3D reconstruction of integrin αIIbβ3 in lipid bilayer nanodisc. (A) Superimposition of 5 random conical tilt reconstructions of αIIbβ3 nanodiscs produced by back projection of tilted EM images obtained at 120 kV aligned according to the αIIbβ3 maps. Note the close alignment of the αIIbβ3 maps and the much more variable alignment of the nanodisc maps, indicating that the αIIbβ3 receptors have 1 consistent conformation but occupy different locations within the nanodiscs. (B) Three-dimensional surface views of αIIbβ3 inserted into lipid bilayer nanodiscs, along with the dimensions of the extracellular portions of αIIbβ3. (C) The 20-Å maps of the αIIb (blue) and β3 (red) domains from the crystal structure (3FCS) fitted into the αIIbβ3 nanodisc map by correlation-based docking.