Abstract
The supramolecular complex Photosystem II (PSII) catalyzes light -driven charge separation, leading to the oxidation of water and the production of molecular oxygen during oxygenic photosynthesis. The components of PSII from cyanobacteria include 17 membrane-spanning subunits, 3 hydrophilic, peripheral subunits, and over 70 cofactors such as chlorophylls, carotenoids, Mn, Ca, Fe, and plastoquinones, which give rise to a total molecular mass of 350 kDa for a monomer. The structure of PSII has been reported at 3.8 - 2.9 angstrom resolution by X-ray crystallographic analysis of PSII isolated from two thermophilic cyanobacteria, Thermosynechococcus elongatus and T. vulcanus. However, these resolutions are not enough for elucidating the detailed structure of PSII. Especially, the structure of the Mn4Ca cluster, the catalytic center for light-induced water oxidation, is not clearly resolved due to the limited resolution as well as radiation damage induced during the X-ray experiment.
In order to improve the resolution of PSII crystals, we have been involved in screening the crystallization conditions for PSII, and will report the results of our screening trials.
