Miyata T, Kawabata S, Iwanaga S, Takahashi I, Alving B, Saito H
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan.
Proc Natl Acad Sci U S A. 1989 Nov;86(21):8319-22. doi: 10.1073/pnas.86.21.8319.
Structural studies on a congenital abnormal coagulation factor XII (Hageman factor), factor XII Washington D.C., have been performed to identify the defect responsible for its lack of procoagulant activity. Amino acid sequence analysis of a tryptic peptide isolated from the abnormal factor XII indicated that Cys-571 (equivalent to Cys-220 in the chymotrypsin numbering system) had been replaced by serine. No other substitutions in the active-site triad--namely, His-393, Asp-442, and Ser-544--were found. We propose that the Cys-571----Ser replacement found in this factor XII variant destroys the formation of the disulfide linkage between Cys-540 and Cys-571, giving rise to an altered conformation of the active-site serine residue or the secondary substrate-binding site and, thus, leads to the loss of enzyme activity.
对一种先天性异常凝血因子XII（哈格曼因子），即华盛顿特区因子XII进行了结构研究，以确定导致其缺乏促凝血活性的缺陷。从异常因子XII中分离出的一种胰蛋白酶肽的氨基酸序列分析表明，半胱氨酸-571（在胰凝乳蛋白酶编号系统中相当于半胱氨酸-220）已被丝氨酸取代。在活性位点三联体中，即组氨酸-393、天冬氨酸-442和丝氨酸-544，未发现其他取代。我们提出，在这种因子XII变体中发现的半胱氨酸-571至丝氨酸的替换破坏了半胱氨酸-540和半胱氨酸-571之间二硫键的形成，导致活性位点丝氨酸残基或二级底物结合位点的构象改变，从而导致酶活性丧失。
