What does the Sr-substituted 2.1 Å resolution crystal structure of photosystem II reveal about the water oxidation mechanism?

Abstract

A density functional study of the Sr-substituted photosystem II water oxidising complex demonstrates that its recent X-ray crystal structure is consistent with a (Mn^III)₄ oxidation state pattern, and with a Sr-bound hydroxide ion. The Sr-water-hydroxide interactions rationalize differences in the exchange rates of substrate water and kinetics of dioxygen bond formation relative to the Ca-containing structure.