van de Locht A, Lamba D, Bauer M, Huber R, Friedrich T, Kröger B, Höffken W, Bode W
Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Martinsried, Germany.
EMBO J. 1995 Nov 1;14(21):5149-57. doi: 10.1002/j.1460-2075.1995.tb00199.x.
Rhodniin is a highly specific inhibitor of thrombin isolated from the assassin bug Rhodnius prolixus. The 2.6 Angstrum crystal structure of the non-covalent complex between recombinant rhodniin and bovine alpha-thrombin reveals that the two Kazal-type domains of rhodniin bind to different sites of thrombin. The amino-terminal domain binds in a substrate-like manner to the narrow active-site cleft of thrombin; the imidazole group of the P1 His residue extends into the S1 pocket to form favourable hydrogen/ionic bonds with Asp189 at its bottom, and additionally with Glu192 at its entrance. The carboxy-terminal domain, whose distorted reactive-site loop cannot adopt the canonical conformation, docks to the fibrinogen recognition exosite via extensive electrostatic interactions. The rather acidic polypeptide linking the two domains is displaced from the thrombin surface, with none of its residues involved in direct salt bridges with thrombin. The tight (Ki = 2 x 10(-13) M) binding of rhodniin to thrombin is the result of the sum of steric and charge complementarity of the amino-terminal domain towards the active-site cleft, and of the electrostatic interactions between the carboxy-terminal domain and the exosite.
红猎蝽素是一种从吸血猎蝽（Rhodnius prolixus）中分离出的高度特异性凝血酶抑制剂。重组红猎蝽素与牛α-凝血酶非共价复合物的2.6埃晶体结构表明，红猎蝽素的两个卡扎尔型结构域与凝血酶的不同位点结合。氨基末端结构域以底物样方式结合到凝血酶狭窄的活性位点裂隙；P1组氨酸残基的咪唑基团延伸到S1口袋中，与底部的天冬氨酸189形成有利的氢键/离子键，并在入口处与谷氨酸192额外形成氢键/离子键。羧基末端结构域，其扭曲的反应位点环不能采用典型构象，通过广泛的静电相互作用与纤维蛋白原识别外位点对接。连接两个结构域的相当酸性的多肽从凝血酶表面移位，其残基均未参与与凝血酶的直接盐桥形成。红猎蝽素与凝血酶的紧密结合（Ki = 2 x 10(-13) M）是氨基末端结构域与活性位点裂隙之间空间和电荷互补以及羧基末端结构域与外位点之间静电相互作用的总和结果。
