How Molecular Chaperones Promote Pathogen Survival During Starvation

项目总结 所有的生命形式都会合成并维持蛋白质，以执行基本的细胞过程。蛋白质合成 维护和维护需要巨大的能量和资源，包括最丰富的二价镁 活细胞中的阳离子。微生物病原体在哺乳动物巨噬细胞内经常面临营养限制 而且必须恢复蛋白质的动态平衡，才能在宿主组织中持续存在。我建议决定如何 鼠伤寒沙门氏菌兼性胞内致病菌 使用分子伴侣来控制蛋白质的动态平衡，从而使在镁离子期间存活 饿死了。我发现了DNAK的两个新功能，它是一种高度保守的分子伴侣 在营养充足的条件下，在折叠蛋白中与辅伴侣一起发挥作用。首先，我确立了， 令人惊讶的是，DNAK通过与不依赖辅伴侣的核糖体结合来抑制蛋白质合成 当鼠伤寒沙门氏菌的镁离子含量较低时，这种方法可帮助节约能源和资源。 第二，我确定DNAK拮抗典型的核糖体相关的伴侣触发 在低镁离子的情况下，该因子也在新生多肽的共翻译折叠中发挥作用。这就做 现在阐明DNAK取代Trigger的共翻译多肽折叠的机制 在镁饥饿过程中的因素；并确定这一新的DNAK功能的生理益处。这就做 还要研究镁饥饿是如何改变典型的DNAK/DNAJ/GRPE和 作用于现有蛋白质的GroEL/GroES伴侣系统，因为蛋白质稳态不涉及 不仅合成新的蛋白质，而且还维持现有的蛋白质。通过改变这些组织的活动 两个伴侣系统，鼠伤寒沙门氏菌，假设保持某些蛋白质的溶解和活性， 以及其他不能溶解和不起作用的蛋白质。饥饿诱导的向缓慢生长状态的转变使 细菌对抗菌剂具有表型抗药性，阻碍了细菌感染的治愈。这个 这项研究的分子和生理结果将揭示伴侣介导的新的控制 人类病原体的适应性。此外，镁离子依赖性、伴侣和 蛋白质动态平衡使这项研究广泛适用于生命各个领域的不同生物体。

PROJECT SUMMARY All life forms synthesize and maintain proteins to carry out fundamental cell processes. Protein synthesis and maintenance require tremendous energy and resources, including Mg2+, the most abundant divalent cation in living cells. Microbial pathogens often face nutrient limitation inside mammalian macrophages and must restore protein homeostasis to persist in host tissues. I propose to determine how the facultative intracellular pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) uses molecular chaperones to control protein homeostasis, thereby enabling survival during Mg2+ starvation. I discovered two novel functions for DnaK, the highly conserved molecular chaperone that functions with cochaperones in folding proteins under nutrient-replete conditions. First, I established that, surprisingly, DnaK represses protein synthesis by binding ribosomes in a cochaperone-independent manner when S. Typhimurium experiences low Mg2+, thereby helping conserve energy and resources. And second, I determined that DnaK antagonizes the canonical ribosome-associated chaperone Trigger Factor, assuming its role in cotranslational folding of nascent polypeptides also during low Mg2+. I will now elucidate the mechanism by which DnaK takes over cotranslational polypeptide folding from Trigger Factor during Mg2+ starvation; and identify the physiological benefits of this novel DnaK function. I will also examine how Mg2+ starvation changes the balance between the canonical DnaK/DnaJ/GrpE and GroEL/GroES chaperone systems that act on existing proteins because protein homeostasis involves not only synthesis of new proteins but also maintenance of existing proteins. By altering the activities of these two chaperone systems, S. Typhimurium is hypothesized to maintain certain proteins soluble and active, and other proteins insoluble and inactive. The starvation-induced transition to a slow growth state renders bacteria phenotypically resistant to antibacterial agents, hindering the cure of bacterial infections. The molecular and physiological results from this research will reveal novel control of chaperone-mediated adaptations in human pathogens. Moreover, the universal nature of Mg2+ dependence, chaperones, and protein homeostasis makes this study widely applicable to diverse organisms across all domains of life.