Mirroring perfection: The structure of methylglyoxal synthase complexed with the competitive inhibitor 2-phosphoglycolate

The crystal structure of the transition-state analogue 2-phosphoglycolate ( 2PG) bound to methylglyoxal synthase (MGS) is presented at a resolution of 2.0 Angstrom. This structure is very similar to the previously determined s tructure of MGS complexed to formate and phosphate, Since 2PG is a competit ive inhibitor of both MGS and triosephosphate isomerase (TIM), the carboxyl ate groups of each bound 2PG from this structure and the structure of 2PG b ound to TIM were used to align and compare the active sites despite differe nces in their protein folds. The distances between the functional groups of Asp 71, His 98, His 19, and the carboxylate oxygens of the 2PG molecule in MGS are similar to the corresponding distances between the functional grou ps of Glu 165, His 95, Lys 13, and the carboxylate oxygens of the 2PG molec ule in TIM. However, these spatial relationships are enantiomorphic to each other. Consistent with the known stereochemical data, the catalytic base A sp 71 is positioned on the opposite face of the 2PG-carboxylate plane as Gl u 165 of TIM. Both His 98 of MGS and His 95 of TIM are in the plane of the carboxylate of 2PG, suggesting that these two residues are homologous in fu nction. While His 19 of MGS and Lys 13 of TIM appear on the opposite face o f the 2PG carboxylate plane, their relative location to the 2PG molecule is quite different, suggesting that they probably have different functions. M ost remarkably, unlike the coplanar structure found in the 2PG molecule bou nd to TIM, the torsion angle around the C1-C2 bond of 2PG bound to MGS brin gs the phosphoryl moiety out of the molecule's carboxylate plane, facilitat ing elimination. Further, the superimposition of this structure with the st ructure of MGS bound to formate and phosphate suggests a model for the enzy me bound to the first transition state.