Integrin cytoplasmic tails and binding sites for proteins that regulate activation. The amino acid sequences of the cytoplasmic tails of human αL, α2, α4, αIIb, αv, and αM, as well as of β1-3, β5, β7, and β8, are shown. With the exception of the “clasp” region, the cytoplasmic tails of α-subunits differ considerably in sequence and length, whereas a number of conserved motifs in β-cytoplasmic tails are identified. Gray shading indicates the membrane-proximal (MP) and membrane-distal (MD) NxxY motifs, yellow shading denotes the T/S region, and light blue shading demarcates the α-tail GFFKR and β-tail HDRxE sequences that form the “clasp” to stabilize the bent conformation. Underscored residues indicate sites of calpain cleavage, whereas regions that can be phosphorylated are indicated by an arrow. Binding sites for regulators of integrin activation are indicated, with the integrin subunits in parentheses indicating those to which binding has been shown. Dashed lines indicate that the exact binding site has not been mapped. CIB1, calcium- and integrin-binding protein 1; hsp, heat shock protein; SFK, Src-family kinases.