Rivas G, Ingham K C, Minton A P
Laboratory of Biochemical Pharmacology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Biochemistry. 1992 Dec 1;31(47):11707-12. doi: 10.1021/bi00162a006.
The weight-average molecular weight of C1s, an activated serine protease subcomponent of human complement C1, has been measured by means of sedimentation equilibrium over a wide range of both protein and calcium ion concentrations. The combined data may be accounted for quantitatively by a simple model for Ca(2+)-dependent self-association of C1s to a dimer. According to this model, the monomer contains a single Ca2+ binding site with K approximately equal to 3 x 10(5) M-1, and the dimer contains three independent Ca binding sites, two having a Ca2+ affinity lower than that of the monomer (K approximately equal to 3 x 10(4) M-1). The third binding site in the dimer, which presumably lies at the interface between the two amino-terminal alpha domains, has a higher Ca2+ affinity (K approximately equal to 1 x 10(8) M-1) and provides the driving force for C1s dimerization in the presence of calcium.
人补体C1的活化丝氨酸蛋白酶亚组分C1s的重均分子量，已通过沉降平衡法在较宽的蛋白质和钙离子浓度范围内进行了测定。综合数据可用一个简单的模型进行定量解释，该模型认为C1s在钙离子依赖下自缔合形成二聚体。根据此模型，单体含有一个单一的Ca2+结合位点，其K值约等于3×10(5) M-1，二聚体含有三个独立的钙结合位点，其中两个的Ca2+亲和力低于单体（K值约等于3×10(4) M-1）。二聚体中的第三个结合位点大概位于两个氨基末端α结构域之间的界面处，具有较高的Ca2+亲和力（K值约等于1×10(8) M-1），并在有钙存在的情况下为C1s二聚化提供驱动力。
