Structural Basis for Rabbit Hemorrhagic Disease Virus Antibody Specificity.

Area of Science:

• Virology
• Structural Biology
• Immunology

Background:

• Rabbit hemorrhagic disease virus (RHDV) causes fatal disease in rabbits and exists as diverse, antigenically distinct variants.
• Diagnostic antibodies are crucial for distinguishing RHDV variants, monitoring evolution, and assessing neutralizing capacities.

Purpose of the Study:

• To determine the X-ray crystal structure of an RHDV GI.2 P domain in complex with a diagnostic monoclonal antibody (2D9) Fab.
• To elucidate the structural basis of 2D9 antibody specificity and cross-reactivity against different RHDV variants.
• To investigate the potential of 2D9 to block histo-blood group antigen (HBGA) attachment.

Main Methods:

• X-ray crystallography was used to determine the structure of RHDV GI.2 P domain-2D9 Fab complex.
• Structural analysis was performed on RHDV GI.1b (a 2D9 non-binder) to identify key amino acid substitutions.
• Modeling of the GI.2 P domain-Fab complex onto an RHDV VLP structure was used to assess antibody binding occupancy and HBGA site interaction.

Main Results:

• The 2D9 antibody binds to conserved and variable residues on the RHDV GI.2 P domain with nanomolar affinity.
• Amino acid substitutions in the RHDV GI.1b P domain were identified as restricting 2D9 binding.
• Structural modeling suggested that 2D9 binding may obstruct the RHDV HBGA co-factor binding site, potentially blocking attachment.

Conclusions:

• This study provides the first structural basis for RHDV antibody specificity, explaining how amino acid variations influence antibody binding and cross-reactivity.
• The findings highlight the potential of the 2D9 antibody to block HBGA attachment, suggesting a mechanism for neutralization.
• This structural information is vital for characterizing RHDV antigenic variants and advancing the development of novel monoclonal antibodies for diagnostics and therapeutics.