Definition of an Unexpected Ligand Recognition Motif for αvβ6 Integrin

Integrin interactions with extracellular matrix proteins are mediated by brief oligopeptide recognition sequences, and synthetic peptides containing such sequences can inhibit integrin binding to the matrix. The RGD peptide motif is recognized by many integrins including αvβ6, a specific receptor for fibronectin thought to support epithelial cell proliferation during wound healing and carcinoma progression. We report here the discovery of an unexpected non-RGD recognition motif for integrin αvβ6. We compared the recognition profiles of recombinant αvβ6 and αvβ3 integrins by using phage display screening employing 7-mer and 12-mer peptide libraries. As predicted, phages binding strongly to αvβ3 contained ubiquitous RGD sequences. However, on αvβ6, in addition to RGD- containing phages, one-quarter of the population from the 12-mer library contained the distinctive consensus motif DL XX L. A synthetic DL XX L peptide, RT DL DS L RTYTL, selected from the phage sequences (clone-1) was a selective inhibitor of RGD-dependent ligand binding to αvβ6 in isolated receptor assays (IC 50 = 20 n m ), and in cell adhesion assays (IC 50 = 50 μ m ). DL XX L peptides were highly specific inhibitors of αvβ6-fibronectin interaction as synthetic scrambled or reversed DL XX L peptides were inactive. NH 2 - and COOH-terminal modifications of the flanking amino acids suggested that the preceding two and a single trailing amino acid were also involved in interaction with αvβ6. The DL XX L sequence is present in several matrix components and in the β chain of many integrins. Although there is as yet no precise biological role known for DL XX L, it is clearly a specific inhibitory sequence for integrin αvβ6 which has been unrecognized previously.