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Functional comparison of the two gene products of Thogoto virus segment 6
Kathrin Hagmaier1, Hans R Gelderblom2, Georg Kochs1
1Abteilung Virologie, Institut für Medizinische Mikrobiologie und Hygiene, Universität Freiburg, D-79008 Freiburg, Germany.
Abstract:
The sixth genomic segment of Thogoto virus (THOV) encodes two proteins, the viral matrix protein (M) and an accessory protein with an interferon (IFN)-antagonistic function named ML. M and ML are shown in this study to be structural components of the virion. Using an in vivo system based on the reconstitution of functional THOV ribonucleoprotein complexes from cloned cDNAs, it was demonstrated that M has an inhibitory effect on the viral RNA-dependent RNA polymerase (RdRP) and is essential for the formation of virus-like particles (VLPs). The functional domain responsible for the regulation of RdRP activity resides within the C-terminal half of M, while full-length M protein is required for VLP formation. The ML protein cannot complement M with respect to either RdRP downregulation or particle formation, although it is identical to M apart from a 38 aa extension at the C terminus. In contrast, ML, but not M, is able to prevent the induction of IFN-beta by double-stranded RNA. This function is contained within the C-terminal half of ML. These data suggest major structural differences between M and ML that could explain the different activities of the two proteins.
Insights
Thogoto virus (THOV) matrix (M) protein regulates viral polymerase and forms virus-like particles. The accessory ML protein antagonizes interferon (IFN) production, showing distinct functions despite structural similarities.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Thogoto virus (THOV) is an Orthoflavivirus with a segmented genome.
- The sixth genomic segment encodes the matrix (M) and accessory ML proteins.
- M and ML proteins are structural components of the THOV virion.
Purpose of the Study:
- To investigate the distinct functions of THOV M and ML proteins.
- To identify the functional domains of M and ML proteins.
- To elucidate the roles of M and ML in viral replication and host immune response.
Main Methods:
- Reconstitution of functional THOV ribonucleoprotein complexes in vivo from cloned cDNAs.
- Analysis of viral RNA-dependent RNA polymerase (RdRP) activity.
- Assessment of virus-like particle (VLP) formation.
- Evaluation of interferon-beta (IFN-β) induction by double-stranded RNA.
Main Results:
- M protein inhibits viral RdRP activity and is essential for VLP formation.
- The C-terminal half of M contains the RdRP regulatory domain; full-length M is needed for VLP formation.
- ML protein, despite a 38 amino acid C-terminal extension, cannot complement M's functions.
- ML protein, but not M, antagonizes IFN-β induction, with this function located in ML's C-terminal half.
- Structural differences between M and ML explain their distinct biological activities.
Conclusions:
- M and ML proteins possess distinct functions critical for THOV replication and pathogenesis.
- M protein plays a dual role in regulating viral polymerase and virion assembly.
- ML protein acts as an interferon antagonist, contributing to viral immune evasion.
- The differential functions of M and ML highlight complex viral strategies for replication and host interaction.
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