Recombinant human tissue transglutaminase produced into tobacco suspension cell cultures is active and recognizes autoantibodies in the serum of coeliac patients

Human tissue transglutaminase (htTG) is one of the most important member within the transglutaminase family, enzymes that for their capacity of catalyzing post-translational modifications of proteins and peptides, rise an high interest for industrial applications. More recently, for its implication as the major autoantigen in the coeliac disease, availability of human tissue transglutaminase as recombinant form is required for accurate diagnostic tests. The aim of this study was to find an alternative and inexpensive source to produce human tissue transglutaminase. To date, plant systems are proposed as heterologous hosts to produce recombinant proteins for use in disease diagnosis and therapy. Here, we describe the stable expression of human tissue transglutaminase into Nicotiana tabacum cultured cells (cultivar Bright Yellow 2 (BY-2)). The recombinant enzyme was successfully expressed in different plant cell compartments and both apoplast (apo) and chloroplast (chl) purified proteins were shown to be catalytically active and able to bind GTP, a property possessed by the natural counterpart. Importantly, plant produced human tissue transglutaminase recognized autoantibodies in the serum of coeliac patients, suggesting possible applications in the diagnosis of coeliac disease.