Photosensitized Oxidative DNA Damage: From Hole Injection to Chemical Product Formation and Strand Cleavage
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- 作者：Byeong Hwa Yun ; Young Ae Lee ; Seog K. Kim ; Vladimir Kuzmin ; Alexander Kolbanovskiy ; Peter C. Dedon ; Nicholas E. Geacintov ; Vladimir Shafirovich
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：August 1, 2007
- 年：2007
- 卷：129
- 期：30
- 页码：9321 - 9332
- 全文大小：295K
- 年卷期：v.129,no.30(August 1, 2007)
- ISSN：1520-5126
文摘
Oxidatively generated damage to DNA induced by a pyrenyl photosensitizer residue (Py)covalently attached to a guanine base in the DNA sequence context 5'-d(CAT[G1Py]CG2TCCTAC) in aeratedsolutions was monitored from the initial one-electron transfer, or hole injection step, to the formation ofchemical end-products monitored by HPLC, mass spectrometry, and high-resolution gel electrophoresis.Hole injection into the DNA was initiated by two-photon excitation of the Py residue with 355 nm laserpulses, thus producing the radical cation Py
+ and hydrated electrons; the latter are trapped by O2, thusforming the superoxide anion O2-. The decay of the Py+ radical is correlated with the appearance of theG+/G(-H) radical on microsecond time scales, and O2- combines with guanine radicals at G1 to formalkali-labile 2,5-diamino-4H-imidazolone lesions (Iz1Py). Product formation in the modified strand is smallerby a factor of 2.4 in double-stranded than in single-stranded DNA. In double-stranded DNA, hot piperidine-mediated cleavage at G2 occurs only after G1Py, an efficient hole trap, is oxidized thus generating tandemlesions. An upper limit of hole hopping rates, khh < 5 × 103 s-1 from G1+-Py to G2 can be estimated fromthe known rates of the combination reaction of the G(-H) and O2- radicals. The formation of Iz productsin the unmodified complementary strand compared to the modified strand in the duplex is ~10 times smaller.The formation of tandem lesions is observed even at low levels of irradiation corresponding to "single-hit"conditions when less than ~10% of the oligonucleotide strands are damaged. A plausible mechanism forthis observation is discussed.
+ and hydrated electrons; the latter are trapped by O2, thusforming the superoxide anion O2-. The decay of the Py+ radical is correlated with the appearance of theG+/G(-H) radical on microsecond time scales, and O2- combines with guanine radicals at G1 to formalkali-labile 2,5-diamino-4H-imidazolone lesions (Iz1Py). Product formation in the modified strand is smallerby a factor of 2.4 in double-stranded than in single-stranded DNA. In double-stranded DNA, hot piperidine-mediated cleavage at G2 occurs only after G1Py, an efficient hole trap, is oxidized thus generating tandemlesions. An upper limit of hole hopping rates, khh < 5 × 103 s-1 from G1+-Py to G2 can be estimated fromthe known rates of the combination reaction of the G(-H) and O2- radicals. The formation of Iz productsin the unmodified complementary strand compared to the modified strand in the duplex is ~10 times smaller.The formation of tandem lesions is observed even at low levels of irradiation corresponding to "single-hit"conditions when less than ~10% of the oligonucleotide strands are damaged. A plausible mechanism forthis observation is discussed.