CHARACTERIZATION OF PHAGE THAT BIND PLASTIC FROM PHAGE-DISPLAYED RANDOM PEPTIDE LIBRARIES

During routine screenings of random peptide libraries displayed at the N terminus of the pIII coat protein of M13 bacteriophage, clones were isolated that bound directly to the polystyrene (PS) surface used to immobilize the target protein. The plastic-binding phage (P-b phi) bin d to both unblocked plastic (PS and polyvinyl chloride, PVC) and plast ic blocked with bovine serum albumin (BSA) but require non-ionic deter gent to bind to plastic blocked with milk. Comparison of the P-b phi t o antibody-binding phage (Ab-b phi) indicates that similar numbers of phage particles are bound, but fewer P-b phi are recovered by acid elu tion. Sequence determination of the displayed peptides reveals they la ck aminoacid sequence similarity yet are highly enriched for the Tyr a nd Trp residues. However, because not all phage that display peptides rich in Tyr and Trp residues bind to plastic, and other methods of scr eening random peptide libraries have identified different classes of p lastic-binding peptides, the relative abundance of Tyr and Trp residue s should not be considered diagnostic of plastic-binding. In summary, these results help characterize one of the most common methods used to screen random peptide libraries and suggest strategies to avoid isola ting P-b phi. Furthermore, while it is generally believed that protein s bind to plastic by non-specific interactions, these results show tha t a bias in aa composition can exist.