Binding stoichiometry of the cytotoxic T lymphocyte-associated molecule-4 (CTLA-4). A disulfide-linked homodimer binds two CD86 molecules

• Published in: The Journal of biological chemistry 1995-06, Vol.270 (25), p.15417-15424
• Main Authors: Linsley, P S, Nadler, S G, Bajorath, J, Peach, R, Leung, H T, Rogers, J, Bradshaw, J, Stebbins, M, Leytze, G, Brady, W
• Format: Article
• Language: English
• Subjects: Abatacept; Amino Acid Sequence; Animals; Antigens, CD - isolation & purification; Antigens, CD - metabolism; Antigens, Differentiation - biosynthesis; Antigens, Differentiation - isolation & purification; Antigens, Differentiation - metabolism; B7-1 Antigen - isolation & purification; B7-1 Antigen - metabolism; B7-2 Antigen; Binding Sites; Cell Line; Cells, Cultured; Chlorocebus aethiops; CTLA-4 Antigen; Disulfides; Flow Cytometry; Humans; Immunoconjugates; Kidney; Kinetics; Macromolecular Substances; Membrane Glycoproteins - isolation & purification; Membrane Glycoproteins - metabolism; Molecular Sequence Data; Peptide Fragments - chemistry; Protein Binding; Recombinant Fusion Proteins - biosynthesis; Recombinant Fusion Proteins - isolation & purification; Recombinant Fusion Proteins - metabolism; T-Lymphocytes, Cytotoxic - immunology; Thrombin; Transfection
• ISSN: 0021-9258
• DOI: 10.1074/jbc.270.25.15417

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.