Identification of an allosteric binding site on the transcription factor p53 using a phage-displayed peptide library.

Monoclonal antibody PAb1620 recognizes a conformational epitope on the transcription factor p53 and, upon binding, allosterically inhibits p53 binding to DNA. A highly diverse (1.5 x 10(10) members) phage-displayed library of peptides containing 40 random amino acids was used to identify the PAb1620 binding site on p53. Panning this library against PAb1620 resulted in three unique peptides which have statistically significant sequence identities with p53 sufficient to identify the binding site as being composed of amino acids 106-113 and 146-156. Based on these results, we propose a mechanism by which PAb1620 can allosterically inhibit p53 binding to DNA through an indirect interaction between the antibody binding site and the L1 loop (amino acids 112-124) of p53, which is a component of the DNA binding region.