PARENT SESSION
Posters P6A Type II reaction centres: Excited state dynamics and donor side. Abstracts (313-346)

Functional analysis of psbX deletion mutant in Synechocystis sp. PCC6803. Hiroyuki Koike^*,1, Masashi Taniguchi¹, Kazuhiko Satoh¹, ¹ Department of Life Science, Graduate School of Life Science, University of Hyogo, Koto, Hyogo, Japan

ABSTRACT- Oxygen-evolving photosystem II (PSII) core complex is composed of many of low molecular mass proteins. The PsbX protein is one of the PSII low molecular mass subunits. It has a molecular mass of 4.1 kDa with a single transmembrane helix. The protein is found in the PSII core complex so far investigated suggesting an important role in PSII function. However, little is known about the function of the protein. Crystal structure of the core complex has been reported from three different groups and the protein is tentatively allocated in the vicinity of cytochrome b559. However, the exact position of the protein is not conclusively established yet due to limited resolution of the crystallographic analysis. We have constructed a psbX deletion mutant of Synechocystis 6803 and characterized the mutant focusing on the electron transport properties. The growth rates of the cells were not much different between wild type and the mutant under various light intensities and CO₂ concentrations. Effects of DCMU on oxygen evolution activity supported by various quinone derivatives were compared between the wild type and the mutant. The concentrations of DCMU which brings about half inhibition of oxygen evolution were different depending on the quinone derivatives used. Reoxidation rates of Q_A after single turnover flashes measured by fluorescence decay were also affected in the mutant. These results suggest that quinone-binding site of the mutant is modified and the electron transport of the PSII reaction center is affected. A possible functional role of the PsbX protein in the core complex in relation to the structure will be discussed.

KEY WORDS: psbX, photosystem II, electron transport, Synechocystis 6803