Skinner R, Abrahams J P, Whisstock J C, Lesk A M, Carrell R W, Wardell M R
Department of Haematology, University of Cambridge, MRC Centre, UK.
J Mol Biol. 1997 Feb 28;266(3):601-9. doi: 10.1006/jmbi.1996.0798.
The crystal structure of a dimeric form of intact antithrombin has been solved to 2.6 A, representing the highest-resolution structure of an active, inhibitory serpin to date. The crystals were grown under microgravity conditions on Space Shuttle mission STS-67. The overall confidence in the structure, determined earlier from lower resolution data, is increased and new insights into the structure-function relationship are gained. Clear and continuous electron density is present for the reactive centre loop region P12 to P14 inserting into the top of the A-beta-sheet. Areas of the extended amino terminus, unique to antithrombin and important in the binding of the glycosaminoglycan heparin, can now be traced further than in the earlier structures. As in the earlier studies, the crystals contain one active and one latent molecule per asymmetric unit. Better definition of the electron density surrounding the D-helix and of the residues implicated in the binding of the heparin pentasaccharide (Arg47, Lys114, Lys125, Arg129) provides an insight into the change of affinity of binding that accompanies the change in conformation. In particular, the observed hydrogen bonding of these residues to the body of the molecule in the latent form explains the mechanism for the release of newly formed antithrombin-protease complexes into the circulation for catabolic removal.
完整抗凝血酶二聚体形式的晶体结构已解析至2.6埃，这是迄今为止活性抑制性丝氨酸蛋白酶抑制剂的最高分辨率结构。这些晶体是在航天飞机任务STS - 67的微重力条件下生长的。基于早期较低分辨率数据确定的该结构的整体可信度得到提高，并且对结构 - 功能关系有了新的认识。对于插入Aβ片层顶部的反应中心环区域P12至P14，存在清晰且连续的电子密度。抗凝血酶特有的、在糖胺聚糖肝素结合中起重要作用的延伸氨基末端区域，现在比早期结构中能追踪得更远。与早期研究一样，每个不对称单元的晶体包含一个活性分子和一个潜在分子。对D螺旋周围电子密度以及与肝素五糖结合相关残基（Arg47、Lys114、Lys125、Arg129）的更好定义，有助于深入了解构象变化伴随的结合亲和力变化。特别是，观察到这些残基以潜在形式与分子主体形成氢键，这解释了新形成的抗凝血酶 - 蛋白酶复合物释放到循环中进行分解代谢清除的机制。
