Elucidating the role of a trans-envelope MCE transport system in Pseudomonas aeruginosa

In Gram-negative bacteria, hydrophobic transport between the inner membrane and outer membrane (OM) is necessary for several cellular processes such as nutrient acquisition and maintenance of the OM. The proteins of the Mammalian Cell Entry (MCE) superfamily form tunnels with diverse architectures for the transport of hydrophobic molecules directly from one membrane to another, and are integral components of trans-envelope protein complexes. However, the class of MCE protein that is most broadly prevalent across double-membraned bacterial species, as well as MCE systems found in plant chloroplasts, remains largely uncharacterized. Here we will describe our initial structural, biochemical and genetic characterization of one such MCE system, encoded by the PA3211-PA3214 operon in Pseudomonas aeruginosa. These studies have shed light on how the PA3211-PA3214 system may facilitate the movement of hydrophobic molecules across the OM and the periplasmic space, and suggest possible cellular functions of the PA3211-PA3214 system in P. aeruginosa.