PT  - JOURNAL ARTICLE
AU  - Nilaweera, Thushani D.
AU  - Nyenhuis, David A.
AU  - Cafiso, David S.
TI  - Structural intermediates observed only in intact <em>Escherichia coli</em> indicate a mechanism for TonB-dependent transport
AID  - 10.1101/2021.03.18.436049
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.03.18.436049
4099  - http://biorxiv.org/content/early/2021/03/18/2021.03.18.436049.short
4100  - http://biorxiv.org/content/early/2021/03/18/2021.03.18.436049.full
AB  - 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, where TonB binding alone is sufficient to produce allosteric rearrangements in the transporter. They also demonstrate the importance of studying outer membrane proteins in their native environment.Competing Interest StatementThe authors have declared no competing interest.