Membrane-Dependent Interaction of Factor Xa and Prothrombin with Factor Va in the Prothrombinase Complex

详细信息    查看全文

• 作者：Shabir H. Qureshi ; Likui Yang ; Chandrashekhara Manithody ; Alireza R. Rezaie
• 刊名：Biochemistry
• 出版年：2009
• 出版时间：June 9, 2009
• 年：2009
• 卷：48
• 期：22
• 页码：5034-5041
• 全文大小：751K
• 年卷期：v.48,no.22(June 9, 2009)
• ISSN：1520-4995

文摘

Because all three protein components of prothrombinase, factors (f) Xa and Va and prothrombin, bind to negatively charged membrane phospholipids, the exact role of the membrane in the prothrombinase reaction has not been fully understood. In this study, we prepared deletion derivatives of fXa and prothrombin in which both the Gla and first EGF-like domains of the protease (E2-fXa) as well as the Gla and both kringle domains of the substrate (prethrombin-2) had been deleted. The fVa-mediated catalytic activity of E2-fXa toward prethrombin-2 was analyzed in both the absence and presence of phospholipids composed of 80% phosphatidylcholine (PC) and 20% phosphatidylserine (PS). PCPS markedly accelerated the initial rate of prethrombin-2 activation by E2-fXa, with the cofactor exhibiting saturation only in the presence of phospholipids (apparent K_d of 60 nM). Competitive kinetic studies in the presence of the two exosite-1-specific ligands Tyr⁶³-sulfated hirudin⁵⁴⁻⁶⁵ and TM456 suggested that while both peptides are highly effective inhibitors of the fVa-mediated activation of prethrombin-2 by E2-fXa in the absence of PCPS, they are ineffective competitors in the presence of phospholipids. Since neither E2-fXa nor prethrombin-2 can interact with membranes, these results suggest that interaction of fVa with PCPS improves the affinity of the activation complex for proexosite-1 of the substrate. Direct binding studies employing OG₄₈₈-EGR-labeled fXa and E2-fXa revealed that the interaction of the Gla domain of fXa with PCPS also induces conformational changes in the protease to facilitate its high-affinity interaction with fVa.