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Proc Natl Acad Sci U S A. 2012 Jan 17;109(3):947-52. doi: 10.1073/pnas.1115796109. Epub 2012 Jan 4.

Promiscuous archaeal ATP synthase concurrently coupled to Na+ and H+ translocation.

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Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany.


ATP synthases are the primary source of ATP in all living cells. To catalyze ATP synthesis, these membrane-associated complexes use a rotary mechanism powered by the transmembrane diffusion of ions down a concentration gradient. ATP synthases are assumed to be driven either by H(+) or Na(+), reflecting distinct structural motifs in their membrane domains, and distinct metabolisms of the host organisms. Here, we study the methanogenic archaeon Methanosarcina acetivorans using assays of ATP hydrolysis and ion transport in inverted membrane vesicles, and experimentally demonstrate that the rotary mechanism of its ATP synthase is coupled to the concurrent translocation of both H(+) and Na(+) across the membrane under physiological conditions. Using free-energy molecular simulations, we explain this unprecedented observation in terms of the ion selectivity of the binding sites in the membrane rotor, which appears to have been tuned via amino acid substitutions so that ATP synthesis in M. acetivorans can be driven by the H(+) and Na(+) gradients resulting from methanogenesis. We propose that this promiscuity is a molecular mechanism of adaptation to life at the thermodynamic limit.

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