Department of Biosciences, Durham University, Durham, DH1 3LE, UK.
Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
Nat Commun. 2017 Dec 1;8(1):1884. doi: 10.1038/s41467-017-02085-z.
Bacteria possess transcription factors whose DNA-binding activity is altered upon binding to specific metals, but metal binding is not specific in vitro. Here we show that tight regulation of buffered intracellular metal concentrations is a prerequisite for metal specificity of Zur, ZntR, RcnR and FrmR in Salmonella Typhimurium. In cells, at non-inhibitory elevated concentrations, Zur and ZntR, only respond to Zn(II), RcnR to cobalt and FrmR to formaldehyde. However, in vitro all these sensors bind non-cognate metals, which alters DNA binding. We model the responses of these sensors to intracellular-buffered concentrations of Co(II) and Zn(II) based upon determined abundances, metal affinities and DNA affinities of each apo- and metalated sensor. The cognate sensors are modelled to respond at the lowest concentrations of their cognate metal, explaining specificity. However, other sensors are modelled to respond at concentrations only slightly higher, and cobalt or Zn(II) shock triggers mal-responses that match these predictions. Thus, perfect metal specificity is fine-tuned to a narrow range of buffered intracellular metal concentrations.
细菌拥有转录因子，这些转录因子的 DNA 结合活性在与特定金属结合时会发生改变，但金属结合在体外并不具有特异性。在这里，我们表明，缓冲细胞内金属浓度的严格调节是沙门氏菌 Zur、ZntR、RcnR 和 FrmR 金属特异性的前提条件。在细胞中，在非抑制性的升高浓度下，Zur 和 ZntR 仅对 Zn(II) 有反应，RcnR 对钴有反应，FrmR 对甲醛有反应。然而，在体外，所有这些传感器都能结合非同源金属，从而改变 DNA 结合。我们根据每个脱辅基和金属化传感器的丰度、金属亲和力和 DNA 亲和力，对这些传感器对细胞内缓冲浓度的 Co(II) 和 Zn(II) 的响应进行建模。对同源传感器进行建模，使其对其同源金属的最低浓度作出响应，从而解释了特异性。然而，其他传感器被建模为在仅略高的浓度下作出响应，钴或 Zn(II) 冲击会引发与这些预测相符的错误响应。因此，完美的金属特异性被精细地调整到一个狭窄的缓冲细胞内金属浓度范围内。
