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Characterization and functional analysis of Serp3: a novel myxoma virus-encoded serpin involved in virulence
Jean-Luc Guerin1, Jacqueline Gelfi1, Christelle Camus1
1UMR de Microbiologie Moléculaire1 and Laboratoire d'Anatomie-Pathologique2, Institut National de la Recherche Agronomique and Ecole Nationale Vétérinaire, Toulouse, France.
Abstract:
Myxoma virus (MV), a member of the family Poxviridae, is the causative agent of myxomatosis, a fatal disease of the European rabbit. The MV genome is a linear, double-stranded DNA molecule that encodes several factors important for evasion of the host immune system. Sequencing the right-end region of the MV genome identified an 801 bp open reading frame (ORF) encoding a polypeptide that belongs to the serpin superfamily. To date, two MV-encoded serpins have been characterized: SERP-1 binds to several targets and is an anti-inflammatory molecule, whereas Serp2 is essential for virus virulence and has both anti-inflammatory and anti-apoptotic effects. Thus, Serp3 is the third MV-encoded serpin. DNA sequence analysis of Serp3 indicated a similarity to poxvirus late promoters, which was confirmed by mRNA expression analysis. Serp3 has an atypical serpin motif and has significant sequence deletions as compared to most cellular and viral serpins. However, molecular modelling studies suggested that Serp3 can retain the overall serpin fold. Insertional inactivation of the serp3 ORF led to a significant attenuation of virulence in vivo (as measured by the increase in survival of infected rabbits) and limited dissemination of the virus to secondary sites of infection. In rabbits infected with a Serp3 deletion mutant (MV-Serp3(-)), the main histopathological feature is the absence of secondary myxomas. Both wild-type MV and MV-Serp3(-) replicate at comparable levels in vivo. Serp3 may represent a significant virulence factor of MV and probably acts in synergy with other viral proteins.
Insights
Myxoma virus (MV) encodes Serp3, a novel serpin. Deleting Serp3 significantly reduces MV virulence and spread in rabbits, identifying it as a key viral factor.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Myxoma virus (MV) causes a fatal disease in European rabbits.
- MV utilizes viral factors to evade host immune responses.
- Two MV-encoded serpins (SERP-1, Serp2) with immune-modulating functions are known.
Purpose of the Study:
- To characterize the third MV-encoded serpin, termed Serp3.
- To investigate the role of Serp3 in MV pathogenesis and virulence.
Main Methods:
- DNA sequencing and sequence analysis of the Serp3 open reading frame (ORF).
- mRNA expression analysis to confirm promoter similarity.
- Molecular modeling to predict protein structure.
- Insertional inactivation of the serp3 ORF to create a deletion mutant (MV-Serp3(-)).
- In vivo virulence studies in rabbits, measuring survival and viral dissemination.
Main Results:
- Serp3 is a novel serpin with atypical features but retains the overall serpin fold.
- Insertional inactivation of serp3 significantly attenuated MV virulence in rabbits.
- The MV-Serp3(-) mutant showed limited dissemination and absence of secondary myxomas.
- Viral replication levels were comparable between wild-type MV and MV-Serp3(-) in vivo.
Conclusions:
- Serp3 is a significant virulence factor for Myxoma virus.
- Serp3 likely contributes to MV pathogenesis by influencing viral spread and immune evasion.
- Serp3 may act synergistically with other viral proteins to promote disease.