The CpxQ sRNA Negatively Regulates Skp To Prevent Mistargeting of β-Barrel Outer Membrane Proteins into the Cytoplasmic Membrane.
The CpxQ sRNA Negatively Regulates Skp To Prevent Mistargeting of β-Barrel Outer Membrane Proteins into the Cytoplasmic Membrane.
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DOI：
10.1128/mbio.00312-16
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发表时间：
2016-04-05
期刊：
影响因子：
6.4
通讯作者：
Silhavy TJ
中科院分区：
文献类型：
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作者：
Grabowicz M;Koren D;Silhavy TJ
在Cpx双组分包膜应激反应活化后诱导最强烈的启动子是cpxP启动子。cpxP转录物的3′非转录区（UTR）显示产生小RNA（sRNA）CpxQ。我们研究了CpxQ在对抗包络应力中的作用。值得注意的是，转录物指定的两种效应物被部署来对抗不同细胞区室中的不同压力。CpxP在调节负反馈环和作为对抗周质蛋白错误折叠的效应器两者中起作用。我们发现CpxQ通过下调周质伴侣Skp的合成来对抗内膜（IM）的毒性。我们的数据表明，这种调节阻止Skp将β-桶外膜蛋白（OMP）插入IM，这是一种可能破坏质子动力的致命事件。我们的研究结果表明，Skp可以折叠，并直接插入OMPs到脂质双层在体内没有援助的BAM复合物。Skp是一种充分表征的结合未折叠OMP的周质伴侣。令人惊讶的是，我们发现Skp可以催化OMPs折叠和错误定位到内膜中，而不需要通常组装OMPs的其他细胞蛋白的帮助。几种OMP起到扩散孔的作用。因此，它们的错误定位是致命的，因为它使内膜去极化。我们发现，Cpx应激反应的最高表达转录本从3′ UTR产生一种sRNA，CpxQ，它通过下调Skp的产生来对抗这种潜在的毒性。OMP组装中的缺陷触发σE响应以上调促进OMP折叠的因子，包括Skp。Cpx反应下调σE。我们的发现揭示了这个迄今为止令人困惑的层次结构是为了保护内膜而存在的。
The promoter most strongly induced upon activation of the Cpx two-component envelope stress response is the cpxP promoter. The 3′ untranscribed region (UTR) of the cpxP transcript is shown to produce a small RNA (sRNA), CpxQ. We investigated the role of CpxQ in combating envelope stress. Remarkably, the two effectors specified by the transcript are deployed to combat distinct stresses in different cellular compartments. CpxP acts in both a regulatory negative-feedback loop and as an effector that combats periplasmic protein misfolding. We find that CpxQ combats toxicity at the inner membrane (IM) by downregulating the synthesis of the periplasmic chaperone Skp. Our data indicate that this regulation prevents Skp from inserting β-barrel outer membrane proteins (OMPs) into the IM, a lethal event that likely collapses the proton motive force. Our findings suggest that Skp can fold and directly insert OMPs into a lipid bilayer in vivo without the aid of the Bam complex. Skp is a well-characterized periplasmic chaperone that binds unfolded OMPs. Surprisingly, we find that Skp can catalyze the folding and mistargeting of OMPs into the inner membrane without the aid of the other cellular proteins that normally assemble OMPs. Several OMPs function as diffusion pores. Accordingly, their mistargeting is lethal because it depolarizes the inner membrane. We show that the most highly expressed transcript of the Cpx stress response produces an sRNA from the 3′ UTR, CpxQ, which combats this potential toxicity by downregulating Skp production. Defects in OMP assembly trigger the σE response to upregulate factors, including Skp, that promote OMP folding. The Cpx response downregulates σE. Our findings reveal that this heretofore puzzling hierarchy exists to protect the inner membrane.