Abstract
The components of photosystem II (PSII) from cyanobacteria include 20 subunits and over 70 cofactors such as chlorophylls (Chls), carotenoids, Mn, Ca, Fe, and plastoquinones. In a recent study, we have succeeded in improving the resolution of PSII crystals significantly. As a result, we were able to collect a diffraction data set at a 1.9 angstrom resolution with the beamline BL44XU of SPring-8 in JAPAN, and resolve the crystal structure of PSII at this resolution.
More than one thousand of water molecules per monomer were found in the structure of PSII dimer, some of which form a network linking the metal cluster. In addition, 4 water molecules were found to be associated with the metal cluster, which may function as substrates for the oxygen-evolving reaction. Most of water molecules existed in the surface of the lumenal side and the stromal side, however, very few molecules of water existed in the membrane regions, most of which served as ligands to chlorophylls. Moreover, the precise arrangements of cofactors such as chlorophylls and β-carotenes were determined, allowing a detailed analysis of their functions in energy and electron transfer reactions in PSII possible.
