The structure of the linkage between the O-specific polysaccharide and the core region of the lipopolysaccharide from Salmonella enterica serovar Typhimurium revisited.

Salmonella enterica sv. Typhimurium strain 1135 possesses smooth(S)-form lipopolysaccharide (LPS). Although the structures of the core region and the O-specific polysaccharide were investigated intensively between the 1960s and the 1980s, the structure of the linkage region between the O-chain and the core was not elucidated unequivocally. By using modern MS and high-field NMR spectroscopy for analysis of the isolated carbohydrate backbone of the LPS, it has been shown that it is a beta-D-Galp residue that links the first repeating unit of the O-specific polysaccharide to O-4 of the last D-Glcp residue of the core region. Interestingly, this particular D-Galp residue is alpha-linked in all following repeating units. The data are discussed with regard to the ligation of O-specific polysaccharide and core region during LPS biosynthesis.