Identification of crucial residues of conformational epitopes on VP2 protein of infectious bursal disease virus by phage display.

A new method for identifying epitopes in viral proteins expressed by filamentous phage has been developed. Filamentous phage fUSE 1 containing the variable region of the VP2 gene of infectious bursal disease virus (IBDV) strain 002-73 was constructed. Neutralizing monoclonal antibodies 17-82 and 33-10 raised against VP2 protein were used to bind phage containing the original variable region of VP2. The phage bound to monoclonal antibodies, were removed by protein G Sepharose and the unbound phage (escape mutants) were isolated for sequencing to locate the mutations. The crucial amino acid residues for conformational neutralizing epitopes recognized by the monoclonal antibodies were located in the first main hydrophilic region (amino acids from 210 to 225) and the central region of the variable region of VP2. The amino acid residues on both ends of the variable region of VP2 affected considerably the binding of monoclonal antibodies. This technique might be useful for selecting escape mutants of phage displaying the original antigenic regions of other viruses to define the crucial amino acid residues of their conformational epitopes, especially viruses that cannot be grown in cell cultures.