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A multiply substituted G-H loop from foot-and-mouth disease virus in complex with a neutralizing antibody: a role for
W F Ochoa1, S G Kalko, M G Mateu
1Instituto Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Jordi-Girona 18-26, 08034 Barcelona, Spain.
Abstract:
The crystal structure of a 15 amino acid synthetic peptide, corresponding to the sequence of the major antigenic site A (G-H loop of VP1) from a multiple variant of foot-and-mouth disease virus (FMDV), has been determined at 2.3 A resolution. The variant peptide includes four amino acid substitutions in the loop relative to the previously studied peptide representing FMDV C-S8c1 and corresponds to the loop of a natural FMDV isolate of subtype C(1). The peptide was complexed with the Fab fragment of the neutralizing monoclonal antibody 4C4. The peptide adopts a compact fold with a nearly cyclic conformation and a disposition of the receptor-recognition motif Arg-Gly-Asp that is closely related to the previously determined structure for the viral loop, as part of the virion, and for unsubstituted synthetic peptide antigen bound to neutralizing antibodies. New structural findings include the observation that well-defined solvent molecules appear to play a major role in stabilizing the conformation of the peptide and its interactions with the antibody. Structural results are supported by molecular-dynamic simulations. The multiply substituted peptide developed compensatory mechanisms to bind the antibody with a conformation very similar to that of its unsubstituted counterpart. One water molecule, which for steric reasons could not occupy the same position in the unsubstituted antigen, establishes hydrogen bonds with three peptide amino acids. The constancy of the structure of an antigenic domain despite multiple amino acid substitutions has implications for vaccine design.
Insights
Structural analysis of a foot-and-mouth disease virus (FMDV) peptide reveals conserved antigenic sites. Water molecules stabilize peptide-antibody interactions, offering insights for FMDV vaccine design.
Area of Science:
- Structural biology
- Virology
- Immunology
Background:
- Foot-and-mouth disease virus (FMDV) is a significant threat to livestock.
- Antigenic site A on the VP1 protein is a key target for neutralizing antibodies.
- Previous studies characterized synthetic peptides of FMDV antigenic sites.
Purpose of the Study:
- To determine the crystal structure of a variant FMDV peptide (site A) complexed with a neutralizing antibody.
- To investigate the structural basis for antibody recognition of a mutated viral epitope.
- To understand the role of solvent molecules in stabilizing peptide-antibody interactions.
Main Methods:
- X-ray crystallography at 2.3 A resolution.
- Complex formation between a synthetic FMDV peptide (site A, variant) and a Fab fragment of monoclonal antibody 4C4.
- Molecular-dynamic simulations.
Main Results:
- The variant peptide adopted a compact, nearly cyclic conformation, similar to previous structures.
- The Arg-Gly-Asp motif's disposition was conserved, crucial for receptor recognition.
- Well-defined solvent molecules, particularly one water molecule, were found to stabilize peptide-antibody interactions through hydrogen bonding.
- Compensatory mechanisms allowed the substituted peptide to bind the antibody with a conformation similar to the unsubstituted counterpart.
Conclusions:
- The structure of the FMDV antigenic site A is remarkably conserved despite amino acid substitutions.
- Solvent molecules play a critical role in maintaining the structural integrity and antibody-binding capability of the peptide.
- These findings have significant implications for the rational design of FMDV vaccines targeting conserved epitopes.