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Effect of monensin on Mason-Pfizer monkey virus glycoprotein synthesis
Abstract:
The effect of the monovalent carboxylic ionophore monensin on the biosynthesis, intracellular transport, and surface expression of the glycoproteins of Mason-Pfizer monkey virus was examined. Cells treated with monensin at concentrations of 10(-7) or 10(-6) M continued to synthesize virus particles, which from electron microscopic studies appeared to bud normally from the plasma membrane of the cells. However, the particles released had an altered buoyant density in sucrose gradients and were noninfectious. These noninfectious virions had a normal complement of non-glycosylated polypeptides but showed a significantly reduced amount of glycosylated proteins. The gp70 and gp20 polypeptides appeared to be completely absent, and a heterogeneous, higher-molecular-weight protein was observed on the virions instead. Studies on intracellular protein synthesis indicated that the precursor (Pr86env) to gp70 and gp20 is synthesized normally but is not cleaved to the mature proteins. Immunofluorescence studies showed, however, that the uncleaved molecule is expressed on the cell surface. In this system, therefore, Mason-Pfizer monkey virus glycoprotein migration appears to occur in the presence of monensin, whereas the cleavage and insertion of the glycoproteins into virions are inhibited.
Insights
Monensin disrupts Mason-Pfizer monkey virus glycoprotein processing, inhibiting cleavage and virion insertion. This results in noninfectious viral particles with altered surface proteins.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Mason-Pfizer monkey virus (MPMV) glycoproteins are crucial for viral infectivity.
- Monensin is an ionophore known to affect intracellular transport and protein processing.
Purpose of the Study:
- To investigate the impact of monensin on MPMV glycoprotein biosynthesis, transport, and surface expression.
- To elucidate the mechanism by which monensin affects viral particle formation and infectivity.
Main Methods:
- Cell culture and treatment with monensin.
- Electron microscopy to observe viral budding.
- Sucrose gradient centrifugation to analyze viral particle density.
- Analysis of viral protein composition.
- Immunofluorescence to detect cell surface protein expression.
Main Results:
- Monensin treatment led to the release of noninfectious MPMV particles with altered buoyant density.
- These particles contained normal non-glycosylated proteins but reduced glycosylated proteins, with gp70 and gp20 absent.
- The precursor Pr86env was synthesized but not cleaved into mature glycoproteins.
- The uncleaved precursor was detected on the cell surface via immunofluorescence.
Conclusions:
- Monensin inhibits the cleavage and incorporation of MPMV glycoproteins into virions.
- Intracellular glycoprotein transport and cell surface expression occur despite monensin treatment.
- Monensin disrupts the final maturation steps required for infectious MPMV production.