PARENT SESSION
Posters P7A Mechanisms of water oxidation. Abstracts (347-381)

The functional difference between two extrinsic 33-kDa proteins, PsbO1 and PsbO2, in Arabidopsis. Reiko Murakami^*,1, Kentaro Ifuku¹, Atsushi Takabayashi¹, Toshiharu Shikanai⁴, Fumihiko Sato¹, Tsuyoshi Endo¹, ¹ Grad. Sch. Biostudies, Kyoto Univ. , Kyoto 606-8502, Japan⁴ Grad. Sch. Biol. Sci. , Nara Institute Sci. & Tech. , Ikoma, Nara, 630-1101, Japan

ABSTRACT- An extrinsic 33-kDa protein in photosystem II is essential for photosynthetic oxygen evolution. It is present in all oxygen-evolving organisms, and plays a central role in the stabilization of the manganese cluster. In Arabidopsis, however, 33-kDa proteins are encoded by two genes, psbO1 and psbO2. Our previous study showed that an Arabidopsis mutant with a defect in psbO1 and an intact psbO2 showed considerably reduced photosynthetic activity and the retarded growth, whereas both genes are expressed in wild-type. This and other results suggested that there is a difference between two PsbO proteins in function as well as expression. To investigate the functional differences between two proteins, we produced the recombinant PsbO1 and PsbO2 in E. coli. The activities of PsbO1/PsbO2 proteins were analyzed by the reconstitution experiment using urea-washed PSII particles of spinach. Interestingly the restored oxygen evolution activity with PsbO2 was about 80% of that with PsbO1, whereas the primary structures of two proteins were quite similar. To examine which amino acid among 11 substitutions between PsbO1 and PsbO2, the chimeric PsbOs between PsbO1 and PsbO2 were produced in E. coli., and is on going.

KEY WORDS: PsbO2, the extrinsic 33-kDa protein, PsbO1, oxygen evolving complex