Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail Available to Purchase

Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the α and β tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the α tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membranedistal region of the αIIb tail. Alanine substitution of the RPP residues in the αIIb tail rendered αIIbβ3 constitutively active in a metabolic energy-dependent manner. Although an αIIb/α6Aβ3 chimaeric integrin, in which the αIIb tail was replaced by the α6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the α6A tail inhibited binding of an activation-dependent antibody PAC1. In αIIb/α6Aβ3, deleting the TSDA sequence from the α6A tail or single amino acid substitutions of the TSDA residues inhibited αIIb/α6Aβ3 activation and replacing the membrane-distal region of the αIIb tail with TSDA rendered αIIbβ3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the αIIb tail containing the RPP sequence of the membrane-distal region failed to activate αIIbβ3. These results suggest that the RPP sequence after the GFFKR motif of the αIIb tail suppresses energy-dependent αIIbβ3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by α subunit tails.