Snapshot Structures of Thiamine-Dependent Dehydration Reaction by Phosphoketolase from Bifi dobacterium breve

Thiamine diphosphate functions as a cofactor in enzymes that catalyze essential reactions in metabolic pathways of all organisms. Phosphoketolase is a thiamine diphosphate-dependent key enzyme in the catabolism of sugar in various microbes. In particular, this enzyme is indispensable for unusually high effi ciency of energy production of the glycolytic pathway of benefi cial commensal bacteria, bifi dobacteria. However, its structure and mechanism have long been enigmatic. We determined the three-dimensional structure of phosphoketolase from Bifi dobacterium breve. Details of its unique reaction mechanism involving dehydration and nucleophilic attack by phosphate were revealed based on “snapshot” X-ray crystal structures.