Limited proteolysis indicates that the structure of the photosystem II extrinsic 33 kDa protein is different among different plant species

Abstract

The extrinsic 33 kDa protein is present in all oxygen-evolving organisms from cyanobacteria to higher plants and is needed to maintain the function of the Mn cluster. The homology of the amino acid sequence is around 40-50% among cyanobacteria, red algae and higher plants. The cleavage sites of the 33 kDa protein by protease, however, have been reported to be different between cyanobacteria and higher plants. The cyanobacterial 33 kDa protein was cleaved at 157F and 190F by chymotorypsin, but the higher plant 33 kDa protein was cleaved at 16Y. In order to compare the structure of the protein, we determined the cleavage sites of the 33 kDa protein from various species. The 33 kDa protein from a red alga, Cyanidium caldarium, was cleaved at 5D, 159M and 192L by chymotorypsin; the latter two sites resemble those in the cyanobacterial 33 kDa protein. Upon treatment with V8 protease, cyanobacterial or red algal 33 kDa protein was cleaved at 187E or 182E and 195E, whereas the higher plant 33 kDa protein was cleaved at 18E. These results imply that the structure of the red algal 33 kDa protein is similar to that of the cyanobacterial protein but not the higher plant one. Furthermore, the cleavage patterns of the 33 kDa protein from Chlamydomonus and Euglena were similar to the higher plant and cyanobacterial one, respectively. We will discuss the evolution of the 33 kDa protein in terms of the structural differences revealed by the protease-cleavage patterns of the protein from various species.