STRUCTURE OF THE MAJOR OLIGOSACCHARIDE FROM THE LIPOOLIGOSACCHARIDE OF HAEMOPHILUS-DUCREYI STRAIN-35000 AND EVIDENCE FOR ADDITIONAL GLYCOFORMS

Haemophilus ducreyi is a sexually transmitted pathogen that colonizes the genital epithelium in humans, causing genital ulcers or chancroid. Its surface lipooligosaccharides (LOSs) have been shown to play a rol e in ulcer formation and may also be important in cell adhesion and in vasion of host tissue. Earlier we presented a preliminary structure of the major LOS from strain 35000 that suggested the presence of termin al lactosamine [Melaugh, W., Phillips, N. J., Campagnari, A. A., Karal us, R., & Gibson, B. W. (1992) J. Biol. Chem. 267, 13434-13439]. We ha ve now confirmed this structure and assigned the anomeric linkages by 2D NMR studies. In addition to this major structure, analysis by elect rospray ionization mass spectrometry of both O-deacylated LOSs and the oligosaccharides released after treatment with mild acid indicates th e presence of several other LOS glycoforms. These glycoforms constitut e a series of both truncated and elongated analogs of the major oligos accharide determined by NMR. One of these glycoforms exists as a small er oligosaccharide corresponding to the major structure minus terminal galactose. Three other glycoforms appear as larger molecular weight s pecies formed by the addition of phosphoethanolamine, N-acetylhexosami ne, and N-acetylhexosamine plus hexose. Two sialylated glycoforms were also identified and subsequently confirmed by treatment with neuramin idase, but these glycoforms were not found in the released oligosaccha ride pool due to the acid lability of sialic acid. This study clearly indicates that the LOSs from H. ducreyi strain 35000 exist as a hetero geneous population whose structures differ primarily in their phosphor ylation states and terminal sugars and whose terminal glycan structure s can resemble those of human antigens.