Transcription induction of the ferric citrate transport genes via the N-terminus of the FecA outer membrane protein, the Ton system and the electrochemical potential of the cytoplasmic membrane
Transcription induction of the ferric citrate transport genes via the N-terminus of the FecA outer membrane protein, the Ton system and the electrochemical potential of the cytoplasmic membrane
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DOI：
10.1046/j.1365-2958.1997.2401593.x
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发表时间：
1997-01-01
影响因子：
3.6
通讯作者：
Braun, V
中科院分区：
文献类型：
--
作者：
Kim, I;Stiefel, A;Braun, V
柠檬酸铁诱导柠檬酸铁转运基因 fecABCDE 的转录，但不进入大肠杆菌 K-12 细胞。外膜受体蛋白 FecA 的点突变体在诱导过程中受到影响，与 FecA 转运活性无关，表明 FecA 直接参与诱导。 FecA 与大肠杆菌的其他铁铁载体受体的比对揭示了 FecA 中的 N 末端延伸，而在其合成不是由其同源铁铁载体诱导的受体中未发现这种延伸。在这项研究中，我们发现 N 末端区域的切除消除了 FecA 的诱导活性，但保留了其转运活性。 N 端 FecA 片段的过量产生抑制了 FecA 依赖性诱导，但不抑制转运。由 C 端截短的 FecR 衍生物引起的组成型表达不受 N 端 FecA 片段的抑制。 FecA 的 N 端区域位于周质中，这表明 FecA 可能与 FecR 相互作用，FecR 参与跨细胞质膜的信号转导。 fec 转运基因的转录起始需要由 TonB、ExbB 和 ExbD 组成的 Ton 系统，并受到羰基氰化物间氯苯腙 (CCCP) 和 2,4-二硝基苯酚 (DNP) 的抑制，从而消除细胞质膜的电化学势。突变体 fecA4 的 fec 转录在没有 TonB 的情况下显示出组成型 fec 转录，不受 CCCP 的影响。该数据支持一个模型，该模型提出通过柠檬酸铁与 FecA 结合来启动费用转运基因转录。转录起始信号通过 Ton 系统的活性跨外膜转移，但会牺牲细胞质膜的电化学势。 FecA 的 N 端在周质中与 FecR 的 C 端相互作用，信号通过细胞质膜转移到细胞质中，增加 sigma 因子 Feel 的活性，然后将 RNA 聚合酶引导至 fecA 上游的 fee 启动子。
Ferric citrate induces transcription of the ferric citrate transport genes fecABCDE without entering the cells of Escherichia coli K-12. Point mutants of the outer membrane-receptor protein FecA are affected in induction independent of the FecA transport activity, suggesting that FecA is directly involved in induction. Alignment of FecA with the other ferric siderophore receptors of E. coli reveals an N-terminal extension in FecA that is not found in the receptors whose synthesis is not induced by their cognate ferric siderophores. In this study, we show that excision of the N-terminal region abolished the inducing activity of FecA, but retained its transport activity. Overproduction of the N-terminal FecA fragment inhibited FecA-dependent induction, but not transport. Constitutive expression caused by C-terminally truncated FecR derivatives was not inhibited by the N-terminal FecA fragment. The N-terminal region of FecA was localized in the periplasm, which indicates that FecA probably interacts with FecR, which is involved in signal transduction across the cytoplasmic membrane. Transcription initiation of the fec transport genes required the Ton system, consisting of TonB, ExbB, and ExbD, and was inhibited by carbonylcyanide-m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), which dissipate the electrochemical potential of the cytoplasmic membrane. fec transcription of mutant fecA4, which displays constitutive fee transcription in the absence of TonB, was not affected by CCCP. The data support a model that proposes initiation of fee transport gene transcription by binding of ferric citrate to FecA. The transcription initiation signal is transferred across the outer membrane through the activity of the Ton system at the expense of the electrochemical potential of the cytoplasmic membrane. The N-terminus of FecA interacts in the periplasm with the C-terminus of FecR, through which the signal is transferred across the cytoplasmic membrane into the cytoplasm, where it increases the activity of the sigma factor Feel, which then directs the RNA polymerase to the fee promoter upstream of fecA.