TY - JOUR T1 - Evidence for phospholipid export from the gram-negative inner membrane: time to rethink the Mla pathway? JF - bioRxiv DO - 10.1101/388546 SP - 388546 AU - Gareth W. Hughes AU - Stephen C. L. Hall AU - Claire S. Laxton AU - Pooja Sridhar AU - Amirul H. Mahadi AU - Caitlin Hatton AU - Thomas J. Piggot AU - Mohammed Jamshad AU - Vaclav Spana AU - Cadby T. Ian AU - Christopher Harding AU - Georgia L. Isom AU - Jack Bryant AU - Rebecca J. Parr AU - Yasin Yakub AU - Mark Jeeves AU - Damon Huber AU - Henderson R. Ian AU - Luke A. Clifton AU - Lovering L. Andrew AU - Timothy J. Knowles Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/08/09/388546.abstract N2 - The Mla pathway is believed to be involved in maintaining the asymmetrical Gram-negative outer membrane via retrograde phospholipid transport. The pathway is composed of 3 components: the outer membrane MlaA-OmpC/F complex, a soluble periplasmic protein, MlaC, and the inner membrane ATPase, MlaFEDB complex. Here we solve the crystal structure of MlaC in its phospholipid free closed apo conformation, revealing a novel pivoting β-sheet mechanism which functions to open and close the phospholipid-binding pocket. Using the apo form of MlaC we provide evidence that the Mla pathway functions in an anterograde rather than a retrograde direction by showing the inner membrane MlaFEDB machinery exports phospholipids and transfers them to MlaC in the periplasm. We confirm that the lipid export process occurs through the MlaD component of the MlaFEDB complex. This lipid export process is shown to be independent of ATP. Our data provides, for the first time, evidence of an apparatus for lipid export to the outer membrane. ER -