The conserved membrane-proximal region of an integrin cytoplasmic domain specifies ligand binding affinity.
Integrin affinities for ligands can change markedly via a process termed inside-out signaling. We expressed several truncations of the beta 3 cytoplasmic domain in conjunction with an "activating" alpha subunit chimera, alpha IIb alpha 6B. Deletion of the 4 C-terminal residues of the beta 2 tail blocked inside-out signaling as assessed by the binding of an activation-specific antibody, PAC1. Several additional truncations remained in the low affinity state, but complete truncation (beta 3 delta 717) caused PAC1 binding. Activation by this truncation mutant did not depend on the alpha subunit cytoplasmic domain and was resistant to inhibitors of cellular metabolism and the over-expression of an isolated beta 3 cytoplasmic domain. Since deletion of beta 3(Leu717-Asp723) results in a constitutively activated integrin, this membrane-proximal seven amino acids of the beta 3 cytoplasmic domain is required to maintain alpha IIb beta 3 in a default low affinity state. The amino acid sequence of this region is conserved among integrins. Moreover, the conserved membrane-proximal sequence in alpha subunit tails seems to serve a similar function. Consequently, the conserved membrane-proximal regions of both integrin cytoplasmic domains control the ligand binding affinity of the extracellular domain.
Hughes
P E
PE
Department of Vascular Biology, Scripps Research Institute, La Jolla, California 92037, USA.
O'Toole
T E
TE
Ylänne
J
J
Shattil
S J
SJ
Ginsberg
M H
MH
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D016764:Cell Polarity; D017124:Conserved Sequence; D006224:Cricetinae; D004252:DNA Mutational Analysis; D039661:Integrin beta3; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction
D015703:Antigens, CD; D039661:Integrin beta3; D016023:Integrins; D008024:Ligands; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins