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Cleavage fragments of the retrovirus surface protein gp70 during virus entry
Abstract:
The surface protein gp70 of an ecotropic murine retrovirus was followed during entry of [3H]glucosamine-labelled virions into SC-1 mouse fibroblasts. Upon entry, gp70 was cleaved into fragments with molecular weights 35K, 30K and 17K. The 35K and 17K fragments were also observed after trypsin or thermolysin cleavage of the virion, indicating that certain locations on the gp70 molecule are easily accessible from the outside of the virion. The conformation of gp70 on the membrane was shown to have a major effect on the cleavage. This protein is known to be important for early interactions with the cell (binding and membrane fusion). The results indicate that gp70 cleavage may be important for membrane fusion.
Insights
Murine retrovirus surface protein gp70 undergoes cleavage upon cell entry, yielding fragments. This cleavage, influenced by protein conformation, may be crucial for viral membrane fusion during infection.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- The surface glycoprotein gp70 of murine retroviruses mediates critical early interactions with host cells, including binding and membrane fusion.
- Understanding the molecular mechanisms of retroviral entry is essential for developing antiviral strategies.
Purpose of the Study:
- To investigate the fate and potential function of the murine retrovirus surface protein gp70 during viral entry into fibroblasts.
- To determine if gp70 cleavage is associated with viral entry and membrane fusion.
Main Methods:
- Tracking [3H]glucosamine-labeled ecotropic murine retrovirus virions during entry into SC-1 mouse fibroblasts.
- Analyzing the cleavage products of the surface protein gp70 using molecular weight characterization.
- Comparing in-cell cleavage products with those obtained from in vitro enzymatic digestion (trypsin, thermolysin).
Main Results:
- Upon entry into fibroblasts, the surface protein gp70 was cleaved into 35K, 30K, and 17K fragments.
- The 35K and 17K fragments were also generated by external enzymatic cleavage of the virion, suggesting their accessibility.
- The conformational state of gp70 on the cell membrane significantly impacted its cleavage pattern.
Conclusions:
- Retroviral surface protein gp70 undergoes significant proteolytic processing during viral entry.
- gp70 cleavage is influenced by its conformation and accessibility, suggesting a role in the fusion process.
- The cleavage of gp70 may be a key event facilitating membrane fusion during retroviral infection.