Direct observation of stepped proteolipid ring rotation in E. coli FoF1-ATP synthase

Although single-molecule experiments have provided mechanistic insight for several molecular motors, these approaches have proved difficult for membrane bound molecular motors like the FoF1-ATP synthase, in which proton transport across a membrane is used to synthesize ATP. Resolution of smaller steps in F-o has been particularly hampered by signal-to-noise and time resolution. Here, we show the presence of a transient dwell between F-o sub-units a and c by improving the time resolution to 10 mu s at unprecedented S/N, and by using Escherichia coli FoF1 embedded in lipid bilayer nanodiscs. The transient dwell interaction requires 163 mu s to form and 175 mu s to dissociate, is independent of proton transport residues aR210 and cD61, and behaves as a leash that allows rotary motion of the c-ring to a limit of similar to 36 degrees while engaged. This leash behaviour satisfies a requirement of a Brownian ratchet mechanism for the F-o motor where c-ring rotational diffusion is limited to 36 degrees. The EMBO Journal (2010) 29, 3911-3923. doi:10.1038/emboj.2010.259; Published online 29 October 2010