A mammalian DNA repair enzyme that excises oxidatively damaged guanines maps to a locus frequently lost in lung cancer
A mammalian DNA repair enzyme that excises oxidatively damaged guanines maps to a locus frequently lost in lung cancer
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DOI：
10.1016/s0960-9822(06)00187-4
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发表时间：
1997-06-01
期刊：
影响因子：
9.2
通讯作者：
Verdine, GL
中科院分区：
文献类型：
--
作者：
Lu, RZ;Nash, HM;Verdine, GL
背景：基因组中的鸟嘌呤残基容易受到自由基和活性氧的攻击。由此产生的一个主要损伤，8-氧代鸟嘌呤（（O）G），在复制过程中与腺嘌呤错配导致突变。在细菌和芽殖酵母中，（O）G通过碱基切除DNA修复（BER）酶的作用从基因组中去除，该酶催化异常碱基的排出和其糖部分从DNA主链的切除。尽管已知（O）G在哺乳动物基因组中产生并从哺乳动物基因组中清除，但负责这些细胞中（O）G修复的酶仍然难以捉摸。结果：在这里，我们报告了专门针对（O）G的哺乳动物BER酶的克隆和生化特征DNA中的G残基。这些8-氧代鸟嘌呤DNA糖基化酶hOgg 1（人）和mOgg 1（鼠）彼此同源，并与酵母Ogg 1同源。它们还含有一个活性位点基序-螺旋-发夹-受阻，Gly/Pro-rich-Asp基序-具有类似核心折叠和活性位点几何结构的BER蛋白超家族的特征。hOgg 1和mOgg 1都对DNA中与（O）G相对的碱基表现出精确的选择性，仅在与胞嘧啶配对的（O）G碱基上高效地工作。此外，hOgg 1和mOgg 1不能处理一组替代性病变，包括8-氧代腺嘌呤，但以高亲和力结合到合成的脱碱基位点类似物。蛋白质通过经典的糖基化酶/裂解酶催化机制进行操作;催化必需的赖氨酸残基的突变导致催化效力的丧失，但保留与含（O）G的寡核苷酸的结合。hOGG 1基因定位于3号染色体（3 p25/26）的短臂上的一个区域通常删除cancers.Conclusions：这些结果最终建立了8-oxoguanine DNA糖基化酶/裂解酶在人类和小鼠细胞的存在和身份，完成了三联体的蛋白质，共同保护哺乳动物免受鸟嘌呤氧化的遗传毒性作用。hOGG 1的至少一个等位基因通常在癌细胞中缺失的观察结果表明，这些细胞可能具有降低的抵抗活性氧的诱变作用的能力，这种缺陷可能增加其整体基因组的不稳定性。这种推测是由最近的观察所推动的，即对Ras/Raf通路具有组成性活性的细胞组成性地产生高水平的超氧化物，一种已知的（O）G产生器。
Background: Guanine residues in the genome are vulnerable to attack by free radicals and reactive oxygen species. A major lesion thus produced, 8-oxoguanine ((O)G), causes mutations by mis-pairing with adenine during replication. In bacteria and budding yeast, (O)G is removed from the genome through the action of base-excision DNA repair (BER) enzymes, which catalyze expulsion of the aberrant base and excision of its sugar moiety from the DNA backbone. Although (O)G is known to be produced in and cleansed from mammalian genomes, the enzymes responsible for (O)G repair in these cells have remained elusive.Results: Here, we report the cloning and biochemical characterization of mammalian BER enzymes that specifically target (O)G residues in DNA. These 8-oxoguanine DNA glycosylases, hOgg1 (human) and mOgg1 (murine), are homologous to each other and to yeast Ogg1. They also contain an active site motif - the Helix-hairpin-Helix, Gly/Pro-rich-Asp motif - characteristic of a superfamily of BER proteins with a similar core fold and active site geometry. Both hOgg1 and mOgg1 exhibit exquisite selectivity for the base opposite (O)G in DNA, operating with high efficiency only on (O)G base-paired to cytosine. Furthermore, hOgg1 and mOgg1 are unable to process a panel of alternative lesions, including 8-oxoadenine, yet bind with high affinity to synthetic abasic site analogs. The proteins operate through a classical glycosylase/lyase catalytic mechanism; mutation of a catalytically essential lysine residue results in loss of catalytic potency but retention of binding to (O)G-containing oligonucleotides. The hOGG1 gene is localized on the short arm of chromosome 3 (3p25/26) in a region commonly deleted in cancers.Conclusions: These results conclusively establish the existence and identity of an 8-oxoguanine DNA glycosylase/lyase in human and murine cells, completing the triad of proteins that together protect mammals from the genotoxic effects of guanine oxidation. The observation that at least one allele of hOGG1 is commonly deleted in cancer cells suggests that such cells may possess a reduced capacity to counter the mutagenic effects of reactive oxygen species, a deficiency that could increase their overall genomic instability. This speculation is fueled by recent observations that cells constitutively active for the Ras/Raf pathway constitutively produce high levels of superoxide, a known generator of (O)G.