Bacillus subtilis glutamine synthetase regulates its own synthesis by acting as a chaperone to stabilize GInR-DNA complexes
Bacillus subtilis glutamine synthetase regulates its own synthesis by acting as a chaperone to stabilize GInR-DNA complexes
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DOI：
10.1073/pnas.0709949105
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发表时间：
2008-01-22
影响因子：
11.1
通讯作者：
Wray, Lewis V., Jr.
中科院分区：
文献类型：
--
作者：
Fisher, Susan H.;Wray, Lewis V., Jr.
枯草芽孢杆菌GlnR阻遏物响应于氮可用性控制基因表达。因为所有GInR调节的基因在缺乏谷氨酰胺合成酶（GS）的突变体中组成型表达，所以GS是GInR阻遏所必需的。反馈抑制GS（FBI-GS）显示激活GInR DNA结合与体外电泳迁移率变动分析（EMSA）。在这些实验中，GS对GInR DNA结合的激活依赖于反馈抑制剂谷氨酰胺，并且在体内调节GM活性有缺陷的突变GS蛋白质中不会发生。虽然在EMSA实验中没有观察到稳定的GS-GInR-DNA三元复合物，但交联实验表明GInR和FBI-GS之间发生了蛋白质-蛋白质相互作用。在不存在反馈抑制剂谷氨酰胺和突变GS蛋白的情况下，这种相互作用减少。由于FBI-GS显著降低了GInR-DNA复合物的解离速率，因此FBI-GS增强了这些复合物的稳定性。这些结果表明，FBI-GS作为一种伴侣，通过短暂的蛋白质-蛋白质相互作用激活Grill DNA结合，稳定GInR-DNA复合物。GS控制着B的活性。通过在FBI-GS和TnrA之间形成抑制TnrA DNA结合的稳定复合物来抑制枯草杆菌氮转录因子TnrA。因此，B。枯草芽孢杆菌GS是具有双重催化和调节功能的酶，其使用不同的机制来控制两种不同转录因子的活性。
The Bacillus subtilis GlnR repressor controls gene expression in response to nitrogen availability. Because all GInR-regulated genes are expressed constitutively in mutants lacking glutamine synthetase (GS), GS is required for repression by GInR. Feedback-inhibited GS (FBI-GS) was shown to activate GInR DNA binding with an in vitro electophoretic mobility shift assay (EMSA). The activation of GInR DNA binding by GS in these experiments depended on the feedback inhibitor glutamine and did not occur with mutant GS proteins defective in regulating GM activity in vivo. Although stable GS-GInR-DNA ternary complexes were not observed in the EMSA experiments, cross-linking experiments showed that a protein-protein interaction occurs between GInR and FBI-GS. This interaction was reduced in the absence of the feedback inhibitor glutamine and with mutant GS proteins. Because FBI-GS significantly reduced the dissociation rate of the GInR-DNA complexes, the stability of these complexes is enhanced by FBI-GS. These results argue that FBI-GS acts as a chaperone that activates Grill DNA binding through a transient protein-protein interaction that stabilizes GInR-DNA complexes. GS was shown to control the activity of the B. subtilis nitrogen transcription factor TnrA by forming a stable complex between FBI-GS and TnrA that inhibits TnrA DNA binding. Thus, B. subtilis GS is an enzyme with dual catalytic and regulatory functions that uses distinct mechanisms to control the activity of two different transcription factors.