Architecture of the Photosynthetic Oxygen-Evolving Center

TLDR

Photosynthesis uses light energy to drive the oxidation of water at an oxygen‑evolving catalytic site within photosystem II (PSII). The study aims to describe the binding sites for cofactors and propose a structure of the oxygen‑evolving center (OEC). The authors discuss the coordination sphere of the metal cluster and its implications for a possible oxygen‑evolving mechanism. The 3.5‑Å structure of Thermosynechococcus elongatus PSII reveals a 650‑kDa dimeric complex with most residues assigned, shows a cubane‑like Mn₃CaO₄ cluster linked to a fourth Mn by a mono‑μ‑oxo bridge, and provides detailed binding sites for cofactors.

Abstract

Photosynthesis uses light energy to drive the oxidation of water at an oxygen-evolving catalytic site within photosystem II (PSII). We report the structure of PSII of the cyanobacterium Thermosynechococcus elongatus at 3.5 angstrom resolution. We have assigned most of the amino acid residues of this 650-kilodalton dimeric multisubunit complex and refined the structure to reveal its molecular architecture. Consequently, we are able to describe details of the binding sites for cofactors and propose a structure of the oxygen-evolving center (OEC). The data strongly suggest that the OEC contains a cubane-like Mn 3 CaO 4 cluster linked to a fourth Mn by a mono-μ-oxo bridge. The details of the surrounding coordination sphere of the metal cluster and the implications for a possible oxygen-evolving mechanism are discussed.