Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
J Am Chem Soc. 2012 Jun 13;134(23):9622-33. doi: 10.1021/ja211960r. Epub 2012 May 31.
3-Methyladenine DNA glycosylase II (AlkA) is an enzyme that cleaves a wide range of damaged bases from DNA. The gas-phase thermochemical properties (tautomerism, acidity, and proton affinity) have been measured and calculated for a series of AlkA purine substrates (7-methyladenine, 7-methylguanine, 3-methyladenine, 3-methylguanine, purine, 6-chloropurine, xanthine) that have not been heretofore examined. The damaged nucleobases are found to be more acidic than the normal nucleobases adenine and guanine. Because of this increased acidity, the damaged bases would be expected to be more easily cleaved from DNA by AlkA (their conjugate bases should be better leaving groups). We find that the gas-phase acidity correlates to the AlkA excision rates, which lends support to an AlkA mechanism wherein the enzyme provides a nonspecific active site, and nucleobase cleavage is dependent on the intrinsic N-glycosidic bond stability.
3-甲基腺嘌呤 DNA 糖基化酶 II（AlkA）是一种能够从 DNA 中切割多种受损碱基的酶。已测量和计算了一系列 AlkA 嘌呤底物（7-甲基腺嘌呤、7-甲基鸟嘌呤、3-甲基腺嘌呤、3-甲基鸟嘌呤、嘌呤、6-氯嘌呤、黄嘌呤）的气相热化学性质（互变异构、酸度和质子亲和力），这些底物以前从未被研究过。研究发现，受损的碱基比正常碱基腺嘌呤和鸟嘌呤更具酸性。由于这种酸度的增加，受损的碱基预计更容易被 AlkA 从 DNA 中切割（它们的共轭碱基应该是更好的离去基团）。我们发现气相酸度与 AlkA 切除率相关，这支持了 AlkA 机制，其中酶提供非特异性活性位点，并且碱基切割取决于内在的 N-糖苷键稳定性。
