(192w) Mapping of Gas Diffusion Pathways in [FeFe]-Hydrogenase

The H₂ production potential of [FeFe]-Hydrogenase, a hydrogen-producing enzyme from green algae, is reported to be promising for economical and large-scale production of H₂ as an alternative source of renewable energy. The production of hydrogen takes place at the catalytic center buried in the enzyme core. Unfortunately, oxygen binding to the catalytic center of the enzyme irreversibly inactivates it, essentially blocking hydrogen production. Therefore, a better understanding of the mechanism of enzyme inhibition by O₂ is necessary to develop strategies for designing oxygen-tolerant enzymes. In this work, we are investigating the pathways and diffusion channels of O₂ gas in this hydrogenase. Through exhaustive mapping of oxygen diffusion channels, we have computed a full thermodynamic map of preferred binding locations of O₂ gas within the enzyme interior. Our results suggest that O₂ can enter and exit the enzyme through multiple pathways along which are key residues that are known to perturb rates of O₂ binding. We find that the global minimum in the free-energy landscape is located near the H-cluster, a metallic center within the enzyme. Along oxygen diffusion channels, we further identify residues that could be potential candidates for mutations to increase the oxygen tolerance of these enzymes.