Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Biochemistry. 2011 Apr 19;50(15):3095-106. doi: 10.1021/bi101683a. Epub 2011 Mar 23.
Transporter ProP mediates osmolyte accumulation in Escherichia coli cells exposed to high osmolality media. The cytoplasmic ProQ protein amplifies ProP activity by an unknown mechanism. The N- and C-terminal domains of ProQ are predicted to be structurally similar to known RNA chaperone proteins FinO and Hfq from E. coli. Here we demonstrate that ProQ is an RNA chaperone, binding RNA and facilitating both RNA strand exchange and RNA duplexing. Experiments performed with the isolated ProQ domains showed that the FinO-like domain serves as a high-affinity RNA-binding domain, whereas the Hfq-like domain is largely responsible for RNA strand exchange and duplexing. These data suggest that ProQ may regulate ProP production. Transcription of proP proceeds from RpoD- and RpoS-dependent promoters. Lesions at proQ affected ProP levels in an osmolality- and growth phase-dependent manner, decreasing ProP levels when proP was expressed from its own chromosomal promoters or from a heterologous plasmid-based promoter. Small RNA molecules are known to regulate cellular levels of sigma factor RpoS. ProQ did not act by changing RpoS levels since proQ lesions did not influence RpoS-dependent stationary phase thermotolerance and they affected ProP production and activity similarly in bacteria without and with an rpoS defect. Taken together, these results suggest that ProQ does not regulate proP transcription. It may act as an RNA-binding protein to regulate proP translation.
转运蛋白 ProP 介导了高渗透压介质中大肠杆菌细胞的渗透溶质积累。细胞质 ProQ 蛋白通过未知机制放大 ProP 活性。ProQ 的 N 端和 C 端结构域预计与大肠杆菌中已知的 RNA 伴侣蛋白 FinO 和 Hfq 在结构上相似。在这里，我们证明 ProQ 是一种 RNA 伴侣，结合 RNA 并促进 RNA 链交换和 RNA 双链形成。使用分离的 ProQ 结构域进行的实验表明，FinO 样结构域作为高亲和力 RNA 结合结构域，而 Hfq 样结构域主要负责 RNA 链交换和双链形成。这些数据表明 ProQ 可能调节 ProP 的产生。ProP 的转录由 RpoD 和 RpoS 依赖性启动子进行。ProQ 中的突变以渗透压和生长阶段依赖的方式影响 ProP 水平，当 ProP 从其自身的染色体启动子或异源基于质粒的启动子表达时，降低 ProP 水平。已知小分子 RNA 调节细胞中 sigma 因子 RpoS 的水平。ProQ 没有通过改变 RpoS 水平来发挥作用，因为 ProQ 中的突变不会影响 RpoS 依赖性静止期耐热性，并且它们在没有和有 rpoS 缺陷的细菌中以相似的方式影响 ProP 的产生和活性。总之，这些结果表明 ProQ 不调节 proP 转录。它可能作为一种 RNA 结合蛋白来调节 proP 翻译。
