title: N-terminal additions to the WE14 peptide of chromogranin A create strong autoantigen agonists in type 1 diabetes.
abstract: Chromogranin A (ChgA) is an autoantigen for CD4(+) T cells in the nonobese diabetic (NOD) mouse model of type 1 diabetes (T1D). The natural ChgA-processed peptide, WE14, is a weak agonist for the prototypical T cell, BDC-2.5, and other ChgA-specific T-cell clones. Mimotope peptides with much higher activity share a C-terminal motif, WXRM(D/E), that is predicted to lie in the p5 to p9 position in the mouse MHC class II, IA(g7) binding groove. This motif is also present in WE14 (WSRMD), but at its N terminus. Therefore, to place the WE14 motif into the same position as seen in the mimotopes, we added the amino acids RLGL to its N terminus. Like the other mimotopes, RLGL-WE14, is much more potent than WE14 in T-cell stimulation and activates a diverse population of CD4(+) T cells, which also respond to WE14 as well as islets from WT, but not ChgA(-/-) mice. The crystal structure of the IA(g7)-RLGL-WE14 complex confirmed the predicted placement of the peptide within the IA(g7) groove. Fluorescent IA(g7)-RLGL-WE14 tetramers bind to ChgA-specific T-cell clones and easily detect ChgA-specific T cells in the pancreas and pancreatic lymph nodes of NOD mice. The prediction that many different N-terminal amino acid extensions to the WXRM(D/E) motif are sufficient to greatly improve T-cell stimulation leads us to propose that such a posttranslational modification may occur uniquely in the pancreas or pancreatic lymph nodes, perhaps via the mechanism of transpeptidation. This modification could account for the escape of these T cells from thymic negative selection.
authors.affiliation: Howard Hughes Medical Institute, Denver, CO 80206; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; Barbara Davis Center for Childhood Diabetes, University of Colorado, Aurora, CO 80045;
authors.forename: Niyun
authors.initials: N
authors.lastname: Jin
authors.affiliation: Department of Biomedical Research, National Jewish Health, Denver, CO 80206;
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Howard Hughes Medical Institute, Denver, CO 80206; Department of Biomedical Research, National Jewish Health, Denver, CO 80206;
authors.forename: Frances
authors.initials: F
authors.lastname: Crawford
authors.affiliation: Department of Biomedical Research, National Jewish Health, Denver, CO 80206;
authors.forename: Janice
authors.initials: J
authors.lastname: White
authors.affiliation: Howard Hughes Medical Institute, Denver, CO 80206; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045;
authors.forename: Philippa
authors.initials: P
authors.lastname: Marrack
authors.affiliation: Department of Biomedical Research, National Jewish Health, Denver, CO 80206; Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; dais@njhealth.org kapplerj@njhealth.org.
authors.forename: Shaodong
authors.initials: S
authors.lastname: Dai
authors.affiliation: Howard Hughes Medical Institute, Denver, CO 80206; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; Barbara Davis Center for Childhood Diabetes, University of Colorado, Aurora, CO 80045; Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Program in Structural Biology and Biochemistry, University of Colorado School of Medicine, Aurora, CO 80045 dais@njhealth.org kapplerj@njhealth.org.
authors.forename: John W
authors.initials: JW
authors.lastname: Kappler
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000276:immunology*; D016367:Baculoviridae / Q000235:genetics; D001483:Base Sequence; D053379:Chromogranin A / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D003460:Crystallization; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology*; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D005434:Flow Cytometry; D006825:Hybridomas / Q000276:immunology; D007376:Interleukin-2 / Q000276:immunology; D051379:Mice; D016688:Mice, Inbred NOD; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D011499:Protein Processing, Post-Translational / Q000235:genetics
chemical_list: D001324:Autoantigens; D053379:Chromogranin A; D000939:Epitopes; D007376:Interleukin-2; D010446:Peptide Fragments; C000604951:WE14 protein, mouse
keywords: antigen processing; autoimmunity; crystallography; posttranslational modification; transpeptidation