Theoretical investigation on peripheral ligands of oxygen-evolving center in photosystem II

Abstract

The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is still unclear. Theoretical investigation on the coordination of histidine, H(2)O, and CI to Mn2O2 units in OEC is conducted. The following conclusions are obtained: (i) both histidine and H(2)O molecule, bound to the two Mn ions, respectively, are vertical to the Mn2O2 plane, and maintain a large distance; (ii) the two H(2)O molecules cannot bind to the same Mn2O2 unit. Based on Mn-cluster structure in OEC, we theoretically predict that two H(2)O molecules bind to the two Mn ions at the "C"-shaped open end in S(0) state, while two His residues at the closed end. Cl ion can only terminally ligate at the open end. Individual valence for the four Mn ions in S(0) state is assigned.