Model of the alphaLbeta2 integrin I-domain/ICAM-1 DI interface suggests that subtle changes in loop orientation determine ligand specificity.
The interaction of the alphaLbeta2 integrin with its cellular ligand the intercellular adhesion molecule-1 (ICAM-1) is critical for the tight binding interaction between most leukocytes and the vascular endothelium before transendothelial migration to the sites of inflammation. In this article we have modeled the alphaL subunit I-domain in its active form, which was computationally docked with the D1 domain of the ICAM-1 to probe potential protein-protein interactions. The experimentally observed key interaction between the carboxylate of Glu 34 in the ICAM-1 D1 domain and the metal ion-dependent adhesion site (MIDAS) in the open alphaL I-domain was consistently reproduced by our calculations. The calculations reveal the nature of the alphaLbeta2/ICAM-1 interaction and suggest an explanation for the increased ligand-binding affinity in the "open" versus the "closed" conformation of the alphaL I-domain. A mechanism for substrate selectivity among alphaL, alphaM, and alpha2 I-domains is suggested whereby the orientation of the loops within the I-domain is critical in mediating the interaction of the Glu 34 carboxylate of ICAM-1 D1 with the MIDAS.
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA. glegge@uh.edu
Glen B
GB
Legge
Garrett M
GM
Morris
Michel F
MF
Sanner
Yoshikazu
Y
Takada
Arthur J
AJ
Olson
Flavio
F
Grynszpan
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D019295:Computational Biology; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D000596:Amino Acids; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1