Data relating to the structural basis of ligand recognition by integrins are limited. Here we describe the physical requirements for high affinity binding of ligands to αvβ6. By combining a series of structural analyses with functional testing, we show that 20-mer peptide ligands, derived from high affinity ligands of αvβ6 (foot-and-mouth-disease virus, latency associated peptide), have a common structure comprising an Arg-Gly-Asp motif at the tip of a hairpin turn followed immediately by a C-terminal helix. This arrangement allows two conserved Leu/ Ile residues at Asp+1 and Asp+4 to be presented on the outside face of the helix enabling a potential hydrophobic interaction with the αvβ6 integrin, in addition to the Arg-Gly-Asp interaction. The extent of the helix determines peptide affinity for αvβ6 and potency as an αvβ6 antagonist. A major role of this C-terminal helix is likely to be the correct positioning of the Asp+1 and Asp+4 residues. These data suggest an explanation for several biological functions of αvβ6 and provide a structural platform for design of αvβ6 antagonists.
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