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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >ACTIVE SITE TOPOLOGY AND REACTION MECHANISM OF GTP CYCLOHYDROLASE I
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ACTIVE SITE TOPOLOGY AND REACTION MECHANISM OF GTP CYCLOHYDROLASE I

机译：GTP环水解酶I的活性部位拓扑和反应机理

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摘要

GTP cyclohydrolase I of Escherichia coli is a torus-shaped homodecamer with D-5 symmetry and catalyzes a complex ring expansion reaction conducive to the formation of dihydroneopterin triphosphate from GTP, The x-ray structure of a complex of the enzyme with the substrate analog, dGTP bound at the active site was determined at a resolution of 3 Angstrom. In the decamer, 10 equivalent active sites are present, each of which contains a 10-Angstrom deep pocket formed by surface areas of 3 adjacent subunits, The substrate forms a complex hydrogen bond network with the protein, Active site residues were modified by site-directed mutagenesis, and enzyme activities of the mutant proteins were measured. On this basis, a mechanism of the enzyme-catalyzed reaction is proposed. Cleavage of the imidazole ring is initiated by protonation of N7 by His-179 followed by the attack of water at CS of the purine system, Cystine Cys-110 Cys-181 may be involved in this reaction step, Opening of the imidazole ring may be in concert with cleavage of the furanose ring to generate a Schiffs base from the glycoside, The gamma-phosphate of GTP may be involved in the subsequent Amadori rearrangement of the carbohydrate side chain by activating the hydroxyl group of Ser-135.
机译：大肠杆菌的GTP环水解酶I是具有D-5对称性的环形环状同聚体，催化由GTP形成三磷酸二氢蝶呤的复杂的环扩环反应，该酶与底物类似物的复合物的X射线结构，以3埃的分辨率测定结合在活性位点上的dGTP。在decamer中，存在10个等效的活性位点，每个活性位点包含一个10埃深的口袋，该口袋由3个相邻亚基的表面积形成。底物与蛋白质形成复杂的氢键网络，活性位点残基通过位点修饰-直接诱变，并测量了突变蛋白的酶活性。在此基础上，提出了酶催化反应的机理。咪唑环的裂解是由His-179对N7进行质子化，然后是水在嘌呤系统CS处的进攻而引发的，该反应步骤可能涉及Cystine Cys-110 Cys-181，打开咪唑环可能是与呋喃糖环的裂解一起从糖苷生成席夫斯碱基的过程中，GTP的γ-磷酸可能通过激活Ser-135的羟基参与碳水化合物侧链的随后Amadori重排。

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