36° step size of proton-driven c-ring rotation in FoF1-ATP synthase

Synthesis of adenosine triphosphate ATP, the 'biological energy currency', is accomplished by FoF1-ATP synthase. In the plasma membrane of Escherichia coli, proton-driven rotation of a ring of 10 c subunits in the F-o motor powers catalysis in the F-1 motor. Although F-1 uses 120 degrees stepping during ATP synthesis, models of F-o predict either an incremental rotation of c subunits in 36 degrees steps or larger step sizes comprising several fast substeps. Using single-molecule fluorescence resonance energy transfer, we provide the first experimental determination of a 36 degrees sequential stepping mode of the c-ring during ATP synthesis. The EMBO Journal (2009) 28, 2689-2696. doi: 10.1038/emboj.2009.213; Published online 30 July 2009