Integrin-Binding Peptides Derived from Phage Display Libraries

Abstract

Integrins are a family of cell-surface receptors that recognize extracellular matrix proteins and mediate cell adhesion. Certain integrins bind to proteins containing the sequence Arg-Gly-Asp (RGD; ref. 1). Such RGD-binding integrins include α₅β₁, αvβ₃, α_vβ₅ and α_IIbβ₃ (2,3). Peptide libraries displayed on filamentous phage have provided a straightforward method to characterize the peptide-binding specificity of these integrins. In phage display-based strategies, libraries of random peptides are expressed on the surface of bacteriophage. Each individual phage carries a single peptide. The peptide is fused to the phage capsid protein pIII by insertion of its encoding DNA sequence in the pIII gene of the phage genome. Libraries displaying peptides fused to the major capsid protein pVIII have also been used. Libraries using the pIII protein display 3–5 copies of each individual peptide whereas libraries using the pVIII protein display approx 3000 copies (4,5). Analysis of the phage-displayed peptides found during screenings on purified integrins revealed that the majority of the integrin-binding peptides contain an RGD motif (6–11). Other interesting ligand motifs were also found in the remaining population of integrin-binding peptides. Conversely, panning on immobilized fibronectin fragments containing the RGD sequence revealed peptide motifs present within integrins (12). We describe here strategies for the use of phage display libraries in cell-adhesion research, with emphasis on the peptide-binding specificity of different members of the integrin family.