分子结构dihydroorotase:范式通过使用双核的金属催化中心。
文章的细节
-
引用
复制到剪贴板 -
Thoden JB,菲利普斯GN Jr,尼尔TM Raushel调频,霍尔顿嗯
分子结构dihydroorotase:范式通过使用双核的金属催化中心。
生物化学。2001年6月19日,40 (24):6989 - 97。
- PubMed ID
-
11401542 (在PubMed]
- 文摘
-
Dihydroorotase嘧啶生物合成过程中起着关键作用,催化的可逆的互变现象[氨基甲酰天冬氨酸dihydroorotate。在这里,我们描述了三维结构的dihydroorotase大肠杆菌和细化1.7决议决定的。每个homodimeric酶亚基折叠成一个“蒂姆”桶主题8股阿尔法螺旋平行β褶板两侧的外表面。出乎意料,每个单元包含一个双核的锌中心金属离子分离,大约3.6。赖氨酸102,羧酸盐,作为两个阳离子之间的桥接配体。越埋或alpha-metal离子亚基我周围是他16岁,他18岁,赖氨酸102,250 Asp,溶剂分子(最有可能的氢氧离子)在一个三角形双锥体安排。beta-metal离子,这是接近溶剂,由赖氨酸102四面体的结扎,他139年,他177年,桥接氢氧根。L-Dihydroorotate绑定单元我观察到,其羰基氧,O4,躺2.9 beta-metal离子。重要交互定位dihydroorotate到活性部位包括胍盐的盐桥群Arg 20和各种附加静电相互作用蛋白骨干和侧链原子。引人注目的是,在第二单元中,[氨基甲酰L-aspartate双核的金属中心附近观察到的绑定与羧酸盐侧链切断两种金属,从而取代过渡性氢氧根离子。 From the three-dimensional structures of the enzyme-bound substrate and product, it has been possible to propose a unique catalytic mechanism for dihydroorotase. In the direction of dihydroorotate hydrolysis, the bridging hydroxide attacks the re-face of dihydroorotate with general base assistance by Asp 250. The carbonyl group is polarized for nucleophilic attack by the bridging hydroxide through a direct interaction with the beta-metal ion. During the cyclization of carbamoyl aspartate, Asp 250 initiates the reaction by abstracting a proton from N3 of the substrate. The side chain carboxylate of carbamoyl aspartate is polarized through a direct electrostatic interaction with the binuclear metal center. The ensuing tetrahedral intermediate collapses with C-O bond cleavage and expulsion of the hydroxide which then bridges the binuclear metal center.