| (a) Simplified diagram of Gram-negative bacterial cell surface showing LPS and some other major features. Approximately 3 × 106 LPS molecules decorate 75% of the surface of Gram-negative bacteria. (b) The LPS molecule consists of an outer O-specific oligosaccharide that is highly variable among different species, a conserved inner core, and a lipid – lipid A – that forms part of the bacterial outer membrane. (c) Lipid A is a phosphoglycolipid consisting of a core hexosamine disaccharide with ester- and amide-linked acylated fatty acid tails arranged in either asymmetric or symmetric arrays that anchor the structure in the membrane. The asymmetric structure of E. coli lipid A is shown here. The numbers refer to the number of carbon atoms in the tail. |
