Crystal structure of phenylmethanesulfonyl fluoride-treated human chymase at 1.9 A.
Crystal structure of phenylmethanesulfonyl fluoride-treated human chymase at 1.9 A.
复制标题
经苯甲磺酰氟处理的人食糜酶在 1.9 A 下的晶体结构。
作者：
M. Mcgrath;T. Mirzadegan;B. Schmidt
用分子置换方法测定了人凝乳酶的X-射线晶体结构，分辨率为1.9A。人类凝乳酶的第一种结构是甲苯磺酸的Ser195酯。精细结构(Rcrst=0.183)表明，抑制剂苯基部分位于主要特异性口袋S1的顶部，而硫与Ser195-O伽马共价连接。磺酰氧基与氧阴离子空穴和他的57-N增量1相互作用。抑制剂的存在扰乱了他57通常的笨拙位置，并迫使它进入反式构象。尽管主要结合口袋在凝乳酶和胰凝乳酶中具有相似的特异性，但对延伸底物结合部位的检查揭示了凝乳酶在选择底物时具有更大的区分性的结构基础。较大的30S环及其与活性中心的接近表明它将底物残基C-端接触到剪切键。底物在糜酶活性部位的模拟表明，结合能可能是通过底物残基P2‘和P4’提供的三个主链氢键获得的，也可能与底物侧链发生区分作用。人凝乳酶S1‘中Lys 40的存在解释了其对P1’处天冬氨酸/谷氨酸的偏好。此外，S1‘的阳离子性质为血管紧张素II为底物的人糜酶催化效率低提供了结构基础。
The X-ray crystal structure of human chymase has been determined to 1.9 A resolution using molecular replacement methods. This first structure of human chymase is present as the Ser 195 ester of alpha-toluenesulfonic acid. The refined structure (Rcryst = 0.183) shows that the inhibitor phenyl moiety lies at the top of the major specificity pocket, S1, while the sulfur is covalently linked to Ser 195-O gamma. The sulfonyl oxygens interact with the oxyanion hole and with His 57-N delta 1. The presence of the inhibitor disturbs the usual gauche position of His 57 and forces it to the trans conformer. Though the primary binding pockets are similarly specific in chymase and chymotrypsin, examination of the extended substrate binding sites reveals the structural basis for chymase's greater discrimination in choosing substrates. The larger 30s loop and its proximity to the active site indicates that it contacts substrate residues C-terminal to the scissile bond. Modeling of substrate at the chymase active site suggests that binding energy may be gained by three main-chain hydrogen bonds provided by substrate residues P2' and P4' and that discriminating interactions with substrate side chains are also likely. The presence of Lys 40 in S1' of human chymase explains its preference for Asp/Glu at P1'. Moreover, the cationic nature of S1' provides a structural basis for human chymase's poor catalytic efficiency when angiotensin II is the substrate.