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Open AccessArticle

Comprehensive Detection of Isopeptides between Human Tissue Transglutaminase and Gluten Peptides

1
Leibniz-Institute for Food Systems Biology at the Technical University of Munich, Lise-Meitner-Str. 34, 85354 Freising, Germany
2
Bavarian Center for Biomolecular Mass Spectrometry (BayBioMS), Technical University of Munich, Gregor-Mendel-Str. 4, 85354 Freising, Germany
3
Department of Bioactive and Functional Food Chemistry, Institute of Applied Biosciences, Karlsruhe Institute of Technology (KIT), Adenauerring 20a, 76131 Karlsruhe, Germany
*
Author to whom correspondence should be addressed.
Nutrients 2019, 11(10), 2263; https://doi.org/10.3390/nu11102263
Received: 12 August 2019 / Revised: 3 September 2019 / Accepted: 15 September 2019 / Published: 20 September 2019
(This article belongs to the Special Issue Dietary Intake and Gluten-Associated Disease)
Celiac disease (CD) is a chronic inflammation of the small intestine triggered by the ingestion of gluten in genetically predisposed individuals. Tissue transglutaminase (TG2) is a key factor in CD pathogenesis, because it catalyzes both the deamidation of specific glutamine residues and the formation of covalent Nε-(γ-glutamyl)-lysine isopeptide crosslinks resulting in TG2–gluten peptide complexes. These complexes are thought to activate B cells causing the secretion of anti-TG2 autoantibodies that serve as diagnostic markers for CD, although their pathogenic role remains unclear. To gain more insight into the molecular structures of TG2-gluten peptide complexes, we used different proteomics software tools that enable the comprehensive identification of isopeptides. Thus, 34 different isopeptides involving 20 TG2 lysine residues were identified in a model system, only six of which were previously known. Additionally, 36 isopeptides of TG2-TG2 multimers were detected. Experiments with different TG2-gluten peptide molar ratios revealed the most preferred lysine residues involved in isopeptide crosslinking. Expanding the model system to three gluten peptides with more glutamine residues allowed the localization of the preferred glutamine crosslinking sites. These new insights into the structure of TG2-gluten peptide complexes may help clarify the role of extracellular TG2 in CD autoimmunity and in other inflammatory diseases. View Full-Text
Keywords: celiac disease; crosslink; deamidation; gliadin; gluten; isopeptides; LC-MS/MS; tissue transglutaminase; transamidation celiac disease; crosslink; deamidation; gliadin; gluten; isopeptides; LC-MS/MS; tissue transglutaminase; transamidation
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Lexhaller, B.; Ludwig, C.; Scherf, K.A. Comprehensive Detection of Isopeptides between Human Tissue Transglutaminase and Gluten Peptides. Nutrients 2019, 11, 2263.

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