title: A quantitative analysis of transglutaminase 2-mediated deamidation of gluten peptides: implications for the T-cell response in celiac disease.
abstract: Celiac disease develops in genetically predisposed individuals as the result of an inappropriate intestinal immune response to dietary gluten proteins. T cells present in the intestine of celiac patients recognize gluten peptides in the context of HLA-DQ2 or -DQ8 molecules. Notably, T-cell recognition is increased after these peptides have been deamidated by the enzyme transglutaminase 2. Several T-cell epitopes of gluten exist, and most of these epitopes derive from the alcohol-soluble gliadin fraction. For some of these epitopes, specific T cells can be isolated from intestinal biopsies from nearly all patients, whereas for others, T-cell reactivity could be demonstrated in only a few patients. One reason for this observation could be that the rate of transglutaminase 2 (TG2)-mediated deamidation significantly differs between these peptides, resulting in different amounts of epitopes generated in vivo. In this study, we established a quantitative, mass spectrometry-based approach to measure the kinetics of TG2-mediated deamidation of gliadin-derived, DQ2-restricted epitopes. Our results demonstrate large variations in the degree of deamidation between different peptides and also between individual glutamine residues within each peptide. In general, alpha-gliadin derived epitopes that are frequently recognized by patient T cells showed a significant higher level of deamidation compared to the majority of epitopes from gamma-gliadin that are less frequently recognized. The degree of deamidation of individual residues within a peptide also seems to influence whether some epitopes are better recognized in context of DO2 or DQ8. Thus, the rate of deamidation by TG2 appears to be a factor of importance for the T-cell response to gluten in celiac disease.
authors.affiliation: Centre for Immune Regulation, Institute of Immunology, University of Oslo, and Rikshospitalet University Hospital, N-0027 Oslo, Norway. siri.dorum@rr-research.no
authors.forename: Siri
authors.initials: S
authors.lastname: Dørum
authors.forename: Shuo-Wang
authors.initials: SW
authors.lastname: Qiao
authors.forename: Ludvig M
authors.initials: LM
authors.lastname: Sollid
authors.forename: Burkhard
authors.initials: B
authors.lastname: Fleckenstein
mesh_terms: D000595:Amino Acid Sequence; D002446:Celiac Disease / Q000378:metabolism*; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D019204:GTP-Binding Proteins / Q000494:pharmacology / Q000502:physiology*; D005903:Gliadin / Q000276:immunology; D005983:Glutens / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis / Q000378:metabolism*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology*; D053719:Tandem Mass Spectrometry; D011503:Transglutaminases / Q000494:pharmacology / Q000502:physiology*
chemical_list: D018984:Epitopes, T-Lymphocyte; D010455:Peptides; D011994:Recombinant Proteins; D005983:Glutens; D005903:Gliadin; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins