title: Biochemical characterization of the 9.3 antigens of human T-cells: simultaneous expression of disulfide-bonded 90-kilodalton dimers and free subunits at the cell surface.
abstract: Human T-lymphocytes express a heterogeneous family of 90/45-kilodalton (kDa) glycoproteins which bind the 9.3 monoclonal antibody. It was found in previous functional tests carried out with cultures of mononuclear cells or antigen-specific T-cell clones that these glycoproteins have a specific receptor function in early T-cell activation [Gmünder and Lesslauer, Eur. J. Biochem. (1984); Ottenhoff et al., (1985)]; their membrane-biochemical properties are therefore investigated. By screening a number of lines, one continuously growing human T-cell line, HPB-ALL, was identified which expresses the 9.3 antigens in a manner comparable to normal T-cells. Monomeric 45-kDa and dimeric disulfide-bonded 90-kDa forms are precipitated from alkylated surface-iodinated and [35S]methionine-cysteine-labelled cells. The labelled tryptic fragments of surface-iodinated 9.3 antigens have isoelectric points of 4.8 (17-kDa), 4.8 (3-kDa) and 6.0 (17-kDa). By limited proteolysis the 45-kDa monomers are free subunits. The subunits of the 90-kDa dimer appear to be identical. The dimer and the free subunits coexist at the native cell surface and may be in dynamic chemical equilibrium. Human T-cells thus express--in addition to the T-cell antigen receptor--a further disulfide-bonded 90-kDa (homo-) dimeric receptor molecule.
mesh_terms: D000941:Antigens / Q000378:metabolism*; D000954:Antigens, Surface / Q000276:immunology; D001665:Binding Sites; D002460:Cell Line; D003545:Cysteine / Q000378:metabolism; D004220:Disulfides; D004586:Electrophoresis; D006801:Humans; D008715:Methionine / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism
chemical_list: D000941:Antigens; D000954:Antigens, Surface; D004220:Disulfides; D011948:Receptors, Antigen, T-Cell; D008715:Methionine; D003545:Cysteine