Characterization of purified His-tagged CP47-containing photosystem II complexes from a cyanobacterium, Synechocystis sp. PCC 6803

Abstract

For the determination of the exact structure of PS II complexes, all the polypeptide constituents must be identified. For this purpose, highly active photosystem II (PS II) complexes were purified from a HT-3 mutant of Synechocystis sp. PCC 6803 whose CP47 has been His-tagged. Fluorescence measurements showed the intactness of the donor and acceptor sides of purified PS II complexes. It retained 80% of the initial activity of oxygen evolution even after incubation of the complexes for 2 weeks at 4°C in the dark. Using these highly purified PS II complexes, the polypeptide composition was analyzed by SDS-PAGE which can resolve polypeptides of low molecular weight. Separated polypeptides of the purified PS II complexes were subjected to N-terminal amino acid sequencing and matrix assisted laser desorption (MALDI) mass spectrometry. More than 20 Coomassie-stainable polypeptides were identified. All the polypeptides which was known as PS II components were found, except PsbN. Besides 19 polypeptides of well-known PS II member, some polypeptides, which had not been shown to bind to PS II complexes until now, were found. Among such polypeptides, the sll1638 gene product was found to be highly homologous to PsbQ. These PS II complexes contained the FtsH protein, which was assigned to be a protease of the D1 protein, and the Ycf9 (Orf62 in tobacco), which was suggested to be present in stromal thylakoids. The results obtained here showed the usefulness of this HT-3 strain for the investigation of the structure, function and biogenesis of PS II complexes.