Department of Microbiology and Molecular Genetics, Stafford Hall, University of Vermont, Burlington, Vermont 05405, USA.
Biochemistry. 2010 Mar 23;49(11):2502-9. doi: 10.1021/bi902195p.
The oxidation of guanine generates one of the most common DNA lesions, 8-oxo-7,8-dihydroguanine (8-oxoG). The further oxidation of 8-oxoG can produce either guanidinohydantoin (Gh) in duplex DNA or spiroiminodihydantoin (Sp) in nucleosides and ssDNA. Although Gh can be a strong block for replicative DNA polymerases such as RB69 DNA polymerase, this lesion is also mutagenic: DNA polymerases bypass Gh by preferentially incorporating a purine with a slight preference for adenine, which results in G.C --> T.A or G.C --> C.G transversions. The 2.15 A crystal structure of the replicative RB69 DNA polymerase in complex with DNA containing Gh reveals that Gh is extrahelical and rotated toward the major groove. In this conformation Gh is no longer in position to serve as a templating base for the incorporation of an incoming nucleotide. This work also constitutes the first crystallographic structure of Gh, which is stabilized in the R configuration in the two polymerase/DNA complexes present in the crystal asymmetric unit. In contrast to 8-oxoG, Gh is found in a high syn conformation in the DNA duplex and therefore presents the same hydrogen bond donor and acceptor pattern as thymine, which explains the propensity of DNA polymerases to incorporate a purine opposite Gh when bypass occurs.
鸟嘌呤的氧化会产生最常见的 DNA 损伤之一 8-氧代-7,8-二氢鸟嘌呤（8-oxoG）。8-oxoG 的进一步氧化可以在双链 DNA 中产生胍基乙内酰脲（Gh），或者在核苷和单链 DNA 中产生螺环亚氨基二氢嘧啶（Sp）。虽然 Gh 可以强烈抑制 RB69 DNA 聚合酶等复制性 DNA 聚合酶，但这种损伤也是致突变的：DNA 聚合酶通过优先掺入嘌呤来绕过 Gh，略微偏爱腺嘌呤，从而导致 G.C --> T.A 或 G.C --> C.G 颠换。与含有 Gh 的 DNA 结合的复制性 RB69 DNA 聚合酶的 2.15 Å 晶体结构表明，Gh 是额外螺旋的，并向主槽旋转。在这种构象中，Gh 不再适合作为模板碱基，用于引入的核苷酸的掺入。这项工作还构成了 Gh 的第一个晶体结构，它在晶体不对称单位中存在的两个聚合酶/DNA 复合物中稳定为 R 构型。与 8-oxoG 相比，Gh 在 DNA 双链中处于高顺式构象，因此呈现与胸腺嘧啶相同的氢键供体和受体模式，这解释了 DNA 聚合酶在发生旁路时优先掺入与 Gh 相对的嘌呤的倾向。
