C5-methylation of cytosine in B-DNA thermodynamically and kinetically stabilizes BI.
We have examined the backbone dynamics of two alternating purine-pyrimidine dodecamers. One sequence consists of "pure" GC bases; the other one contains 5-methylcytosines. The effect of the methyl groups on the backbone substates BI/BII was investigated by means of molecular dynamics. The methylation influences, on one hand, the transition barrier between BI and BII and, on the other hand, the state of equilibrium. The kinetic consequences are an increase of the DeltaG of Gp5mC steps by 1.5 kcal/mol and a decrease of the DeltaG of 5mCpG steps by 0.8 kcal/mol (compared with the nonmethylated DNA). Thus, the additive group differentiates between the two occurring dinucleotide steps and renders the phosphate of the 5-methylcytosine more rigid, as proposed by experimental studies. The thermodynamic consequences are an increase of the DeltaG of Gp5mC steps by 1.1 kcal/mol and a decrease of the DeltaG of 5mCpG steps by 0.8 kcal/mol. The reason for this shift in equilibrium is still not completely clear on a molecular basis. But we can conclude that the indirect readout of DNA is influenced by methylation.
Rauch
Christine
C
Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria.
Trieb
Michael
M
Wellenzohn
Bernd
B
Loferer
Markus
M
Voegele
Andreas
A
Wibowo
Fajar R
FR
Liedl
Klaus R
KR
D003198:Computer Simulation; D003596:Cytosine / Q000737:chemistry* / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D019175:DNA Methylation; D007700:Kinetics; D009690:Nucleic Acid Conformation; D013816:Thermodynamics
D003596:Cytosine; D004247:DNA