Asakura S, Hirata H, Okazaki H, Hashimoto-Gotoh T, Matsuda M
Division of Hemostasis and Thrombosis Research, Jichi Medical School, Tochigi-Ken, Japan.
J Biol Chem. 1990 Mar 25;265(9):5135-8.
In the presence of a monoclonal antibody raised against the human thrombin-antithrombin III complex, the reaction between thrombin and antithrombin III proceeded to form preferentially a two-chain form of the inhibitor rather than to follow the major pathway of stable acyl complex formation. We thus propose the term "switching antibody" for an antibody that switches the enzyme-inhibitor reaction (Asakura, S., Matsuda, M., Yoshida, N., Terukina, S., and Kihara, H. (1989) J. Biol. Chem. 264, 13736-13739). By analyzing a CNBr fragment of the thrombin-antithrombin III complex that reacts with the antibody we localized the epitope for the antibody to a strongly hydrophobic residue 382-386 peptide segment, Ala-Ala-Ala-Ser-Thr, of the inhibitor, which is also contiguous with a hydrophobic amino acid Ala at its carboxyl terminus. This particular region should be cryptic in nascent antithrombin III, but could have been exposed to provide the reactive site for the antibody at an early stage of the reaction. Thereby a conformational change may have been induced at or near the reactive site of the complex, facilitating hydrolysis of the inhibitor by the enzyme. Interestingly, this hydrophobic region is highly conserved among members of the serpin family.
在存在针对人凝血酶 - 抗凝血酶III复合物产生的单克隆抗体的情况下，凝血酶与抗凝血酶III之间的反应优先形成抑制剂的双链形式，而不是遵循稳定酰基复合物形成的主要途径。因此，我们提出“转换抗体”这一术语来指代一种能转换酶 - 抑制剂反应的抗体（朝仓，S.，松田，M.，吉田，N.，照来田，S.，和木原，H.（1989年）《生物化学杂志》264，13736 - 13739）。通过分析与该抗体反应的凝血酶 - 抗凝血酶III复合物的溴化氰片段，我们将该抗体的表位定位到抑制剂的一个强疏水残基382 - 386肽段，即Ala - Ala - Ala - Ser - Thr，其羧基末端还与一个疏水氨基酸Ala相邻。这个特定区域在新生抗凝血酶III中应该是隐蔽的，但在反应早期可能已经暴露，从而为抗体提供反应位点。由此可能在复合物的反应位点处或其附近诱导了构象变化，促进了酶对抑制剂的水解。有趣的是，这个疏水区域在丝氨酸蛋白酶抑制剂家族成员中高度保守。
