Studies on the oligosaccharide chains of human alpha 1-protease inhibitor. II. Structure of oligosaccharides.

Human alpha 1-protease inhibitor has three oligosaccharide side chains attached to 3 separate asparaginyl residues of the protein by N-glycosyl linkages. Two of the three asparaginyl residues link mostly to the A-type oligosaccharide chains which consist of Man3, Gal2, (GlcNAc)4 and (NeuAc)2. One of the three asparaginyl residues also attaches to a B-type oligosaccharide chain, which consists of Man3, Gal3, (GlcNAc)5, and (NeuAc)3. The ratio of A-chain to B-chain in this particular position is about 2:1. The structures of A- and B-chains of the glycoprotein were examined by periodate oxidation, sequential glycosidase digestion, and permethylation. The results unequivocally revealed the following structure for A-chains. (Formula: see text). B-type oligosaccharide chains have an additional trisaccharide, i.e. NeuAc 2 alpha leads to 3 Gal 1 beta leads to 4 GlcNAc attached to mannose at the (a) and/or (b) position of A-type chains by a beta 1 leads to 4 linkage. The sialic acid of human alpha 1-protease inhibitor was determined to be N-acetylneuraminic acid.