Reconstitution of the extrinsic 23 and 17 kDa proteins with spinach PSII which had been exchanged for the 33 kDa protein from different plant species

Abstract

The 33 kDa protein of photosystem II (PSII) plays an important role in maintaining the function of the Mn cluster, and is common to all of the organisms and totally exchangeable in binding to PSII from various different organisms (Enami et al., 2000, Plant Cell Physiol. 41, 1354-1364). The amino acid sequence of the 33 kDa protein showed a relatively high homology above 40% from cyanobacteria to higher plants. Thus, the structure of the 33 kDa protein has been considered to be conserved during evolution from cyanobacteria to higher plants. In this study, reconstitution experiments were performed for the extrinsic 23 and 17 kDa proteins from spinach with spinach PSII which had been exchanged for the 33 kDa protein from different sources. Spinach PSII was treated with 2.6 M urea/0.2 M NaCl to remove all of the extrinsic proteins, and then reconstituted with the 33 kDa protein from a cyanobacterium (Synechococcus vulcanus), a red alga (Cyanidium caldarium) or a higher plant (Spinach). The results showed that, while spinach PSII bearing the higher plant 33kDa protein retained the full ability of binidng the 23 kDa and 17 kDa proteins, PSII of which the 33 kDa protein had been replaced with the red algal or cyanobacterial 33kDa protein partially rebound the 23kDa protein but totally failed to bind the 17kDa protein. This suggests that the structure of the 33kDa protein interacting with other extrinsic proteins is different between higher plants and red algae or cyanobacteria.