Abstract
Glucose oxidase (GOx) can catalyze the oxidization of β-D-glucose in the mild conditions, which has wide applications in the biofuel cells and monitoring of diabetes. However, the detailed catalytic mechanisms of GOx are ambiguous up to now. A series of protein models containing different micro-surroundings of the active center of GOx were examined through ONIOM calculations. The work reveals that not only the three intimate residues near the active center of GOx (containing His505, His548 and Glu399) are crucial for modulating the dehydrogention of β-D-glucose but also a remote residue (Arg210) play an important role in promoting proton/electron transfer from glucose to isoalloxazine ring of flavin adenine dinucleotide. The change in the protonation state of the three intimate residues causes the change from a double-proton-coupled double-electron transfer mechanism (dPCdET) to a single-proton-coupled double-electron transfer mechanism (sPCdET) for the proton/electron transfer from glucose to GOx. The sPCdET reaction is more favorable in energy than the dPCdET mechanism. In addition, the presence of Arg210 in the other side of isoalloxazine ring relative to glucose can sharply reduce the energy barrier of proton/electron transfer from glucose to FAD. This is because that the positive Arg210 indirectly interact with the isoalloxazine ring through the long-range electrostatic attraction, which can facilitate proton/electron transfer from glucose to the isoalloxazine ring.
