Kuroda Akio, Nomura K, Takiguchi N, Kato J, Ohtake H
Department of Molecular Biotechnology, Hiroshima University, Hiroshima, Japan.
Cell Mol Biol (Noisy-le-grand). 2006 Dec 31;52(4):23-9.
Inorganic polyphosphate (polyP) accumulates in response to amino acid starvation in Escherichia coli. Previously, we found that the complex formation of Lon with polyP stimulates proteolysis of free ribosomal proteins. In the current studies, we examined the effects of polyP on the degradation of major nucleoid proteins. Fusions of green fluorescent protein with HimA, Fis, HupA, and HupB were clearly associated with polyP in vivo. Lon degraded His-tagged HimA protein only in the presence of polyP in vitro as well as in vivo. Whereas, when HimA and HimD formed a heterodimer, Lon could not degrade it even in the presence of polyP. In addition, Lon degraded His-tagged Fis protein in the presence of polyP. However, in vivo, Lon did not efficiently degrade the Fis protein even when cells accumulated polyP in response to amino acid starvation. It appears that this is due to tighter binding of Fis to DNA than to polyP and resistance of the DNA-Fis to Lon-mediated proteolysis. Indeed, we found that at least a five-fold excess of polyP was necessary to displace DNA from the DNA-Fis complex. Furthermore, Lon degraded His-tagged HupA protein efficiently in the presence of polyP. We also showed that degradation of the translational initiation factor InfC depends on polyP.
无机多聚磷酸盐（polyP）在大肠杆菌中会因氨基酸饥饿而积累。此前，我们发现Lon与polyP的复合物形成会刺激游离核糖体蛋白的蛋白水解。在当前研究中，我们研究了polyP对主要类核蛋白降解的影响。绿色荧光蛋白与HimA、Fis、HupA和HupB的融合蛋白在体内与polyP明显相关。Lon仅在体外和体内存在polyP的情况下才能降解His标签的HimA蛋白。然而，当HimA和HimD形成异二聚体时，即使存在polyP，Lon也无法降解它。此外，Lon在存在polyP的情况下能降解His标签的Fis蛋白。然而，在体内，即使细胞因氨基酸饥饿而积累polyP，Lon也不能有效地降解Fis蛋白。这似乎是由于Fis与DNA的结合比与polyP的结合更紧密，以及DNA-Fis对Lon介导的蛋白水解具有抗性。事实上，我们发现至少需要五倍过量的polyP才能将DNA从DNA-Fis复合物中置换出来。此外，Lon在存在polyP的情况下能有效地降解His标签的HupA蛋白。我们还表明，翻译起始因子InfC的降解依赖于polyP。
