Structures of monosialyl oligosaccharides isolated from the respiratory mucins of a non-secretor (O, Lea+b-) patient suffering from chronic bronchitis. Characterization of a novel type of mucin carbohydrate core structure

Abstract

Mucin glycopeptides were prepared from the respiratory mucus of a non-secretor, chronic bronchitis patient with blood group O, Le(a)+b-. Oligosaccharides were released by alkaline borohydride treatment and purified by anion-exchange chromatography, size-exclusion chromatography and high-performance liquid chromatography on a silica-bonded alkylamine column. Structural studies employed 500-MHz 1H-NMR spectroscopy and fast atom bombardment-mass spectrometry. Twenty-six monosialyl oligosaccharides, ranging in size from di- to octasaccharide, were fully characterized in this study. The sialic acid occurs either alpha(2-->3)- or alpha(2-->6)-linked to a galactosyl residue, or alpha(2-->6)-linked to GalNAc-ol. In keeping with the non-secretor status of the patient, no structures with an alpha(-->2)-linked fucose residue were found. Nine of the structures had fucose present in alpha(-->3) linkage, either in the Le(x) determinant or in the sialyl-Le(x) determinant, or both (structure 11). Only one oligosaccharide (structure 3b) was seen with fucose alpha (1-->4)-linked in the Le(a) determinant. Eight structures isolated from the mucins of the non-secretor patient had not been found previously in the respiratory mucins of secretor individuals; they are listed below. Among these, structure 4 alpha represents a novel type of mucin carbohydrate core structure.