Real Science for a Change

To this I say: bravo. As I have noted the remarkable feature of the ATP synthase engine in the past is that it rotates clockwise or counterclockwise for aerobic or anaerobic synthesis for the creation of cellular free energy. Now, a new feature is discovered that this wonderful enzyme also is capable of switching from use of ionic hydrogen and sodium at the extreme thermodynamic boundary condition in the "methanogenic archaeon Methanosarcina acetivorans." It is precisely in the study of these types of such extreme anomalous domains that true scientific progress is secured.

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

1. Katharina Schlegel^a, 
2. Vanessa Leone^b, 
3. José D. Faraldo-Gómez^b,^c,¹, and
4. Volker Müller^a,¹

+Author Affiliations

1. ^aMolecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany;
2. ^bTheoretical Molecular Biophysics Group, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany, and
3. ^cCluster of Excellence ”Macromolecular Complexes,” 60438 Frankfurt am Main, Germany

1. Edited* by E. Peter Greenberg, University of Washington, Seattle, WA, and approved December 2, 2011 (received for review September 27, 2011)

Abstract

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. acetivoranscan 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.