Membrane pore formation by human complement: functional importance of the transmembrane β-hairpin (TMH) segments of C8α and C9.
Membrane pore formation by human complement: functional importance of the transmembrane β-hairpin (TMH) segments of C8α and C9.
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DOI：
10.1016/j.molimm.2013.10.007
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发表时间：
2014-02
影响因子：
3.6
通讯作者：
Sodetz JM
中科院分区：
文献类型：
--
作者：
Weiland MH;Qian Y;Sodetz JM
人C8和C9在细菌细胞上补体的孔样“膜攻击复合物”（MAC）的形成中具有关键作用。当研究显示C8α和C8β亚基的MACPF结构域与成孔细菌胆固醇依赖性溶细胞素（CDC）之间的结构相似性时，提出了这些蛋白质的膜插入的可能机制。这种相似性包括一对α-螺旋束，其在孔形成期间在CDC中重折叠以产生两个跨膜β-发夹（TMH 1和TMH 2）。C9是MAC的主要成孔组分，并且由于其与C8α和C8β的同源性，也可能含有两个TMH片段。为了确定它们的膜插入潜力，将C8α中的TMH序列和预测在C9中的那些序列替换为产气荚膜梭菌溶素O（PFO）（一种充分表征的CDC）中的TMH序列。只有含有C8α（PFO/αT2）或C9（PFO/C9 T2）TMH 2的嵌合蛋白才能以可溶性、活性形式表达。PFO/αT2和PFO/C9 T2嵌合体具有明显的溶血活性，在膜上形成孔状结构，并能与PFO联合收割机形成具有溶血活性的混合复合物，其功能与PFO相似。这些结果为C8α和C9中的TMH片段在MAC膜渗透和孔形成中具有直接作用的假设提供了实验证据。
Human C8 and C9 have a key role in forming the pore-like “membrane attack complex” (MAC) of complement on bacterial cells. A possible mechanism for membrane insertion of these proteins was suggested when studies revealed a structural similarity between the MACPF domains of the C8α and C8β subunits and the pore-forming bacterial cholesterol-dependent cytolysins (CDCs). This similarity includes a pair of α-helical bundles that in the CDCs refold during pore formation to produce two transmembrane β-hairpins (TMH1 and TMH2). C9 is the major pore-forming component of the MAC and is also likely to contain two TMH segments because of its homology to C8α and C8β. To determine their potential for membrane insertion, the TMH sequences in C8α and those predicted to be in C9 were substituted for the TMH sequences in perfringolysin O (PFO), a well-characterized CDC. Only chimeric proteins containing TMH2 from C8α (PFO/αT2) or C9 (PFO/C9T2) could be expressed in soluble, active form. The PFO/αT2 and PFO/C9T2 chimeras retained significant hemolytic activity, formed pore-like structures on membranes, and could combine with PFO to form hemolytically active mixed complexes that were functionally similar to PFO alone. These results provide experimental evidence in support of the hypothesis that TMH segments in C8α and those predicted to be in C9 have a direct role in MAC membrane penetration and pore formation.
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影响因子：
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