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Sendai virus M protein is found in two distinct isoforms defined by monoclonal antibodies
M de Melo1, G Mottet, C Orvell
1Department of Genetics and Microbiology, University of Geneva Medical School, Switzerland.
Abstract:
The use of a monoclonal antibody defines a subset of Sendai virus M protein representing about 30% of total. This M protein acquires, during the hour following synthesis, an epitope not present on the bulk of M. This epitope maturation is observed in acutely as well as in persistently infected cells. It takes place in vivo in absence of other viral proteins, but it is not observed when the protein is synthesized in a reticulocyte lysate. Epitope maturation does not appear to result from phosphorylation, acylation or disulfide bond formation. If immunofluorescent staining seems to indicate a preferential association of this subset of M protein with nucleocapsids, this is not confirmed by immunogold staining or by nucleocapsid isolation. Incubation of cytoplasmic extracts or of purified M protein in conditions which do not favor M to M protein association results in a relative increase of M protein carrying the maturing epitope. It is concluded that M protein exists in two distinct isoforms.
Insights
Sendai virus M protein undergoes epitope maturation, forming a distinct isoform. This post-translational modification occurs in infected cells and influences M protein behavior.
Area of Science:
- Virology
- Molecular Biology
- Protein Chemistry
Background:
- Sendai virus is a paramyxovirus.
- The M protein is a key viral component.
- Understanding M protein modifications is crucial for viral replication studies.
Purpose of the Study:
- To investigate the post-translational modifications of Sendai virus M protein.
- To characterize a specific subset of M protein with a unique epitope.
- To determine the functional significance of M protein epitope maturation.
Main Methods:
- Monoclonal antibody characterization to identify M protein subsets.
- Immunofluorescence and immunogold staining for protein localization.
- Nucleocapsid isolation and biochemical assays.
- In vitro synthesis in reticulocyte lysate.
Main Results:
- A subset of Sendai virus M protein (approx. 30%) acquires a unique epitope within an hour of synthesis.
- Epitope maturation occurs in both acute and persistent infections, independent of other viral proteins.
- This modification is not due to phosphorylation, acylation, or disulfide bond formation.
- While immunofluorescence suggested association with nucleocapsids, further analysis did not confirm this.
- Conditions disfavoring M protein aggregation increased the proportion of mature epitope-bearing M protein.
Conclusions:
- Sendai virus M protein exists in at least two distinct isoforms based on epitope expression.
- Epitope maturation represents a post-translational modification influencing M protein characteristics.
- The precise role of these isoforms in viral assembly or function requires further investigation.