Overexpression and characterization of cyprosin B in transformed suspension cells of Cynara cardunculus

Cynara cardunculus suspension cells were transformed by particle bombardment to overexpress the cypro11 gene coding for cyprosin B. Green fluorescent protein, used as a visual reporter through mgfp4-ER gene, facilitates the screening of transformed cells at the initial stages when antibiotics cause generalized cell death. mgfp4-ER lacks a cryptic intron and has an endoplasmic reticulum target sequence, these traits conferring an adequate use as screenable marker for transformed cells. Selected transformed cells, grown in a bioreactor, produced 3.8 g dcw l⁻¹ of biomass, 80 mg l⁻¹ of total protein and 2,060 U ml⁻¹ of enzymatic activity. Specific activity of cyprosin B, purified by anionic-exchange chromatography, was 215 U mg⁻¹ with a purification degree of 8.3-fold. The cyprosin B activity is optimal at 42°C for pH 5.1 and is inhibited by pepstatin A. The results encourage the overexpression of cypro11 gene in transformed C. cardunculus cells leading to high yields of cyprosin B production in bioreactor, which can be considered adequate for industrial production.