Structure-Function Dissection of Pseudorabies Virus Glycoprotein B Fusion Loops

Area of Science:

• Structural Biology
• Virology
• Membrane Biophysics

Background:

• Herpesviruses, significant human and animal pathogens, utilize glycoprotein B (gB) for cell entry via membrane fusion.
• The precise mechanism of gB-mediated membrane fusion remains incompletely understood despite structural data on gB ectodomains.
• gB utilizes fusion loops (FLs) to anchor into the host cell membrane, but the molecular details of this interaction are unclear.

Purpose of the Study:

• To elucidate the structural basis and molecular mechanism of pseudorabies virus (PrV) glycoprotein B (gB) interaction with lipid bilayers.
• To propose a model for how gB fusion loops initiate membrane fusion across the Herpesviridae family.

Main Methods:

• X-ray crystallography was used to determine the structure of the PrV gB ectodomain.
• Mutagenesis of key fusion loop residues was performed to assess their role in membrane binding and fusion.
• Liposome binding assays and functional fusion assays were conducted to evaluate gB variants.

Main Results:

• The PrV gB ectodomain adopts a class III postfusion trimer structure.
• Specific gB fusion loop residues (Trp187, Tyr192, Phe275, Tyr276) are crucial for cholesterol-dependent liposome binding and viral fusion.
• These essential residues form a hydrophobic patch that interacts with distinct regions of the lipid bilayer, with Phe275 inserting deeper and others forming a rim.

Conclusions:

• A molecular model for herpesvirus gB-mediated membrane fusion is proposed, detailing the interaction of fusion loops with the lipid bilayer.
• The findings suggest a conserved mechanism of membrane interaction for gB across alpha-, beta-, and gamma-herpesviruses.
• Understanding these initial membrane interactions is critical for comprehending herpesvirus entry and developing antiviral strategies.