Bacterial Outer Membranes and Interactions with Membrane Proteins

The outer membrane of gram-negative bacteria is a unique asymmetric membrane bilayer that is composed of phospholipids in the inner leaflet and lipopolysaccharides (LPS) in the outer leaflet. Its function as a selective barrier is crucial for the survival of bacteria in many distinct environments, and it also renders gram-negative bacteria more resistant to antibiotics than their gram-positive counterparts. LPS comprises three regions: lipid A, core oligosaccharide, and O-antigen polysaccharide. In this talk, I will present our ongoing efforts on understanding various bacterial outer membranes and their interactions with outer membrane proteins, including (1) construction of a model of an E. coli R1 (core) O6 (antigen) LPS molecule using the CHARMM36 lipid and carbohydrate force fields and simulations of various E. coli R1.O6 LPS bilayers; (2) modeling of E. coli R2, R3, R4, and K12 cores and other O-antigens and their bilayer simulations; (3) development of LPS Modeler in CHARMM-GUI; (4) modeling and simulation of E. coli outer membranes with phospholipids in the inner leaflet and LPS in the outer leaflet as well as OmpLA in the outer membrane; (5) modeling and simulation of BamA in the E. coli outer membrane; (6) other ongoing outer membrane - protein simulations.

Gram-negative bacterial outer membrane molecular complexity. This image illustrates a typical E. coli outer membrane. The bilayer is composed of (from the top, external leaflet) glycosylated amphipathic molecules known as lipopolysaccharide (LPS) consisting of an O-antigen polysaccharide, a core oligosaccharide, and lipid A and (the bottom, periplasmic leaflet) consisting of various phospholipid molecules. The cyan atoms interspersed with the core oligosaccharides are calcium atoms, which immobilize the membrane by mediating the cross-linking electrostatic interaction network. K⁺ and Cl^- ions are magenta and green spheres.