A model depicting the potential changes in the extracellular domains of αIIbβ3 that are required for high-affinity ligand binding. The top left panel shows an overhead view of the proposed β-propeller domain within the N-terminal segment of αIIb,41 and the top right panel shows the crystal structure of an I-domain,43 a homologue of which appears to be present in the N-terminal segment of β3.42 Open circles denote divalent cations and asterisks denote regions presumed to be directly involved in ligand binding. Thick ribbons are strands of β-sheet, and coiled ribbons are α-helices (adapted from Chothia and Jones172 with permission, from the Annual Review of Biochemistry, Volume 66, ©1997, by Annual Reviews Inc). The bottom panels illustrate potential changes in these domains as αIIbβ3 is converted from a resting state (left panel) to an activated state (right panel). (Adapted from Loftus and Liddington.45 Adapted and reproduced from The Journal of Clinical Investigation, 1997, Vol. 99, pp. 2302, by copyright permission of The American Society for Clinical Investigation.)
