抄録
We have reported a novel protein homologous to plant PsbQ in cyanobacterial PS II. The localization and the function of this protein were carefully assessed in Synechocystis 6803. Although the cyanobacterial PsbQ is predicted to be a soluble protein with one transit peptide, it was unexpectedly extracted to Triton X114 phase. However, trypsin digestion revealed that PsbQ was highly exposed to the lumenal space. PS II complexes purified from the mutant lacking psbQ showed impaired oxygen evolving activity. Furthermore, witout PsbQ, the donor side of PS II became remarkably sensitive to NH2OH. And, the cytochrome c550 (PsbV) partially disappeared in the purified PS II complex suggesting the structural vulnerability without PsbQ. These findings confirm that PsbQ really associates to the lumenal side of PS II with anchor to the lipid layer, and functions at the water oxidizing system.
