The Escherichia coli Toxin MqsR Destabilizes the Transcriptional Repression Complex Formed between the Antitoxin MqsA and the mqsRA Operon Promoter
The Escherichia coli Toxin MqsR Destabilizes the Transcriptional Repression Complex Formed between the Antitoxin MqsA and the mqsRA Operon Promoter
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DOI：
10.1074/jbc.m112.421008
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发表时间：
2013-01-11
影响因子：
4.8
通讯作者：
Page, Rebecca
中科院分区：
文献类型：
--
作者：
Brown, Breann L.;Lord, Dana M.;Page, Rebecca
细菌生物膜是一种复杂的细胞群落，含有越来越多的被称为持续体的休眠细胞，其特征是毒素-抗毒素(TA)模块基因的上调。毒素与其同源抗毒素的结合中和了毒素的活性，使细胞得以正常生长。此外，蛋白质抗毒素结合自己的启动子并抑制转录，而毒素则作为辅助抑制因子。最近，TA对被证明通过一种被称为条件协作性的现象来调节自己的转录，在这种现象中，TA复合体只有在适当的化学计量比存在的情况下才能与操作者DNA结合并抑制转录。持久细胞中差异最大的上调基因是mqsR，这个基因与抗毒素MQSA一起构成TA模块。在这里，我们揭示了与其他TA系统不同的是，MqsR不是转录共抑制因子，而是作用于破坏MQSA-DNA复合体的稳定。我们进一步表明，DNA结合不受条件协作性的调节。最后，利用生物物理研究，我们证明了MqsR和MQSA之间的络合物形成导致了异常稳定的相互作用，导致了亚纳摩尔解离常数，类似于MQSA和DNA之间的观察到的解离常数。结合结晶学研究，本工作揭示了MQSA与DNA和MqsR的结合是相互排斥的。据我们所知，这是第一个毒素不作为转录共抑制因子发挥功能，而是在所有条件下都能破坏抗毒素-操纵子复合体稳定的TA系统，从而定义了mqsRA TA模块的另一个独特功能。
Bacterial biofilms are complex communities of cells containing an increased prevalence of dormant cells known as persisters, which are characterized by an up-regulation of genes known as toxin-antitoxin (TA) modules. The association of toxins with their cognate antitoxins neutralizes toxin activity, allowing for normal cell growth. Additionally, protein antitoxins bind their own promoters and repress transcription, whereas the toxins serve as co-repressors. Recently, TA pairs have been shown to regulate their own transcription through a phenomenon known as conditional cooperativity, where the TA complexes bind operator DNA and repress transcription only when present in the proper stoichiometric amounts. The most differentially up-regulated gene in persister cells is mqsR, a gene that, with the antitoxin mqsA, constitutes a TA module. Here, we reveal that, unlike other TA systems, MqsR is not a transcription co-repressor but instead functions to destabilize the MqsA-DNA complex. We further show that DNA binding is not regulated by conditional cooperativity. Finally, using biophysical studies, we show that complex formation between MqsR and MqsA results in an exceptionally stable interaction, resulting in a subnanomolar dissociation constant that is similar to that observed between MqsA and DNA. In combination with crystallographic studies, this work reveals that MqsA binding to DNA and MqsR is mutually exclusive. To our knowledge, this is the first TA system in which the toxin does not function as a transcriptional co-repressor, but instead functions to destabilize the antitoxin-operator complex under all conditions, and thus defines another unique feature of the mqsRA TA module.