Structural studies of lipooligosaccharides from Haemophilus ducreyi ITM 5535, ITM 3147, and a fresh clinical isolate, ACY1: evidence for intrastrain heterogeneity with the production of mutually exclusive sialylated or elongated glycoforms

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Abstract
The structures of the lipooligosaccharides (LOSs) from Haemophilus ducreyi ITM 5535 and ITM 3147 and a fresh clinical isolate, ACY1, have been investigated. Oligosaccharides were obtained from phenol-water-extracted LOS by mild acid hydrolysis and were studied by methylation analysis, fast atom bombardment and electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy. The major oligosaccharide obtained from all strains was a nonasaccharide with the structure beta-D-Galp-(1-->4)-beta-D-GlcNAcp-(1-->3)-beta-D-Galp-(1-->4)-D-a lpha-D-Hepp- (1-->6)-beta-D-Glcp-(1-->[L-alpha-D-Hepp-(1-->2)-L-alpha-D-Hepp - (1-->3)]4)-L-alpha-D-Hepp-Kdo (Kdo stands for 3-deoxy-D-manno-octulosonic acid) and is thus identical to that identified as the major oligosaccharide in H. ducreyi ITM 2665 (E. K. H. Schweda, A. C. Sundström, L. M. Eriksson, J.A. Jonasson, and A. A. Lindberg, J. Biol. Chem. 269:12040-12048, 1994). Electrospray ionization mass spectrometry on O-deacylated LOS from H. ducreyi ITM 5535 obtained after treatment with anhydrous hydrazine gave evidence for the presence of a sialylated major compound, Neu5Ac alpha(2-->3)-beta-D-Galp-(1-->4)-beta-D-GlcNAcp-(1-->3)-beta-D-Gal p- (1-->4)-D-alpha-D-Hepp-(1-->6)-beta-D-Glcp-(1-->[L-alpha-D-Hepp -(1-->2)-L- alpha-D-Hepp-(1-->3)]4)-L-alpha-D-Hepp-Kdo(P)-O-deacylated lipid A (Neu5Ac stands for N-acetylneuraminic acid). However, an even larger oligosaccharide could be isolated from all strains as a minor component, viz., the undecasaccharide beta-D-Galp-(1-->4)-beta-D-GlcNAcp-(1-->3)-beta-d-Galp-(1-->4)-beta-D-glcNAcp-(1-->3)-beta-D-Galp-(1-->4)-D-alpha-D-Hepp-(1-->6)-beta-D-Glcp-(1-->[L-alpha-D-Hepp-(1-->2)-L-alpha-D-Hepp-(1-->3)]4-L-alpha-D-Hepp-Kdo, which represents an N-acetyl lactosamine disaccharide unit elongation of the LOS outer core. No Sialylation of this latter minor component undecasaccharide was detected.

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