title: Competitive reactions of interstrand and intrastrand DNA-Pt adducts: A dinuclear-platinum complex preferentially forms a 1,4-interstrand cross-link rather than a 1,2 intrastrand cross-link on binding to a GG 14-mer duplex.
abstract: A study of the kinetics and mechanism of the reaction between the dinuclear Pt complex [(trans-PtCl(NH(3))(2))(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1) and the 14-mer duplex 5'-d(ATACATG(7)G(8)TACATA)-3'.5'-d(TATG(25)TACCATG(18)TAT)-3' is reported. [(1)H,(15)N]-HSQC NMR was used to follow the reaction at 298 K, pH 5.4. The product is primarily the 5'-5' 1,4-interstrand cross-link between G(8) and G(18) bases and exists in two conformational forms. No evidence for the possible 1,2-intrastrand G(7)G(8) adduct was seen, confirming the preferential formation of interstrand cross-links by these dinuclear complexes. An initial electrostatic association of (15)N-1 with the duplex is indicated by changes in its (1)H/(15)N chemical shifts, followed by aquation of 1 to form the monoaqua monochloro species 2, with a rate constant of 4.00+/-0.03x10(-5) s(-1). Monofunctional binding to the duplex occurs primarily at G(8), the 3' base of the nucleophilic GG grouping, with a rate constant of 1.5+/-0.7 M(-1) s(-1). Changes in the (1)H/(15)N shifts indicate there is an electrostatic interaction between the unbound (PtN(3)Cl) group of the monofunctional adduct and the duplex. No peaks for a transient aquated monofunctional species are seen and closure of 3 to form the 1,4-G(8)G(18) interstrand cross-link (5) was treated as direct, with a rate constant of 4.47+/-0.06x10(-5) s(-1). The G(8)G(18) cross-link was confirmed from analysis of the NOESY NMR spectrum of the final product. Structural perturbations for the 1,4-interstrand cross-link extend over approximately four base-pairs and are similar to those found for a 1,4-interstrand cross-link with a shorter 8-mer -GTAC- sequence. A major distortion was evident for the 5'T (T(17)) adjacent to the platinated G(18), consistent with the findings from the use of chemical probes to investigate the conformation of 1,4-interstrand cross-links.
authors.affiliation: Department of Chemistry University of Western Australia 35 Stirling Hwy, Crawley, WA 6009, Australia. sbp@chem.uwa.edu.au
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Berners-Price
authors.forename: Murray S
authors.initials: MS
authors.lastname: Davies
authors.forename: John W
authors.initials: JW
authors.lastname: Cox
authors.forename: Donald S
authors.initials: DS
authors.lastname: Thomas
authors.forename: Nicholas
authors.initials: N
authors.lastname: Farrell
mesh_terms: D001483:Base Sequence; D001667:Binding, Competitive; D003432:Cross-Linking Reagents / Q000737:chemistry*; D004247:DNA / Q000737:chemistry / Q000187:drug effects*; D018736:DNA Adducts / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D009944:Organoplatinum Compounds / Q000737:chemistry*; D013696:Temperature
chemical_list: D003432:Cross-Linking Reagents; D018736:DNA Adducts; D009944:Organoplatinum Compounds; D004247:DNA