School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Beijing Royal School, Beijing 102209, China.
Toxins (Basel). 2022 Aug 31;14(9):602. doi: 10.3390/toxins14090602.
Cyanobacterial hepatotoxins, including microcystins (MCs) and nodularins (NODs), are widely produced, distributed and extremely hazardous to human beings and the environment. However, the catalytic mechanism of microcystinase for biodegrading cyanobacterial hepatotoxins is not completely understood yet. The first microcystinase (MlrA) catalyzes the ring opening of cyclic hepatotoxins, while being further hydrolyzed by the third microcystinase (MlrC). Based on the homology modeling, we postulated that MlrC of sp. USTB-05 was a Zn-dependent metalloprotease including five active sites: Glu56, His150, Asp184, His186 and His208. Here, the active recombinant MlrC and five site-directed mutants were successfully obtained with heterologous expression and then purified for investigating the activity. The results indicated that the purified recombinant MlrC had high activity to catalyze linearized hepatotoxins. Combined with the biodegradation of linearized NOD by MlrC and its mutants, a complete enzymatic mechanism for linearized hepatotoxin biodegradation by MlrC was revealed.
蓝藻肝毒素，包括微囊藻毒素（MCs）和节球藻毒素（NODs），广泛存在且分布广泛，对人类和环境具有极大的危害性。然而，微囊藻酶降解蓝藻肝毒素的催化机制尚未完全阐明。第一种微囊藻酶（MlrA）催化环状肝毒素的开环，然后被第三种微囊藻酶（MlrC）进一步水解。基于同源建模，我们推测 sp.USTB-05 的 MlrC 是一种 Zn 依赖性金属蛋白酶，包含五个活性位点：Glu56、His150、Asp184、His186 和 His208。在这里，通过异源表达成功获得了活性重组 MlrC 和五个定点突变体，并进行了纯化以研究其活性。结果表明，纯化的重组 MlrC 对线性化肝毒素具有很高的催化活性。结合 MlrC 及其突变体对线性化 NOD 的生物降解作用，揭示了 MlrC 线性肝毒素生物降解的完整酶促机制。
