The origin of the oxygen-evolving complex

One of the key biochemical developments during the evolution of life was the invention of the oxygen-evolving complex (OEC) of photosystem II, responsible for catalyzing the oxidation of water to molecular oxygen in plants, algae, and cyanobacteria. Though there have been a number of recent, key advances towards understanding how this remarkable chemistry is carried out, it remains a fundamental mystery how this complicated, four electron transfer process originated. Here we review some of these advances and resulting hypotheses on the origin and early evolution of the OEC. In addition, we present evidence suggesting that the four manganese-containing core of the OEC shares structural homology at the atomic level with the active sites of several distinct two manganese-containing enzymes, including manganese catalase, which carries out the oxidation of hydrogen peroxide. We discuss the implications for the plausible origin of oxygenic photosynthesis.