PqiABC forms a membrane-bridging conduit and mediates bidirectional phospholipid transport across the Gram-negative bacterial envelope
- 1School of Biosciences, University of Birmingham, UK. B15 2TT
Abstract
The mechanism by which glycerophospholipids are transported between the inner and outer membranes in Gram-negative bacteria remains poorly understood. In Escherichia coli, the paraquat-inducible (Pqi) pathway, comprising the inner membrane protein PqiA, the periplasm-spanning MCE-family protein PqiB, and the outer membrane lipoprotein PqiC, has been implicated in this process. These components are proposed to assemble into a quaternary complex that forms a continuous channel bridging the inner and outer membranes. Here, using neutron reflectometry and quartz crystal microbalance with dissipation monitoring, we perform a dynamic structural analysis of PqiABC within a planar double bilayer membrane-mimetic system. This approach reveals that PqiABC assembles into a stable, envelope-spanning complex anchored to both membranes, consistent with its proposed conduit architecture. Furthermore, using neutron reflectometry in combination with complementary fluorescence-based assays, we demonstrate that PqiABC mediates passive glycerophospholipid transport, supporting bidirectional lipid exchange between membranes. Together, these findings establish PqiABC as a membrane-bridging lipid transport system and provide direct evidence for a mechanism of passive glycerophospholipid equilibration across the bacterial envelope.
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BibTeX
@misc{johnston2026pqiabc,
title = {{PqiABC forms a membrane-bridging conduit and mediates bidirectional phospholipid transport across the Gram-negative bacterial envelope}},
author = {H. E. Johnston and L. A. Clifton and C. B. Wilson and P. Sridhar and A. Alzahrani and A. Colyer and R. Logan and S. C. L. Hall and D. J. Hardy and T. J. Knowles},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.15.751761},
url = {https://www.biorxiv.org/content/10.64898/2026.09.15.751761v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - PqiABC forms a membrane-bridging conduit and mediates bidirectional phospholipid transport across the Gram-negative bacterial envelope
AU - H. E. Johnston
AU - L. A. Clifton
AU - C. B. Wilson
AU - P. Sridhar
AU - A. Alzahrani
AU - A. Colyer
AU - R. Logan
AU - S. C. L. Hall
AU - D. J. Hardy
AU - T. J. Knowles
PY - 2026
DA - 2026/09/15
PB - bioRxiv
DO - 10.64898/2026.09.15.751761
UR - https://www.biorxiv.org/content/10.64898/2026.09.15.751761v1
AB - The mechanism by which glycerophospholipids are transported between the inner and outer membranes in Gram-negative bacteria remains poorly understood. In Escherichia coli, the paraquat-inducible (Pqi) pathway, comprising the inner membrane protein PqiA, the periplasm-spanning MCE-family protein PqiB, and the outer membrane lipoprotein PqiC, has been implicated in this process. These components are proposed to assemble into a quaternary complex that forms a continuous channel bridging the inner and outer membranes. Here, using neutron reflectometry and quartz crystal microbalance with dissipation monitoring, we perform a dynamic structural analysis of PqiABC within a planar double bilayer membrane-mimetic system. This approach reveals that PqiABC assembles into a stable, envelope-spanning complex anchored to both membranes, consistent with its proposed conduit architecture. Furthermore, using neutron reflectometry in combination with complementary fluorescence-based assays, we demonstrate that PqiABC mediates passive glycerophospholipid transport, supporting bidirectional lipid exchange between membranes. Together, these findings establish PqiABC as a membrane-bridging lipid transport system and provide direct evidence for a mechanism of passive glycerophospholipid equilibration across the bacterial envelope.
ER -