Structural analysis of the lipopolysaccharide oligosaccharide epitopes expressed by Haemophilus influenzae strain RM.118-26

Abstract

The structure of the lipopolysaccharide of Haemophilus influenzae mutant strain, RM.118-26, was investigated. Electrospray ionization-mass spectrometry on intact lipopolysaccharide, O-deacylated lipopolysaccharide and core oligosaccharides obtained from lipopolysaccharide after mild acid hydrolysis provided information on the composition and relative abundance of the glycoforms. Oligosaccharide samples were studied in detail using high- field NMR techniques. The structure of the major glycoform containing phosphocholine is identical to the Hex2 glycoform described for H. influenzae RM. 118-28 [Risberg, A., Schweda, E.K.H. and Jansson, P.-E. (1997) Eur. J. Biochem. 243, 701-707]. A second major glycoform, containing three hexose residues (Hex3), in which a lactose unit, β-D-Galp-(1→4)-β-D-Glcp, is attached at the O-2 position of the terminal heptose of the inner core element, L-α-D-Hepp-(1→2)-L-α-D-Hepp-(1→3)-[β-D-Glcp-(1→4)-]-L-α-D- Hepp-(1→5)-α-Kdo, carries no phosphocholine. Instead this lipopolysaccharide glycoform is partly (40%) substituted by an O-acetyl group linked to the 6-position of the glucose residue in the lactose unit.