PqiABC forms a membrane-bridging conduit and mediates bidirectional phospholipid transport across the Gram-negative bacterial envelope

Authors

Johnston, H. E., Clifton, L. A., Wilson, C. B., Sridhar, P., Alzahrani, A., Colyer, A., Logan, R., Hall, S. C. L., Hardy, D. J., Knowles, T. J.

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.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 18 Sep 2026.

Stats

1-terrible, 9-excellent. How would you rate this preprint? Sign in in to submit your rating.

Post a comment

You need to be signed in to post comments. You can sign in here.

Comments

There are no comments yet.