COMPUTATIONAL STRUCTURAL MODEL OF THE OXYGEN EVOLVING COMPLEX IN PHOTOSYSTEM II: COMPLETE LIGATION BY PROTEIN, WATER AND CHLORIDE

摘要

The recently published 3.5 A resolution X-ray crystal structure of a cyanobacterial photosystem II (PSII) (Ferreira et al 2004) provides the first atomic image of the oxygen-evolving complex (OEC), structurally constraining mechanistic models of photosynthetic water oxidation. The OEC is shown to comprise a Mn_3CaO_4 cuboioal cluster, with the metal ions at four of its corners. In addition, a fourth manganese ion is attached to the cuboid via a mu_4-O atom, forming the so-called "3 + 1 Mn" tetramer predicted by spectro-scopists in recent years (Peloquin & Britt 2001). The moderate crystallographic resolution, however, has hindered the identification both of exogenous species (including vital substrate water molecules) and of the detailed proteinaceous coordination of the complex, leaving the metals of the OEC incompletely ligated.