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.
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.
- David S Cafiso
- David S Cafiso
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Janice L Robertson, Washington University in St Louis, United States
- Preprint posted: March 18, 2021 (view preprint)
- Received: March 18, 2021
- Accepted: July 11, 2021
- Accepted Manuscript published: July 12, 2021 (version 1)
- Accepted Manuscript updated: July 13, 2021 (version 2)
- Accepted Manuscript updated: July 30, 2021 (version 3)
- Version of Record published: August 5, 2021 (version 4)
© 2021, Nilaweera et al.
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