Mutagenesis of the catalytic triad of tissue transglutaminase abrogates coeliac disease serum IgA autoantibody binding

Background and aims: Tissue transglutaminase (tTG) is an autoantigen in coeliac disease and the related disorder, dermatitis herpetiformis. The detection of autoantibodies directed against tTG is a highly specific marker of coeliac disease; however, it is unclear if there is a role for these autoantibodies in the disease process. The aim of this study was to investigate whether the catalytic triad of tTG is targeted by coeliac disease autoantibodies. Methods: A full-length wild-type recombinant tTG and a novel site-directed mutagenic variant lacking the catalytic triad were produced in Escherichia coli. Serum samples from 61 biopsy-proven coeliac disease and 10 dermatitis herpetiformis patients were tested for their recognition of both antigens in enzyme-linked immunosorbent assay. Results: Although IgA autoantibodies from sera of patients with coeliac disease and dermatitis herpetiformis bound wild-type tTG well, a dramatic decrease in binding to the mutant tTG was observed with a mean reduction of 79% in coeliac disease and 58% in dermatitis herpetiformis samples. IgG anti-tTG antibodies did not show a similar pattern of reduction, with no overall difference in recognition of the wild-type or mutant tTGs. Conclusions: These results suggest that the IgA anti-tTG response in coeliac disease and dermatitis herpetiformis is focused on the region of tTG responsible for its transamidation and deamidation reactions, whereas the IgG response may target other regions of the enzyme.