Active site structure and mechanism of human glyoxalase I - An ab initio theoretical study

The structure of the active site of human glyoxalase I and the reaction mec hanism of the enzyme-catalyzed conversion of the thiohemiacetal, formed fro m methylglyoxal and glutathione, to S-D-lactoylglutathione has been investi gated by ab initio quantum chemical calculations. To realistically represen t the environment of the reaction center, the effective fragment potential methodology has been employed, which allows systems of several hundred atom s to be described quantum mechanically. The methodology and the active site model have been validated by optimizing the structure of a known enzyme-in hibitor complex, which yielded structures in good agreement with the experi ment. The same crystal structure has been used to obtain the quantum motif for the investigation of the glyoxalase I reaction. The results of our stud y confirm that the metal center of the active site zinc complex plays a dir ect catalytic role by binding the substrate and stabilizing the proposed en ediolate reaction intermediate. In addition, our calculations yielded detai led information about the interactions of the substrate, the reaction inter mediates, and the product with the active site of the enzyme and about the mechanism of the glyoxalase I reaction. The proton transfers of the reactio n proceed via the two highly flexible residues Glu172 and Glu99. Informatio n about the structural and energetic effect of-the protein on the first-she ll complex has been attained by comparison of the structures optimized in t he local protein environment and in a vacuum. The environment of the zinc c omplex disturbs the C, symmetry found for the complex in a vacuum, which su ggests an explanation for the stereochemical behavior of glyoxalase I.