Purification and activity of the first recombinant enzyme for biodegrading hepatotoxin by Sphingopyxis sp. USTB-05

Cyanobacterial hepatotoxins which are produced and released by bloom-forming cyanobacteria may threaten the safety of drinking water for human beings and animals. Microcystinase (MlrA) catalyzes the first and most important step for biodegrading hepatotoxic microcystins (MCs) and nodularin (NOD), which hydrolyzes the cyclic hepatotoxin into the linear hepatotoxin as the first product. Here the recombinant MlrA of Sphingopyxis sp. USTB-05 for biodegrading hepatotoxins was firstly purified and its activity was also investigated. The purification process of MlrA was comprised of four steps, affinity purification of glutathione S-transferase (GST)-tagged MlrA, thrombin cleavage of GST tag, GST tag removal and thrombin removal with the benzamidine sepharose. The purified recombinant MlrA was found to have a strong ability to catalyze hepatotoxins, and initial microcystin-LR (MC-LR) of 19.9 mg/L and NOD of 25.2 mg/L were removed within 10 min and 12 h at the protein concentration of 60 mg/L, respectively. The results indicated that the enzyme MlrA with a high activity could be purified and obtained with the biotechnology process of expression and purification described here, which is very important in further studies on the enzyme structure and the enzymatic mechanism for biodegrading hepatotoxins.