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首页> 外文期刊>Biochemistry >PH-DEPENDENT STRUCTURAL CHANGES IN THE ACTIVE SITE OF P-HYDROXYBENZOATE HYDROXYLASE POINT TO THE IMPORTANCE OF PROTON AND WATER MOVEMENTS DURING CATALYSIS
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PH-DEPENDENT STRUCTURAL CHANGES IN THE ACTIVE SITE OF P-HYDROXYBENZOATE HYDROXYLASE POINT TO THE IMPORTANCE OF PROTON AND WATER MOVEMENTS DURING CATALYSIS

机译：对羟基苯甲酸酯羟化酶活性位点的PH依赖结构变化对催化过程中质子和水运动的重要性

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摘要

Deprotonation of p-hydroxybenzoate to the phenolate and reprotonation of the hydroxylated dienone intermediate to form the product are essential steps in the reaction catalyzed by p-hydroxybenzoate hydroxylase (PHBH). The mechanism by which protons are transferred in these reactions is not obvious, because the substrate bound in the active site is isolated from solvent. Structure analyses of wild-type and mutant PHBH, with bound p-hydroxybenzoate or p-aminobenzoate, reveal a chain of proton donors and accepters (the hydroxyl groups of Tyr201 and Tyr385, and two water molecules) that can connect the substrate 4-OH to His72, a surface residue. This chain could provide a pathway for proton transfer to and from the substrate. Using various combinations of pH and substrates, we show that in crystalline PHBH ionizable groups in the chain may rotate and change hydrogen-bond orientation. Molecular dynamics simulations have been used to predict the preferred orientation of hydrogen bonds in the chain as a function of the ionization states of substrate and His72. The calculations suggest that changes in the ionization state of the substrate could be associated with changes in orientation of the hydrogen bonds in the chain. Transfer of water between the chain of proton donors and the solvent also appears to be an essential part of the mechanism that provides reversible transfer of protons during the hydroxylation reaction.
机译：对羟基苯甲酸酯对苯酚的去质子化和羟基化二烯酮中间体的再质子化以形成产物是对羟基苯甲酸酯羟化酶（PHBH）催化反应的重要步骤。在这些反应中转移质子的机理尚不明确，因为结合在活性位点上的底物是从溶剂中分离出来的。与结合的对羟基苯甲酸酯或对氨基苯甲酸酯结合的野生型和突变型PHBH的结构分析揭示了可以连接底物4-OH的质子供体和受体链（Tyr201和Tyr385的羟基，以及两个水分子）到His72表面残留物。该链可提供质子往返于底物的传递途径。使用pH和底物的各种组合，我们表明在晶体PHBH中，链中的可电离基团可能旋转并改变氢键方向。分子动力学模拟已被用于预测链中氢键的优选取向，其取决于底物和His72的电离态。计算表明，底物电离状态的变化可能与链中氢键方向的变化有关。水在质子供体链和溶剂之间的转移似乎也是在羟基化反应期间提供质子可逆转移的机理的重要组成部分。

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