Aspects of the mechanism of catalysis of glucose oxidase: A docking, molecular mechanics and quantum chemical study

The complex structure of glucose oxidase (GOX) with the substrate glucose w as determined using a docking algorithm and subsequent molecular dynamics s imulations. Semiempirical quantum chemical calculations were used to invest igate the role of the enzyme and FAD co-enzyme in the catalytic oxidation o f glucose. On the basis of a small active site model, substrate binding res idues were determined and heats of formation were computed for the enzyme s ubstrate complex and different potential products of the reductive half rea ction. The influence of the protein environment on the active site model wa s estimated with a point charge model using a mixed QM/MM method. Solvent e ffects were estimated with a continuum model. Possible modes of action are presented in relation to experimental data and discussed with respect to re lated enzymes. The calculations indicate that the redox reaction of GOX dif fers from the corresponding reaction of free flavins as a consequence of th e protein environment. One of the active site histidines is involved in sub strate binding and stabilization of potential intermediates, whereas the se cond histidine is a proton acceptor. The former one, being conserved in a s eries of oxidoreductases, is also involved in the stabilization of a C4a-hy droperoxy dihydroflavin in the course of the oxidative half reaction.