Fig. 3.

The cell envelope of Gram-negative bacteria. (a) The cytoplasm of E. coli is surrounded by the inner membrane (IM), the periplasm and the outer membrane (OM). The IM is a symmetric phospholipid (shown in orange) bilayer containing integral α-helical membrane proteins. The OM is an asymmetric bilayer of phospholipid and lipopolysaccharide (LPS, shown in purple) and contains β-barrel integral membrane proteins. The periplasm is the aqueous compartment between the two membranes in which the peptidoglycan cell wall is found. Both membranes have associated lipoproteins on their periplasmic faces. (b) The lipid composition of the IM (light blue), inner leaflet of the OM (dark blue) and outer leaflet of the OM (white) in E. coli (percentages based on those reported in [64], [65], [66]). Structures of (c) LPS, (d) phosphatidylethanolamine, (e) phosphatidylglycerol and (f) cardiolipin are shown.