Podack E R, Tschoop J, Müller-Eberhard H J
J Exp Med. 1982 Jul 1;156(1):268-82. doi: 10.1084/jem.156.1.268.
Evidence has been presented suggesting that during assembly of the membrane attack complex (MAC) of complement, the C5b-8 complex induces polymerization of C9. The C9 polymer was detected by sodium dodecyl sulfate (SDS) gel electrophoresis of MAC isolated from complement-lysed erythrocytes. It resembled the previously described polymerized C9 (poly C9) produced from isolated monomeric C9 by prolonged incubation at 37 degrees C in that it was resistant to dissociation by SDS and reducing agents and had an apparent molecular weight of approximately 1.1 million. The presence of poly C9 in the MAC was further supported by the expression of identical neoantigens by the MAC and poly C9 and by the high C9 content of the MAC relative to its other constituents. Isolated C8 in solution was found to have a single C9-binding site. In mixture, the two proteins formed a reversible equimolar complex that had a sedimentation coefficient of 10.5S. In contrast, a single, cell-bound C5b-8 complex was found to bind up to 12-15 C9 molecules and clusters of C5b- 8 bound 6-8 C9 molecules per C8 molecule. In either case, typical ultrastructural membrane lesions were observed, suggesting that the membrane lesion is identical with the tubular poly C9 consisting of 12-16 C9 molecules, and that the MAC can have either the composition (C5b-8)polyC9 or (CSb-8)(2)polyC9. When C9 input was restricted so that the molar C9/C8 ratio was less than or equal to 3, C9-induced aggregates of C5b-8 were observed but virtually no circular membrane lesions were found. We suggest, therefore, that C9, at low dosage, causes cross-linking of multiple C5b-8 complexes within the target membrane and that, at high dosage, C9 is polymerized by C5b-8 to form a transmembrane channel within the MAC assembly. It is primarily the C9 polymer that evokes the ultrastructural image of the MAC or of membrane lesions caused by complement.
已有证据表明，在补体膜攻击复合物（MAC）组装过程中，C5b - 8复合物可诱导C9聚合。通过对从补体裂解的红细胞中分离出的MAC进行十二烷基硫酸钠（SDS）凝胶电泳检测到了C9聚合物。它类似于先前描述的通过在37℃下长时间孵育从分离的单体C9产生的聚合C9（多聚C9），因为它对SDS和还原剂的解离具有抗性，且表观分子量约为110万。MAC中多聚C9的存在进一步得到MAC和多聚C9相同新抗原表达以及MAC相对于其其他成分的高C9含量的支持。发现溶液中的分离C8具有单个C9结合位点。在混合时，这两种蛋白质形成了一种可逆的等摩尔复合物，其沉降系数为10.5S。相比之下，发现单个细胞结合的C5b - 8复合物可结合多达12 - 15个C9分子，且C5b - 8簇每个C8分子结合6 - 8个C9分子。在任何一种情况下，都观察到了典型的超微结构膜损伤，这表明膜损伤与由12 - 16个C9分子组成的管状多聚C9相同，并且MAC可以具有（C5b - 8）多聚C9或（C5b - 8）₂多聚C9的组成。当限制C9输入使得C9/C8摩尔比小于或等于3时，观察到C9诱导的C5b - 8聚集，但几乎未发现圆形膜损伤。因此，我们认为，低剂量的C9会导致靶膜内多个C5b - 8复合物交联，而高剂量时，C9会被C5b - 8聚合以在MAC组装中形成跨膜通道。主要是C9聚合物引发了MAC或补体引起的膜损伤的超微结构图像。
