title: Characterization of the invariant chain C-terminus (Glu183-Glu193) epitope which is obscured in processed Ii, MHC alpha,beta trimers.
abstract: The E1 serum was developed against invariant chain peptide Ii (183-193) in order to study the function of the Ii protein which associates with class II MHC alpha,beta chains from time of synthesis until cleavage and release, possibly regulating the binding of antigenic peptides. Subpopulations of Ii, Ii(VIC) and Ii(E1), respectively, were demonstrated by sequential immunodepletions and immunoprecipitations with: (1) VIC-Y1 monoclonal antibody to an N-terminal epitope of Ii, and (2) E1 rabbit antiserum to Ii(183-193). In 3 hr radiolabeled cells, VIC-Y1 recognized Ii, Ii and N- and O-linked glycosylation (IpN, IpO), p41 and co-precipitated class II alpha,beta chains, while E1 recognized Ii, IpN and immature Ii-alpha complex. In 15 min radiolabeled cells, each antibody recognized similar, immature Ii forms without alpha,beta. Urea denaturation of Ii(VIC) rendered the main Ii species but not IpO immunoprecipitable with E1. E1 recognized O-glycanase-treated Ii (VIC). We conclude that the Ii(183-193) epitope was obscured by interactions of Ii with class II alpha,beta chains and by the O-linked glycosylation of Thr187, which may in part regulate association of Ii to class II alpha and beta chains.
authors.affiliation: Department of Pediatrics, University of Massachusetts Medical School, Worcester 01655.
authors.forename: Q V
authors.initials: QV
authors.lastname: Nguyen
authors.forename: W
authors.initials: W
authors.lastname: Knapp
authors.forename: R E
authors.initials: RE
authors.lastname: Humphreys
mesh_terms: D000918:Antibody Specificity; D000944:Antigens, Differentiation, B-Lymphocyte; D002478:Cells, Cultured; D000939:Epitopes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D014644:Genetic Variation; D006596:Hexosaminidases / Q000494:pharmacology; D000949:Histocompatibility Antigens Class II / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D009439:Neuraminidase / Q000494:pharmacology; D011233:Precipitin Tests; D011487:Protein Conformation; D014508:Urea / Q000494:pharmacology
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D014508:Urea; D006596:Hexosaminidases; D009439:Neuraminidase; C060638:glycopeptide alpha-N-acetylgalactosaminidase