Medical Research Council (MRC) Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College, London SW7 2AZ, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Jun 26;109(26):10546-51. doi: 10.1073/pnas.1201398109. Epub 2012 Jun 11.
The regulation of iron homeostasis is essential for most organisms, because iron is required for a variety of conserved biochemical processes, yet can be toxic at high concentrations. Upon experiencing iron starvation in vitro, the obligate intracellular human pathogen Chlamydia trachomatis exhibits elevated expression of a putative iron-transport system encoded by the ytg operon. The third component of the ytg operon, CT069 (YtgCR), encodes a protein with two distinct domains: a membrane-anchored metal ion permease and a diphtheria toxin repressor (DtxR)-like transcriptional repressor. In this report, we demonstrate that the C-terminal domain of CT069 (YtgR) serves as an iron-dependent autorepressor of the ytg operon. Moreover, the nascent full-length metal permease-transcriptional repressor protein was processed during the course of infection, and heterologously when expressed in Escherichia coli. The products produced by heterologous cleavage in E. coli were functional in the repression of a reporter gene downstream of a putative YtgR operator. We report a bona fide mechanism of iron-dependent regulation of transcription in Chlamydia. Moreover, the unusual membrane permease-DNA-binding polypeptide fusion configuration was found in several bacteria. Therefore, the DNA-binding capability and liberation of the YtgR domain from a membrane-anchored permease in C. trachomatis could represent a previously uncharacterized mechanism for prokaryotic regulation of iron-homeostasis.
铁稳态的调节对于大多数生物体都是至关重要的，因为铁是许多保守生化过程所必需的，但在高浓度下也可能具有毒性。在体外经历缺铁时，专性细胞内病原体沙眼衣原体表现出 ytg 操纵子编码的假定铁转运系统的表达升高。ytg 操纵子的第三个组成部分 CT069（YtgCR）编码一种具有两个不同结构域的蛋白质：一个膜锚定金属离子渗透酶和一个白喉毒素阻遏物（DtxR）样转录阻遏物。在本报告中，我们证明 CT069（YtgR）的 C 末端结构域作为 ytg 操纵子的铁依赖性自身阻遏物。此外，在感染过程中以及在大肠杆菌中异源表达时，新生全长金属渗透酶-转录阻遏物蛋白被加工。在大肠杆菌中异源切割产生的产物可有效抑制报告基因下游假定的 YtgR 操纵子的表达。我们报告了沙眼衣原体中转录的铁依赖性调节的真实机制。此外，在几种细菌中发现了膜渗透酶-DNA 结合多肽融合的特殊构型。因此，C. trachomatis 中从膜锚定渗透酶释放 YtgR 结构域的 DNA 结合能力和释放可能代表原核生物铁稳态调节的先前未表征的机制。
