Copper-mediated nuclease activity of jadomycin B

The natural product jadomycin B, isolated from Streptomyces venezeulae ISP5230, has been found to cleave DNA in the presence of Cu(II) ions without the requirement for an external reducing agent. The efficiency of DNA cleavage was probed using supercoiled plasmid DNA in buffered solution as a model environment. EC50 and t1/2 values for cleavage were 1.7 μM and 0.75 h, respectively, and varied ±5% with the particular batch of plasmid and jadomycin employed. While UV–vis spectroscopy indicates that the cleavage event does not involve direct binding of jadomycin B to DNA, a stoichiometric Cu(II) preference for optimum cleavage suggests a weak binding interaction between jadomycin B and Cu(II) in the presence of DNA. The Cu(II)-mediated cleavage is greatly enhanced by UV light, which implicates the jadomycin B radical cation and Cu(I) as potential intermediates in DNA cleavage. Evidence in favor of this hypothesis was derived from a mechanistic assay which showed reduced cleavage as a function of added catalase and EDTA, scavengers of H2O2 and Cu(II), respectively. Thus, jadomycin B may serve as a source of electrons for Cu(II) reduction, producing Cu(I) which reacts with H2O2 to form hydroxyl radicals that cause DNA strand scission. In addition, scavengers of hydroxyl radicals and superoxide also display inhibitory effects, underscoring the ability of jadomycin B to produce a powerful arsenal of deleterious oxygen species when copper is present.

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