Enlarged view of the potential ligand-binding pocket of integrin αVβ3. The loops on the top of the α-subunit β-propeller implicated in ligand binding are coloured: purple, the 4–1 loop connecting repeats 1–2; orange, the 4–1 loop connecting repeats 2–3; pink, the 4–-1 loop connecting repeats 3–4; green, the 2–3 loop in repeat 2; yellow, the 2–3 loop in repeat 3. The potential site for binding the fibronectin synergy sequence in α5β1, the β-strand 4 in repeat 3, is coloured blue (left side of β-propeller). The CYDMKTTC peptide sequence determining ligand specificity in β3 is coloured blue (top of βA-domain). Cations in the αVβ3 crystal structure are shown as blue spheres. The potential site of the metal ion-dependent adhesion site (MIDAS) cation is shown as a green circle. The site of insertion of an αA-domain would be in the orange loop of the β-propeller. The solid double arrow shows the possible orientation of ligand relative to the integrin, with dashed lines indicating speculative contacts with the MIDAS cation and β-strand 4 in repeat 3.