Purification and characterization of recombinant supersweet protein thaumatin II from tomato fruit

• Supersweet thaumatin II identical to native protein was expressed in tomato plants.
• Recombinant thaumatin II was purified from tomato fruit with high purity.
• Thaumatin II was processed similarly in tomato plants and Thaumatococcus daniellii.
• Taste characteristics of recombinant and native thaumatin II were indistinguishable.

Thaumatin, a supersweet protein from the African plant katemfe (Thaumatococcus daniellii Benth.), is a promising zero-calorie sweetener for use in the food and pharmaceutical industries. Due to limited natural sources of thaumatin, its production using transgenic plants is an advantageous alternative. We report a simple protocol for purification of recombinant thaumatin II from transgenic tomato. Thaumatin was extracted from ripe tomato fruit in a low-salt buffer and purified on an SP-Sephacryl column. Recombinant thaumatin yield averaged 50 mg/kg fresh fruit. MALDI-MS analysis showed correct processing of thaumatin in tomato plants. The recombinant thaumatin was indistinguishable from the native protein in a taste test. The purified tomato-derived thaumatin had an intrinsic sweetness with a threshold value in taste tests of around 50 nM. These results demonstrate the potential of an expression system based on transgenic tomato plants for production of recombinant thaumatin for the food and pharmaceutical industries.