木糖异构酶的氢化metal-mediated转变机制基于1.6的链霉菌属和木糖醇D-xylose rubiginosus结构。
文章的细节
-
引用
复制到剪贴板 -
甲沟炎M,霍华德AJ,公元前Finzel Poulos TL, Winborne E Gilliland GL
木糖异构酶的氢化metal-mediated转变机制基于1.6的链霉菌属和木糖醇D-xylose rubiginosus结构。
蛋白质。1991;9 (3):153 - 73。
- PubMed ID
-
2006134 (在PubMed]
- 文摘
-
的晶体结构重组链霉菌属rubiginosus D-xylose异构酶(D-xylose keto-isomerase, EC 5.3.1.5)解决多个同形替代技术已被提炼分辨率1.64 R = 0.16。作为较早的研究中观察到4.0(卡雷尔et al .,生物。化学。259:3230 - 3236,1984),木糖异构酶是由四个相同的亚基组成的四聚物。eight-stranded平行的单体由beta-barrel周围八个螺旋线与扩展的c端尾与邻近单体提供广泛的联系。活性部位的口袋里被定义为一个开放的桶的入口两旁疏水残留在底部的口袋里主要由谷氨酸、天冬氨酸和组氨酸残基协调两个锰离子。酶的结构在MnCl2面前,抑制剂木糖醇,和衬底D-xylose存在和缺乏MnCl2也被精炼R = 0.14, 1.60, 1.71 R = 0.15, R = 0.15, 1.60,和1.60 R = 0.14。的环氧循环alpha-D-xylose及其C1羟基氢键距离内NE2结晶结构的His-54 D-xylose的存在。抑制剂,木糖醇,底物的扩展形式,D-xylose,绑定的C2和C4哦组与其中一个二价阳离子活性部位和C1与其他阳离子哦。剩下的与周边氨基酸侧链羟基氢键。一个详细的提出了D-xylose异构酶的机制。 Upon binding of cyclic alpha-D-xylose to xylose isomerase, His-54 acts as the catalytic base in a ring opening reaction. The ring opening step is followed by binding of D-xylose, involving two divalent cations, in an extended conformation. The isomerization of D-xylose to D-xylulose involves a metal-mediated 1,2-hydride shift. The final step in the mechanism is a ring closure to produce alpha-D-xylulose. The ring closing is the reverse of the ring opening step. This mechanism accounts for the majority of xylose isomerase's biochemical properties, including (1) the lack of solvent exchange between the 2-position of D-xylose and the 1-pro-R position of D-xylulose, (2) the chemical modification of histidine and lysine, (3) the pH vs. activity profile, and (4) the requirement for two divalent cations in the mechanism.