Crystal structure of photosystem II from Synechococcus elongatus at 3.8 angstrom resolution

Oxygenic photosynthesis is the principal energy converter on earth. It is d riven by photosystems I and II, two large protein-cofactor complexes locate d in the thylakoid membrane and acting in series. In photosystem II, water is oxidized; this event provides the overall process with the necessary ele ctrons and protons, and the atmosphere with oxygen. To date, structural inf ormation on the architecture of the complex has been provided by electron m icroscopy of intact, active photosystem II at 15-30 Angstrom resolution(1), and by electron crystallography on two-dimensional crystals of D1-D2-CP47 photosystem II fragments without water oxidizing activity at 8 Angstrom res olution(2). Here we describe the X-ray structure of photosystem II on the b asis of crystals fully active in water oxidation(3). The structure shows ho w protein subunits and cofactors are spatially organized. The larger subuni ts are assigned and the locations and orientations of the cofactors are def ined. We also provide new information on the position, size and shape of th e manganese cluster, which catalyzes water oxidation.