STRUCTURAL-ANALYSIS OF PHOTOSYSTEM-II - COMPARATIVE-STUDY OF CYANOBACTERIAL AND HIGHER-PLANT PHOTOSYSTEM-II COMPLEXES

Oxygen evolving photosystem II (PSII-OEC) complexes and PSII core comp lexes were isolated from spinach and the thermophilic cyanobacterium S ynechococcus sp. OD24 and characterized by gel electrophoresis, immuno blotting, and absorbance spectroscopy. The mass of the core complexes was determined by scanning transmission electron microscopy (STEM) and found to be 281 +/- 65 kDa for spinach and 313 +/- 52 kDa for Synecho coccus sp, OD24, The mass of the spinach PSII-OEC complex was 327 +/- 64 kDa. Digital images of negatively stained PSII-OEC and PSII core co mplexes were recorded by STEM and analysed by single particle averagin g. All monomeric complexes showed similar morphologies and were of com parable length (14 nm) and width (10 nm). The averages revealed a pseu do-twofold symmetry axis, which is a prominent structural element of t he monomeric form. Difference maps between the averaged projections of the oxygen evolving complexes and the core complexes from both specie s indicated where the 33-kDa extrinsic manganese stabilizing protein i s bound, A symmetric organization of the PSII complex, with the PsbA a nd the PsbD proteins in the center and symmetrically arranged PsbB and PsbC proteins at the periphery of the monomeric complex, is proposed. (C) 1997 Academic Press.