Speina E, Ciesla J M, Wojcik J, Bajek M, Kusmierek J T, Tudek B
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5A, 02-106 Warsaw, Poland.
J Biol Chem. 2001 Jun 15;276(24):21821-7. doi: 10.1074/jbc.M100998200. Epub 2001 Mar 20.
It was previously shown that 1,N(6)-ethenoadenine (epsilonA) in DNA rearranges into a pyrimidine ring-opened derivative of 20-fold higher mutagenic potency in Escherichia coli (AB1157 lacDeltaU169) than the parental epsilonA (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 epsilondA is 20-fold lower than in dA. In alkaline conditions, but also at neutrality, epsilondA depurinates or converts into products: epsilondA --> B --> C --> 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 epsilondA. 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 epsilonA. 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 degrees C, and therefore they may contribute to epsilonA mutations.
先前的研究表明，DNA中的1,N(6)-乙烯腺嘌呤（εA）重排为嘧啶环开环衍生物，其在大肠杆菌（AB1157 lacΔU169）中的诱变效力比亲本εA高20倍（巴苏，A.K.，伍德，M.L.，尼德恩霍费尔，L.J.，拉莫斯，L.A.，和埃西格曼，J.M.（1993年）《生物化学》32卷，12793 - 12801页）。我们发现，在pH 7.0时，εdA中N-糖苷键的稳定性比dA低20倍。在碱性条件下，而且在中性条件下，εdA会脱嘌呤或转化为产物：εdA→B→C→D。化合物B是水分子加成到C(2)-N(3)键上的产物，它与εdA中N(1)-C(2)键断裂的产物处于平衡状态。化合物C是开环化合物B的去甲酰化衍生物，它进一步脱嘌呤生成化合物D。乙烯腺嘌呤降解产物不能被修复εA的人N-烷基嘌呤-DNA糖基化酶识别。产物B可被大肠杆菌甲酰胺嘧啶-DNA糖基化酶（Fpg）和内切核酸酶III（Nth）从寡脱氧核苷酸中切除。当切除的碱基与dT和dC配对时，Fpg蛋白的修复效率与7,8-二氢-8-氧代鸟嘌呤的修复效率一样高，但当与dG和dA配对时则不太有利。乙烯腺嘌呤重排产物在中性pH条件下也会在寡脱氧核苷酸中形成，在37℃时每周形成的速率约为2 - 3%，因此它们可能导致εA突变。
