Distribution of extrinsic proteins among various organisms as an index of evolution of oxygen-evolving PSII

Abstract

Photosystem II (PSII) contains different extrinsic proteins among different plant species. Higher plant PSII binds the three extrinsic proteins of 33, 23 and 17 kDa, whereas in cyanobacterial and red algal PSII, only the 33 kDa protein is present but the other two proteins are absent. Instead, two different proteins, cytochrome c-550 and 12 kDa protein, were found in the latter organisms. In red algal PSII, a fourth extrinsic protein, a 20 kDa protein, was also found. These facts imply that the oxygen-evolving complex changed the extrinsic proteins during its evolution from cyanobacteria to higher plants. This study aimed to elucidate the evolutionary process of oxygen-evolving PSII in terms of the changes of the extrinsic proteins. For this purpose, we prepared the antibodies against the extrinsic 20 and 12 kDa proteins and cytochrome c-550 from a red alga, Cyanidium caldarium. Since the antibody against the red algal 12 kDa protein did not cross-react with the 12 kDa protein of cyanobacterial PSII, two antibodies against the 20 kDa protein and cytochrome c-550 from the red algal PSII were used to detect the presence of these extrinsic proteins in various organisms. The results obtained showed that the 20 kDa protein and cytochrome c-550 are present in a diatom and a brown alga but not in green algae and euglena. This suggests that the extrinsic cytochrome c-550 and the 20 kDa protein (and the 12 kDa protein) distribute in chl. a/c-type plants, whereas the extrinsic 23 and 17 kDa proteins distribute in chl.a/b-type plants.