Pumping lipids across the gram-negative envelope

The PqiABC complex has been implicated in phospholipid (PL) transport between the inner and outer membrane of gram-negative bacteria. This one complex spans the periplasm with components in both membranes, tethering them together. In a recent experiment, RB2220703, we proposed utilising this trans-envelope complex as a scaffold to create a planar double membrane architecture, providing a unique gram-negative envelope mimetic to probe envelope biology. Our Preliminary Neutron Reflectometry (NR) experiments confirmed its successful creation. Furthermore, we predicted PqiABC to be a proton motive force (PMF) driven PL pump based on structural homology. By altering the buffer pH, we were able to emulate the PMF leading to a time dependent drop in the Scattering Length Density of the bilayer attached to the solid support. Suggestive of influx of hydrogenous material into the membrane, consistent with PMF driven PL transport. We have known for 40 years that PLs are transported to the outer membrane via a PMF mediated process. However, to date, no process has been identified. Our results provide tentative clues that PqiABC may be responsible. In this proposal we want to probe the system further and understand phospholipid selectivity.