Lipopolysaccharide of Escherichia coli : structure, biosynthesis and functions

peer reviewedThe lipopolysaccharide (LPS) is a major component of the surface of the Gram negative bacteria. The LPS is composed of three separately synthesized entities: the lipid A, the core oligosaccharide and the O antigen, that will be linked together after their respective synthesis. The lipid A, embedded inside the outer membrane, is the proximal part of the LPS and the core is the medial part, whereas the O antigen represents the distal part free in the external environment. Amongst the Enterobacteriaceae family, the lipid A is structurally highly conserved and the variation in the structure of the core oligosaccharide is limited whereas the O antigen is the hypervariable region. Diverse biological activities have been associated with LPS, amongst which the endotoxinic activity carried by the lipid A, and the strain immunogenic specificity carried by the O antigen. In this review manuscript we summarize the state of knowledge on the structures and biosynthesis of the different components of the LPS of Escherichia coli and on their respective roles in the virulence of pathogenic bacteria