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Published online October 1, 2007
doi:10.1083/jcb.200702082
The Journal of Cell Biology, Vol. 179, No. 1, 87-99
The Rockefeller University Press, 0021-9525 $30.00
© 2007 Bageshwar et al.
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Article

 Two electrical potential–dependent steps are required for transport by the Escherichia coli Tat machinery

Umesh K. Bageshwar and Siegfried M. Musser

Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX 77843

Correspondence to Siegfried Musser: smusser{at}tamu.edu

The twin-arginine translocation (Tat) pathway in Escherichia coli transports fully folded and assembled proteins across the energy-transducing periplasmic membrane. In chloroplasts, Tat transport requires energy input only from the proton motive force. To elucidate the mechanism and energetics of bacterial Tat protein transport, we developed an efficient in vitro transport assay using TatABC-enriched inverted membrane vesicles and the physiological precursor pre-SufI. We report transport efficiencies of 60–80% for nanomolar pre-SufI concentrations. Dissipation of the pH gradient does not reduce pre-SufI transport efficiency. Instead, pre-SufI transport requires at least two electrical potential ({Delta}{psi})–dependent steps that differ in both the duration and minimum magnitude of the required {Delta}{psi}. The data are consistent with a model in which a substantial {Delta}{psi} of short duration is required for an early transport step, and in which a small {Delta}{psi} of long duration is necessary to drive a later transport step.

Abbreviations used in this paper: IMV, inverted membrane vesicle; PMF, proton motive force; Tat, twin-arginine translocation.


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