title: Isolation of HLA-DR1.(staphylococcal enterotoxin A)2 trimers in solution.
abstract: Mutational studies indicate that the superantigen staphylococcal enterotoxin A (SEA) has two separate binding sites for major histocompatibility complex (MHC) class II molecules. Direct evidence is provided here for the formation of SEA-MHC class II trimers in solution. Isoelectric focusing separated SEA-HLA-DR1 complexes into both dimers and HLA-DR1.SEA2 trimers. The molar ratio of components was determined by dual isotope labeling. The SEA mutant SEA-F47S, L48S, Y92A, which is deficient in MHC class II alpha-chain binding, formed only dimers with HLA-DR1, whereas a second SEA mutant, SEA-H225A, which lacks high-affinity MHC class II beta-chain binding was incapable of forming any complexes. Thus SEA binding to its MHC receptor is a two-step process involving initial beta-chain binding followed by cooperative binding of a second SEA molecule to the class II alpha chain.
authors.affiliation: Department of Molecular Medicine, School of Medicine, University of Auckland, New Zealand.
authors.forename: R E
authors.initials: RE
authors.lastname: Tiedemann
authors.forename: R J
authors.initials: RJ
authors.lastname: Urban
authors.forename: J L
authors.initials: JL
authors.lastname: Strominger
authors.forename: J D
authors.initials: JD
authors.lastname: Fraser
mesh_terms: D001402:B-Lymphocytes; D001665:Binding Sites; D002460:Cell Line; D004768:Enterotoxins / Q000737:chemistry* / Q000276:immunology* / Q000302:isolation & purification; D015798:HLA-DR1 Antigen / Q000737:chemistry* / Q000302:isolation & purification; D006801:Humans; D007525:Isoelectric Focusing; D046911:Macromolecular Substances; D008961:Models, Structural; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D012996:Solutions; D013211:Staphylococcus aureus / Q000276:immunology; D018089:Superantigens / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D016335:Zinc Fingers
chemical_list: D004768:Enterotoxins; D015798:HLA-DR1 Antigen; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D012996:Solutions; D018089:Superantigens; C026066:enterotoxin A, Staphylococcal