Multiscale modelling of the electrocatalysis of enzymes: Insights into the performance of microperoxidase at an aqueous/graphene interface and their exploitation to improve performance

There is great interest in systems where enzymes are adsorbed on and act at electrode surfaces – enzymatic biofuel cells, bioreactors and biosensors are just three examples. Whilst such systems have been the subject of extensive study and development since the 1960s, the rate of progress in this research is hindered by a lack of molecular-level understanding of the enzyme adsorption process and adsorbed states, and the associated electron transfer processes. Herein, we present and then demonstrate a multiscale approach that combines molecular dynamics simulation to elucidate the former and density functional theory (MD/DFT) for the latter. The demonstration of the new approach focused on a system involving the microperoxidase-11 (MP-11) enzyme, a microenzyme made up of a Fe-containing heme ring attached to an 11-residue scaffold, a graphene electrode, and a neutral-pH saline solution. For this system, the adsorbed MP-11 was found to adopt six possible heme configurations, where the configurations are defined by the distance of the iron from the graphene and the angle between the normals of the heme ring and graphene electrode. The rate constant for electron transfer between the MP-11 and graphene evaluated through combining the MD and DFT results and their variation with overpotential are comparable to the limited experimental data. The results were used to illustrate how the new multiscale approach could be used to improve electrocatalytic performance of the system.