Hillarp A, Hessing M, Dahlbäck B
Department of Clinical Chemistry, University of Lund, Malmö General Hospital, Sweden.
FEBS Lett. 1989 Dec 18;259(1):53-6. doi: 10.1016/0014-5793(89)81492-9.
The human regulatory complement component C4b-binding protein (C4BP) circulates in plasma either as a free protein or in a bimolecular complex with the vitamin K-dependent protein S. The major form of C4BP is composed of 7 identical, disulfide-linked 70 kDa subunits (alpha-chains), the arrangement of which gives the C4BP molecule a spider-like appearance. Recently, we identified a unique 45 kDa subunit (beta-chain) in C4BP. We have now isolated a subpopulation of C4BP, which does not bind protein S. This C4BP species, which had a molecular weight slightly lower than that of the predominant form, was found to lack the beta-chain. Another lower molecular weight form of C4BP was also purified. It contained the beta-chain and was efficient in binding protein S. Its subunit composition was judged to comprise six alpha-chains and one beta-chain. These results indicate C4BP in plasma to be heterogeneous at a molecular level vis-a-vis subunit composition and/or protein S binding ability and provide support for the concept that the beta-chain of C4BP contains the single protein S binding site.
人类调节性补体成分C4b结合蛋白（C4BP）以游离蛋白形式或与维生素K依赖性蛋白S形成双分子复合物的形式在血浆中循环。C4BP的主要形式由7个相同的、通过二硫键连接的70 kDa亚基（α链）组成，其排列使C4BP分子呈现出蜘蛛状外观。最近，我们在C4BP中鉴定出一种独特的45 kDa亚基（β链）。我们现在分离出了C4BP的一个亚群，它不与蛋白S结合。这种C4BP种类的分子量略低于主要形式，发现其缺乏β链。另一种分子量较低的C4BP形式也被纯化。它含有β链，并且能有效地结合蛋白S。其亚基组成被判定为包含六个α链和一个β链。这些结果表明，血浆中的C4BP在亚基组成和/或蛋白S结合能力方面在分子水平上是异质的，并为C4BP的β链包含单个蛋白S结合位点这一概念提供了支持。
