Oppegard Lisa M, Hamann Bree L, Streck Kathryn R, Ellis Keith C, Fiedler Hans-Peter, Khodursky Arkady B, Hiasa Hiroshi
Department of Pharmacology, University of Minnesota Medical School-Twin Cities, 6-120 Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455, USA.
Antimicrob Agents Chemother. 2009 May;53(5):2110-9. doi: 10.1128/AAC.01440-08. Epub 2009 Mar 9.
Simocyclinone D8 (SD8) exhibits antibiotic activity against gram-positive bacteria but not against gram-negative bacteria. The molecular basis of the cytotoxicity of SD8 is not fully understood, although SD8 has been shown to inhibit the supercoiling activity of Escherichia coli gyrase. To understand the mechanism of SD8, we have employed biochemical assays to directly measure the sensitivities of E. coli and Staphylococcus aureus type II topoisomerases to SD8 and microarray analysis to monitor the cellular responses to SD8 treatment. SD8 is a potent inhibitor of either E. coli or S. aureus gyrase. In contrast, SD8 exhibits only a moderate inhibitory effect on S. aureus topoisomerase IV, and E. coli topoisomerase IV is virtually insensitive to SD8. The antimicrobial effect of SD8 against E. coli has become evident in the absence of the AcrB multidrug efflux pump. As expected, SD8 treatment exhibits the signature responses to the loss of supercoiling activity in E. coli: upregulation of gyrase genes and downregulation of the topoisomerase I gene. Unlike quinolone treatment, however, SD8 treatment does not induce the SOS response. These results suggest that DNA gyrase is the target of SD8 in both gram-positive and gram-negative bacteria and that the lack of the antibacterial effect against gram-negative bacteria is due, in part, to the activity of the AcrB efflux pump.
西莫环素D8（SD8）对革兰氏阳性菌具有抗菌活性，但对革兰氏阴性菌无抗菌活性。尽管已证明SD8可抑制大肠杆菌gyrase的超螺旋活性，但其细胞毒性的分子基础尚未完全明确。为了解SD8的作用机制，我们采用生化分析直接测定大肠杆菌和金黄色葡萄球菌II型拓扑异构酶对SD8的敏感性，并通过微阵列分析监测细胞对SD8处理的反应。SD8是大肠杆菌或金黄色葡萄球菌gyrase的有效抑制剂。相比之下，SD8对金黄色葡萄球菌拓扑异构酶IV仅表现出中等抑制作用，而大肠杆菌拓扑异构酶IV实际上对SD8不敏感。在缺乏AcrB多药外排泵的情况下，SD8对大肠杆菌的抗菌作用变得明显。正如预期的那样，SD8处理表现出大肠杆菌超螺旋活性丧失的典型反应：gyrase基因上调和拓扑异构酶I基因下调。然而，与喹诺酮处理不同，SD8处理不会诱导SOS反应。这些结果表明，DNA gyrase是SD8在革兰氏阳性菌和革兰氏阴性菌中的作用靶点，而对革兰氏阴性菌缺乏抗菌作用部分归因于AcrB外排泵的活性。
