Definition of an unexpected ligand recognition motif for ανβ6 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 alpha v beta 6, 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 alpha v beta 6. We compared the recognition profiles of recombinant alpha v beta 6 and alpha v beta 3 integrins by using phage display screening employing 7-mer and 12-mer peptide libraries. As predicted, phages binding strongly to alpha v beta 3 contained ubiquitous RGD sequences.:However, on alpha v beta 6, in addition to RGD- containing phages, one-quarter of the population from the 12-mer library contained the distinctive consensus motif DLXXL, A synthetic DLXXL peptide, RTDLDSLRTYTL, selected from the phage sequences (clone-l) was a selective inhibitor of RGD-dependent ligand binding to alpha v beta 6 in isolated receptor assays (IC50 = 20 nM), and in cell adhesion assays (IC50 = 50 mu M). DLXXL peptides were highly specific inhibitors of alpha v beta 6-fibronectin interaction as synthetic scrambled or reversed DLXXL peptides were inactive. NH2- 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 alpha v beta 6. The DLXXL sequence is present in several matrix components and in the beta chain of many integrins. Although there is as yet no precise biological role known for DLXXL, it is clearly a specific inhibitory sequence for integrin alpha v beta 6 which has been unrecognized previously.