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Proteolytic cleavage of the murine coronavirus surface glycoprotein is not required for its fusion activity
R Stauber1, M Pfleiderer, S Siddell
1Institut für Virologie, Universität Würzburg.
Abstract:
The surface glycoprotein (S) of the murine hepatitis coronavirus MHV normally undergoes proteolytic cleavage during transport to the cell surface. To determine whether the cleavage of the MHV-JHM S glycoprotein is required to activate its ability to fuse cellular membranes, the protease recognition sequence in a cDNA copy of the S gene was altered from Arg-Arg-Ala-Arg-Arg into Ser-Val-Ser-Gly-Gly by site directed mutagenesis. The mutated and wild type S genes were expressed by means of recombinant vaccinia viruses and it could be shown that the mutated S protein was not cleaved when it was expressed in mouse DBT cells, in contrast to the wild type S protein. Nevertheless, the non-cleaved S protein induced extensive syncytium formation in mouse DBT cells. These results clearly indicate that the non-cleaved form of the MHV S protein is able to mediate cell membrane fusion. Thus, proteolytic cleavage is not an absolute requirement for its fusion function.
Insights
Proteolytic cleavage of the murine hepatitis coronavirus (MHV) surface glycoprotein (S) is not essential for its membrane fusion activity. Uncleaved MHV S protein effectively mediates syncytium formation, indicating fusion function is independent of cleavage.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- The surface glycoprotein (S) of murine hepatitis coronavirus (MHV) is crucial for viral entry and cell-to-cell spread.
- MHV S protein typically undergoes proteolytic cleavage during its maturation and transport to the cell surface.
Purpose of the Study:
- To investigate whether proteolytic cleavage of the MHV-JHM S glycoprotein is a prerequisite for its cell membrane fusion activity.
- To determine the role of S protein cleavage in mediating viral fusion.
Main Methods:
- Site-directed mutagenesis was used to alter the protease recognition sequence of the MHV-JHM S gene.
- Recombinant vaccinia viruses were employed to express both wild-type and mutated S genes in mouse DBT cells.
- Syncytium formation was assessed to evaluate the fusion-mediating capacity of the S protein.
Main Results:
- The mutated S protein, lacking the wild-type cleavage site, was not proteolytically cleaved in mouse DBT cells.
- Despite remaining uncleaved, the mutated S protein efficiently induced extensive syncytium formation.
- The wild-type S protein, as expected, underwent cleavage and also mediated syncytium formation.
Conclusions:
- Proteolytic cleavage of the MHV S protein is not an absolute requirement for its ability to mediate cell membrane fusion.
- The uncleaved form of the MHV S protein retains its fusion function, suggesting alternative pathways or intrinsic fusogenicity.