Bhakdi S, Tranum-Jensen J
Mol Immunol. 1982 Sep;19(9):1167-77. doi: 10.1016/0161-5890(82)90327-3.
the SC5b-8 complex of human complement is a hydrophilic molecule of mol. wt 800,000-850,000 that is seen in the electron microscope as an elongated, straight or curved structure of 50-55 nm total length and 8-9 nm width. Tryptic attack on the fluid-phase complex exposes lipid-binding surfaces on the molecule. The trypsinized complex can be incorporated into liposomal lipid bilayers, and the majority of protein is then viewed as ill-defined, larger tufts projecting exterior to the liposomal membrane. These tufts possibly represent clusters of a unit lesion, which consists of two diverging projections, each approximately 25 nm in length. The two projections are possibly joined to each other to give the membrane-bound complex a shape akin to that of an incomplete funnel. Analyses by SDS-polyacrylamide gel electrophoresis show that the polypeptide subunits C5b, C7 and C8 beta entirely resist tryptic degradation in both SC5b-8 and SC5b-9 complement complexes. Limited proteolysis of C6, C8 alpha gamma and C9, and extensive degradation of the S-protein are effected by trypsin. The results are compatible with the concept that proteolytic cleavage of the S-protein in SC5b-8 and SC5b-9 is the cause of the trypsin-dependent, hydrophilic-amphiphilic transition of the terminal, fluid-phase complement complexes.
人补体的SC5b-8复合物是一种分子量为800,000 - 850,000的亲水分子，在电子显微镜下呈总长度为50 - 55 nm、宽度为8 - 9 nm的细长、笔直或弯曲结构。对液相复合物进行胰蛋白酶处理会暴露出分子上的脂质结合表面。经胰蛋白酶处理的复合物可整合到脂质体脂质双层中，此时大部分蛋白质表现为脂质体膜外部不明确的较大簇状突出物。这些簇状突出物可能代表一个单位损伤的簇，该单位损伤由两个发散的突出物组成，每个突出物长度约为25 nm。这两个突出物可能相互连接，使膜结合复合物呈现出类似于不完全漏斗的形状。SDS - 聚丙烯酰胺凝胶电泳分析表明，多肽亚基C5b、C7和C8β在SC5b - 8和SC5b - 9补体复合物中完全抵抗胰蛋白酶降解。胰蛋白酶对C6、C8αγ和C9进行有限的蛋白水解，并对S蛋白进行广泛降解。这些结果与以下概念相符：SC5b - 8和SC5b - 9中S蛋白的蛋白水解裂解是末端液相补体复合物依赖胰蛋白酶的亲水性 - 两亲性转变的原因。
