8-oxoguanine is a common oxidation product in DNA and can lead to missense mutations. The metallointercalator Ru(phen)2dppz2+ is a useful luminescent probe for DNA that has also found use as a guanine-selective oxidizing agent via the flash-quench technique. Here, we show that its osmium analogue can selectively oxidize 8-oxoguanine in double-stranded DNA. With a 3+/2+ couple of 1.15 V, Os(phen)2dppz3+ should be able to oxidize 8-oxo-G (~0.7 V) without oxidizing guanine (~1.3 V). MALDI mass spectrometry data confirms that oxidizing guanine using Ru(NH3)63+ and Ru(phen)2dppz2+ produces 8-oxo-G. In plasmid DNA where 8-oxo-G has been incorporated as above, further flash-quench treatment with Os(phen)2dppz2+ and Co(NH3)5Cl2+ leads to crosslinking with histone protein in gel shift experiments. Similarly, for sonicated genomic DNA oxidized at G as above, further flash-quench treatment with Os(phen)2dppz2+ and Co(NH3)5Cl2+ decreases the amount of free DNA in the chloroform extraction assay, a uv spectroscopy based method. Furthermore, in gel shift experiments with a duplex of the oligonucleotide 5’-ATATGATAT8GATATGATAT -3’ (8 = 8-oxo-G), flash-quench treatment with Ru(phen)2dppz2+ in the presence of histone produces a band of intermediate mobility (presumably 1:1 crosslink) and well-shifted material. In contrast, analogous treatment with Os(phen)2dppz2+ produces only the band of intermediate mobility, consistent with the presence of only a single site that is oxidizable by the osmium complex. Lastly, control experiments indicate that with a duplex of the oligonucleotide 5’-ATATGATATGGATATGATAT -3’ flash quench treatment with Ru(phen)2dppz2+ in the presence of histone produces well-shifted material, whereas treatment with Os(phen)2dppz2+ does not produce crosslinked material, as expected since the osmium (III) complex formed should not be capable of guanine oxidation. Taken together, these results show that Os(phen)2dppz3+ is a promising selective oxidant of 8-oxoguanine in double stranded DNA.

Os(phen)2dppz3+ : An osmium metallointercalator that selectively oxidizes guanine oxidation products

255th National Meeting (2018)

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