Comprehensive Detection of Isopeptides between Human Tissue Transglutaminase and Gluten Peptides.

Lexhaller Lexhaller,Ludwig Ludwig,Scherf Scherf

doi:10.3390/nu11102263

Abstract

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.

Highlights

Celiac disease (CD) is one of the most frequent food hypersensitivities with a global seroprevalence of 1.4% and a biopsy-confirmed prevalence of 0.7% [1]
In this study we used a workflow with the proteomics tool MaxQuant, its integrated search engine Andromeda and Skyline as well as the crosslinking software tool pLink2 to identify isopeptides between TG2 and gluten-derived model peptides
We identified 34 isopeptides with 20 different lysine residues as crosslinking sites. Six of these crosslinking sites were already known as TG2-gluten peptide binding sites [17] and eleven as lysine residues involved in TG2 multimer self-crosslinking [18]

Summary

Introduction

Celiac disease (CD) is one of the most frequent food hypersensitivities with a global seroprevalence of 1.4% and a biopsy-confirmed prevalence of 0.7% [1]. This chronic immune-mediated enteropathy of the small intestine is triggered by the ingestion of storage proteins (gluten) from wheat, rye, and barley in genetically predisposed individuals [2]. Most CD patients (≈90%) carry the HLA-DQ2.5 allele and the remaining patients carry the HLA-DQ8 or HLA-DQ2.2 alleles These class II molecules are expressed on the surface of B cells and antigen-presenting cells and bind gluten peptides.

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Conclusion