摘要

毒素 - 抗毒素（TA）系统存在于许多细菌中，并且在细菌生长，生理学和致病性中起重要作用。最好研究的是II型TA系统，其中毒素和抗毒素都是蛋白质。 HicAB系统是许多细菌物种中发现的原型TA系统之一。蛋白质毒素（HicA），蛋白质抗毒素（HicB）和编码基因上游的DNA之间的复杂相互作用调节了该系统的活性，但很少有关于HicA如何使HicB-DNA复合物不稳定的结构细节。在这里，我们分别确定HicB和HicAB复合物的X射线结构分辨率为1.8和2.5Å，并描述了它们的DNA相互作用。这表明HicB形成四聚体，HicA和HicB形成异八聚体复合物，其涉及HicB的C末端（DNA结合）区域的结构重组。我们的观察表明，HicA以化学计量依赖的方式对HicB与hicAB上游的DNA序列的结合具有深远的影响。在HicA：HicB的低比例下，对DNA结合没有影响，但是在较高比例下，对DNA的亲和力协同下降，驱使HicA：HicB：DNA复合物解离。这些结果揭示了HicA de-的结构机制。抑制HicB-DNA复合物。

Toxin-antitoxin (TA) systems are present in many bacteria and play important roles in bacterial growth, physiology, and pathogenicity. Those that are best studied are the type II TA systems, in which both toxins and antitoxins are proteins. The HicAB system is one of the prototypic TA systems, found in many bacterial species. Complex interactions between the protein toxin (HicA), the protein antitoxin (HicB), and the DNA upstream of the encoding genes regulate the activity of this system, but few structural details are available about how HicA destabilizes the HicB-DNA complex. Here, we determined the X-ray structures of HicB and the HicAB complex to 1.8 and 2.5 Å resolution respectively and characterized their DNA interactions. This revealed that HicB forms a tetramer and HicA and HicB form a hetero-octameric complex that involves structural reorganization of the C-terminal (DNA-binding) region of HicB. Our observations indicated that HicA has a profound impact on binding of HicB to DNA sequences upstream of hicAB in a stoichiometric-dependent way. At low ratios of HicA:HicB, there was no effect on DNA binding, but at higher ratios, the affinity for DNA declined cooperatively, driving dissociation of the HicA:HicB:DNA complex.These results reveal the structural mechanisms by which HicA de-represses the HicB-DNA complex.

https://www.ncbi.nlm.nih.gov/pubmed/30337369