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Filamentous phage particles have been central in the construction of libraries displaying vast numbers of random peptides. These random peptides can be antigenically presented as fusions to coat proteins III and VIII of the phage. The isolation of ligate-reactive phage from an immense background of nonspecific phage is achieved by the biopanning process. Enrichment of reactive phage relative to unreactive phage occurs with alternate rounds of affinity selection to the desired molecular target and amplification of the specifically bound phage. This allows the isolation of rare binding species contained in the phage peptide libraries. Each phage particle contains the information in its genome pertaining to the type of random peptide insert displayed. Hence, the identification of binding motifs displayed on ligate-reactive phage is revealed by sequencing the relevant insert site in the phage genome. Phage peptide libraries have been used to isolate ligands to an array of protein ligates. The libraries have proved particularly effective in defining the binding sites of monoclonal antibodies and to some extent polyclonal sera. The analysis of the peptide insert sequences of a number of different clones of antibody binding phage can reveal a great deal about the nature and restriction of the amino acid residues critical for the antibody-antigen interaction.

Peptide phage display libraries were screened for peptides that bind to the tumour suppressor protein, human p53. Three p53 binding peptides were isolated respectively from hexamer (6-mer), dodecamer (12-mer) and icosomer (20-mer) libraries. We have characterised their interaction with p53 in detail. The phage appear to bind regions on native p53 common between mouse and man. Two conformation-specific anti-p53 monoclonal antibodies were used to dissect the phage-p53 interaction, the phage were found to preferentially bind the PAb1620-p53 conformation rather than the PAb240-p53 conformation. Mapping experiments indicated the C-terminal 30 amino acid residues of p53 were dispensable for phage binding and that the binding of SV40 large T-antigen and the phage were not mutually exclusive. Interestingly the phage were seen to exhibit differential binding to wild-type human p53 over the two point mutant p53 proteins, His175 and Trp248. Ultimately the phage appear to selectively target native wild-type p53, mimicking the specificity of SV40 large T-antigen. The ability to target specific sub-populations of p53 could be an important step in the development of therapeutics for the treatment of p53-based human malignancy.