Selection of antibody ligands from a large library of oligopeptides expressed on a multivalent exposition vector.

Practically any oligopeptide can be exposed on the surface of the bacteriophage capsid by fusion to the major coat protein of filamentous bacteriophages. A phage expressing a particular peptide tag can be selected from a mixture of tens of millions of clones, exposing oligopeptides of random sequence, by affinity purification with a protein ligand. In this respect, pVIII can be used as an alternative and complement to the exposition vectors based on the product of gene III (pIII). We have constructed a phagemid vector that contains gene VIII under the control of the pLac promoter. This vector can be conveniently used to construct libraries of oligopeptides with a random amino acid sequence. An antipeptide monoclonal antibody was used to affinity-purify phagemids exposing oligopeptides which can interact with the monoclonal antibody. DNA sequencing of the amino terminus of gene VIII of the recovered clones predicts the synthesis of hybrid proteins whose aminoterminal amino acid sequence is related to that of the oligopeptide used to raise the antibody. In other words, only oligopeptides that bind a very small portion of the immunoglobulin G surface are affinity-purified by this method, implying that the antigen binding site possesses molecular properties that renders it much stickier than the remainder of the molecule.