Abstract 2613 Exploring a proton relay mechanism involving Glu28, His273, and Ser26 in the folate half-reaction of E. coli methylenetetrahydrofolate reductase (MTHFR)

Methylenetetrahydrofolate reductase from E. coli is a flavoprotein, which uses enzyme-bound FAD to catalyze the NADH-linked reduction of 5,10-methylenetetrahydrofolate (CH2-H4folate) to 5-methyltetrahydrofolate (CH3-H4folate). In the oxidative half-reaction, CH2-H4folate is proposed to accept a proton at the N10 position to open up the imidazolidine ring and form a 5-iminium cation intermediate, which undergoes reduction by the reduced flavin. The X-ray crystal structure of the Eox•CH3-H4folate complex1 has revealed a hydrogen bonding network that involves amino acid residues Ser26, His273, Glu28, a structural water molecule, and the N10 of the folate.