Epitopes described in "High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase."

Article Authors:H L Schwartz; J M Chandonia; S F Kash; J Kanaani; E Tunnell; A Domingo; F E Cohen; J P Banga; A M Madec; W Richter; S Baekkeskov
Article Title:High-resolution autoreactive epitope mapping and structural modeling of the 65 kDa form of human glutamic acid decarboxylase.
Reference Detail
Reference ID:1014039
Abstract:The smaller isoform of the GABA-synthesizing enzyme, glutamic acid decarboxylase 65 (GAD65), is unusually susceptible to becoming a target of autoimmunity affecting its major sites of expression, GABA-ergic neurons and pancreatic beta-cells. In contrast, a highly homologous isoform, GAD67, is not an autoantigen. We used homolog-scanning mutagenesis to identify GAD65-specific amino acid residues which form autoreactive B-cell epitopes in this molecule. Detailed mapping of 13 conformational epitopes, recognized by human monoclonal antibodies derived from patients, together with two and three-dimensional structure prediction led to a model of the GAD65 dimer. GAD65 has structural similarities to ornithine decarboxylase in the pyridoxal-5'-phosphate-binding middle domain (residues 201-460) and to dialkylglycine decarboxylase in the C-terminal domain (residues 461-585). Six distinct conformational and one linear epitopes cluster on the hydrophilic face of three amphipathic alpha-helices in exons 14-16 in the C-terminal domain. Two of those epitopes also require amino acids in exon 4 in the N-terminal domain. Two distinct epitopes reside entirely in the N-terminal domain. In the middle domain, four distinct conformational epitopes cluster on a charged patch formed by amino acids from three alpha-helices away from the active site, and a fifth epitope resides at the back of the pyridoxal 5'-phosphate binding site and involves amino acid residues in exons 6 and 11-12. The epitopes localize to multiple hydrophilic patches, several of which also harbor DR*0401-restricted T-cell epitopes, and cover most of the surface of the protein. The results reveal a remarkable spectrum of human autoreactivity to GAD65, targeting almost the entire surface, and suggest that native folded GAD65 is the immunogen for autoreactive B-cells.
Affiliations:Departments of Microbiology/Immunology and Medicine, Hormone Research Institute, San Francisco, CA, 94143-0534, USA.
Reference Type:Literature
PubMed ID:10222205
Journal:J Mol Biol
Journal Volume:287
Article Pages:983-99
Journal ISSN:0022-2836
Article Chemical List:Antibodies, Monoclonal;Isoenzymes;Recombinant Proteins;Glutamate Decarboxylase
Article MeSH List:Amino Acid Sequence; Antibodies, Monoclonal(metabolism); Binding Sites; Epitope Mapping(methods); Glutamate Decarboxylase(chemistry; genetics; immunology); Humans; Isoenzymes(chemistry; genetics; immunology); Models, Molecular; Molecular Sequence Data; Mutagenesis; Protein Conformation; Recombinant Proteins(genetics; metabolism); Sequence Homology, Amino Acid
Curation Last Updated:2014-10-03 21:26:28