LFA-1 binding site in ICAM-3 contains a conserved motif and non-contiguous amino acids.
The intercellular adhesion molecule-3 (ICAM-3) is a counter receptor for the integrin LFA-1 that supports cell-cell adhesion dependent functions. ICAM-3 is a member of the immunoglobulin superfamily possessing five immunoglobulin-like domains. Here, we characterize the overall shape of ICAM-3 and the amino acid residues involved in binding LFA-1 and monoclonal antibodies (Mab). Electron microscopic observations show that ICAM-3 is predominantly a straight rod of 15 nm in length, suggesting a head to tail arrangement of the immunoglobulin-like domains. Six out of nine ICAM-3 Mab described blocked the interaction with LFA-1 to varying degrees. Domain assignment of blocking Mab epitopes and characterization of LFA-1-dependent cell adhesion to ICAM-3 mutants demonstrate that the amino-terminal domain of ICAM-3 interacts with LFA-1. A conserved amino acid motif including residues E37 and T38 form an integrin binding site (IBS) in ICAM-3. This motif has also been shown to function as an IBS in ICAM-3 and VCAM-1 and hence many form a common site of contact in all CAMs of this type. Other ICAM-3 residues critical to adhesive interactions, such as Q75, conserved in ICAM-1 and ICAM-2, but not VCAM-1, may confer specificity to LFA-1 binding. This residue, Q75, is predicted to locate in a model of ICAM-3 to the same site as RGD in the immunoglobulin-like domain of fibronectin that binds several integrins. This suggest an evolutionary relationship between ICAMs and fibronectin interactions with integrins.
Sadhu
C
C
ICOS Corporation, Bothell, WA 98021.
Lipsky
B
B
Erickson
H P
HP
Hayflick
J
J
Dick
K O
KO
Gallatin
W M
WM
Staunton
D E
DE
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D001483:Base Sequence; D001665:Binding Sites; D015815:Cell Adhesion Molecules / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D002460:Cell Line; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D000939:Epitopes / Q000032:analysis; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C / Q000276:immunology; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D017384:Sequence Deletion; D014162:Transfection
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D015815:Cell Adhesion Molecules; D000939:Epitopes; C483616:ICAM3 protein, human; D016169:Lymphocyte Function-Associated Antigen-1; D011993:Recombinant Fusion Proteins