Oral Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

Osmoporin OmpC forms a complex with MlaA to maintain outer membrane lipid asymmetry in Escherichia coli (#7)

Zhi Soon Chong 1 , Shu Sin Chng 1 2
  1. Department of Chemistry, National University of Singapore, Singapore
  2. Singapore Center on Environmental Life Sciences Engineering, Singapore
The ability of Gram-negative bacteria to survive in harsh environments is partly attributed to the asymmetric outer membrane (OM) lipid bilayer that hinders the entry of toxic compounds. Lipid asymmetry in the OM is established by having phospholipids (PLs) confined to the inner leaflet of the membrane and lipopolysaccharides (LPS) to the outer leaflet. Perturbation of lipid asymmetry, characterized by PL accumulation in the outer leaflet of the OM, disrupts proper LPS packing and results in increased membrane permeability. A multi-component Mla (maintenance of OM lipid asymmetry) system that prevents PL accumulation in the outer leaflet of the OM has recently been identified. This system is widely conserved and is known to be important in the virulence of several pathogens. How the Mla system maintains OM lipid asymmetry is not known. Neither has its role in bacterial pathogenesis been elucidated. Here, we demonstrate that in Escherichia coli, the Mla system maintains OM lipid asymmetry with the help of osmoporin OmpC. We show that OmpC interacts specifically with the OM lipoprotein MlaA. This interaction is sufficient to localize MlaA without its lipid anchor to the OM. Removing OmpC from cells causes accumulation of PLs in the outer leaflet of the OM when cells are in stationary phase. Therefore, we conclude that OmpC is an additional component of the Mla system; the OmpC-MlaA complex functions to remove PLs from the outer leaflet of the OM to maintain lipid asymmetry. A possible role of this two-protein complex in pathogenesis will be discussed.