Bioinformatic analyses and enzymatic properties of microcystinase

Microcystinase (MlrA) is a key protease in the microcystin (MC) degradation pathway identified in bacterial strains. MlrA hydrolyzes the Adda-arginine peptide bond of cyclic MCs, leading to linearized MCs and a significant reduction in the toxicity of cyanobacteria. In this study, the major biological characteristics of this class of enzymes were analyzed by utilizing the amino acid sequence information of MlrA from Sphingopyxis sp. USTB-05. The encoded gene mlrA was expressed heterologously and its enzymatic properties were characterized. The results showed that MlrA has a highly conserved Abi domain, which participates in immunity via degradation of bacteria through MCs and transmits genetic information through horizontal gene transfer. Enzymatic analysis showed that MlrA is a neutral protease (enzyme activity was highest when pH = 7.4), and it had good stability at 40 °C and pH of ~6.2–8.6. In addition, the effects of metal ions on MlrA revealed that Cu2+ and Zn2+ inactivated MlrA. This research expands the knowledge about MC biodegradation and provides broad scope for future research.