FtsH proteases (FtsHs) belong to intramembrane ATP-dependent metalloproteases which are widely distributed in eubacteria, mitochondria, and chloroplasts. The best studied role of FtsH in Escherichia coli includes quality control of membrane proteins, regulation of response to heat shock, superoxide stress and viral infection, and control of lipopolysaccharide biosynthesis. While heterotrophic bacteria mostly contain a single indispensable FtsH complex, the photosynthetic cyanobacteria usually contain three FtsH complexes: two heterocomplexes and one homocomplex. The essential cytoplasmic FtsH1/3 most probably fulfils a role similar to other bacterial FtsHs whereas the thylakoid FtsH2/3 heterocomplex and FtsH4 homocomplex appear to maintain the photosynthetic apparatus of cyanobacteria and optimize its functionality. Moreover, recent studies suggested involvement of all FtsH proteases in a complex response to nutrient stresses. In this review, we aim to comprehensively review the functions of the cyanobacterial FtsH complexes specifically under stress conditions with emphasis on nutrient deficiency and high irradiance. We also point to various unresolved issues concerning the FtsH functions, which deserve further attention.

中文翻译：

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FtsH 复合物在蓝藻非生物胁迫响应中的作用

FtsH蛋白酶（FtsHs）属于膜内ATP依赖性金属蛋白酶，广泛分布于真细菌、线粒体和叶绿体中。 FtsH 在大肠杆菌中研究最多的作用包括膜蛋白的质量控制、热休克反应的调节、超氧化物应激和病毒感染以及脂多糖生物合成的控制。异养细菌大多含有一个不可或缺的 FtsH 复合物，而光合蓝细菌通常含有三个 FtsH 复合物：两个异源复合物和一个同源复合物。必需的细胞质 FtsH1/3 最有可能发挥与其他细菌 FtsH 类似的作用，而类囊体 FtsH2/3 异质复合物和 FtsH4 同质复合物似乎维持蓝细菌的光合作用装置并优化其功能。此外，最近的研究表明所有 FtsH 蛋白酶都参与对营养胁迫的复杂反应。在这篇综述中，我们的目标是全面综述蓝藻 FtsH 复合物的功能，特别是在胁迫条件下，重点是营养缺乏和高辐照度。我们还指出了有关 FtsH 功能的各种尚未解决的问题，值得进一步关注。