Synthesis and structural characterization of the N2G-mitomycin C-N2G interstrand cross-link in a model synthetic 23 base pair oligonucleotide DNA duplex.
Mitomycin C (MMC) is a genotoxic cancer chemotherapeutic agent that reacts principally at the N2 position of guanine to form one of two predominant monoadducts, or a G-G interstrand cross-link at CpG sites, or a G-G intrastrand cross-link at GpG sites. Previous studies of MMC adduction have principally used very short duplex oligonucleotides (5-15 bp) or very long native duplex DNAs. We examined the formation and structural features of the MMC CpG interstrand cross-link on a model 23 bp synthetic oligonucleotide duplex having the (upper strand) sequence 5'-ATAAATACGTATTTATTTATAAA-3'. MMC was reacted with the duplex oligonucleotide in the presence of sodium dithionite at ratios of 6 mM dithionite: 1.5 mM MMC:0.03 mM duplex. The yield of cross-link in the reaction was determined to be approximately 4.8% by denaturing gel electrophoresis, which represented approximately 75% of the total bound MMC. The cross-linked DNA was isolated to greater than 97% purity in a single step by high temperature size exclusion column chromatography. Characterization of the purified product confirmed that the complex contained exclusively the N2G-MMC-N2G cross-link at the single central CpG site. CD spectroscopy demonstrated a negative band at approximately 290-320 nm which has previously been shown to be characteristic of the MMC cross-link. The relative intensity of this band compared to those reported for shorter duplexes suggested that the majority of the duplex is in a normal B-DNA helical configuration. Base-specific chemical footprinting techniques also indicated that there were subtle but distinct structural perturbations principally within the central four to six base pairs containing and adjacent to the cross-link.
Warren
A J
AJ
Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755-3564, USA.
Hamilton
J W
JW
D001482:Base Composition; D003432:Cross-Linking Reagents / Q000737:chemistry* / Q000378:metabolism*; D018736:DNA Adducts / Q000138:chemical synthesis* / Q000302:isolation & purification; D016685:Mitomycin / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D009841:Oligonucleotides / Q000138:chemical synthesis*; D013329:Structure-Activity Relationship
D003432:Cross-Linking Reagents; D018736:DNA Adducts; D009841:Oligonucleotides; D016685:Mitomycin