Influence of the Greater Protein Environment on the Electrostatic Potential in Metalloenzyme Active Sites: the Case of Formate Dehydrogenase

The Mo/W containing metalloenzyme formate dehydrogenase (FDH) is an efficient and selective natural catalyst which reversibly converts CO2 to formate under ambient conditions. A greater understanding of the role of the protein environment in determining the local properties of the FDH active site would enable rational bioinspired catalyst design. In this study, we investigate the impact of the greater protein environment on the electrostatic potential (ESP) of the active site. To model the enzyme environment, we used a combination of long-timescale classical molecular dynamics (MD) and multiscale quantum-mechanical/molecular-mechanical (QM/MM) simulations. We leverage the charge shift analysis method to systematically construct QM regions and analyze the electronic environment of the active site by evaluating the degree of charge transfer between the core active site and the protein environment. The contribution of the terminal chalcogen ligand to the ESP of the metal center is substantial and dependent on the chalcogen identity, with ESPs less negative and similar for Se and S terminal chalcogens than for O regardless of whether the Mo6+ or W6+ metal center is present. Our evaluation reveals that the orientation of the sidechains and ligand conformations will alter the relative trends in the ESP observed for a given metal center or terminal chalcogen, highlighting the importance of sampling dynamic fluctuations in the protein. Overall, our observations suggest that the terminal chalcogen ligand identity plays an important role in the enzymatic activity of FDH.