Lipopolysaccharides (LPS) are complex cell-surface glycolipids that are essential for viability of most gram-negative bacteria. LPS molecules typically contain three structural domains: lipid A, core oligosaccharide and a hyper-variable O-antigen polysaccharide. The polymannose O antigens of E. coli serotypes O8, O9 and O9a are synthesized on a polyisoprenoid lipid carrier at the cytosol/cytoplasmic membrane interface and exported across the membrane by an ATP-binding cassette (ABC) transporter. Once in the periplasm, O antigen is ligated to lipid A-core prior to trafficking the completed LPS molecule to the cell surface. Synthesis of polymannose O antigens requires interplay between polymerizing enzymes possessing multiple glycosyltransferase modules with different linkage specificities, and chain-terminating enzymes that modify the non-reducing terminus to prevent further glycan elongation and mark the product for export. These competing activities must be fine-tuned in an enzyme complex in order to generate glycans within a defined size range, optimized to protect the cell from host responses.

Stop and go: Biosynthesis and export of polymannose lipopolysaccharide O antigens in <i>Escherichia coli</i>

245th National Meeting (2013)

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Stop and go: Biosynthesis and export of polymannose lipopolysaccharide O antigens in Escherichia coli