CONSTRUCTION, EXPLOITATION AND EVOLUTION OF A NEW PEPTIDE LIBRARY DISPLAYED AT HIGH-DENSITY BY FUSION TO THE MAJOR COAT PROTEIN OF FILAMENTOUS PHAGE

The amino-terminus of the major coat protein (PVIII) of filamentous ph age can be extended, up to 6-7 residues, without interfering with the phage life cycle. We have constructed a library of approximately ten m illions different phage each displaying a different octapeptide joined to the amino-terminus of the 2700 copies of PVIII. Most of the result ing clones are able to produce infective particles. This molecular rep ertoire constituted by the periodic regular decoration of the phage fi lament surface, can be utilized to search elements that bind proteins or relatively small organic molecules like the textile dye Cibacron bl ue. By sequential growth cycles we have performed a library evolution experiment to select phage clones that have a growth advantage in the absence of any requirement for binding a specific target. The consensu s of the best growers reveals a Pro rich sequence with large hydrophob ic residues at position 7 and Asn at position 1 of the random peptide insert, We propose that the assembly secretion process is favoured in phages displaying this family of peptides since they fit the groove be tween two adjacent PVIII subunits by making advantageous molecular con tacts on the phage surface.