Cellular activation of leukocyte function-associated antigen-1 and its affinity are regulated at the I domain allosteric site.
The I domain of the integrin LFA-1 possesses a ligand binding interface that includes the metal ion-dependent adhesion site. Binding of the LFA-1 ligand, ICAM-1 to the metal ion-dependent adhesion site is regulated by the I domain allosteric site (IDAS). We demonstrate here that intracellular signaling leading to activation of LFA-1 binding to ICAM-1 is regulated at the IDAS. Inhibitory mutations in or proximal to the IDAS are dominant to cytoplasmic signals that activate binding to ICAM-1. In addition, mutational activation at the IDAS greatly increases the binding of lymphocyte-expressed LFA-1 to ICAM-1 in response to PMA, but does not result in constitutive binding. Binding of a novel CD18 activation epitope mAb to LFA-1 in response to soluble ICAM-1 binding was also blocked by inhibitory and was enhanced by activating IDAS mutations. Surface plasmon resonance using soluble wild-type LFA-1 and an IDAS mutant of LFA-1 indicate that the IDAS can regulate a 6-fold change in the K(d) of ICAM-1 binding. The K(d) of wild-type LFA-1 (1.2 x 10(-1) s(-1)) differed with that of the activating IDAS mutant (1.9 x 10(-2) s(-1)), but their K(a) values were identical (2.2 x 10(5) M(-1)s(-1)). We propose that IDAS regulates the binding of LFA-1 to ICAM-1 activated by intracellular signals. IDAS can control the affinity state of LFA-1 with concomitant I domain and CD18 conformational changes.
Lupher
M L
ML
ICOS Corporation, 22021 20th Avenue SE, Bothell, WA 98021, USA.
Harris
E A
EA
Beals
C R
CR
Sui
L M
LM
Liddington
R C
RC
Staunton
D E
DE
D000495:Allosteric Site / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002448:Cell Adhesion / Q000235:genetics; D002999:Clone Cells; D006224:Cricetinae; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism* / Q000502:physiology; D008214:Lymphocytes / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D020349:Surface Plasmon Resonance
D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1