Abstract
The outer membrane of Gram-negative bacteria is a unique and highly asymmetric lipid bilayer composed of phospholipids in the inner leaflet and mostly lipopolysaccharide (LPS) in the outer leaflet. Outer membrane phospholipase A (OmpLA) is an integral membrane enzyme in Escherichia coli. The structure of monomeric OmpLA consists of a 12-stranded antiparallel β-strands with a convex and a flat side, six loops at the extracellular side and five turns at the periplasmic side of the membrane. Utilizing the latest C36 CHARMM lipid and carbohydrate force field, we have constructed a model of OmpLA embedded in an asymmetric lipid bilayer with rough LPS molecules (without O-antigen) in one leaflet and phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin in the other leaflet to model the realistic outer membrane environment. The simulation results will be discussed in terms of the key structural properties of the bacterial outer membrane including hydrophobic thickness, area per lipid, and acyl chain order parameter. We will also show the difference of OmpLA structure and dynamics compared to that in a DLPC bilayer. At the same time a comparison between simulations with different numbers of LPS molecules on the outer leaflet will elucidate the potential technical difficulties in building asymmetric bilayer.
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