Abstract
Photosystem II (PSII) is a membrane-protein complex containing 14-16 transmembrane and 3 extrinsic subunits with a total molecular mass of 350 kDa, which catalyzes light-induced electron transfer and water-splitting reactions. Crystal structures of PSII have been reported at around 3.5 A resolutions, which are apparently not enough to reveal detailed structures of amino acid side chains as well as that of the Mn cluster. In order to expand the current limit of observable reflections from crystals, we reexamined the preparation and crystallization procedures for PSII from the thermophilic cyanobacterium Thermosynechococcus vulcanus. By modifying the final ion-exchange chromatography step and employing the vapor-diffusion method to grow crystals, we obtained better quality crystals. Furthermore, by optimizing cryogenic conditions for the crystals, we succeeded in obtaining diffraction data of 3.3 A resolution, which are used to reconstruct the structure model of PSII. We will report the current status of crystallization of PSII.
