Selection of peptides with surface affinity for alpha-chymotrypsin using a phage display library.

Peptides with affinity for the surface of alpha-chymotrypsin (EC 3.4.21.1) were selected from a hexapeptide phage display library consisting of approximately 10(7) different clones. Seven selections were performed and five individual phage clones analysed. Compared to the primary library, the five peptide phage clones all interacted more strongly with alpha-chymotrypsin, and DNA sequencing of the phage clones revealed five different amino acid sequences: Gly-Ala-Val-Ile-Thr-His, Arg-Asp-Ile-Val-Val-Ala, Val-Tyr-Ser-His-Ala-Ser, Gly-Ser-Tyr-Ser-Ala-Gly and Leu-Asp-Ile-Val-Val-Ala. Two of the peptides exhibited 83% identity (i.e. a difference of just one amino acid). The chemically synthesized peptides competitively reduced the binding of the corresponding peptide phage clone to alpha-chymotrypsin. Binding of some of the selected peptide phage clones to alpha-chymotrypsin was also reduced by several of the other non-corresponding synthesized peptides, suggesting that these peptides have common recognition areas on the enzyme. Three of the synthesized peptides were poor substrates of alpha-chymotrypsin and they did not inhibit enzyme activity. Our results suggest that it is possible to select peptides from peptide phage display libraries with affinity for different surface structures on the enzyme, not involved in the biologically active site.