Polymerase Activity, Protein-Protein Interaction, and Cellular Localization of the Usutu Virus NS5 Protein

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Usutu virus (USUV) is an emerging flavivirus causing outbreaks in wildlife and sporadic human infections.
• Viral RNA replication relies on nonstructural protein 5 (NS5), which contains methyltransferase and RNA-dependent RNA polymerase domains (RdRpD).
• Viral polymerases are key targets for antiviral drug development due to their conserved nature.

Purpose of the Study:

• To characterize the biochemical properties of the USUV NS5 protein and its RdRpD.
• To investigate the optimal conditions for USUV RNA polymerase activity.
• To determine the subcellular localization of USUV NS5 and RdRpD in eukaryotic cells.

Main Methods:

• Cloning and expression of full-length USUV NS5 and its RdRpD in a heterologous system.
• Protein purification and characterization of RNA polymerization activity under varying physicochemical conditions (buffer concentration, temperature, pH).
• Expression of USUV NS5 and RdRpD in eukaryotic cells to analyze subcellular localization.

Main Results:

• Optimal reaction conditions for USUV RNA polymerase activity were determined.
• USUV RdRpD, but not full-length NS5, exhibited cooperative RNA synthesis activity.
• USUV RdRp activity was not inhibited by sofosbuvir.
• USUV NS5 predominantly localized to the cytoplasm, with a portion translocating to the nucleus via nuclear localization signals (NLS).

Conclusions:

• The biochemical and cellular characteristics of USUV NS5 and its RdRpD have been elucidated.
• The lack of inhibition by sofosbuvir highlights the need for alternative antiviral strategies against USUV.
• Understanding NS5 localization provides insights into USUV replication mechanisms.