Schulz Vladislava, Schmidt-Vogler Christopher, Strohmeyer Phillip, Weber Stefanie, Kleemann Daniel, Nies Dietrich H, Herzberg Martin
Molecular Microbiology, Martin-Luther-University Halle-Wittenberg.
Molecular Microbiology, Martin-Luther-University Halle-Wittenberg
J Bacteriol. 2021 Jun 1;203(11). doi: 10.1128/JB.00052-21. Epub 2021 Mar 8.
In the metallophilic beta-proteobacterium , the plasmid-encoded Czc metal homeostasis system adjusts the periplasmic zinc, cobalt and cadmium concentration, which influences subsequent uptake of these metals into the cytoplasm. Behind this shield, the P-type APTase ZntA is responsible for removal of surplus cytoplasmic zinc ions, thereby providing a second level of defense against toxic zinc concentrations. ZntA is the counterpart to the Zur-regulated zinc uptake system ZupT and other import systems; however, the regulator of expression was unknown. The chromid-encoded gene is adjacent to the genes , which are located on the complementary DNA strand and transcribed from a common promoter region. These genes encode homologs of plasmid pMOL30-encoded Czc components. Candidates for possible regulators of were identified and subsequently tested: CzcI, CzcI, and the MerR-type gene products of the locus tags Rmet_2302, Rmet_0102, Rmet_3456. This led to the identification of Rmet_3456 as ZntR, the main regulator of expression. Moreover, both CzcIs decreased Czc-mediated metal resistance, possibly to avoid "over-excretion" of periplasmic zinc ions, which could result in zinc starvation due to diminished zinc uptake into the cytoplasm. Rmet_2302 was identified as CadR, the regulator of the gene for an important cadmium-exporting P-type ATPase, which provides another system for removal of cytoplasmic zinc and cadmium. Rmet_0102 was not involved in regulation of the metal resistance systems examined here. Thus, ZntR forms a complex regulatory network with CadR, Zur and the CzcIs. Moreover, these discriminating regulatory proteins assign the efflux systems to their particular function.Zinc is an essential metal for numerous organisms from humans to bacteria. The transportome of zinc uptake and efflux systems controls the overall cellular composition and zinc content in a double feed-back loop. Zinc starvation mediates, via the Zur regulator, an up-regulation of the zinc import capacity via the ZIP-type zinc importer ZupT and an amplification of zinc storage capacity, which together raise the cellular zinc content again. On the other hand, an increasing zinc content leads to ZntR-mediated up-regulation of the zinc efflux system ZntA, which decreases the zinc content. Together, the Zur regulon components and ZntR/ZntA balance the cellular zinc content under both high external zinc concentrations and zinc starvation conditions.
在嗜金属β-变形杆菌中，质粒编码的Czc金属稳态系统可调节周质中锌、钴和镉的浓度，这会影响这些金属随后进入细胞质的摄取。在这个保护机制背后，P型ATP酶ZntA负责清除多余的细胞质锌离子，从而提供了抵御有毒锌浓度的第二道防线。ZntA与Zur调控的锌摄取系统ZupT及其他导入系统相对应；然而，其表达调节因子尚不清楚。染色体编码基因与位于互补DNA链上且从共同启动子区域转录的基因相邻。这些基因编码质粒pMOL30编码的Czc组分的同源物。确定并随后测试了可能的调节因子候选物：CzcI、CzcI以及基因座标签为Rmet_2302、Rmet_0102、Rmet_3456的MerR型基因产物。这导致鉴定出Rmet_3456为ZntR，即表达的主要调节因子。此外，两种CzcI均降低了Czc介导的金属抗性，这可能是为了避免周质锌离子的“过度排泄”，过度排泄可能因细胞质对锌摄取减少而导致锌饥饿。Rmet_2302被鉴定为CadR，即一种重要的镉输出P型ATP酶基因的调节因子，它提供了另一个清除细胞质锌和镉的系统。Rmet_0102不参与此处所研究的金属抗性系统的调节。因此，ZntR与CadR、Zur和CzcI形成了一个复杂的调节网络。此外，这些具有区分作用的调节蛋白赋予了外排系统特定功能。锌对于从人类到细菌的众多生物体而言都是一种必需金属。锌摄取和外排系统的转运组通过双反馈回路控制细胞的整体组成和锌含量。锌饥饿通过Zur调节因子介导，经由ZIP型锌导入蛋白ZupT上调锌导入能力并增强锌储存能力，这二者共同作用可再次提高细胞锌含量。另一方面，锌含量增加会导致ZntR介导的锌外排系统ZntA上调，从而降低锌含量。总之，Zur调节子组分以及ZntR/ZntA在高外部锌浓度和锌饥饿条件下均可平衡细胞锌含量。
