Review

Journal of Biomedical Science

, Volume 10, Issue 6, pp 676-688

First online:

Carbohydrate structural units in glycoproteins and polysaccharides as important ligands for Gal and GalNAc reactive lectins

  • Albert M. WuAffiliated withGlyco-Immunochemistry Research Laboratory, Institute of Molecular and Cellular Biology College of Medicine, Chang-Gung University

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Abstract

Glycoproteins (gps) contain many carbohydrate epitopes or crypto-glycotopes for Gal and GalNAc reactive lectins. They are present on the cell surface and function as receptors in various life processes. Many exist in soluble or gel form and serve as biological lubricants or as barriers against microbial invasion. During the past two decades, eleven mammalian structural units have been used to express the binding domain of applied lectins. They are:F, GalNAcα1 → 3GalNAc;A, GalNAcα1 → 3Gal;T, Galβ1 → 3GalNAc;I, Galβ1 → 3GlcNAc;II, Galβ1 → 4GlcNAc;B, Galα1 → 3Gal;E, Galα1 → 4Gal;L, Galβ1 → 4Glc;P, GalNAcβ1 → 3Gal;S, GalNAcβ1 → 4Gal andTn, GalNAcα1 → Ser(Thr). ExceptL andP, all of the units can be found in glycoproteins.Tn, which is an important marker for breast/colon cancer and vaccine development, exists only inO-glycans. NaturalTn gp, the simplest mammalianO-glycan, is exclusively expressed in the armadillo salivary gland. Antifreeze gp is composed of repeating units ofT.Pneumococcus type XIV capsular polysaccharide has uniformII disaccharide as carbohydrate side chains. Asialo human α1-acid gp and asialo fetuin provide multi-antennaryII structures. Human ovarian cyst gps, which belong to the complex type of glycoform, comprise most of the structural units. To facilitate the selection of lectins that could serve as structural probes, the carbohydrate binding properties of Gal/GalNAc reactive lectins have been classified according to their highest affinity for structural units and their binding profiles are expressed in decreasing order of reactivity. Hence, the binding relationship between glycoproteins and Gal/GalNAc specific lectins can be explored.

Key Words

Disaccharide units Glycoproteins Applied lectins and carbohydrate specificities