Conformational Flexibility in Respiratory Syncytial Virus G Neutralizing Epitopes

Area of Science:

• Virology
• Immunology
• Structural Biology

Background:

• Respiratory syncytial virus (RSV) is a major cause of severe respiratory illness and death in vulnerable populations, with no current vaccine or treatment.
• The RSV G glycoprotein is crucial for viral attachment and pathogenesis, interacting with host immune factors.
• Antibodies targeting conserved regions of the G glycoprotein show protective potential in preclinical models.

Purpose of the Study:

• To determine the crystal structure of a broadly neutralizing human monoclonal antibody (3G12) in complex with the RSV G central conserved domain.
• To understand the structural basis for broad neutralization activity against RSV.
• To provide insights for rational vaccine design against RSV.

Main Methods:

• X-ray crystallography was used to determine the structure of the antibody-antigen complex.
• Structural comparisons were made with previously determined RSV G-antibody structures.
• Mutational analysis (proline substitution) was employed to assess the role of flexibility in antibody binding.

Main Results:

• The crystal structure revealed antibody 3G12 binding to a conserved conformational epitope on the RSV G central conserved domain.
• The RSV G-antigen captured in the complex adopted a novel conformation, indicating flexibility in this region.
• Restricting flexibility via mutation affected binding of specific antibodies, highlighting conformational dynamics.

Conclusions:

• The RSV G central conserved domain is both structured and conformationally flexible.
• Understanding antigen flexibility is critical for designing vaccines that elicit broadly protective antibodies.
• These findings pave the way for developing more effective RSV vaccines and therapeutics.