Localization and function of small protein subunits of the cyanobacterial Photosystem II complex

The Photosystem II complex (PSII) contains besides D1, D2, CP43, CP47 and several lumenal extrinsic proteins also a large number of small intrinsic subunits. These subunits are found in all kinds of oxygenic phototrophs and their sequences are usually highly conserved. It is assumed that the small subunits are involved in stabilization, assembly or dimerization of the PSII complex but their exact function remains largely unknown. Thus, we chose four small PSII proteins: cytochrome b-559, PsbH, PsbI and Psb28, and we studied their function and location in PSII of the cyanobacterium Synechocystis sp. PCC 6803. We attempted: (i) to better define the role of cyt b-559 in the assembly of PSII using various mutant strains lacking one or more PSII core protein subunits; (ii) to clarify the location of the PsbH subunit using NTA gold labelling methodology; (iii) to improve the available knowledge on function of the PsbI protein in the assembly and repair of the cyanobacterial PSII; and (iv) to confirm the presence of the Psb28 protein in PSII, to localize it and to establish its importance for the cyanobacterial PSII