complex/perforin (MACPF) domain. The C8 gamma subunit is unrelated and belongs to the lipocalin family of proteins that display a beta-barrel fold and generally bind small, hydrophobic ligands. Several hundred proteins with MACPF domains have been identified based on sequence similarity; however, the structure and function of most are unknown. Crystal structures of the secreted bacterial protein Plu-MACPF and the human C8 alpha MACPF domain were recently reported and both display a fold similar to those of the bacterial pore-forming cholesterol-dependent cytolysins (CDCs). In the present study, we determined the crystal structure of the human C8(x MACPF domain disulfide-linked to C8 gamma (alpha MACPF-gamma) at 2.15 angstrom resolution. The alpha MACPF portion has the predicted CDC-like fold and shows two regions of interaction with C8 gamma. One is in a previously characterized 19-residue insertion (indel) in C8 alpha and fills the entrance to the putative C8 gamma ligand-binding site. The second is a hydrophobic pocket that makes contact with residues on the side of the C8 gamma beta-barrel. The latter interaction induces conformational changes in alpha MACPF that are likely important for C8 function. Also observed is structural conservation of the MACPF signature motif Y/W-G-T/S-H-F/Y-X-6-G-G in alpha MACPF and Plu-MACPF, and conservation of several key glycine residues known to be important for refolding and pore formation by CDCs. (C) 2008 Elsevier Ltd. All rights reserved.