title: Mn4Ca Cluster of Photosynthetic Oxygen-Evolving Center: Structure, Function and Evolution.
abstract: Photosystem II is the chlorophyll-containing enzyme in which the very first chemical energy storing reaction of photosynthesis occurs, when water is split into molecular oxygen and hydrogen equivalents at a catalytic center composed of four Mn ions and one Ca2+. All the oxygen in the atmosphere is derived from this reaction, and without it the biosphere, as we know it, would not exist. Indeed, the appearance of this catalytic center ∼3 billion years ago gave rise to the "big bang of evolution". Thus, understanding the structure and functioning of this metal cluster is a major topic in science, and here I discuss it in terms of research that has occurred over the past 12 years dating back to when it was first proposed to be a Mn3CaO4cubane with the fourth Mn attached to cubane by one of its oxo bridging bonds. Since then, a number of novel properties have emerged for this metalloprotein with implications for its catalytic mechanism and evolutionary origin.
authors.affiliation: Department of Life Sciences, Imperial College London , Sir Ernst Chain Building, South Kensington Campus, London SW7 2AZ, U.K.
authors.forename: James
authors.initials: J
authors.lastname: Barber