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Polypeptides of Mason-Pfizer monkey virus. II. Synthesis and processing of the env gene products
Abstract:
Mason-Pfizer monkey virus (M-PMV), the prototype D-type retrovirus, encodes two glycosylated virion proteins, gp20 and gp70. The polyprotein precursor to these proteins was identified by immunoprecipitation of pulse labeled M-PMV-infected cells with an antiserum raised against gp70, the major glycoprotein of the virus. The relationship of this precursor to the two viral glycoproteins was verified by tryptic peptide mapping, which demonstrated that gp20 and gp70 were independent products of the env gene. The types and degree of glycosylation of the precursor and its products was investigated by tunicamycin inhibition of glycosylation, endo-beta-N-acetyl glucosaminidase H (Endo-H) and endo-beta-N-acetylglucosaminidase F (Endo-F) catalyzed removal of glycosylated residues. The results suggest that the precursor, a molecule with a mol wt of 86,000, is composed of approximately 55,000 Da of protein to which 14-15 oligosaccharide chains are attached. The precursor is cleaved post-translationally to yield the two glycoproteins of M-PMV, gp70 and gp20. Most, if not all, of the glycan units associated with the gp70 molecule are of the complex variety, as shown by their resistance to Endo-H cleavage. The gp20 molecule, on the other hand, appears to contain a single glycan unit predominantly of the high mannose type since this side chain is sensitive to digestion by Endo-H.
Insights
Mason-Pfizer monkey virus (M-PMV) retrovirus encodes two glycoproteins, gp20 and gp70, from a single precursor. Tryptic peptide mapping and glycosylation analysis reveal distinct glycan types on each protein, impacting their structure and function.
Area of Science:
- Retroviral biology
- Molecular virology
- Glycoprotein structure
Background:
- Mason-Pfizer monkey virus (M-PMV) is a D-type retrovirus.
- M-PMV virions contain two major glycosylated proteins: gp20 and gp70.
Purpose of the Study:
- To identify the precursor to M-PMV's viral glycoproteins.
- To elucidate the relationship between the precursor and its mature glycoprotein products.
- To characterize the glycosylation patterns of the M-PMV glycoproteins.
Main Methods:
- Immunoprecipitation of pulse-labeled M-PMV-infected cells.
- Tryptic peptide mapping.
- Tunicamycin inhibition of glycosylation.
- Enzymatic deglycosylation using endo-beta-N-acetylglucosaminidase H (Endo-H) and endo-beta-N-acetylglucosaminidase F (Endo-F).
Main Results:
- A precursor polyprotein (86,000 Da) was identified, containing approximately 55,000 Da of protein and 14-15 attached oligosaccharide chains.
- Tryptic peptide mapping confirmed gp20 and gp70 are independent products of the env gene.
- gp70 contains complex-type glycans resistant to Endo-H, while gp20 has a high mannose-type glycan sensitive to Endo-H.
Conclusions:
- The M-PMV env gene product is a precursor polyprotein that is post-translationally cleaved into gp70 and gp20.
- Differential glycosylation of gp70 and gp20 suggests distinct roles or processing pathways.
- The characterized glycosylation patterns provide insights into retroviral glycoprotein maturation and structure.