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J. Bacteriol. doi:10.1128/JB.00581-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The oligomeric state of c rings from cyanobacterial F-ATP synthases varies from 13 to 15

Institute of Microbiology, Eidgenössische Technische Hochschule (ETH) Zurich, Wolfgang-Pauli-Str. 10, CH-8093, Zurich, Switzerland; Max-Planck-Institute of Biophysics, Max-von-Laue-Str. 3, 60438, Frankfurt am Main, Germany; Center for Biotechnology, University of Technology, Tatzberg 49, 01307, Dresden, Germany; Functional Genomics Center Zurich, University of Zurich and ETH, Winterthurerstrasse 190, 8057, Zurich, Switzerland

^* To whom correspondence should be addressed. Email: dimroth{at}micro.biol.ethz.ch. thomas.meier{at}mpibp-frankfurt.mpg.de.

	Abstract

We have isolated the c rings of F-ATP synthases from eight cyanobacterial strains belonging to four different taxonomic classes (Chroococcales, Nostocales, Oscillatoriales, Gloeobacteria). These c rings showed different mobilities on SDS-polyacrylamide gel electrophoresis (SDS-PAGE), probably reflecting their molecular masses. This supposition was validated with the previously characterized c₁₁, c₁₄ and c₁₅ rings, which migrated on SDS-PAGE in proportion to their molecular masses. Hence, the masses of the cyanobacterial c rings can be conveniently deduced from their electrophoretic mobilities and allow together with the masses of the c monomers to calculate the c ring stoichiometries. The method allows a simple and fast way to determine stoichiometries of SDS-stable c rings and hence a convenient means to unambiguously determine the ‘ion to ATP ratio’, a parameter reflecting the bioenergetic efficacy of F-ATP synthases. AFM imaging was used to proof the accuracy of the method and confirms that the c ring of Synechococcus elongatus SAG 89.79 is a tridecameric oligomer. Despite the high conservation of the c subunits sequences from cyanobacterial strains from various environmental groups the stoichiometries of their c rings varied between c₁₃ and c₁₅. This systematic study of the c ring stoichiometries suggests that variability of c ring sizes might represent an adaptation of the individual cyanobacterial species to their particular environmental and physiological conditions. Furthermore, the two new examples of c₁₅ rings underline once more that an F₁/F_o symmetry mismatch is not an obligatory feature of all F-ATP synthases.

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