N-linked glycan

Harnett, W., Houston, KM., Amess, R. and Worms, M.J. (1993) Acanthocheilonema viteae. phosphorylcholine is attached to the major excretory-secretory product via a N-linked glycan. Experimental Parasitology 77, 498-502. 

Figure 1.36 A space-filling model of an N-linked glycan showing four branch points.

Plant-based production systems are now being used commercially for the synthesis of foreign proteins [1-3]. Post-translational modification in plant cells is similar to that carried out by animal cells plant cells are also able to fold multimeric proteins correctly. The sites of glycosylation on plant-produced mammalian proteins are the same as on the native protein however, processing of N-linked glycans in the secretory pathway of plant cells results in a more diverse array of glycoforms than is produced in animal expression systems [4]. Glycoprotein activity is retained in plant-derived mammalian proteins. 

Similar results were recently obtained with a human monoclonal antibody, with KDEL sequences fused to the C-termini of both heavy chains, expressed in tobacco [33]. As observed for the invertase-HDEL fusion, about 90% of the N-linked glycans on this antibody were of the high-mannose type, with 6-9 mannose residues, while a fraction contained the immunogenic P(l,2)-xylose glyco-epitope (Fig. 15.6). However, this antibody was not a(l,3)-fucosylated, a glycan modification occurring in the trans Golgi [34]. 

Plant-made Pharmaceuticals and their Native Mammalian Counterparts Contain Structurally-distinct N-linked Glycans 238... 

Glycoprotein was digested using the peptide N-Glycosidase F (PNGase F) to release N-linked glycan, then labeled with 8-aminopyrene-l,3,6-trisulfonate (APTS). The detection used LIF with a argon-ion laser. 

Another factor influencing nonspecific tissue distribution is the carbohydrate portion of the IgG molecule, which is attached to the therapeutic protein via an N-linked glycan in the constant domain (Fc). Loss of terminal sialylated residues on the carbohydrate of IgG exposes galactose and promotes receptor-mediated binding of IgG to hepatocytes. Consequently this results in an increase in nonspecific distribution to the liver. Details of desialyation of IgG and its consequences are discussed in Chapter 10. Other glycoproteins may exert similar mechanisms of nonspecific distribution. 

Helenius A, Aebi M (2001) Intracellular functions of N-linked glycans. Science 23 2364-2369... 

Figure 4-17 A large N-linked glycan from the fertilized egg of the teleost fish oryzias. 7 On the average, only two of the "antenna" contain the repeated emit in parenthesis, i.e., p + q + r + s + t = 1.9 an average of about 4.6 residues of sialic acid are present.

N-linked glycan is pictured in Fig. 4-17. Like many others, it has a number of sialic acid residues at the nonreducing ends and also contains N-acetyllactos-amine units. The major component of the cell walls of yeast (S. cerevisiae) is a mannoprotein that carries long N-linked oligosaccharides with highly branched outer chains of over 100 mannose residues170 (see also Section C,3). 

Haslam, S.M., Restrepo, B.I., Obregon-Henao, A., Teale, J.M., Morris, H.R. and Dell, A. (2003) Structural characterization of the N-linked glycans from Taenia solium metacestodes. Molecular and Biochemical Parasitology 126, 103-107. 

---