ja6b03437_si_002.cif (65.05 MB)

A Thiamine-Dependent Enzyme Utilizes an Active Tetrahedral Intermediate in Vitamin K Biosynthesis

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posted on 23.05.2016, 00:00 by Haigang Song, Chen Dong, Mingming Qin, Yaozong Chen, Yueru Sun, Jingjing Liu, Wan Chan, Zhihong Guo
Enamine is a well-known reactive intermediate mediating essential thiamine-dependent catalysis in central metabolic pathways. However, this intermediate is not found in the thiamine-dependent catalysis of the vitamin K biosynthetic enzyme MenD. Instead, an active tetrahedral post-decarboxylation intermediate is stably formed in the enzyme and was structurally determined at 1.34 Å resolution in crystal. This intermediate takes a unique conformation that allows only one proton between its tetrahedral reaction center and the exo-ring nitrogen atom of the aminopyrimidine moiety in the cofactor with a short distance of 3.0 Å. It is readily convertible to the final product of the enzymic reaction with a solvent-exchangeable proton at its reaction center. These results show that the thiamine-dependent enzyme utilizes a tetrahedral intermediate in a mechanism distinct from the enamine catalytic chemistry.