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Journal of Bacteriology, October 2009, p. 6425-6435, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00644-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Structural and Mutational Analysis of Band 7 Proteins in the Cyanobacterium Synechocystis sp. Strain PCC 6803 {triangledown} ,{dagger}

Marko Boehm,1 Jon Nield,2 Pengpeng Zhang,3 Eva-Mari Aro,3 Josef Komenda,4,5 and Peter J. Nixon1*

Division of Biology, Faculty of Natural Sciences, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom,1 School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom,2 Laboratory of Plant Physiology and Molecular Biology, Department of Biology, University of Turku, 20014 Turku, Finland,3 Institute of Microbiology, Academy of Sciences, Opatovicky Mlyn, 37981 Trebon, Czech Republic,4 Institute of Physical Biology, University of South Bohemia, Zámek 136, 37333 Nové Hrady, Czech Republic5

Received 15 May 2009/ Accepted 3 August 2009

Band 7 proteins, which encompass members of the stomatin, prohibitin, flotillin, and HflK/C protein families, are integral membrane proteins that play important physiological roles in eukaryotes but are poorly characterized in bacteria. We have studied the band 7 proteins encoded by the cyanobacterium Synechocystis sp. strain PCC 6803, with emphasis on their structure and proposed role in the assembly and maintenance of the photosynthetic apparatus. Mutagenesis revealed that none of the five band 7 proteins (Slr1106, Slr1128, Slr1768, Sll0815, and Sll1021) was essential for growth under a range of conditions (including high light, salt, oxidative, and temperature stresses), although motility was compromised in an Slr1768 inactivation mutant. Accumulation of the major photosynthetic complexes in the thylakoid membrane and repair of the photosystem II complex following light damage were similar in the wild type and a quadruple mutant. Cellular fractionation experiments indicated that three of the band 7 proteins (Slr1106, Slr1768, and Slr1128) were associated with the cytoplasmic membrane, whereas Slr1106, a prohibitin homologue, was also found in the thylakoid membrane fraction. Blue native gel electrophoresis indicated that these three proteins, plus Sll0815, formed large (>669-kDa) independent complexes. Slr1128, a stomatin homologue, has a ring-like structure with an approximate diameter of 16 nm when visualized by negative stain electron microscopy. No evidence for band 7/FtsH supercomplexes was found. Overall, our results indicate that the band 7 proteins form large homo-oligomeric complexes but do not play a crucial role in the biogenesis of the photosynthetic apparatus in Synechocystis sp. strain PCC 6803.

* Corresponding author. Mailing address: Division of Biology, Faculty of Natural Sciences, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom. Phone: 44 (0) 207 594 5269. Fax: 44 (0) 207 594 5267. E-mail: p.nixon{at}imperial.ac.uk

{triangledown} Published ahead of print on 14 August 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2009, p. 6425-6435, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00644-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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