TY - JOUR T1 - Architecture of a lipid transport system for the bacterial outer membrane JF - bioRxiv DO - 10.1101/064360 SP - 064360 AU - Damian C. Ekiert AU - Gira Bhabha AU - Garrett Greenan AU - Sergey Ovchinnikov AU - Jeffery S. Cox AU - Ronald D. Vale Y1 - 2016/01/01 UR - http://biorxiv.org/content/early/2016/07/18/064360.abstract N2 - How phospholipids are trafficked between the bacterial inner and outer membranes through the intervening hydrophilic space of the periplasm is not known. Here we report that members of the mammalian cell entry (MCE) protein family, which were previously implicated in outer membrane function, form hexameric rings with a central hydrophobic channel that can mediate phospholipid transport. The E. coli MCE protein MlaD forms part of a large multi-protein complex in the inner membrane that includes an unconventional ABC transporter. MlaC, a soluble lipid-binding protein, interacts with MlaD and an outer membrane protein complex, suggesting that it ferries lipids between the two membranes. In contrast, the syringe-like architecture of a second E. coli MCE protein, PqiB, creates a continuous channel of sufficient length to potentially span the entire periplasmic space. This work reveals a system of highly conserved protein-based channels that translocate lipids between the inner and outer membranes of bacteria and some eukaryotic organelles.One Sentence Summary Structural characterization of a widely-conserved transport system suggests a new model for lipid trafficking in double-membraned bacteria and organelles. ER -