Structural studies on the oligosaccharides of a glycoprotein isolated from alveoli of patients with alveolar proteinosis

The carbohydrate composition and structure of the oligosaccharide units of the major glycoprotein (Mr=36,000) isolated from alveoli of patients with alveolar proteinosis have been determined. This glycoprotein was found to contain 3.0 mol of sialic acid 4.0 mol of galactose, 4.0 mol of mannose, 1.0 mol of fucose, and 6.0 mol of N-acetylglucosamine/mol of peptide. Two major glycopeptide fractions hvae been isolated from this glycoprotein by pronase digestion followed by gel filtration and DEAE-cellulose column fractionation. Glycopeptide I contained 1 residue of sialic acid, 2 residues of galactose, 2 residues of mannose, 3 residues of N-acetylglucosamine, and no fucose. Glycopeptide II contained 2-residues of sialic acid, 2 residues of galactose, 2 residues of mannose, 1 residue of fucose, and 3 residues of N-acetylglucosamine. In both cases, the major amino acid was found to be aspartic acid. Glycopeptides I and II appeared to be homogeneous and the molecular weights of these glycopeptides were estimated to be 2,150 and 2,400 by gel filtration. The carbohydrate structure of these two glycopeptides has been determined by sequential hyrolysis with specific glycosidases and methylation analyses. N-Acetylglucosamine was found to be attached to asparagine of the peptide chain of both oligosaccharides.