Orotidine 5′-Monophosphate Decarboxylase: Transition State Stabilization from Remote Protein–Phosphodianion Interactions

Mutants of orotidine 5'-monophosphate decarboxylase containing all possible single (Q215A, Y217F, and R235A), double, and triple substitutions of the side chains that interact with the phosphodianion group of the substrate orotidine 5'-monophosphate have been prepared. Essentially the entire effect of these mutations on the decarboxylation of the truncated neutral substrate 1-(β-d-erythrofuranosyl)orotic acid that lacks a phosphodianion group is expressed as a decrease in the third-order rate constant for activation by phosphite dianion. The results are consistent with a model in which phosphodianion binding interactions are utilized to stabilize a rare closed enzyme form that exhibits a high catalytic activity for decarboxylation.