New Insight Into Catalytic Mechanism of Glucose-6-Phosphate Dehydrogenase Enzyme: A DFT Study

The glucose-6-phosphate dehydrogenase (G6PD) enzyme plays a vital role in converting glucose-6-phosphate (G6P) to 6-phosphogluconolactone, as well as in reducing NADP(+) to NADPH. The Asp/His moiety of G6PD acts as a catalytic dyad in the active site of G6PD. This catalytic mechanism describes erythrocyte protection from oxidative stress and prevention of hemolysis; hence their exact understanding is important in the normal functioning of red blood cells. Herein, computational investigations were carried out to describe a plausible mechanism of the G6PD enzyme by using a series of DFT theoretical calculations using the M06-2X/6-31G (d, p) basis set and performed in the following three discrete steps: (i) Proton transfer from His309 to Asp246, (ii) A subsequent proton transfer from G6P to His309, and (iii) A rate-limiting hydride transfer that reduces NADP(+) to NADPH. The final overall mechanism, therefore, results in the production of phosphogluconolactone and NADPH. The DFT calculations indicate that, in the absence of the His/Asp dyad, the chemical reaction changes from a low-energy sequential mechanism to the proposed concurrent mechanism with a very high energy barrier (Erel=76.6kcalmol-1). These results show that the Asp246 residue is responsible for transforming a high energy concurrent reaction into a low energy multistep sequential reaction in the G6PD enzyme for the production of NADPH. This work supports the study and design of the mechanism-based inhibitors and provides a detailed understanding of the catalytic mechanism of the enzyme thereby opening new possibilities towards an understanding of controlling detoxification processes due to premature breaking in red blood cells.