Bittner Lisa-Marie, Kraus Alexander, Schäkermann Sina, Narberhaus Franz
Microbial Biology, Ruhr University Bochum Bochum, Germany.
Front Mol Biosci. 2017 Feb 28;4:9. doi: 10.3389/fmolb.2017.00009. eCollection 2017.
The trace element copper serves as cofactor for many enzymes but is toxic at elevated concentrations. In bacteria, the intracellular copper level is maintained by copper efflux systems including the Cue system controlled by the transcription factor CueR. CueR, a member of the MerR family, forms homodimers, and binds monovalent copper ions with high affinity. It activates transcription of the copper tolerance genes and via a conserved DNA-distortion mechanism. The mechanism how CueR-induced transcription is turned off is not fully understood. Here, we report that CueR is prone to proteolysis by the AAA proteases Lon, ClpXP, and ClpAP. Using a set of CueR variants, we show that CueR degradation is not altered by mutations affecting copper binding, dimerization or DNA binding of CueR, but requires an accessible C terminus. Except for a twofold stabilization shortly after a copper pulse, proteolysis of CueR is largely copper-independent. Our results suggest that ATP-dependent proteolysis contributes to copper homeostasis in by turnover of CueR, probably to allow steady monitoring of changes of the intracellular copper level and shut-off of CueR-dependent transcription.
微量元素铜是许多酶的辅因子，但在浓度升高时具有毒性。在细菌中，细胞内铜水平通过包括由转录因子CueR控制的Cue系统在内的铜外排系统来维持。CueR是MerR家族的成员，形成同二聚体，并与单价铜离子高亲和力结合。它通过保守的DNA扭曲机制激活铜耐受基因 和 的转录。CueR诱导的转录如何关闭的机制尚未完全了解。在这里，我们报告CueR易于被AAA蛋白酶Lon、ClpXP和ClpAP进行蛋白水解。使用一组CueR变体，我们表明影响CueR铜结合、二聚化或DNA结合的突变不会改变CueR的降解，但需要一个可及的C末端。除了在铜脉冲后不久有两倍的稳定性外，CueR的蛋白水解在很大程度上不依赖于铜。我们的结果表明，ATP依赖性蛋白水解通过CueR的周转有助于细菌中的铜稳态，可能是为了允许对细胞内铜水平的变化进行持续监测并关闭CueR依赖性转录。
