Abstract
PsbK and PsbZ are two low-molecular mass subunits of PSII and are conserved from cyanobacteria to higher plants. PsbK has a single trans-membrane helix, whereas PsbZ has two trans-membrane helices. Both subunits are located in the periphery of PSII dimer in adjacent to CP43. Functional analysis of mutants lacking each of the two subunits from various organisms has shown different phenotypes depending on the organisms. In order to study the role of these subunits from a structural point of view, we purified, crystallized PSII from mutants of thermophilic cyanobacteria lacking either PsbK or PsbZ. The crystals from both mutants belonged to the same space group with similar unit cell constants. The space group was also the same as that of wild-type, whereas the unit cell constants of the mutants were significantly different from those of wild-type, indicating an effect on the molecular contact between PSII dimers within the crystal lattice.
