Abstract
Although the central part of photosystem II (PSII) is highly conserved from prokaryotic cyanobacteria to eukaryotes, there are some differences in the extrinsic proteins involved in oxygen evolution among different organisms. The crystal structure of PSII from cyanobacteria has been reported; however, no reports have been published on the structure of any eukaryotic PSII. Red alga is one of the eukaryotic algae closely related to cyanobacteria, but its PSII differs from that of cyanobacteria in that the former contains a 20 kDa protein, the fourth extrinsic protein. In order to elucidate the structure of red algal PSII, we initiated the crystallization trials with PSII from a red alga Cyanidium caldarium. In order to do so, we established a procedure for the large-scale purification of PSII from the red alga, which yielded PSII dimer with a high oxygen-evolving activity. We will report the results of our purification procedures and crystallization trials.
