Definition of an unexpected ligand recognition motif for alpha nu beta 6 integrin

Integrin interactions with extracellular matrix proteins are mediated by br ief oligopeptide recognition sequences, and synthetic peptides containing s uch sequences can inhibit integrin binding to the matrix. The RGD peptide m otif is recognized by many integrins including alpha v beta 6, a specific r eceptor for fibronectin thought to support epithelial cell proliferation du ring 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-m er peptide libraries. As predicted, phages binding strongly to alpha v beta 3 contained ubiquitous RGD sequences.:However, on alpha v beta 6, in addit ion to RGD- containing phages, one-quarter of the population from the 12-me r library contained the distinctive consensus motif DLXXL, A synthetic DLXX L peptide, RTDLDSLRTYTL, selected from the phage sequences (clone-l) was a selective inhibitor of RGD-dependent ligand binding to alpha v beta 6 in is olated 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 w ere inactive. NH2- and COOH-terminal modifications of the flanking amino ac ids 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 pre sent 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 ha s been unrecognized previously.