Evolution of oxygenic photosynthesis: genome-wide analysis of the OEC extrinsic proteins.

The appearance of oxygenic photosynthesis was a key event in the evolution of our green biosphere. Oxygen in the atmosphere is generally believed to come from the biomolecular water-splitting reaction that occurs in oxyphotosynthetic organisms catalysed by the oxygen evolving centre (OEC) of Photosystem II. Using knowledge from complete genomes and current databases, we have investigated the nature and composition of the extrinsic proteins forming the OECs of different organisms, with particular focus on the manganese stabilizing protein that is present in all known oxyphototrophs. This analysis traces the evolution of the extrinsic proteins from ancient cyanobacteria to higher plants and gives hints about the ancestral form of the OEC.