Structural transition of GP64 triggered by a pH-sensitive multi-histidine switch

Area of Science:

• Structural biology
• Virology
• Biochemistry

Background:

• Enveloped viruses fuse with host cells via viral fusion proteins.
• The pH-dependent conformational changes of these proteins are crucial for fusion, but the precise mechanisms remain unclear.

Purpose of the Study:

• To elucidate the structural intermediates and pH-sensing mechanisms of viral membrane fusion.
• To investigate the role of pH-sensitive switches in viral fusion proteins.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine structures of GP64 in prefusion and intermediate states.
• Cell-cell syncytium formation assays and dual dye-labeling to validate pH sensing.

Main Results:

• Cryo-EM structures revealed early intermediate states of the class III fusion protein GP64.
• A pH-sensitive switch involving histidine residues (H23, H245, H304) was identified as the trigger for membrane fusion.
• Experimental assays confirmed the role of this multi-histidine switch in pH sensing and fusion activation.

Conclusions:

• A coordinated multi-histidine switch acts as a pH sensor and activator in viral fusion.
• Understanding this mechanism can inform the development of novel antiviral therapies and vaccines targeting viral fusion.
• The findings are relevant to human-infecting thogotoviruses and other enveloped viruses.