Fine epitope mapping based on phage display and extensive mutagenesis of the target antigen

The residues contributing to the formation of the epitope recognized by a monoclonal antibody can be defined in several ways. Mutagenesis on the target antigen, followed by screening of the reactivity of the new variants with the antibody, is particularly powerful to reveal the functional contribution of each amino acid in the context of the native antigen. The current protocol provides a relatively simple procedure to study the surface of the target antigen in the search for residues involved in recognition. If the antigen is successfully displayed on the surface of filamentous bacteriophages, it can be quickly scanned by simultaneous mutagenesis of multiple solvent-exposed residues and high-throughput screening of the new variants with the antibody to be mapped. Once a few amino acids critically involved in recognition are defined, they can be used as starting points for a comprehensive exploration of the antigenic region by randomization of their whole neighborhood. The analysis of binding and sequence data allows delineating a detailed picture of the epitope recognized by the antibody under investigation.