Neutron structures of Leishmania mexicana triosephosphate isomerase in complex with reaction-intermediate mimics shed light on the proton-shuttling steps

Triosephosphate isomerase (TIM) is a key enzyme in glycolysis that catalyses the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. This simple reaction involves shuttling protons mediated by protolysable side chains. The catalytic power TIM thought to stem from its ability facilitate deprotonation carbon next carbonyl group generate an enediolate intermediate. intermediate believed be mimicked inhibitor 2-phosphoglycolate (PGA) subsequent enediol phosphoglycolohydroxamate (PGH). Here, neutron structures Leishmania mexicana have been determined with both inhibitors, joint neutron/X-ray refinement followed quantum has performed. show PGA complex postulated general base Glu167 protonated, while PGH it remains deprotonated. deuteron clearly localized on PGA–TIM structure, suggesting asymmetric hydrogen bond instead low-barrier bond. full picture active-site protonation states allowed investigation mechanism using density-functional theory calculations.