A PHAGE DISPLAY TECHNIQUE FOR A FAST, SENSITIVE, AND SYSTEMATIC INVESTIGATION OF PROTEIN-PROTEIN INTERACTIONS

Phage display is a technique in which a foreign protein or peptide is presented at the surface of a (filamentous) bacteriophage. This system , developed by Smith [(1985), Science 228, 1315-1317], was originally used to create large libraries of antibodies for the purpose of select ing those that strongly bound a particular antigen. More recently it w as also employed to present peptides, domains of proteins, or intact p roteins at the surface of phages, again to identify high-affinity inte ractions with ligands. Here we want to illustrate the use of phage dis play, in combination with PCR saturation mutagenesis, for the study of protein-protein interactions. Rather than selecting for mutants havin g high affinity, we systematically investigate the binding of every va riant with its natural ligand. Via a modified ELISA we can calculate a relative affinity. As a model system we chose to display thymosin bet a 4 on the phage surface in order to study its interaction with actin.