Structural intermediates observed only in intact Escherichia coli indicate a mechanism for TonB-dependent transport
Abstract
Outer membrane TonB-dependent transporters facilitate the uptake of trace nutrients and carbohydrates in Gram negative bacteria and are essential for pathogenic bacteria and the health of the microbiome. Despite this, their mechanism of transport is still unknown. Here, pulse EPR measurements were made in intact cells on the Escherichia coli vitamin B12 transporter, BtuB. Substrate binding was found to alter the C-terminal region of the core and shift an extracellular substrate binding loop 2 nm towards the periplasm; moreover, this structural transition is regulated by an ionic lock that is broken upon binding of the inner membrane protein TonB. Significantly, this structural transition is not observed when BtuB is reconstituted into phospholipid bilayers. These measurements suggest an alternative to existing models of transport, and they demonstrate the importance of studying outer membrane proteins in their native environment.
Data availability
Raw unprocessed DEER data are available in a compressed folder called "SourceData". The Pymol session file used to produce Fig. 6b is included as a supplementary file.
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Funding
Office of Extramural Research, National Institutes of Health (NIGMS GM035215)
- David S Cafiso
Office of Extramural Research, National Institutes of Health (NIGMS S10OD025149)
- David S Cafiso
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2021, Nilaweera et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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