Baglia F A, Walsh P N
Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
J Biol Chem. 1996 Feb 16;271(7):3652-8. doi: 10.1074/jbc.271.7.3652.
Previously we defined a binding site for high molecular weight kininogen (HK) in the A1 domain of factor XI (FXI). Since thrombin can activate FXI and HK inhibits the activation of FXI by thrombin, we have identified a thrombin binding site in FXI. Both the recombinant A1 domain (Glu1-Ser90) and a synthetic peptide (Phe56-Ser86) containing the HK binding site inhibited FXI activation by thrombin. Both a monoclonal antibody, 5F7, recognizing the A1 domain, and the rA1 domain were shown to be competitive inhibitors of thrombin-catalyzed FXI activation. The peptides Ala45-Arg54 and Val59-Arg70 acted synergistically to inhibit FXI activation by thrombin. Mutant rA1 domain constructs (Val64 --> Ala and Ile77 --> Ala), which do not inhibit FXI binding to HK, retain full capacity to inhibit FXI activation by thrombin. The peptide Ala45-Arg54 inhibited thrombin-catalyzed FXI activation, whereas it had no effect on FXI binding to HK. In contrast, the peptide Asn72-Leu83 (which inhibited FXI binding to HK) did not inhibit FXI activation by thrombin. Thus, a thrombin binding site exists in the A1 domain of FXI spanning residues Ala45-Arg70 that is contiguous with but separate and distinct from the HK binding site. These sites may regulate which ligand is bound to FXI and through which pathway FXI is activated.
此前我们在因子 XI（FXI）的 A1 结构域中定义了一个高分子量激肽原（HK）的结合位点。由于凝血酶可激活 FXI，且 HK 抑制凝血酶对 FXI 的激活，我们在 FXI 中鉴定出了一个凝血酶结合位点。重组 A1 结构域（Glu1 - Ser90）和包含 HK 结合位点的合成肽（Phe56 - Ser86）均抑制凝血酶对 FXI 的激活。识别 A1 结构域的单克隆抗体 5F7 和 rA1 结构域均被证明是凝血酶催化的 FXI 激活的竞争性抑制剂。肽段 Ala45 - Arg54 和 Val59 - Arg70 协同作用抑制凝血酶对 FXI 的激活。不抑制 FXI 与 HK 结合的突变型 rA1 结构域构建体（Val64 --> Ala 和 Ile77 --> Ala）保留了完全抑制凝血酶激活 FXI 的能力。肽段 Ala45 - Arg54 抑制凝血酶催化的 FXI 激活，而对 FXI 与 HK 的结合无影响。相反，肽段 Asn72 - Leu83（抑制 FXI 与 HK 的结合）不抑制凝血酶对 FXI 的激活。因此，在 FXI 的 A1 结构域中存在一个凝血酶结合位点，其跨越 Ala45 - Arg70 残基，与 HK 结合位点相邻但分开且不同。这些位点可能调节哪个配体与 FXI 结合以及 FXI 通过哪条途径被激活。
