O-linked GlcNAc

Torres CR, Hart GW. Topography and polypeptide distribution of terminal N-acetylglucosamine residues on the surfaces of intact lymphoc)des. Evidence for O-linked GlcNAc. J. Biol. Chem. 1984 259 3308-3317. 

Liu K, Paterson AJ, Chin E, Kudlow JE. Glucose stimulates protein modification by O-linked GlcNAc in pancreatic beta cells Linkage of O-linked GlcNAc to beta cell death. Proc. Natl. Acad. Sci. U.S.A. 2000 97 2820-2825. 

W.A. Lubas, D.W. Frank, M. Krause, J.A. Hanover, O-linked GlcNAc transferase is a conserved nucleocytoplasmic protein containing tetratricopeptide repeats, J Biol Chem. 1997,272, 9316-9324. 

G.D. Holt and G.W. Hart, J. Biol Chem., 1986,261, 8049-8057, The subcellular distribution of terminal N-acetylglucosamine moieties. Localization of a novel protein-saccharide linkage, O-linked GlcNAc. 

Figure 2.10 Structure of two sample oligosaccharide side chains (one N-linked the other O-linked) found in glycoproteins. Man manose Gal galactose SA sailic acid GlcNAc W-acetyl glucosamine GalNAc W-acetyl galactosamine...

Compound 6 can be isolated62 from the urine of patients with Sand-hoff s disease (GM2-gangIiosidosis variant O). The 500-MHz, H-n.m.r. spectrum of this reducing oligosaccharide is depicted in Fig. 6 its spectral parameters are compiled in Table IV. Compound 6 contains the 3,6-disubstituted Man-3, characteristic for diantennary structures. Each branch is terminated with a /3-(l— 2)-linked GlcNAc residue. 

GlcNAc. KSII members are O-linked to a Ser/Thr residue of the core protein they are primarily found in cartilage, are highly sulfated, and are terminated by sialic acids. KSIII are found in brain tissue and have a unique linker between the keratan sulfate chain and the protein a Man O-linked to a Ser of the protein. 

Once the number of antennae is established, further extension is possible through addition of backbone polymers and terminal structures similar to those found on mucin-type glycans. LacNAc polymers can be added to any of the aforementioned GlcNAcs (Fig. 4A, w-x). Similarly, these polymers can be elaborated with fucose, sulfate, and sialic acid added in the same linkages described for mucin-type structures (Fig. 4A, y-z). Most fucosyltransferases and sulfotransferases, as well as the sialyltransferases that cap polyLacNAc, are capable of modifying both O-linked and A-linked glycans some exhibit a preference for one or the other. These biases are likely a result of differences in enzyme localization. 

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