Department of Protein Engineering, Genentech, Inc., South San Francisco, CA 94080, USA.
Department of Protein Engineering, Genentech, Inc., South San Francisco, CA 94080, USA; Department of Antibody Engineering, Genentech, Inc., South San Francisco, CA 94080, USA.
Structure. 2009 Dec 9;17(12):1614-1624. doi: 10.1016/j.str.2009.09.014.
Recent structural studies have outlined the mechanism of protease inhibition by active site-directed antibodies. However, the molecular basis of allosteric inhibition by antibodies has been elusive. Here we report the 2.35 A resolution structure of the trypsin-like serine protease hepatocyte growth factor activator (HGFA) in complex with the allosteric antibody Ab40, a potent inhibitor of HGFA catalytic activity. The antibody binds at the periphery of the substrate binding cleft and imposes a conformational change on the entire 99-loop (chymotrypsinogen numbering). The altered conformation of the 99-loop is incompatible with substrate binding due to the partial collapse of subsite S2 and the reorganization of subsite S4. Remarkably, a single residue deletion of Ab40 abolished inhibition of HGFA activity, commensurate with the reversal of the 99-loop conformation to its "competent" state. The results define an "allosteric switch" mechanism as the basis of protease inhibition by an allosteric antibody.
最近的结构研究概述了活性位点定向抗体对蛋白酶抑制的机制。然而，抗体变构抑制的分子基础一直难以捉摸。在这里，我们报告了胰蛋白酶样丝氨酸蛋白酶肝细胞生长因子激活剂（HGFA）与变构抗体 Ab40 的 2.35 A 分辨率复合物结构，Ab40 是 HGFA 催化活性的有效抑制剂。该抗体结合在底物结合裂隙的外围，并对整个 99-环（糜蛋白酶原编号）施加构象变化。由于亚基 S2 的部分塌陷和亚基 S4 的重组，99-环的改变构象与底物结合不兼容。值得注意的是，Ab40 的单个残基缺失消除了对 HGFA 活性的抑制，与 99-环构象恢复其“有能力”状态一致。结果定义了“变构开关”机制作为变构抗体抑制蛋白酶的基础。
