Journal Article

Targeted Disruption of <i>psbX</i> and Biochemical Characterization of Photosystem II Complex in the Thermophilic Cyanobacterium <i>Synechococcus elongatus</i>

Hiroshi Katoh and Masahiko Ikeuchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 2, pages 179-188
Published in print February 2001 | ISSN: 0032-0781
Published online February 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce024
Targeted Disruption of psbX and Biochemical Characterization of Photosystem II Complex in the Thermophilic Cyanobacterium Synechococcus elongatus

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PSII-X is a small hydrophobic protein, which is universally present in photosystem II (PSII) core complex among cyanobacteria and plants. The role of PSII-X was studied by directed mutagenesis and biochemical analysis in the thermophilic cyanobacterium Synechococcus elongatus. The psbX-disrupted mutant could grow photoautotrophically indicative of non-essential function, while it showed growth defect under low CO2 conditions. An active O2-evolving PSII complex was successfully isolated from the mutant and wild type. Protein composition of the isolated PSII complex was the same as wild type except for the absence of PSII-X. O2 evolution supported by artificial quinones was affected in the psbX-disrupted mutant. At high concentration of 2,6-dichlorobenzoquinone or 2,6-dimethylbenzoquinone, the mutant showed much lower activity than wild type, while not much difference was found at low concentration. These results imply that binding or turnover of quinones at the QB site depends, at least in part, on PSII-X protein in the PSII complex. Gel filtration chromatography of the PSII complex revealed that the dimeric structure of the complex was not greatly affected in the psbX-disrupted mutant.

Keywords: Key words: Cyanobacterium — O2 evolution — Photosystem II — psbX — Synechococcus elongatus — Thermophilic.; Abbreviations: 2,6DCBQ, 2,6-dichlorobenzoquinone; 2,6DMBQ, 2,6-dimethyl benzoquinone.; The nucleotide sequence in this paper has been submitted to the EMBL, GenBank and DDBJ under accession number AB046708.

Journal Article.  5767 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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