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Date of Award

1984

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry

Supervisor

Professor H.P. Ghosh

Abstract

The purpose of this study was to investigate some of the structural features in the glycoprotein molecule of vesicular stomatitis virus (VSV) which could be of importance in its biosynthesis. The approach involved

(1) A comparative study of the primary structure of the in vitro synthesized form and the mature form of the glycoproteins of three serotypes of VSV namely Indiana, New Jersey (Concan) and Cocal.

(2) Biochemical characterization of tsY1, a temperature sensitive mutant of the Cocal serotype of VSV defective in glycosylation.

(3) Investigation of the labeling of the three serotypes of VSV and of Chandipura and Piry viruses, grown in the presence of [³H]palmitate.

Studies of Irving et. al. (1979) using the Indiana (Toronto) serotype of VSV demonstrated that the in vitro synthesized unglycosylated form of the membrane glycoprotein G₁ contains at the NH₂-terminus an extra polypeptide not present in the mature glycoprotein(G). In order to determine the function related properties of the transient region of the protein (signal peptide), the primary structure of the NH₂-terminus of the G, protein of two other serotypes of VSV, New Jersey (concan) and Cocal which contain variable sizes of the glycoprotein in their virions was determined. A comparison of the partial NH₂-terminal sequence of the G₁ and G proteins of the three serotypes of VSV revealed that each of the three serotypes have a signal peptide that is made up of a minimum of 16 amino acids with a high proportion of hydrophobic amino acids. There is a striking unrelatedness in the signal region in contrast to the high degree of homology in the NH₂-terminal sequences of the mature virion glycoprotein G. In spite of the lack of homology in the signal region there was a similarity if the overall hydrophobicity.

Temperature sensitive (ts) mutants corresponding to the complementation group (V) of VSV Indiana, which include the mutants with specific lesion(s) in the structural gene of G, have been isolated on the basis of characteristics to grow at the two temperatures of 32°C (permissive) and 39°C (nonpermissive) (Lafay, 1974; Lodish and Weiss, 1979; Pringle, 1982). A temperature sensitive mutant of the Cocal serotype of VSV tsΥ1 synthesizes at the permissive temperature a glycoprotein which size is smaller (molecular weight 68,000) than the wild type (molecular weight 71,000). At the nonpermissive temperature reduced amounts of noninfectious virus-like particles deficient in glycoproteins were produced. The size of the intracellular glycoprotein was further decreased (molecular weight 64,000) at the nonpermissive temperature. Biochemical studies including sugar labeling, tryptic peptide analysis and NH₂-terminal sequence analysis of the glycoprotein suggest that at the nonpermissive temperature unglycosylated product blocked in its transport to the cell surface is synthesized while at the permissive temperature a fully functional product with a single oligosaccharide chain is synthesized. In contrast, the wild type VSV Cocal glycoprotein contains two oligosaccharide chains at both temperatures. In addition, neither the wild type nor the mutant glycoprotein contain covalently bound fatty acid.

Glycoproteins present in a number of enveloped viruses have been shown to contain covalently bound fatty acid residues (Schmidt, 1982a). The glycoproteins of the three serotypes of VSV and of Piry and Chandipura viruses were examined for the presence of fatty acid (palmitic acid). The results showed that while the mature G protein of VSV Indiana (Toronto) serotype and Piry and Chandipura viruses contain palmitic acid residues, the glycoproteins of VSV Cocal and New Jersey serotypes do not contain palmitic acid, suggesting that acylation of the G glycoprotein is not essential for some vesiculoviruses while it is important (if not required) for others.

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