Nucleic Acids Research Advance Access published online on July 24, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn466
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Nucleic Acid Enzymes |
Human topoisomerase II
uses a two-metal-ion mechanism for DNA cleavage
1Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, 2deCODE biostructures, Bainbridge Island, WA 98110, USA and 3Department of Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, TN 37232-0146
*To whom correspondence should be addressed: Tel: +1 615 322 4338; Fax: +1 615 343 1166; Email: neil.osheroff{at}vanderbilt.edu
Received May 20, 2008. Revised July 2, 2008. Accepted July 3, 2008.
The DNA cleavage reaction of human topoisomerase II
is critical to all of the physiological and pharmacological functions of the protein. While it has long been known that the type II enzyme requires a divalent metal ion in order to cleave DNA, the role of the cation in this process is not known. To resolve this fundamental issue, the present study utilized a series of divalent metal ions with varying thiophilicities in conjunction with DNA cleavage substrates that replaced the 3'-bridging oxygen of the scissile bond with a sulfur atom (i.e. 3'-bridging phosphorothiolates). Rates and levels of DNA scission were greatly enhanced when thiophilic metal ions were included in reactions that utilized sulfur-containing substrates. Based on these results and those of reactions that employed divalent cation mixtures, we propose that topoisomerase II
mediates DNA cleavage via a two-metal-ion mechanism. In this model, one of the metal ions makes a critical interaction with the 3'-bridging atom of the scissile phosphate. This interaction greatly accelerates rates of enzyme-mediated DNA cleavage, and most likely is needed to stabilize the leaving 3'-oxygen.
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