title: Binding stoichiometry of the cytotoxic T lymphocyte-associated molecule-4 (CTLA-4). A disulfide-linked homodimer binds two CD86 molecules.
abstract: CD28 and CTLA-4 are homologous T cell receptors of the immunoglobulin (Ig) superfamily, which bind B7 molecules (CD80 and CD86) on antigen-presenting cells and transmit important costimulatory signals during T cell activation. Here we have investigated the subunit structure of CTLA-4 and the stoichiometry of its binding to B7 molecules. We demonstrate CTLA-4 is a homodimer interconnected by one disulfide bond in the extracellular domain at cysteine residue 120. Each monomeric polypeptide chain of CTLA-4 contains a high affinity binding site for B7 molecules; soluble CTLA-4 and CD86 form complexes containing equimolar amounts of monomeric CTLA-4 and CD86 (i.e. a 2:2 molecular complex). Thus, CTLA-4 and probably CD28 have a receptor structure consisting of preexisting covalent homodimers with two binding sites. Dimerization of CTLA-4 and CD28 is not required for B7 binding, nor is it sufficient to trigger signaling.
authors.affiliation: Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Linsley
authors.forename: S G
authors.initials: SG
authors.lastname: Nadler
authors.forename: J
authors.initials: J
authors.lastname: Bajorath
authors.forename: R
authors.initials: R
authors.lastname: Peach
authors.forename: H T
authors.initials: HT
authors.lastname: Leung
authors.forename: J
authors.initials: J
authors.lastname: Rogers
authors.forename: J
authors.initials: J
authors.lastname: Bradshaw
authors.forename: M
authors.initials: M
authors.lastname: Stebbins
authors.forename: G
authors.initials: G
authors.lastname: Leytze
authors.forename: W
authors.initials: W
authors.lastname: Brady
mesh_terms: D000069594:Abatacept; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000302:isolation & purification / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D018122:B7-1 Antigen / Q000302:isolation & purification / Q000378:metabolism*; D051940:B7-2 Antigen; D001665:Binding Sites; D060908:CTLA-4 Antigen; D002460:Cell Line; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004220:Disulfides; D005434:Flow Cytometry; D006801:Humans; D018796:Immunoconjugates; D007668:Kidney; D007700:Kinetics; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D013917:Thrombin; D014162:Transfection
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D051940:B7-2 Antigen; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D004220:Disulfides; D018796:Immunoconjugates; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D000069594:Abatacept; D013917:Thrombin