Methylation of cytosine at C5 in a CpG sequence context causes a conformational switch of a benzo[a]pyrene diol epoxide-N2-guanine adduct in DNA from a minor groove alignment to intercalation with base displacement.
It is well known that CpG dinucleotide steps in DNA, which are highly methylated at the 5-position of cytosine (meC) in human tissues, exhibit a disproportionate number of mutations within certain codons of the p53 gene. There is ample published evidence indicating that the reactivity of guanine with anti-B[a]PDE (a metabolite of the environmental carcinogen benzo[a]pyrene) at CpG mutation hot spots is enhanced by the methylation of the cytosine residue flanking the target guanine residue on the 5'-side. In this work we demonstrate that such a methylation can also dramatically affect the conformational characteristics of an adduct derived from the reaction of one of the two enantiomers of anti-B[a]PDE with the exocyclic amino group of guanine ([BP]G adduct). A detailed NMR study indicates that the 10R (-)-trans-anti-[BP]G adduct undergoes a transition from a minor groove-binding alignment of the aromatic BP ring system in the unmethylated C-[BP]G sequence context, to an intercalative BP alignment with a concomitant displacement of the modified guanine residue into the minor groove in the methylated meC-[BP]G sequence context. By contrast, a minor groove-binding alignment was observed for the stereoisomeric 10S (+)-trans-anti-[BP]G adduct in both the C-[BP]G and meC-[BP]G sequence contexts. This remarkable conformational switch resulting from the presence of a single methyl group at the 5-position of the cytosine residue flanking the lesion on the 5'-side, is attributed to the hydrophobic effect of the methyl group that can stabilize intercalated adduct conformations in an adduct stereochemistry-dependent manner. Such conformational differences in methylated and unmethylated CpG sequences may be significant because of potential alterations in the cellular processing of the [BP]G adducts by DNA transcription, replication, and repair enzymes.
Zhang
Na
N
Program in Cellular Biochemistry and Biophysics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Lin
Chin
C
Huang
Xuanwei
X
Kolbanovskiy
Aleksandr
A
Hingerty
Brian E
BE
Amin
Shantu
S
Broyde
Suse
S
Geacintov
Nicholas E
NE
Patel
Dinshaw J
DJ
D001483:Base Sequence; D001564:Benzo(a)pyrene / Q000737:chemistry*; D018899:CpG Islands / Q000235:genetics*; D003596:Cytosine / Q000378:metabolism*; D018736:DNA Adducts / Q000737:chemistry* / Q000378:metabolism; D019175:DNA Methylation; D004260:DNA Repair; D004852:Epoxy Compounds / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry* / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D011522:Protons; D013237:Stereoisomerism
D018736:DNA Adducts; D004852:Epoxy Compounds; D011522:Protons; D001564:Benzo(a)pyrene; D006147:Guanine; D003596:Cytosine