AUTHOR=Gresock Michael G., Savenkova Marina I., Larsen Ray A., Ollis Anne A., Postle Kathleen TITLE=Death of the TonB Shuttle Hypothesis JOURNAL=Frontiers in Microbiology VOLUME=2 YEAR=2011 URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2011.00206 DOI=10.3389/fmicb.2011.00206 ISSN=1664-302X ABSTRACT=
A complex of ExbB, ExbD, and TonB couples cytoplasmic membrane (CM) proton motive force (pmf) to the active transport of large, scarce, or important nutrients across the outer membrane (OM). TonB interacts with OM transporters to enable ligand transport. Several mechanical models and a shuttle model explain how TonB might work. In the mechanical models, TonB remains attached to the CM during energy transduction, while in the shuttle model the TonB N terminus leaves the CM to deliver conformationally stored potential energy to OM transporters. Previous studies suggested that TonB did not shuttle based on the activity of a GFP–TonB fusion that was anchored in the CM by the GFP moiety. When we recreated the GFP–TonB fusion to extend those studies, in our hands it was proteolytically unstable, giving rise to potentially shuttleable degradation products. Recently, we discovered that a fusion of the