The crystal structure of the nucleotide-free alpha 3 beta 3 subcomplex of F-1-ATPase from the thermophilic Bacillus PS3 is a symmetric trimer

Background: F-1-ATPase, an oligomeric assembly with subunit stoichiometry alpha 3 beta 3 gamma delta epsilon, is the catalytic component of the ATP synthase complex, which plays a central role in energy transduction in bacteria, chloroplasts and mitochondria. The crystal structure of bovine mitochondrial F-1-ATPase displays a marked asymmetry in the conformation and nucleotide content of the catalytic beta subunits, The alpha 3 beta 3 subcomplex of F-1-ATPase has been assembled from subunits of the moderately thermophilic Bacillus PS3 made in Escherichia coli, and the subcomplex is active but does not show the catalytic cooperativity of intact F-1-ATPase. The structure of this subcomplex should provide new information on the conformational variability of F-1-ATPase and may provide insights into the unusual catalytic mechanism employed by this enzyme.Results: The crystal structure of the nucleotide-free bacterial alpha 3 beta 3 subcomplex of F-1-ATPase, determined at 3.2 Angstrom resolution, shows that the oligomer has exact threefold symmetry. The bacterial beta subunits adopt a conformation essentially identical to that of the nucleotide-free beta subunit in mitochondrial F-1-ATPase; the alpha subunits have similar conformations in both structures.Conclusions: The structures of the bacterial F-1-ATPase alpha and beta subunits are very similar to their counterparts in the mitochondrial enzyme, suggesting a common catalytic mechanism. The study presented here allows an analysis of the different conformations adopted by the alpha and beta subunits and may ultimately further our understanding of this mechanism.