Mapping the pH Sensors Critical for Host Cell Entry by a Complex Nonenveloped Virus

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Bluetongue virus (BTV) is an insect-borne virus causing hemorrhagic disease in livestock.
• Virus entry into host cells is a critical step in infection and a potential target for prevention.
• Understanding the mechanisms of BTV cell entry is crucial for developing antiviral strategies.

Purpose of the Study:

• To elucidate the roles of outer capsid proteins VP2 and VP5 in BTV cell entry.
• To identify key residues and conformational changes involved in pH-dependent viral entry.
• To reveal the novel mechanism of cell entry for this multicapsid nonenveloped virus.

Main Methods:

• Site-directed mutagenesis and reverse genetics for virus recovery.
• Expression and characterization of recombinant mutant proteins.
• In vitro and in vivo assays to study viral entry and membrane penetration.

Main Results:

• A CCCH-type zinc finger in VP2 acts as the primary low pH sensor, initiating VP2 detachment.
• Specific histidine residues in VP5 sense low pH, triggering conformational changes for membrane penetration.
• The VP5 anchoring domain alone can sense low pH, indicating its crucial role.

Conclusions:

• BTV employs a novel, multi-conformational entry mechanism involving coordinated pH sensing by VP2 and VP5.
• Key residues in VP2 and VP5 are critical for overcoming entry barriers and facilitating cell entry.
• This study provides new insights into the molecular mechanisms of nonenveloped virus entry.