Storage, transport, release: heme versatility in nitrite reductase electron transfer studied by molecular dynamics simulations.

Using molecular dynamics simulations of the thermodynamic integration type, we study the energetics and kinetics of electron transfer through the nitrite reductase enzyme of Sulfurospirillum deleyianum, Wolinella succinogenes and Campylobacter jejuni. In all of these five-heme proteins, the storage of an even number of electrons within a monomeric chain is thermodynamically favoured. Kinetically, two of these electrons are usually transferred almost simultaneously towards the active site. Although the free energy landscape for charge transfer varies significantly from organism to organism, the heme cofactor closest to the interface of a protein dimer always exhibits a particularly low free energy, suggesting that protein dimerization is functional. Interheme electron interaction effects do not play a significant role.