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Glycosylation differences between pig gastric mucin populations: a comparative study of the neutral oligosaccharides using mass spectrometry.

ABSTRACT: Five mucin populations were isolated from the cardiac region,corpus and antrum of pig gastric mucosa. The released neutral oligosaccharides were permethylated and analysed using high-temperature gas chromatography-mass spectrometry (GC-MS) as well as matrix-assisted laser-desorption mass spectrometry (MALDI-MS). Thirty different oligosaccharides with up to six monosaccharide residues were characterized using both techniques, but the presence of an additional 49 structures was suggested on the basis of their molecular mass by MALDI-MS. Oligosaccharides based on core-1 (Galbeta1-3GalNAcalpha1-) and core-2 [Galbeta1-3(GlcNAcbeta1-6)GalNAcalpha1-] structures were widely distributed, whereas core-3 structures (GlcNAcbeta1-3GalNAcalpha1-) were present only in mucins from the cardiac region and corpus, and core-4 structures [GlcNAcbeta1-3(GlcNAcbeta1-6)GalNAcalpha1-] were present exclusively in mucins from the cardiac region. Furthermore the oligosaccharides from one of the mucins from the corpus were significantly longer than those from the other populations. The results illustrate vast structural diversity, but the relative abundances show only a few dominating structures, suggesting that many oligosaccharides may be quite rare in pig gastric mucins. Well-defined mucin populations with distinctly different glycosylation can thus be identified in pig stomach, suggesting that glycosylation of the large secreted mucins from this tissue is not a random event.

SUBMITTER: Karlsson NG

PROVIDER: S-EPMC1218750 | biostudies-other | 1997 Sep

REPOSITORIES: biostudies-other

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Project description:Mucin glycoproteins consist of tandem-repeating glycosylated regions flanked by non-repetitive protein domains with little glycosylation. These non-repetitive domains are involved in polymerization of mucin and play an important role in the pH-dependent gelation of gastric mucin, which is essential for protecting the stomach from autodigestion. We examine folding of the non-repetitive sequence of PGM-2X (242 amino acids) and the von Willebrand factor vWF-C1 domain (67 amino acids) at neutral and low pH using discrete molecular dynamics (DMD) in an implicit solvent combined with a four-bead peptide model. Using the same implicit solvent parameters, folding of both domains is simulated at neutral and low pH. In contrast to vWF-C1, PGM-2X folding is strongly affected by pH as indicated by changes in the contact order, radius of gyration, free-energy landscape, and the secondary structure. Whereas the free-energy landscape of vWF-C1 shows a single minimum at both neutral and low pH, the free-energy landscape of PGM-2X is characterized by multiple minima that are more numerous and shallower at low pH. Detailed structural analysis shows that PGM-2X partially unfolds at low pH. This partial unfolding is facilitated by the C-terminal region GLU236-PRO242, which loses contact with the rest of the domain due to effective "mean-field" repulsion among highly positively charged N- and C-terminal regions. Consequently, at low pH, hydrophobic amino acids are more exposed to the solvent. In vWF-C1, low pH induces some structural changes, including an increased exposure of CYS at position 67, but these changes are small compared to those found in PGM-2X. For PGM-2X, the DMD-derived average ?-strand propensity increases from 0.26 ± 0.01 at neutral pH to 0.38 ± 0.01 at low pH. For vWF-C1, the DMD-derived average ?-strand propensity is 0.32 ± 0.02 at neutral pH and 0.35 ± 0.02 at low pH. The DMD-derived structural information provides insight into pH-induced changes in the folding of two distinct mucin domains and suggests plausible mechanisms of the aggregation/gelation of mucin.

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Glycosylation differences between pig gastric mucin populations: a comparative study of the neutral oligosaccharides using mass spectrometry.

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