Structure of Glycopeptides Isolated from Bovine Milk Component PP3


J. M. Girardet, Laboratoire des BioSciences de l'Aliment, associé INRA, Faculté des Sciences, Université Henri Poincaré-Nancy 1, B. P. 239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
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The heat-stable acid-soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides were released by pronase digestion of the milk component PP3 and were subsequently separated by high-pH anion-ex-change chromatography on Carbopac PA-1. The primary structures of the glycan and peptide moieties of eight N-glycopeptides have been established by combining methylation analysis, mass spectrometry, 400-MHz 1H-NMR spectroscopy, and peptide sequence analysis. All the analyzed fractions contained biantennary N-acetyllactosamine-type carbohydrate chains, some of them with a GalNAc(β1–4)GlcNAc or a NeuAc(α2–6)GalNAc(β1–4)GlcNAc group. This particular sequence did or did not replace the Gal(β–4)GlcNAc group usually found in most N-linked glycans. Moreover, the sialylated Gal and GalNAc residues were only found on the Man(α1–3) antenna.