Peptides on phage: a vast library of peptides for identifying ligands.

TLDR

The fAFF1 vector, derived from fd‑tet, permits cloning of oligonucleotides in multiple sites of gene III, enabling the creation of peptide libraries that can identify ligands for diverse receptors and aid drug discovery. Millions of hexapeptides were displayed on the N‑terminus of phage protein pIII, generating a 3×10^8 recombinant library that was screened by panning against the monoclonal antibody 3‑E7 to isolate high‑avidity binders. The screen yielded 51 unique hexapeptide ligands, all beginning with tyrosine and most with glycine, with affinities from 0.35 to 8.3 µM—demonstrating that phage‑displayed peptide libraries can identify antibody ligands without prior specificity information.

Abstract

We have constructed a vast library of peptides for finding compounds that bind to antibodies and other receptors. Millions of different hexapeptides were expressed at the N terminus of the adsorption protein (pIII) of fd phage. The vector fAFF1, derived from the tetracycline resistance-transducing vector fd-tet, allows cloning of oligonucleotides in a variety of locations in the 5' region of gene III. A library of 3 x 10(8) recombinants was generated by cloning randomly synthesized oligonucleotides. The library was screened for high-avidity binding to a monoclonal antibody (3-E7) that is specific for the N terminus of beta-endorphin (Tyr-Gly-Gly-Phe). Fifty-one clones selected by three rounds of the affinity purification technique called panning were sequenced and found to differ from previously known ligands for this antibody. The striking finding is that all 51 contained tyrosine as the N-terminal residue and that 48 contained glycine as the second residue. The binding affinities of six chemically synthesized hexapeptides from this set range from 0.35 microM (Tyr-Gly-Phe-Trp-Gly-Met) to 8.3 microM (Tyr-Ala-Gly-Phe-Ala-Gln), compared with 7.1 nM for a known high-affinity ligand (Tyr-Gly-Gly-Phe-Leu). These results show that ligands can be identified with no prior information concerning antibody specificity. Peptide libraries are also likely to be useful in finding ligands that bind to other classes of receptors and in discovering pharmacologic agents.