Unravelling the Molecular Origin of the Regiospecificity in Extradiol Catechol Dioxygenases,Inorganic Chemistry

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Unravelling the Molecular Origin of the Regiospecificity in Extradiol Catechol Dioxygenases
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2016-04-06 00:00:00 , DOI: 10.1021/acs.inorgchem.5b02978
Gemma J. Christian _{1,

2} , Frank Neese ₁ , Shengfa Ye ₁

Affiliation

Many factors have been suggested to control the selectivity for extradiol or intradiol cleavage in catechol dioxygenases. The varied selectivity of model complexes and the ability to force an extradiol enzyme to do intradiol cleavage indicate that the problem may be complex. In this paper we focus on the regiospecificity of the proximal extradiol dioxygenase, homoprotocatechuate 2,3-dioxygenase (HPCD), for which considerable advances have been made in our understanding of the mechanism from an experimental and computational standpoint. Two key steps in the reaction mechanism were investigated: (1) attack of the substrate by the superoxide moiety and (2) attack of the substrate by the oxyl radical generated by O–O bond cleavage. The selectivity at both steps was investigated through a systematic study of the role of the substrate and the first and second coordination spheres. For the isolated native substrate, intradiol cleavage is calculated to be both kinetically and thermodynamically favored, therefore nature must use the enzyme environment to reverse this preference. Two second sphere residues were found to play key roles in controlling the regiospecificity of the reaction: Tyr257 and His200. Tyr257 controls the selectivity by modulating the electronic structure of the substrate, while His200 controls selectivity through steric effects and by preventing alternative pathways to intradiol cleavage.

中文翻译：

揭示胞外二醇邻苯二酚双加氧酶区域特异性的分子起源。

已经提出许多因素来控制儿茶酚双加氧酶中的二醇外切或二醇内切的选择性。模型配合物选择性的变化和迫使二醇外酶进行二醇内切割的能力表明该问题可能很复杂。在本文中，我们集中于近端二醇外加双加氧酶，高蛋白儿茶酸2,3-双加加氧酶（HPCD）的区域特异性，从我们的实验和计算角度，我们在机理上已取得了长足的进步。研究了反应机理中的两个关键步骤：（1）超氧化物部分对底物的攻击和（2）O-O键断裂产生的羟基自由基对底物的攻击。通过系统研究底物以及第一和第二配位球的作用，研究了这两个步骤的选择性。对于分离的天然底物，二醇内裂解被计算为在动力学和热力学上均有利，因此自然界必须使用酶环境来逆转这种偏好。发现两个第二球残基在控制反应的区域特异性中起关键作用：Tyr257和His200。Tyr257通过调节底物的电子结构来控制选择性，而His200通过空间效应并通过防止二醇内切割的替代途径来控制选择性。因此，自然界必须利用酶环境来扭转这种偏好。发现两个第二球残基在控制反应的区域特异性中起关键作用：Tyr257和His200。Tyr257通过调节底物的电子结构来控制选择性，而His200通过空间效应并通过防止二醇内切割的替代途径来控制选择性。因此，自然界必须利用酶环境来扭转这种偏好。发现两个第二球残基在控制反应的区域特异性中起关键作用：Tyr257和His200。Tyr257通过调节底物的电子结构来控制选择性，而His200通过空间效应并通过防止二醇内切割的替代途径来控制选择性。

更新日期：2016-04-06

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