Virus glycosylation

Interferons [alFN, piFN and ylFN]. Interferons are a family of glycosylated proteins and are cytokines which are produced a few hours after cells have been infected with a virus. Interferons protect cells from viral infections and have antiviral activities at very low concentrations ( 3 x 10 M, less than 50 molecules are apparently sufficient to protect a single cell). Double stranded RNA are very efficient inducers of IFNs. There are three main types of IFNs. The aIFNs are synthesised in lymphocytes and the piFNs are formed in infected fibroblasts. The a and P families are fairly similar consisting of ca 166 to 169 amino acids. Although ylFNs are also small glycosylated proteins (ca 146 amino acids), they are different because they are not synthesised after viral infections but are produced by lymphocytes when stimulated by mitogens (agents that induced cell division). 

For other plant-derived antibodies, stability was shown to be similar to mammalian counterparts. For instance, a humanized anti-herpes simplex virus monoclonal antibody (IgGl) was expressed in soybean and showed stability in human semen and cervical mucus over 24 h similar to the antibody obtained from mammalian cell culture. In addition, the plant-derived and mammalian antibodies were tested in a standard neutralization assay with no apparent differences in their ability to neutralize HSV-2. As glycans may play a role in immune exclusion mechanisms in mucus, the diffusion of these monoclonal antibodies in human cerival mucus was tested. No differences were found in terms of the prevention of vaginal HSV-2 transmission in a mouse model, i.e. the plant-derived antibody provided efficient protection against a vaginal inoculum of HSV-2 [58]. This shows that glycosylation differences do not necessarily affect efficacy. 

In viruses where the genome is contained within a single nucleic acid molecule, translation produces a large multifunctional protein, a polyprotein, which is then cleaved enzymatically to produce a number of distinct proteins. In viruses where the genome is distributed over a number of molecules, several mRNAs are produced, each being translated into separate proteins. After translation they may be glycosylated using host enzymes. 

Fig. 1. Nucleotide sequence of the SFV 26 S RNA (top row), the corresponding amino acid sequence (middle row), and the amino acid sequence of the Sindbis virus structural proteins (bottom row). Nucleotides are numbered from the 5 end of the RNA molecule and all amino adds from the amino terminus of each protein. The amino- and the carboxyl-terminal ends of each protein are indicated hy arrows, glycosylation sites by triangles, and membrane-spanning regions of the viral glycoproteins by underlines for Sindbis virus and overlines for SFV. Amino acids in boxes are negatively charged (Asp and Glu), and those circled are positively charged (Lys and Arg). Some restriction endonuclease cleavage sites are shown on the nucleotide sequence. The alignment of the amino acid...

Albumin, tetanus toxin, autocrine motility factor, interleukin-2, alkaline phosphatase, glycosyl-phosphatidylinositol (GPI)-GFP, polyoma virus, and echo virus 1 (26). 

CMP, CDP, CTP, and synthetic derivatives of these nueleotides have been found to inhibit sialyltransferase activity.301" 02 Interest in such inhibitors is increasing, as they may be expected to serve as anticancer agents.269 901,303 Therefore, regulation of Golgi sialyltransferase activity appears possible by nucleotides as products of sialyl- and other glycosyl-transferase activities.1" 2 Interestingly, Epstein-Barr virus infection of human B, lymphoblastoid cell-lines leads to a diminution of sialyltransferase activity.304... 

Thus, the effects of glycosylation inhibitors on intact cells may also be studied best with virus-infected cells. Before release of virus, the glycoproteins are detected in the water-insoluble, membranous fraction. Furthermore, the lipid-linked oligosaccharides may be rather specifically extracted from whole cells, and monosaccharide-lipids may also be determined.3-116 It is thus seen that the various tools of virology and of lipid and carbohydrate biochemistry have proved productive in establishing the mode of action of inhibitors of lipid-depen-dent glycosylation of proteins. 

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