Department of Microbiology, Cornell University, Ithaca, New York, USA.
Department of Microbiology, Cornell University, Ithaca, New York, USA
J Bacteriol. 2020 Mar 26;202(8). doi: 10.1128/JB.00697-19.
The physiological relevance of bacterial iron efflux has only recently been appreciated. The P-type ATPase PfeT (eroxide-induced errous fflux ransporter) was one of the first iron efflux pumps to be characterized, and cells lacking accumulate high levels of intracellular iron. The promoter region has binding sites for both PerR, a peroxide-sensing Fur-family metalloregulator, and the ferric uptake repressor Fur. Both Fur and PerR bind DNA with Fe(II) as a cofactor. While reaction of PerR-Fe(II) with peroxide can account for the induction of under oxidative stress, binding of Fur-Fe(II) would be expected to lead to repression, which is inconsistent with the known role of PfeT as an iron efflux protein. Here, we show that expression of is repressed by PerR, as anticipated, and induced by Fur in response to Fe(II). Activation by Fur is mediated both by antagonism of the PerR repressor and by direct transcriptional activation, as confirmed using transcription assays. A similar mechanism of regulation can explain the iron induction of the PfeT ortholog and virulence factor, FrvA. Mutational studies support a model in which Fur activation involves regions both upstream and downstream of the promoter, and Fur and PerR have overlapping recognition of a shared regulatory element in this complex promoter region. This work demonstrates that Fur can function as an iron-dependent activator of transcription. Iron homeostasis plays a key role at the host-pathogen interface during the process of infection. Bacterial growth restriction resulting from host-imposed iron starvation (nutritional immunity) highlights the importance of iron import during pathogenesis. Conversely, bacterial iron efflux pumps function as virulence factors in several systems. The requirement for iron efflux in pathogens such as , , and suggests that both import and efflux are needed for cells to successfully navigate rapidly changing levels of iron availability in the host. Here, we provide insight into how iron efflux genes are controlled, an aspect of bacterial iron homeostasis relevant to infectious disease processes.
细菌铁外排的生理相关性最近才被认识到。P 型 ATP 酶 PfeT（过氧化物诱导的亚铁外流转运蛋白）是最早被表征的铁外排泵之一，缺乏 PfeT 的细胞会积累大量细胞内铁。 启动子区域具有结合位点，一个是 PerR，一种过氧化物感应 Fur 家族金属调节剂，另一个是铁摄取阻遏物 Fur。Fur 和 PerR 都可以用 Fe(II)作为辅助因子结合 DNA。虽然 PerR-Fe(II)与过氧化物的反应可以解释氧化应激下 的诱导，但 Fur-Fe(II)的结合预计会导致抑制，这与 PfeT 作为铁外排蛋白的已知作用不一致。在这里，我们表明，如预期的那样， 受 PerR 抑制，受 Fur 诱导，对 Fe(II)作出反应。通过 Fur 的激活是通过拮抗 PerR 抑制剂和直接转录激活来介导的，这一点通过 使用 转录测定得到了证实。类似的调控机制可以解释 PfeT 同源物和毒力因子 FrvA 的铁诱导。突变研究支持这样一种模型，即 Fur 激活涉及 启动子上下游的区域，Fur 和 PerR 对这个复杂启动子区域的共享调节元件具有重叠的识别。这项工作表明，Fur 可以作为转录的铁依赖性激活因子发挥作用。铁稳态在感染过程中的宿主-病原体界面起着关键作用。宿主施加的铁饥饿（营养免疫）导致细菌生长受限，突出了发病机制中铁导入的重要性。相反，细菌铁外排泵在几个系统中作为毒力因子发挥作用。铁外排对 、 和 等病原体的要求表明，细胞需要铁导入和铁外排才能成功应对宿主中快速变化的铁可用性水平。在这里，我们深入了解了铁外排基因是如何被控制的，这是与传染病过程相关的细菌铁稳态的一个方面。
