A quantitative analysis of transglutaminase 2-mediated deamidation of gluten peptides: implications for the T-cell response in celiac disease

J Proteome Res. 2009 Apr;8(4):1748-55. doi: 10.1021/pr800960n.

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.

MeSH terms

  • Amino Acid Sequence
  • Celiac Disease / metabolism*
  • Epitopes, T-Lymphocyte / immunology*
  • GTP-Binding Proteins / pharmacology
  • GTP-Binding Proteins / physiology*
  • Gliadin / immunology
  • Glutens / immunology*
  • Humans
  • Molecular Sequence Data
  • Peptides / analysis
  • Peptides / metabolism*
  • Protein Glutamine gamma Glutamyltransferase 2
  • Protein Processing, Post-Translational / drug effects
  • Protein Processing, Post-Translational / physiology
  • Recombinant Proteins / metabolism
  • Recombinant Proteins / pharmacology
  • T-Lymphocytes / immunology*
  • Tandem Mass Spectrometry
  • Transglutaminases / pharmacology
  • Transglutaminases / physiology*

Substances

  • Epitopes, T-Lymphocyte
  • Peptides
  • Recombinant Proteins
  • Glutens
  • Gliadin
  • Protein Glutamine gamma Glutamyltransferase 2
  • Transglutaminases
  • GTP-Binding Proteins