Cheng Bokun, Annamalai Thirunavukkarasu, Sandhaus Shayna, Bansod Priyanka, Tse-Dinh Yuk-Ching
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York, United States of America.
Department of Chemistry and Biochemistry, Florida International University, Miami, Florida, United States of America.
PLoS One. 2015 Mar 23;10(3):e0120022. doi: 10.1371/journal.pone.0120022. eCollection 2015.
Type IA topoisomerase activities are essential for resolving DNA topological barriers via an enzyme-mediated transient single strand DNA break. Accumulation of topoisomerase DNA cleavage product can lead to cell death or genomic rearrangement. Many antibacterial and anticancer drugs act as topoisomerase poison inhibitors that form stabilized ternary complexes with the topoisomerase covalent intermediate, so it is desirable to identify such inhibitors for type IA topoisomerases. Here we report that organomercury compounds were identified during a fluorescence based screening of the NIH diversity set of small molecules for topoisomerase inhibitors that can increase the DNA cleavage product of Yersinia pestis topoisomerase I. Inhibition of relaxation activity and accumulation of DNA cleavage product were confirmed for these organomercury compounds in gel based assays of Escherichia coli topoisomerase I. Hg(II), but not As(III), could also target the cysteines that form the multiple Zn(II) binding tetra-cysteine motifs found in the C-terminal domains of these bacterial topoisomerase I for relaxation activity inhibition. Mycobacterium tuberculosis topoisomerase I activity is not sensitive to Hg(II) or the organomercury compounds due to the absence of the Zn(II) binding cysteines. It is significant that the type IA topoisomerases with Zn(II) binding domains can still cleave DNA when interfered by Hg(II) or organomercury compounds. The Zn(II) binding domains found in human Top3α and Top3β may be potential targets of toxic metals and organometallic complexes, with potential consequence on genomic stability and development.
IA型拓扑异构酶活性对于通过酶介导的瞬时单链DNA断裂来解决DNA拓扑障碍至关重要。拓扑异构酶DNA切割产物的积累会导致细胞死亡或基因组重排。许多抗菌和抗癌药物作为拓扑异构酶毒物抑制剂，与拓扑异构酶共价中间体形成稳定的三元复合物，因此需要鉴定IA型拓扑异构酶的此类抑制剂。在此我们报告，在基于荧光的美国国立卫生研究院小分子多样性集筛选拓扑异构酶抑制剂的过程中，鉴定出有机汞化合物，这些化合物可增加鼠疫耶尔森菌拓扑异构酶I的DNA切割产物。在基于凝胶的大肠杆菌拓扑异构酶I测定中，证实了这些有机汞化合物对松弛活性的抑制作用以及DNA切割产物的积累。Hg(II)而非As(III)也可靶向这些细菌拓扑异构酶I C端结构域中形成多个Zn(II)结合四半胱氨酸基序的半胱氨酸，以抑制松弛活性。结核分枝杆菌拓扑异构酶I活性对Hg(II)或有机汞化合物不敏感，因为不存在Zn(II)结合半胱氨酸。重要的是，具有Zn(II)结合结构域的IA型拓扑异构酶在受到Hg(II)或有机汞化合物干扰时仍能切割DNA。在人类Top3α和Top3β中发现的Zn(II)结合结构域可能是有毒金属和有机金属复合物的潜在靶点，对基因组稳定性和发育可能产生影响。
