Structural studies of the lipopolysaccharide from Haemophilus parainfluenzae strain 20

Haemophilus parainfluenzae is a Gram-negative bacterium that colonizes the upper respiratory tract of humans and is a part of normal flora. In this study, we investigated the lipopolysaccharide (LPS) expressed by H. parainfluenzae strain 20. Using NMR and MS techniques on LPS, oligosaccharide samples and lipid A, the structures for O-antigen, core oligosaccharide and lipid A could be established. It was found that the biological repeating unit of the O-antigen is →4)-α-D-GalpNAc-(1→P→6)-β-D-Glcp-(1→3)-α-D-FucpNAc4N-(1→, in which D-FucpNAc4N is 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose. This sugar is in β-configuration when linked to O-4 of the glucose residue of β-D-Galp-(1→2)-L-α-D-Hepp-(1→2)-[PEtn→6]-L-α-D-Hepp-(1→3)-[β-D-Glcp-(1→4)]-L-α-D-Hepp-(1→5)-[PPEtn→4]-α-Kdo-(2→6)-lipid A. LPS from a wbaP mutant of H. parainfluenzae strain 20 did not contain an O-antigen, consistent with the wbaP gene product being required for expression of O-antigen in fully extended LPS.