The Pyrimidine Ring-opened Derivative of 1,N super(6)-Ethenoadenine Is Excised from DNA by the Escherichia coli Fpg and Nth Proteins

• Published in: The Journal of biological chemistry Vol. 276; no. 24; pp. 21821 - 21827
• Main Authors: Speina, E, Ciesla, J M, Wojcik, J, Bajek, M, Tudek, B
• Format: Journal Article
• Language: English
• Published: 15.06.2001
• Subjects: 1,N-Ethenoadenine; 1,N6-ethenoadenine; endonuclease III; Escherichia coli; formamidopyrimidine-DNA glycosylase; Fpg protein; N-Alkylpurine-DNA glycosylase; Nth protein
• ISSN: 0021-9258

It was previously shown that 1,N super(6)-ethenoadenine ( epsilon A) in DNA rearranges into a pyrimidine ring-opened derivative of 20-fold higher mutagenic potency in Escherichia coli (AB1157 lac Delta U169) than the parental epsilon A (Basu, A. K., Wood, M. L., Niedernhofer, L. J., Ramos, L. A., and Essigmann, J. M. (1993) Biochemistry 32, 12793-12801). We have found that at pH 7.0, the stability of the N-glycosidic bond in epsilon dA is 20-fold lower than in dA. In alkaline conditions, but also at neutrality, epsilon dA depurinates or converts into products: epsilon dA arrow right B arrow right C arrow right D. Compound B is a product of water molecule addition to the C(2)-N(3) bond, which is in equilibrium with a product of N(1)-C(2) bond rupture in epsilon dA. Compound C is a deformylated derivative of ring-opened compound B, which further depurinates yielding compound D. Ethenoadenine degradation products are not recognized by human N-alkylpurine-DNA glycosylase, which repairs epsilon A. Product B is excised from oligodeoxynucleotides by E. coli formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease III (Nth). Repair by the Fpg protein is as efficient as that of 7,8-dihydro-8-oxoguanine when the excised base is paired with dT and dC but is less favorable when paired with dG and dA. Ethenoadenine rearrangement products are formed in oligodeoxynucleotides also at neutral pH at the rate of about 2-3% per week at 37 degree C, and therefore they may contribute to epsilon A mutations.