Brownian simulation of cytochrome c551 association and electron self-exchange

Abstract

In this paper we describe the results of a theoretical study of the dynamics of electron self-exchange in Pseudomanas aeruginosa cytochrome c551 using the Brownian Dynamics computer simulation method. The proteins are treated as spheres with imbedded monopole/dipole charge arrangements based on an electrostatic analysis of the crystallographic coordinate sets. For the first time, the electron transfer event is explicitly coupled to the Brownian association dynamics. The intrinsic electron transfer rate constant is modelled as an exponential function ∼exp(-αr) of distance r between porphyrin edges. Reasonable agreement of this simple theory with kinetic data from NMR line-broadening experiments is obtained. The role of factors such as solvent electrolyte screening effects, protein-protein electrostatic interactions, heme exposure and overall protein size are elucidated. An estimate is made of the electron transfer exponential distance factor α which agrees quite well with various experiments.