3RD COMPONENT OF COMPLEMENT (C3) - STRUCTURAL-PROPERTIES IN RELATION TO FUNCTIONS
3RD COMPONENT OF COMPLEMENT (C3) - STRUCTURAL-PROPERTIES IN RELATION TO FUNCTIONS
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DOI：
10.1073/pnas.72.6.1989
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发表时间：
1975-01-01
影响因子：
11.1
通讯作者：
MULLEREBERHARD, HJ
中科院分区：
文献类型：
--
作者：
BOKISCH, VA;DIERICH, MP;MULLEREBERHARD, HJ
补体的第三个成分（C3）在补体系统的功能中发挥着关键作用。我们研究了其多肽链、生理片段、酶攻击区域和功能位点之间的拓扑关系。 C3由两条链（α和β）组成，这两条链通过二硫键和非共价力连接，分子量分别为120,000和75,000。 C3 通过 C3 转化酶对 α 链的作用而被激活。随着一个多肽键 C3a 的水解，9000 道尔顿的活化肽从 α 链的 NH2 末端部分脱位。由此，先前隐藏的结合区域在 C3b 片段（181,000 道尔顿）中短暂显露出来，该片段对生物膜上存在的明显非特异性受体表现出亲和力。新生 C3b 膜的结合通过片段的 C3d 部分发生，因为 C3b 灭活剂或胰蛋白酶对结合的 C3b 的后续作用导致 C3c 释放，但不释放 C3d。结合的 C3b 和 C3d 具有稳定的位点，能够与有限种类的细胞上存在的特定受体结合。我们认为所有已知的生理上发生的 C3 片段都是通过 α 链的酶裂解产生的：C3a、C3b、C3c 和 C3d。 C3a (alpha1) 和 C3e (alpha2) 由单链组成，C3b 由两条链（α' 和 beta）组成，而 C3c 由整个 β 链和 α 链的多个片段组成，每个片段通过二硫键与 β 链连接。
The third component of complement (C3) fulfills a pivotal role in the functions of the complement system. We have investigated the topological relationships among its polypeptide chains, physiologic fragments, enzyme attack regions, and functional sites. C3 consists of two chains (alpha and beta) which are linked by disulfide bonds and noncovalent forces and which have molecular weights of, respectively, 120,000 and 75,000. C3 is activated by action of C3 convertase on the alpha-chain. With hydrolysis of one polypeptide bonds, C3a, the 9000 dalton activation peptide is dislocated from the NH2-terminal portion of the alpha-chain. A previously concealed binding region is thereby transiently revealed in the C3b-fragment (181,000 dalton) which displays affinity for apparently nonspecific acceptors present on biological membranes. Binding of nascent C3b membranes occurs through the C3d portion of the fragment because subsequent action of the C3b-inactivator or trypsin on bound C3b causes release of C3c, but not of C3d. Bound C3b and C3d possess stable sites that are capable of binding to specific receptors present on a limited variety of cells. We propose that all known physiologically occurring fragments of C3 arise by enzymatic cleavage of the alpha-chain: C3a, C3b, C3c, and C3d. Whereas C3a (alpha1) and C3e (alpha2) consist of a single chain and C3b consists of two chains (alpha' and beta), C3c is composed of the entire beta-chain and multiple fragments of the alpha-chain, each of which is linked by disulfide bonds to the beta-chain.