Variants of the Bacillus subtilis LysR-Type Regulator GltC With Altered Activator and Repressor Function
Variants of the Bacillus subtilis LysR-Type Regulator GltC With Altered Activator and Repressor Function
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DOI：
10.3389/fmicb.2019.02321
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发表时间：
2019-10-09
影响因子：
5.2
通讯作者：
Commichau, Fabian M.
中科院分区：
文献类型：
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作者：
Dormeyer, Miriam;Lentes, Sabine;Commichau, Fabian M.
革兰氏阳性土壤细菌枯草芽孢杆菌依靠谷氨酰胺合成酶和谷氨酸合成酶从氨和2-氧葡萄糖酸酯中合成谷氨酸。在碳源葡萄糖的生长过程中，lysr型转录调节因子GltC激活gltAB谷氨酸合成酶基因的表达。当细胞内谷氨酸过量时，由于谷氨酸脱氢酶（GDHs）抑制GltC， gltAB基因无法转录。先前的体外研究表明，2-氧葡萄糖酸盐和谷氨酸盐分别刺激GltC的激活和抑制功能。在这里，我们分离出具有增强激活或抑制功能的GltC变体。大多数GltC变体具有增强的激活剂功能，对GDHs和谷氨酸的反应不同。在没有GDH的情况下，具有增强抑制功能的GltC变体仍然能够激活PgltA启动子。使用独立于GltC的PgltA启动子变体（PgltA），我们发现野生型GltC和具有增强抑制功能的GltC变体在天然GDHs存在下使PgltA启动子失活。这些发现表明，GltC在体内也可能作为gltAB基因的抑制因子。我们讨论了一个模型结合以前的模型，从体内和体外实验得出。
The Gram-positive soil bacterium Bacillus subtilis relies on the glutamine synthetase and the glutamate synthase for glutamate biosynthesis from ammonium and 2-oxoglutarate. During growth with the carbon source glucose, the LysR-type transcriptional regulator GltC activates the expression of the gltAB glutamate synthase genes. With excess of intracellular glutamate, the gltAB genes are not transcribed because the glutamatedegrading glutamate dehydrogenases (GDHs) inhibit GltC. Previous in vitro studies revealed that 2-oxoglutarate and glutamate stimulate the activator and repressor function, respectively, of GltC. Here, we have isolated GltC variants with enhanced activator or repressor function. The majority of the GltC variants with enhanced activator function differentially responded to the GDHs and to glutamate. The GltC variants with enhanced repressor function were still capable of activating the PgltA promoter in the absence of a GDH. Using PgltA promoter variants (PgltA ) that are active independent of GltC, we show that the wild type GltC and the GltC variants with enhanced repressor function inactivate PgltA promoters in the presence of the native GDHs. These findings suggest that GltC may also act as a repressor of the gltAB genes in vivo. We discuss a model combining previous models that were derived from in vivo and in vitro experiments.