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.
Journal article
2016-06-15T00:00:00+00:00
138
7244 - 7247
3
Catalysis, Decarboxylation, Escherichia coli Proteins, Models, Molecular, Protein Conformation, Pyruvate Oxidase, Thiamine, Thiamine Pyrophosphate, Vitamin K