Effect of Glycosylation on Viral Envelope Glycoproteins

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The properties of viral glycoproteins are heavily influenced by the nature, position, and extent of glycosylation. This is not surprising if one considers that the average molecular weight of an N-linked glycan is more than 20 times that of an amino acid residue, and that glycans cover a greater volume of space, with

Fig. 1. Schematic diagram of the G protein primary structure. A straight line of 298 amino acids denotes the Gm polypeptide of the Long strain of human respiratory syncytial virus (RSV), in which the hydrophobic transmembrane region is indicated by a thick solid line (residues 38 to 66). The potential N-glycosylation sites (black triangle), the O-glycosylation sites (vertical line) predicted with the NetOGlyc software (9,12), and the cluster of four cysteines (black circle) are also indicated. Formation of soluble G protein (Gs) occurs by translation initiation at Met48, and subsequent cleavage after residue 65 (27). The locations of Gs fragments partially resistant to Staphylococcus aureus V8 protease and the C-terminal 85 amino acids fused to glutathione-S-transferase, both mentioned in this Chapter, are indicated below the protein diagrams.

Fig. 1. Schematic diagram of the G protein primary structure. A straight line of 298 amino acids denotes the Gm polypeptide of the Long strain of human respiratory syncytial virus (RSV), in which the hydrophobic transmembrane region is indicated by a thick solid line (residues 38 to 66). The potential N-glycosylation sites (black triangle), the O-glycosylation sites (vertical line) predicted with the NetOGlyc software (9,12), and the cluster of four cysteines (black circle) are also indicated. Formation of soluble G protein (Gs) occurs by translation initiation at Met48, and subsequent cleavage after residue 65 (27). The locations of Gs fragments partially resistant to Staphylococcus aureus V8 protease and the C-terminal 85 amino acids fused to glutathione-S-transferase, both mentioned in this Chapter, are indicated below the protein diagrams.

the surface area of the Man3GlcNAc2 pentasaccharide covering the same surface area as an antibody footprint (6). Moreover, glycans exhibit far greater structural complexity than amino acids. The position of viral envelope glyco-proteins on the external surface of the virion means that they are involved in host cell binding and entry and are major targets for neutralizing antibodies produced by the host immune response. Hence differential glycosylation has the potential to affect not only the folding (7) and stability (8) of viral glycopro-teins, but also binding to host cell components, including those of the innate immune response (9,10) and virus receptors (11-13), which in turn may influence viral infectivity (14) and tropism. Finally, altered glycosylation can influence the immunogenicity of viral envelope proteins (15), facilitate escape from the cellular immune response (16), or affect antigenicity (17). Thus, it is important to consider the effect of glycosylation changes when working with glyco-proteins.

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