Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
NODAI Genome Research Center, Tokyo University of Agriculture, Tokyo, Japan.
Mol Microbiol. 2020 Jun;113(6):1155-1169. doi: 10.1111/mmi.14484. Epub 2020 Feb 25.
In bacteria, guanosine (penta)tetra-phosphate ([p]ppGpp) is essential for controlling intracellular metabolism that is needed to adapt to environmental changes, such as amino acid starvation. The (p)ppGpp strain of Bacillus subtilis, which lacks (p)ppGpp synthetase, is unable to form colonies on minimal medium. Here, we found suppressor mutations in the (p)ppGpp strain, in the purine nucleotide biosynthesis genes, prs, purF and rpoB/C, which encode RNA polymerase core enzymes. In comparing our work with prior studies of ppGpp suppressors, we discovered that methionine addition masks the suppression on minimal medium, especially of rpoB/C mutations. Furthermore, methionine addition increases intracellular GTP in rpoB suppressor and this effect is decreased by inhibiting GTP biosynthesis, indicating that methionine addition activated GTP biosynthesis and inhibited growth under amino acid starvation conditions in (p)ppGpp backgrounds. Furthermore, we propose that the increase in intracellular GTP levels induced by methionine is due to methionine derivatives that increase the activity of the de novo GTP biosynthesis enzyme, GuaB. Our study sheds light on the potential relationship between GTP homeostasis and methionine metabolism, which may be the key to adapting to environmental changes.
在细菌中，鸟苷（五）四磷酸（[p]ppGpp）对于控制细胞内代谢至关重要，这种代谢是适应环境变化所必需的，例如氨基酸饥饿。芽孢杆菌缺乏（p）ppGpp 合成酶的菌株无法在最小培养基上形成菌落。在这里，我们在嘌呤核苷酸生物合成基因 prs、purF 和 rpoB/C 中发现了（p）ppGpp 菌株的抑制突变，这些基因编码 RNA 聚合酶核心酶。在将我们的工作与先前的 ppGpp 抑制剂研究进行比较时，我们发现添加蛋氨酸掩盖了最小培养基上的抑制作用，尤其是 rpoB/C 突变的抑制作用。此外，添加蛋氨酸会增加 rpoB 抑制剂中细胞内 GTP 的含量，而抑制 GTP 生物合成会降低这种效果，表明添加蛋氨酸激活了 GTP 生物合成，并抑制了（p）ppGpp 背景下氨基酸饥饿条件下的生长。此外，我们提出，蛋氨酸诱导的细胞内 GTP 水平增加是由于蛋氨酸衍生物增加了从头合成 GTP 的酶 GuaB 的活性。我们的研究揭示了 GTP 动态平衡和蛋氨酸代谢之间可能存在的潜在关系，这可能是适应环境变化的关键。
