Novel biological functions of ppGpp in Escherichia coli

信号分子（p）ppGpp（鸟苷五磷酸或四磷酸）是广泛存在的细菌第二信使。它最为人所知的是警报素，它能提醒细胞饥饿状态，并导致细菌生理学的重大重排。在大肠杆菌中，（p）ppGpp的积累抑制核糖体基因的转录并促进生物合成途径基因的转录。我们发现，（p）ppGpp影响生长速率控制的蛋白水解的至少两个底物的FtsH蛋白酶。底物LpxC是脂多糖（LPS）生物合成所必需的，YfgM是参与应激条件信号传导的膜蛋白。在待测试的候选者中将是已知的和FtsH和Lon蛋白酶的新客户。接下来，我们将讨论蛋白水解是如何协调的（p）ppGpp的存在或不存在。我们将阐明（p）ppGpp是否通过与蛋白酶或底物结合直接起作用，或者是否通过蛋白质因子间接起作用。最后，我们计划建立一个捕获方案，以富集（p）ppGpp结合蛋白和RNA在E。杆菌我们希望提供新的见解（p）ppGpp蛋白水解过程中的作用，特别是进入细菌生理学中的第二信使的中心位置一般。

The signaling molecule (p)ppGpp (guanosine pentaphosphate or tetraphosphate) is a widespread bacterial second messenger. It is best known as alarmone that alerts the cell to starvation conditions and leads to major re-arrangements in bacterial physiology. In Escherichia coli, the accumulation of (p)ppGpp inhibits transcription of ribosomal genes and promotes transcription of genes for biosynthetic pathways. We found that (p)ppGpp affects the growth-rate controlled proteolysis of at least two substrates of the FtsH protease. The substrate LpxC is essential for lipopolysaccharide (LPS) biosynthesis and YfgM is a membrane protein involved in signaling of stress conditions.The first aim of this proposal is to determine whether degradation of other proteins is also affected by (p)ppGpp. Among the candidates to be tested will be known and novel clients of the FtsH and Lon proteases. Next, we will address how proteolysis is coordinated by the absence or presence of (p)ppGpp. We will clarify whether (p)ppGpp acts directly by binding to either the protease or the substrate or whether it acts indirectly by protein factors. Finally, we plan to establish a capture protocol to enrich (p)ppGpp-binding proteins and RNAs in E. coli. We expect to provide new insights into the role of (p)ppGpp in proteolytic processes in particular and into the central position of the second messenger in bacterial physiology in general.