Abstract
An extrinsic 33-kDa component protein (PsbO) in photosystem II is essential for photosynthetic oxygen evolution. The extrinsic 33-kDa protein is present in all oxygen-evolving organisms, and plays a central role in the stabilization of the manganese cluster. In Arabidopsis, the extrinsic 33-kDa proteins are encoded by two genes, psbO and psbO2. Immunoblot analysis showed that PsbO was more abundant than PsbO2. Furthermore, an Arabidopsis mutant with a defect in psbO showed the lower photosynthetic activity, suggesting functional differences of two proteins as well as those in expression. Thus, we produced the recombinant PsbO and PsbO2 without transit peptide in E. coli and purified them to characterize their functions. The reconstitution experiment using spinach PSII particles without their extrinsic 33-kDa proteins indicated that the restoration of oxygen evolution activity with PsbO2 was lower than PsbO. Further analysis is on going.
