SIGNAL TRANSFER THROUGH 3 COMPARTMENTS - TRANSCRIPTION INITIATION OF THE ESCHERICHIA-COLI FERRIC CITRATE TRANSPORT-SYSTEM FROM THE CELL-SURFACE
SIGNAL TRANSFER THROUGH 3 COMPARTMENTS - TRANSCRIPTION INITIATION OF THE ESCHERICHIA-COLI FERRIC CITRATE TRANSPORT-SYSTEM FROM THE CELL-SURFACE
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DOI：
10.1002/j.1460-2075.1995.tb07129.x
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发表时间：
1995-04-03
期刊：
影响因子：
11.4
通讯作者：
BRAUN, V
中科院分区：
文献类型：
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作者：
HARLE, C;KIM, I;BRAUN, V
柠檬酸铁转运到大肠杆菌K-12细胞中涉及两个能量耦合的转运系统，一个穿过外膜，一个穿过细胞质膜。以前，我们已经表明，柠檬酸铁并不一定要进入大肠杆菌K-12的细胞质，以诱导转录的fec柠檬酸铁转运基因。在这里，我们证明，柠檬酸铁摄取到外和细胞质膜之间的周质空间是不需要fec基因诱导。相反，FecA和TonB，ExbB和ExbD蛋白参与诱导fee转运基因，而不依赖于它们在柠檬酸铁跨外膜转运中的作用。通过孔蛋白通道扩散柠檬酸铁进入fecA和tonB突变体的周质空间的摄取没有诱导fec转运基因的转录。点突变体在FecA中显示的fec转运基因的组成型表达，在柠檬酸铁的情况下，但仍然需要TonB，除了一个FecA突变体显示TonB独立的诱导。FecA突变体的表型表明信号转导机制跨越三个隔室：外膜，周质空间和细胞质膜。该信号在柠檬酸铁与FecA蛋白相互作用后触发。据推测，FecA、TonB、ExbB和ExbD跨外膜传递信号，而调节蛋白FecR跨细胞质膜将信号传递到细胞质中的FecI。FecI作为σ因子，其促进RNA聚合酶与fecA上游的fec转运基因启动子的结合。信号传递可能涉及FecA、FecR和FecI的一系列构象变化。
Transport of ferric citrate into cells of Escherichia coli K-12 involves two energy-coupled transport systems, one across the outer membrane and one across the cytoplasmic membrane. Previously, we have shown that ferric citrate does not have to enter the cytoplasm of E.coli K-12 to induce transcription of the fec ferric citrate transport genes. Here we demonstrate that ferric citrate uptake into the periplasmic space between the outer and the cytoplasmic membranes is not required for fec gene induction. Rather, FecA and the TonB, ExbB and ExbD proteins are involved in induction of the fee transport genes independent of their role in ferric citrate transport across the outer membrane. The uptake of ferric citrate into the periplasmic space of fecA and tonB mutants via diffusion through the porin channels did not induce transcription of fec transport genes. Point mutants in FecA displayed the constitutive expression of fec transport genes in the absence of ferric citrate but still required TonB, with the exception of one FecA mutant which showed a TonB-independent induction. The phenotype of the FecA mutants suggests a signal transduction mechanism across three compartments: the outer membrane, the periplasmic space and the cytoplasmic membrane. The signal is triggered upon the interaction of ferric citrate with FecA protein. It is postulated that FecA, TonB, ExbB and ExbD transfer the signal across the outer membrane, while the regulatory protein FecR transmits the signal across the cytoplasmic membrane to FecI in the cytoplasm. FecI serves as a sigma factor which facilitates binding of the RNA polymerase to the fec transport gene promoter upstream of fecA. Signal transfer presumably involves a sequence of conformational changes in FecA, FecR and FecI.