Discovering peptide ligands using epitope libraries.

Epitope libraries are large collections of peptides. Each peptide is displayed on the surface of a bacteriophage particle and is encoded by a randomly mutated region of the phage genome, thus associating each unique peptide with the DNA molecule encoding it. Antibodies and other binding proteins are used to select specifically for rare, phage-bearing peptide ligands; sequencing of the corresponding viral DNA will reveal their amino acid sequences. Relatively high-affinity peptides for a variety of peptide- and non-peptide-binding ligates have been affinity-isolated from epitope libraries. This technology has been used to map epitopes on proteins and to find peptide mimics for non-peptide-binding ligates. The current challenge lies in developing epitope library technology so that tight-binding peptide ligands can be detected for a wider variety of ligates, including those that recognize folded proteins. Should this be accomplished, many powerful applications can be envisioned in the areas of drug design and the development of diagnostic markers and vaccines.