Role of microcystin in oxidative stress acclimation in the cyanobacterium Microcystis aeruginosa

微囊藻毒素是淡水水华蓝藻产生的一种多肽毒素。环七肽的生物合成是在非核糖体肽合成酶（NRPS）和聚酮酶（PKS）的复合物上实现的。毒素能够与真核蛋白磷酸酶形成共价键。我们可以证明，微囊藻毒素结合到一组蛋白质的半胱氨酸在生产蓝藻微囊藻。有趣的是，结合伴侣包括卡尔文循环的关键酶Rubisco。结合微囊藻毒素强烈增强条件下触发氧化应激。此外，在突变体中缺乏微囊藻毒素导致对氧化应激的敏感性明显增加。总之，这些数据支持微囊藻毒素在天然生产者中的生理功能。我们认为微囊藻毒素具有氧化还原依赖的蛋白调节作用。这将是一个复杂的次级代谢产物的全新功能，可以为其他次级代谢产物的功能提供提示。此外，微囊藻毒素的拟议作用可能反映了生态多样性的氧化胁迫驯化机制在蓝藻。了解微囊藻毒素的作用可以帮助有毒蓝藻的新的管理策略的发展。

Microcystin is a peptide toxin that is produced by various genera of bloom-forming freshwater cyanobacteria. The biosynthesis of the cyclic heptapeptide is achieved on a complex of non-ribosomal peptide synthetases (NRPS) and polyketide synthases (PKS). The toxins are capable of forming a covalent bond to eukaryotic protein phosphatases. We could show that microcystin binds to cysteines of a set of proteins in the producing cyanobacterium Microcystis. Interestingly, the binding partners include the key enzyme of the Calvin cycle, Rubisco. Binding of microcystin is strongly enhanced under conditions triggering oxidative stress. Moreover, the lack of microcystin in the mutant leads to a clear increase in the sensitivity against oxidative stress. Together, these data support a physiological function of microcystin in the natural producer. We suggest a redox-dependent protein-modulating role for microcystin. This would be an entirely new function for a complex secondary metabolite that could provide hints on the functionality of other secondary metabolites. Moreover, the proposed role of microcystin may reflect the ecological diversity of oxidative stress acclimation mechanisms in cyanobacteria. Understanding the role of microcystin can assist in the development of new management strategies of toxic cyanobacteria.