Journal Article

N-terminal additions to the WE14 peptide of chromogranin A create strong autoantigen agonists in type 1 diabetes

Wang, Yang, Jin, Niyun, White, Janice, Kappler, John W., Marrack, Philippa, Dai, Shaodong, Crawford, Frances

2015

Overview

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, IAg7binding 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 IAg7–RLGL–WE14 complex confirmed the predicted placement of the peptide within the IAg7groove. Fluorescent IAg7–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 post-translational 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.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Amino Acid Sequence / Amino acids / Animals / antigen processing / Autoantigens - immunology / autoimmunity / Baculoviridae - genetics / Base Sequence / BASIC BIOLOGICAL SCIENCES / Biological Sciences / Chromogranin A - chemistry / Chromogranin A - genetics / Chromogranin A - immunology / Crystal structure / Crystallization / crystallography / Diabetes / Diabetes Mellitus, Type 1 - immunology / Epitopes - genetics / Epitopes - immunology / Flow Cytometry / Hybridomas - immunology / Interleukin-2 - immunology / Lymph nodes / Mice / Mice, Inbred NOD / Models, Molecular / modification / Molecular Sequence Data / Peptide Fragments - chemistry / Peptide Fragments - genetics / Peptide Fragments - immunology / Peptides / posttranslational / Protein Processing, Post-Translational - genetics / Rodents / transpeptidation