Ribosome-dependent activation of stringent control.
Ribosome-dependent activation of stringent control.
复制标题
严格控制核糖体依赖性激活。
DOI：
10.1038/nature17675
复制
发表时间：
2016-06-09
期刊：
影响因子：
64.8
通讯作者：
Ramakrishnan V
中科院分区：
文献类型：
--
作者：
Brown A;Fernández IS;Gordiyenko Y;Ramakrishnan V
为了生存，细菌不断地感知环境的波动，并对其做出反应。严格的控制代表了细菌对营养饥饿的关键应激反应，导致代谢和转录模式的快速和全面的重新编程。总体而言，与生长和增殖有关的基因转录下调，而那些对生存和毒力至关重要的基因则受到青睐。氨基酸饥饿是通过耗尽氨基酰-tRNA池来感觉的，这导致核糖体在核糖体A位点上积累与非氨基酰化(未带电)的tRNA一起停滞。RelA被招募到停滞的核糖体中，并被激活以合成一种过度磷酸化的鸟苷类似物，(P)ppGpp，它起着多效性第二信使的作用。然而，关于RelA如何识别停滞的核糖体并区别于氨基酰化tRNA的结构信息尚不清楚。在这里，我们提出了RELA的电子冷冻显微镜(CRYO-EM)结构结合到细菌核糖体与未带电的tRNA停滞。结构表明，与翻译因子相比，RELA利用了不同的结合位点，具有包裹在高度扭曲的A-位点tRNA周围的多结构域结构。RELA的TGS结构域与CCA尾部结合，使末端腺苷的自由3‘羟基朝向β-链，从而在该位置上的氨基酰化tRNA将被空间排除。该结构支持一种模型，在该模型中，relA与核糖体的结合抑制了自动抑制，以激活(P)ppGpp的合成并启动严格的反应。由于严格的控制负责病原菌在应激条件下的生存，并有助于慢性感染和抗生素耐药，RELA是开发新型抗菌治疗药物的良好靶点。
In order to survive, bacteria continually sense, and respond to, environmental fluctuations. Stringent control represents a key bacterial stress response to nutrient starvation that leads to a rapid and comprehensive reprogramming of metabolic and transcriptional patterns. In general, transcription of genes for growth and proliferation are down-regulated, while those important for survival and virulence are favored. Amino acid starvation is sensed by depletion of the aminoacyl-tRNA pools, which results in accumulation of ribosomes stalled with non-aminoacylated (uncharged) tRNA in the ribosomal A-site. RelA is recruited to stalled ribosomes, and activated to synthesize a hyperphosphorylated guanosine analog, (p)ppGpp, which acts as a pleiotropic second messenger. However, structural information for how RelA recognizes stalled ribosomes and discriminates against aminoacylated tRNAs is missing. Here, we present the electron cryo-microscopy (cryo-EM) structure of RelA bound to the bacterial ribosome stalled with uncharged tRNA. The structure reveals that RelA utilizes a distinct binding site compared to the translational factors, with a multi-domain architecture that wraps around a highly distorted A-site tRNA. The TGS domain of RelA binds the CCA tail to orient the free 3’ hydroxyl group of the terminal adenosine towards a β-strand, such that an aminoacylated tRNA at this position would be sterically precluded. The structure supports a model where association of RelA with the ribosome suppresses auto-inhibition to activate synthesis of (p)ppGpp and initiate the stringent response. Since stringent control is responsible for the survival of pathogenic bacteria under stress conditions, and contributes to chronic infections and antibiotic tolerance, RelA represents a good target for the development of novel antibacterial therapeutics.