脱羧
化学
活动站点
基质(水族馆)
立体化学
羧酸盐
取代基
裂解酶
酶
反应机理
催化循环
催化作用
有机化学
海洋学
地质学
作者
Xiang Sheng,Y. Patskovsky,Anna Vladimirova,J.B. Bonanno,Steven C. Almo,Fahmi Himo,Frank M. Raushel
出处
期刊:Biochemistry
[American Chemical Society]
日期:2017-12-28
卷期号:57 (22): 3167-3175
被引量:30
标识
DOI:10.1021/acs.biochem.7b01213
摘要
γ-Resorcylate decarboxylase (γ-RSD) has evolved to catalyze the reversible decarboxylation of 2,6-dihydroxybenzoate to resorcinol in a nonoxidative fashion. This enzyme is of significant interest because of its potential for the production of γ-resorcylate and other benzoic acid derivatives under environmentally sustainable conditions. Kinetic constants for the decarboxylation of 2,6-dihydroxybenzoate catalyzed by γ-RSD from Polaromonas sp. JS666 are reported, and the enzyme is shown to be active with 2,3-dihydroxybenzoate, 2,4,6-trihydroxybenzoate, and 2,6-dihydroxy-4-methylbenzoate. The three-dimensional structure of γ-RSD with the inhibitor 2-nitroresorcinol (2-NR) bound in the active site is reported. 2-NR is directly ligated to a Mn2+ bound in the active site, and the nitro substituent of the inhibitor is tilted significantly from the plane of the phenyl ring. The inhibitor exhibits a binding mode different from that of the substrate bound in the previously determined structure of γ-RSD from Rhizobium sp. MTP-10005. On the basis of the crystal structure of the enzyme from Polaromonas sp. JS666, complementary density functional calculations were performed to investigate the reaction mechanism. In the proposed reaction mechanism, γ-RSD binds 2,6-dihydroxybenzoate by direct coordination of the active site manganese ion to the carboxylate anion of the substrate and one of the adjacent phenolic oxygens. The enzyme subsequently catalyzes the transfer of a proton to C1 of γ-resorcylate prior to the actual decarboxylation step. The reaction mechanism proposed previously, based on the structure of γ-RSD from Rhizobium sp. MTP-10005, is shown to be associated with high energies and thus less likely to be correct.
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