BPS2026 – Photosynthetic reaction center: A nonergodic, dynamically anisotropic, and nonlinear charge-transport engine

Protein complexes of biological energy chains are the principal media for biological electron transport, yet their high cellular cost raises the key question: what is special about proteins, in particular photosynthetic reaction centers, as media for transporting electrons across the lipid membrane? Using all-atom simulations, we have shown that ergodicity is broken for the statistics of electrostatic fluctuations in the heliobacterial reaction center. Nonergodicity applies even to the simulation time of ∼1 μs, and it is a key factor in lowering the activation barrier for electron hops. Furthermore, medium’s dynamics strongly depend on the oxidation states of cofactors participating in charge transport. This dynamic anisotropy is a nonlinear protein response to altering oxidation state that promotes a unidirectional flow of charge. These special features of the protein medium are combined with a strong coupling of cofactor polarizabilities with intraprotein electric fields. The overall result is nonparabolic and nonergodic free-energy surfaces of electron transfer, allowing low-barrier, unidirectional charge conductivity in proteins.