48 research outputs found
One-electron Oxidation of a Pyrenyl Photosensitizer Covalently Attached to DNA and Competition Between its Further Oxidation and DNA Hole Injection
The photosensitized hole injection and guanine base damage phenomena have been investigated in the DNA sequence, 5âČ-d(CATG[subscript 1] [superscript Py]CG[subscript 2]TCCTAC) with a site-specifically positioned pyrene-like (Py) benzo[a]pyrene 7,8-diol 9,10-epoxide-derived N[superscript 2]-guanine adduct (G[subscript 1] [superscript Py]). Generation of the Py radical cation and subsequent hole injection into the DNA strand by a 355 nm nanosecond laser pulses (âŒ4 mJ cm[superscript â2]) results in the transformation of G[subscript 1] [superscript Py] to the imidazolone derivative Iz[subscript 1] [superscript Py] and a novel G[subscript 1] [superscript Py*] photoproduct that has a mass larger by 16 Da (M+16) than the mass (M) of G[subscript 1] [superscript Py]. In addition, hole transfer and the irreversible oxidation of G[subscript 2], followed by the formation of Iz[subscript 2] was observed (Yun et al. [2007], J. Am. Chem. Soc., 129, 9321). Oxygen-18 and deuterium isotope labeling methods, in combination with an extensive analysis of the MS/MS fragmentation patterns of the individual dG[superscript Py*] nucleoside adduct and other data show that dG[superscript Py*] has an unusual structure with a ruptured cyclohexenyl ring with a carbonyl group at the rupture site and intact guanine and pyrenyl residues. The formation of this product competes with hole injection and thus diminishes the efficiency of oxidation of guanines within the oligonucleotide strand by at least 15% in comparison with that in the dG[superscript Py] nucleoside adduct.National Institutes of Health (U.S.) (Grant R01 CA110261
Oxidation of single-stranded oligonucleotides by carbonate radical anions: generating intrastrand cross-links between guanine and thymine bases separated by cytosines
The carbonate radical anion is a biologically important one-electron oxidant that can directly abstract an electron from guanine, the most easily oxidizable DNA base. Oxidation of the 5âČ-d(CCTACGCTACC) sequence by photochemically generated CO3·â radicals in low steady-state concentrations relevant to biological processes results in the formation of spiroiminodihydantoin diastereomers and a previously unknown lesion. The latter was excised from the oxidized oligonucleotides by enzymatic digestion with nuclease P1 and alkaline phosphatase and identified by LC-MS/MS as an unusual intrastrand cross-link between guanine and thymine. In order to further characterize the structure of this lesion, 5âČ-d(GpCpT) was exposed to CO3·â radicals, and the cyclic nature of the 5âČ-d(G*pCpT*) cross-link in which the guanine C8-atom is bound to the thymine N3-atom was confirmed by LC-MS/MS, 1D and 2D NMR studies. The effect of bridging C bases on the cross-link formation was studied in the series of 5âČ-d(GpCnpT) and 5âČ-d(TpCnpG) sequences with n = 0, 1, 2 and 3. Formation of the G*-T* cross-links is most efficient in the case of 5âČ-d(GpCpT). Cross-link formation (n = 0) was also observed in double-stranded DNA molecules derived from the self-complementary 5âČ-d(TTACGTACGTAA) sequence following exposure to CO3·â radicals and enzymatic excision of the 5âČ-d(G*pT*) product
Excision of Oxidatively Generated Guanine Lesions by Competitive DNA Repair Pathways
The base and nucleotide excision repair pathways (BER and NER, respectively) are two major mechanisms that remove DNA lesions formed by the reactions of genotoxic intermediates with cellular DNA. It is generally believed that small non-bulky oxidatively generated DNA base modifications are removed by BER pathways, whereas DNA helix-distorting bulky lesions derived from the attack of chemical carcinogens or UV irradiation are repaired by the NER machinery. However, existing and growing experimental evidence indicates that oxidatively generated DNA lesions can be repaired by competitive BER and NER pathways in human cell extracts and intact human cells. Here, we focus on the interplay and competition of BER and NER pathways in excising oxidatively generated guanine lesions site-specifically positioned in plasmid DNA templates constructed by a gapped-vector technology. These experiments demonstrate a significant enhancement of the NER yields in covalently closed circular DNA plasmids (relative to the same, but linearized form of the same plasmid) harboring certain oxidatively generated guanine lesions. The interplay between the BER and NER pathways that remove oxidatively generated guanine lesions are reviewed and discussed in terms of competitive binding of the BER proteins and the DNA damage-sensing NER factor XPC-RAD23B to these lesions
Generation of GuanineâThymidine Cross-Links in DNA by Peroxynitrite/Carbon Dioxide
Luftföroreningar Ă€r ett lokalt men ocksĂ„ grĂ€nsöverskridande problem. Sveriges luftkvalitet pĂ„verkas av lokala utslĂ€ppskĂ€llor, men Ă€ven av lĂ„ngdistanstransport frĂ„n stora emissionsomrĂ„den i Europa. UtslĂ€ppen av mĂ„nga luftföroreningar har minskat kraftigt under de senaste Ă„rtiondena pĂ„ grund av kontinuerligt skĂ€rpta emissionskrav. Betydande förbĂ€ttringar har bland annat gjorts inom vĂ€gtransportsektorn. Via europeiska utslĂ€ppsnormer definieras acceptabla grĂ€nser för avgasutslĂ€pp för nya fordon som sĂ€ljs i EUs medlemsstater. Dessa, och andra, utslĂ€ppskrav kommer att leda till fortsatt minskande emissioner i Europa och dĂ€rmed Ă€ven lĂ€gre föroreningsnivĂ„er i den luft som kommer in över Sverige. Hur stort Ă€r det kvarstĂ„ende behovet av lokala Ă„tgĂ€rder i Sverige för att minska haltnivĂ„erna till en nivĂ„ dĂ€r normer och miljömĂ„l uppfylls? Det Ă€r en av de frĂ„gestĂ€llningar som denna rapport utgĂ„r frĂ„n.Den lokala miljö som undersöks Ă€r gaturum, varför förĂ€ndringar av vĂ€gtrafikens emissioner och halter i Sverige Ă€r central. Liknande emissionstrender, som i Europa, finns ocksĂ„ i Sverige, med kraftigt minskande emissioner beroende bland annat pĂ„ de europeiska utslĂ€ppsnormerna. Viktiga skillnader finns ocksĂ„. VĂ„rt kalla svenska vinterklimat skapar bland annat hala vĂ€gbanor och ogynnsamma spridningsförhĂ„llanden. Ă
tgÀrder för att undvika hala vÀgbanor leder till ökat vÀgslitage och vÀgdamm som ackumuleras i vÀgmiljön, vilket i sin tur leder till höga partikelhalter. I norra delarna av Sverige skapas under vintern ogynnsamma spridningsförhÄllanden med stabil skiktning och lÄga inversioner. I kombination med höga emissioner av luftföroreningar frÄn bostadsuppvÀrmning och kallstarter leder detta till höga halter av bland annat kvÀveoxider.Trots kraftiga minskningar av utslÀppen bÄde i Sverige och övriga Europa har inte luftkvaliteten, med avseende pÄ kvÀvedioxid (NO2), ozon (O3) och partiklar (PM10 respektive PM2.5), förbÀttrats pÄ nÄgot avgörande sÀtt sedan Är 2000. Fortfarande Àr luftföroreningshalterna i mÄnga trafikmiljöer höga sÄvÀl i Sverige som i övriga Europa. Orsakerna till det diskuteras i rapporten. Syftet med denna undersökning Àr att analysera hur framtidens luftkvalitet pÄ lokal nivÄ (gaturum) kan komma att utvecklas pÄ grund av troliga emissionsminskningar i Europa och i Sverige, samt att bedöma hur stora lokala ÄtgÀrder som ytterligare kan komma att fordras för att klara miljökvalitetsnormer och miljömÄl