Structural and Quantitative Characterization of Mucin-Type -Glycans and the Identification of -Glycosylation Sites in Bovine Submaxillary Mucin.

Bovine submaxillary mucin (BSM) is a gel-forming glycoprotein polymer, and Ser/Thr-linked glycans (-glycans) are important in regulating BSM's viscoelasticity and polymerization. However, details of -glycosylation have not been reported. This study investigates the structural and quantitative characteristics of -glycans and identifies -glycosylation sites in BSM using liquid chromatography-tandem mass spectrometry. The -glycans (consisting of di- to octa-saccharides) and their quantities (%) relative to total -glycans (100%; 1.1 pmol per 1 μg of BSM) were identified with 14 major (>1.0%), 12 minor (0.1%-1.0%), and eight trace (<0.1%) -glycans, which were characterized based on their constituents (sialylation (14 -glycans; 81.9%, sum of relative quantities of each glycan), non-sialylation (20; 18.1%), fucosylation (20; 17.5%), and terminal-galactosylation (6; 3.6%)) and six core structure types [Gal-GalNAc, Gal-(GlcNAc)GalNAc, GlcNAc-GalNAc, GlcNAc-(GlcNAc)GalNAc, and GalNAc-GalNAc]. -glycosylation sites were identified using -glycopeptides (bold underlined; GERVI, HGRRI, GPVAEQI, RPYGAL, QLGPL, MRVVV, and RPEDNAVA) obtained from proteolytic BSM; these sites are in the four domains of BSM. The gel-forming mucins share common domain structures and glycosylation patterns; these results could provide useful information on mucin-type -glycans. This is the first study to characterize -glycans and identify -glycosylation sites in BSM.