Structural Features of Tissue Glycoproteins

Fractionation and Methylation Analysis of Glycopeptides Derived from Rat Brain, Kidney and Liver

Authors


Abstract

  • 1Glycopeptides were prepared by papain digestion from delipidated brain, kidney and liver and fractionated by the combination of concanavalin-A-affinity chromatography, and gel filtration after prior treatment with NaOH/NaBH4. All tissues contained four fractions of structurally distinct carbohydrate chains: O-glycosidically-linked oligosaccharides, two different types of acidic N-glycosidically-linked oligosaccharides (fractions A and B) and mannose-rich N-glycosidically-linked oligosaccharides (fraction C). The relative amounts of these fractions varied in different tissues. The O-glycosidically-linked oligosaccharides accounted for 3–9%, fraction A glycopeptides for 50–60%, fraction B glycopeptides for 21–34% and fraction C glycopeptides for 21–34% of total glycopeptide carbohydrate.
  • 2The O-glycosidically-linked oligosaccharides are mainly composed of β-galactosyl(1–3)-N-acetylgalactosamine and its monosialosyl and disialosyl derivatives. No large molecular size O-glycosidically-linked carbohydrate chains similar to those present in mucus of the digestive tract and ovarian cysts were detected. Fraction A and B glycopeptides resemble by their carbohydrate composition and substitution pattern of their sugar components the N-glycosidically-linked oligosaccharides of fetuin and transferrin, which behave similarly on concanavalin A-affinity chromatography, respectively. However, the results of the methylation analysis suggest that considerable heterogeneity occurs at the mannose branch-points of fraction A and B glycopeptides as compared to the reference compounds. Fraction C contained only mannose-rich glycopeptides with a structure similar to those of ovalbumin and thyroglobulin type-A glycopeptides.
  • 3Methylation analysis showed clear differences in the substitution pattern of galactose and N-acetylglucosamine, which together with N-acetylneuraminic acid are supposed to form the peripheral branches of fraction A and B glycopeptides. Brain glycopeptides contained relatively high amounts of terminal nonsubstituted galactose and N-acetylglucosamine suggesting that the peripheral branches often are incomplete. N-Acetylneuraminic acid was mainly attached to the C-3 of the galactose residues in brain glycopeptides. Kidney glycopeptides contained less terminal nonsubstituted N-acetylglucosamine and proportionally more galactose substituted at C-6 than brain glycopeptides. In contrast to brain and kidney, no terminal N-acetylglucosamine and only small amounts of terminal nonsubstituted galactose occurred in liver suggesting that the peripheral branches are mainly complete. In liver galactose was substituted nearly as often at C-6 as at C-3.
  • 4Considerable differences occurred in the relative amount of fucose from one tissue to another. Brain glycopeptides contained fucose 2 and 4 times more than kidney and liver glycopeptides, respectively. Fucose was mainly bound to C-3 and C-6 of N-acetylglucosamine and not to galactose as proposed generally.
  • 5Based on the results of the present study it may be concluded that brain, kidney and liver glycoproteins contain four structurally distinct types of carbohydrate chains resembling each other. However, the structure of the terminal parts of the carbohydrate chains are glycosylated in a pattern characteristic to each tissue.
Abbreviations
AcNeu

N-acetylneuraminic acid

Gal

galactose

GlcNAc

N-acetylglucosamine

GalNAc

N-acetylgalactosamine

Man

mannose

Enzymes
 

Vibrio cholerae neuraminidase, (EC 3.2.1.18)

 

α-l-fucosidase (EC 3.2.1.51)

Ancillary