Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT, United States of America.
Yale Microbial Sciences Institute, West Haven, CT, United States of America.
PLoS Genet. 2020 Oct 30;16(10):e1009085. doi: 10.1371/journal.pgen.1009085. eCollection 2020 Oct.
DNA supercoiling is essential for all living cells because it controls all processes involving DNA. In bacteria, global DNA supercoiling results from the opposing activities of topoisomerase I, which relaxes DNA, and DNA gyrase, which compacts DNA. These enzymes are widely conserved, sharing >91% amino acid identity between the closely related species Escherichia coli and Salmonella enterica serovar Typhimurium. Why, then, do E. coli and Salmonella exhibit different DNA supercoiling when experiencing the same conditions? We now report that this surprising difference reflects disparate activation of their DNA gyrases by the polyamine spermidine and its precursor putrescine. In vitro, Salmonella DNA gyrase activity was sensitive to changes in putrescine concentration within the physiological range, whereas activity of the E. coli enzyme was not. In vivo, putrescine activated the Salmonella DNA gyrase and spermidine the E. coli enzyme. High extracellular Mg2+ decreased DNA supercoiling exclusively in Salmonella by reducing the putrescine concentration. Our results establish the basis for the differences in global DNA supercoiling between E. coli and Salmonella, define a signal transduction pathway regulating DNA supercoiling, and identify potential targets for antibacterial agents.
DNA 超螺旋是所有活细胞所必需的，因为它控制着所有涉及 DNA 的过程。在细菌中，全局 DNA 超螺旋是由拓扑异构酶 I 和 DNA 旋转酶的相反作用产生的，拓扑异构酶 I 可松弛 DNA，而 DNA 旋转酶可压缩 DNA。这些酶广泛保守，在密切相关的物种大肠杆菌和肠炎沙门氏菌血清型 Typhimurium 之间具有>91%的氨基酸同一性。那么，为什么大肠杆菌和沙门氏菌在经历相同条件时表现出不同的 DNA 超螺旋呢？我们现在报告说，这种惊人的差异反映了它们的 DNA 旋转酶被多胺亚精胺及其前体腐胺的不同激活。在体外，沙门氏菌 DNA 旋转酶的活性对生理范围内腐胺浓度的变化敏感，而大肠杆菌酶的活性则不敏感。在体内，腐胺激活了沙门氏菌 DNA 旋转酶，而亚精胺则激活了大肠杆菌酶。高细胞外 Mg2+ 通过降低腐胺浓度，仅使沙门氏菌的 DNA 超螺旋减少。我们的结果为大肠杆菌和沙门氏菌之间的全局 DNA 超螺旋差异奠定了基础，定义了调节 DNA 超螺旋的信号转导途径，并确定了抗菌剂的潜在靶标。
