The glycans of soybean peroxidase

Abstract

Soybean hull peroxidase (SEP, E.C. 1.11.1.7), an anionic glycoprotein, was found to contain 18.2% carbohydrate with the average composition: 2 mol GlcNAc, 3.3 mol Man, 0.9 mol Fuc, and 0.7 mol Xyl. The oligosaccharides of SEP, after release with glycopeptidase A, were investigated by a combination of high pH anion exchange chromatography with pulsed amperometric detection, methylation analysis and matrix assisted laser desorption/ionization-time-of-flight mass spectrometry. The structure of the major oligosaccharide, accounting for 60 to 65% of the total, is Manα1 → 6(Manβ1 → 3)(Xylβ1 → 2)Manβ1→4GlcNAcβ1 → 4(Fucα1 → 3)GlcNAc. A further 20 to 25% of the released oligosaccharides belong to the (Xyl)(x)Man(m)(Fuc)(f)GlcNAc2 (m = 2, 4, 5, 6; f = 0 or 1, x = 0 or 1) family, The rest of the oligosaccharides were of the high-mannose type, Investigation of the six tryptic fractions containing carbohydrate revealed considerable heterogeneity in the N-linked oligosaccharides present in each fraction, The major glycan (4,Table III) was present in each fraction. Two of the fractions contained the major part of the high-mannose type glycans, Man(m)GlcNAc2 (m = 5-9), the major species being Man7GlcNAc2. The other four fractions contained mainly members of the (Xyl)(x)Man(m)(Fuc)(f)GlcNAc2 (m = 2, 4, 5, 6; f = 0 or 1; x = 0 or 1) family. Methylation analysis of the hole- and apo-SBP provide support for the structures proposed for the oligosaccharides as well as for the heterogeneity of the glycopeptide fractions.