The dual structural roles of the membrane distal region of α integrin cytoplasmic tail in integrin inside-out activation

Studies on the mechanism of integrin inside-out activation have been focused on the role of β cytoplasmic tails that are relatively conserved and bear binding sites for the intracellular activators including talin and kindlin. Integrin α cytoplasmic tails share a conserved GFFKR motif at the membrane-proximal region forming specific interface with β membrane-proximal region that keeps integrin inactive. The α membrane-distal regions after the GFFKR motif are diverse both in length and sequence and their roles in integrin activation have not been well-defined. In this study, we report that the α cytoplasmic membrane-distal region contributes to maintaining integrin in the resting state and to integrin inside-out activation. Complete deletion of the α membrane-distal region diminished talin and kindlin mediated integrin ligand binding and conformational change. A proper length and amino acids of α membrane-distal region is important for integrin inside-out activation. Our data establish an essential role of the α integrin cytoplasmic membrane-distal region in integrin activation and provide new insights into how talin and kindlin induce the high affinity integrin conformation that is required for fully functional integrins.