A single conformational transglutaminase 2 epitope contributed by three domains is critical for celiac antibody binding and effects

Abstract

The multifunctional, protein cross-linking transglutaminase 2 (TG2) is the main autoantigen in celiac disease, an autoimmune disorder with defined etiology. Glutamine-rich gliadin peptides from ingested cereals, after their deamidation by TG2, induce T-lymphocyte activation accompanied by autoantibody production against TG2 in 1-2% of the population. The pathogenic role and exact binding properties of these antibodies to TG2 are still unclear. Here we show that antibodies from different celiac patients target the same conformational TG2 epitope formed by spatially close amino acids of adjacent domains. Glu153 and 154 on the first alpha-helix of the core domain and Arg19 on first alpha-helix of the N-terminal domain determine the celiac epitope that is accessible both in the closed and open conformation of TG2 and dependent on the relative position of these helices. Met659 on the C-terminal domain also can cooperate in antibody binding. This composite epitope is diseasespecific, recognized by antibodies derived from celiac tissues and associated with biological effects when passively transferred from celiac mothers into their newborns. These findings suggest that celiac antibodies are produced in a surface-specific way for which certain homology of the central glutamic acid residues of the TG2 epitope with deamidated gliadin peptides could be a structural basis. Monoclonal mouse antibodies with partially overlapping epitope specificity released celiac antibodies from patient tissues and antagonized their harmful effects in cell culture experiments. Such antibodies or similar specific competitors will be useful in further functional studies and in exploring whether interference with celiac antibody actions leads to therapeutic benefits.conformational epitope | endomysial antibodies | immunotherapy

Antibody biomarker discovery through in vitro directed evolution of consensus recognition epitopes

“…Interestingly, the immunodominant B-cell epitopes were highly similar to recently elucidated immunodominant T-cell epitopes (27). We did not observe linear B-cell epitopes derived from the CD-specific autoantigen TG2, which is consistent with the proposed existence of immundominant structural epitopes within TG2 (28). However, we cannot rule out the possibility that lower-abundance linear epitopes or structural mimotopes were enriched during library screening but outcompeted by DGP and D S / T FV Y / F Q peptides.…”

Activity-regulating structural changes and autoantibody epitopes in transglutaminase 2 assessed by hydrogen/deuterium exchange

“…We previously reported that epitope 2 can be disrupted by introduction of the triple mutation R19S E153S M659S (30). This triple mutation was first described by SimonVecsei et al, who showed that it inhibits the binding of serum antibodies from celiac disease patients (31). Of the residues that were mutated in the previous study, Arg19 is located within the peptide we identified as an epitope-2 candidate by HDX-MS. We therefore tested the effect of the R19S mutation on mAb 2Q3Z) and the closed conformation (PDB ID code 1KV3) crystal structure, containing bound peptide inhibitor and GDP, respectively (bound molecules are shown in red stick representation).…”

Transglutaminase 2-specific coeliac disease autoantibodies induce morphological changes and signs of inflammation in the small-bowel mucosa of mice

“…Several factors might account for this difference. Firstly, the current study was performed by injecting TG2-specific autoantibodies targeting a single previously identified classical coeliac epitope, while autoantibodies against an additional three major TG2-epitopes also exist in coeliac patients (Iversen et al 2013;Simon-Vecsei et al 2012). Secondly, even though not reported, DGP-antibodies were found in the majority of the mice injected with coeliac patient-derived sera or immunoglobulins in the previous study, and also other antibody populations in addition to the TG2-antibodies were very likely present in the injections.…”