The amino-terminal immunoglobulin-like domain of activated leukocyte cell adhesion molecule binds specifically to the membrane-proximal scavenger receptor cysteine-rich domain of CD6 with a 1:1 stoichiometry.
Activated leukocyte cell adhesion molecule (ALCAM) was recently identified as a ligand for CD6, a signaling receptor expressed on T cells, a subset of B cells, and some cells in the brain. Receptor-ligand binding assays, antibody blocking experiments, and examination of the tissue distribution of these two cell surface proteins suggest that CD6-ALCAM interactions play an important role in mediating the binding of thymocytes to thymic epithelial cells and of T cells to activated leukocytes. Presently, the details of CD6-ALCAM interactions and of signaling through CD6 are unknown. A series of truncated human ALCAM and CD6 immunoglobulin fusion proteins were produced and tested in different binding assays to analyze ALCAM-CD6 interactions in more detail. In this study, we report that the amino-terminal Ig-like domain of human ALCAM specifically binds to the third membrane-proximal scavenger receptor cysteine-rich (SRCR) domain of human CD6. Using thrombin-cleaved Ig fusion proteins containing single or multiple ALCAM or CD6 domains, we were able to determine that the stoichiometry of the interaction between the amino-terminal ALCAM domains and the membrane-proximal CD6 SRCR domain is 1:1. These results provide the first example of an Ig-like domain mediating an interaction with an SRCR domain.
Bowen
M A
MA
Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, Washington 98121, USA.
Bajorath
J
J
Siadak
A W
AW
Modrell
B
B
Malacko
A R
AR
Marquardt
H
H
Nadler
S G
SG
Aruffo
A
A
D020410:Activated-Leukocyte Cell Adhesion Molecule; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D015703:Antigens, CD / Q000302:isolation & purification / Q000378:metabolism*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000302:isolation & purification / Q000378:metabolism*; D016175:B-Lymphocyte Subsets / Q000276:immunology; D001921:Brain / Q000276:immunology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D002850:Chromatography, Gel; D003545:Cysteine; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D010446:Peptide Fragments / Q000302:isolation & purification / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D012867:Skin; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection
D020410:Activated-Leukocyte Cell Adhesion Molecule; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; C062279:CD6 antigen; D015815:Cell Adhesion Molecules; D006023:Glycoproteins; D008024:Ligands; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D003545:Cysteine