Glycogen storage disease type III (GSDIII or Cori/Forbes disease) is a rare metabolic disorder due to the deficiency of the Glycogen Debranching Enzyme (GDE). This is a large monomeric protein (about 170 kDa) with two distinct enzymatic activities: 4-α-glucantransferase and amylo-α-1,6-glucosidase. We have expressed the human GDE gene in bacteria, plants and in vitro root cultures (Lycopersicon esculentum, Micro-Tom). In particular, GDE was purified under native conditions from the soluble fraction of bacteria and from leaves of Nicotiana benthamiana. Specific tests have shown that the recombinant enzyme, produced from the various systems, holds glycogen debranching activity, and is able to release glucose molecules. In particular, the enzyme purified from bacteria was found to be enzymatically active after lyophilization and after storage at 4° C for more than one year.
The production of recombinant pharmaceuticals through plant biotechnology (Molecular Pharming) represents an opportunity to get improved, safe and cheaper biotherapeutics. The first plant biotechnology-derived biopharmaceutical approved for the market (2012) was an enzyme used for ERT of Gaucher disease, a rare heritable disorder (Protalix Biotherapeutics/ Pfizer.) This biopharmaceutical has been demonstrated to have superior efficacy, at lower cost, compared to that produced in other expression systems.
Although, at the moment, the unique treatment for GSDIII is based only on diet, ERT with recombinant GDE represents a conceivable therapeutic strategy. In particular, the production of GDE in plant tissues (roots) opens the way for the exploration of an oral ERT. Indeed, recent evidence indicates that the plant cell wall protects a biopharmaceutical from digestion/degradation in the gastrointestinal tract, increasing the bioavailability of a recombinant enzyme. In addition, since GDE has been recently recognized as a 'tumour suppressor', this might open new scenarios for its therapeutic use. Finally, being this enzyme able to bind phthalates, it is conceivable the use of the recombinant GDE for toxicological purposes (e.g. biosensor development).