Abstract
The extrinsic 23-kDa protein in an oxygen-evolving complex (OEC23) of photosystem II (PS II) has a function of retaining calcium and chloride ions, which are essential cofactors for photosynthetic oxygen evolution. OEC23 is found in PS II complex from higher plants and green algae but not in that of cyanobacterium and other ancestral photosynthetic organisms.
In order to elucidate its structure and the molecular evolution, OEC23 was crystallized by the hanging-drop vapour-diffusion technique. Diffraction data to 2.0Å were collected from a native crystal belonging to space group P21221, with unit-cell parameters a=74.15, b=91.36, c=52.16Å. A heavy-atom derivative was prepared, and the phase problem was solved by multi-wavelength anomalous dispersion (MAD) experiments using synchrotron X-ray radiation at SPring-8 (Hyogo, Japan). The crystal structure of OEC23 was determined at 2.0Å resolution.
