Nagasawa S, Unno H, Ichihara C, Koyama J, Koide T
FEBS Lett. 1983 Nov 28;164(1):135-8. doi: 10.1016/0014-5793(83)80036-2.
C4bp, a regulator of the classical pathway of complement system, is composed of 6-8 disulfide-linked subunit chains of 75 kDa. Upon incubation with chymotrypsin, C4bp was rapidly cleaved into a nicked C4bp, composed of disulfide-linked 48 kDa and 27 kDa fragments. Subsequent slow cleavage on the 27 kDa fragment resulted in the liberation of the active site-containing 48 kDa fragment from the nicked C4bp. The N-terminal amino acid sequence of the 48 kDa fragment was identical to that of the parent subunit chain of C4bp, indicating that the 48 kDa active fragment was released from the N-terminal side of the parent subunit chain. Based on these results, a possible gross structure of C4bp is proposed.
C4bp是补体系统经典途径的一种调节因子，由6至8条75 kDa的二硫键连接亚基链组成。用胰凝乳蛋白酶孵育后，C4bp迅速裂解为带切口的C4bp，它由二硫键连接的48 kDa和27 kDa片段组成。随后27 kDa片段的缓慢裂解导致含活性位点的48 kDa片段从带切口的C4bp中释放出来。48 kDa片段的N端氨基酸序列与C4bp亲本亚基链的序列相同，表明48 kDa活性片段是从亲本亚基链的N端一侧释放出来的。基于这些结果，提出了C4bp可能的总体结构。
