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Structure of the O-glycopeptides isolated from bovine milk component PP3
B Coddeville1, J M Girardet, Y Plancke
1Laboratoire de Chimie Biologique, Unité Mixte de Recherche du Centre National de la Recherche Scientifique no 111, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
Abstract:
The heat-stable acid-soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides from the ConA-bound fraction corresponding to the component PP3 were obtained by Pronase digestion and were separated by gel filtration into high and low-molecular-mass glycopeptides. In a previous work, we have investigated the structure of the N-glycans from the high-molecular-mass glycopeptides [Girardet et al. (1995) Eur J Biochem 234: 939-46]. Here, we describe the structure of the O-glycans from the low-molecular-mass glycopeptides. By combining methylation analysis, mass spectrometry, 400 MHz 1H-NMR spectroscopy and peptide sequence analysis, we show that the low-molecular-mass fraction contains several neutral glycopeptides. A mixture of the following three glycan structures linked to the Thr86 has been identified: GalNac alpha1-O-Thr, Gal(beta1-3)GalNAc alpha1-O-Thr and Gal(beta1-4)GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc alpha1-O-Thr.