Reiterative Screening of Phage-Display Peptide Libraries with Antibodies

Filamentous bacteriophage can tolerate the insertion of a foreign DNA into their gene encoding phage minor coat protein III. Such recombinant phage particles display on their surface foreign peptide sequences fused with the gene III product, which is a protein represented by five copies on the top of the virion. The N-terminal part of this coat protein (cp III) is involved in binding phage to the F-pilus of a bacterium at an early stage of the infection process. The exposed peptide region exists, therefore, in a form accessible for immune recognition (1 ). Modern gene engineering allows the creation of phage libraries in which every possible combination of amino acid sequence is expressed as fusion proteins (2 –5 ). An important difference between random peptides and specific peptides (e.g., PEPSCAN) or antigen fragmentation methods is that the former not only localizes the epitope in the antigen sequence, but also provides information on which amino acid residues are most important for antibody binding.