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

Identification of a requirement for the PsbQ-like protein in Synechocystis sp. PCC 6803. Tina Summerfield^*,1, Jackie Shand¹, Fiona Bentley¹, Julian Eaton-Rye¹, ¹ Department of Biochemistry, Dunedin, New Zealand

ABSTRACT- Identification of a requirement for the PsbQ-like protein in Synechocystis sp. PCC 6803 T. C. Summerfield, J. A. Shand, F. Bentley, and J. J. Eaton-Rye Department of Biochemistry, University of Otago, P. O. Box 56, Dunedin, New Zealand A PsbQ-like protein (Sll1638) has been reported to be associated with photosystem II (PSII) complexes in Synechocystis sp. PCC 6803 [Kashino, Y., Lauber, W.M., Carroll, J.A., Wang, Q., Whitmarsh, J., Satoh, K. and Pakrasi, H.B. (2002) Biochemistry 41, 8004-8012]. By inactivating sll1638 in wild type, and several strains of cyanobacteria carrying PSII-specific mutations, we have demonstrated a requirement for the PsbQ-like protein for photoautotrophic growth and stable rates of oxygen evolution. Unlike the extrinsic proteins PsbO, PsbU and PsbV, the Sll1638 polypeptide did not appear to have a role in acquisition of thermotolerance; however, photoautotrophic growth at elevated temperatures was impaired in the mutant lacking this protein. At the routine growth temperature photoautotrophic growth, oxygen evolution rates and assembly of PSII centers in the absence of Sll1638 were similar to wild type. However, photoautotrophic growth of these cells was compromised in media where calcium and chloride were both limiting and there was no photoautotrophic growth in media that was additionally limiting for iron. Similarly, removal of Sll1638 in a strain lacking the PsbU protein introduced an altered requirement of calcium and chloride during photoautotrophic growth. When combined, the removal of PsbV and Sll1638 produced a strain that was not photoautotrophic and which assembled approximately 50% of PSII centers associated with the mutant lacking only PsbV. Growth of the double-deletion mutant for PsbV and Sll1638 was restored at pH 10.0: in contrast other pH-dependent PSII-specific mutants were no longer recoverable at pH 10 upon removal of Sll1638. All strains lacking this PsbQ-like protein could grow photoheterotrophically with a doubling time that was indistinguishable from that of wild type under the same conditions: indicating the phenotypes observed result from inactivation of PSII.

KEY WORDS: oxygen evolution, Synechocystis, extrinsic proteins, PsbQ