Elimination and Utilization of Oxidized Guanine Nucleotides in the Synthesis of RNA and Its Precursors
Elimination and Utilization of Oxidized Guanine Nucleotides in the Synthesis of RNA and Its Precursors
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DOI：
10.1074/jbc.m112.418723
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发表时间：
2013-03-22
影响因子：
4.8
通讯作者：
Sekiguchi, Mutsuo
中科院分区：
文献类型：
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作者：
Sekiguchi, Takeshi;Ito, Riyoko;Sekiguchi, Mutsuo
活性氧物质作为氧利用的副产物产生，并且可导致核酸及其前体核苷酸的氧化。在各种氧化碱基中，8-氧代-7，8-二氢鸟嘌呤在遗传信息传递过程中似乎是最关键的，因为它可以与胞嘧啶和腺嘌呤配对。在鸟嘌呤核苷酸的从头合成过程中，GMP首先形成，并通过鸟苷酸激酶转化为GDP。该酶几乎不作用于GMP的氧化形式（8-oxo-GMP），该氧化形式是通过GMP的氧化或通过MutT蛋白切割8-oxo-GDP和8-oxo-GTP而形成的。虽然由此防止了从8-氧代-GMP形成8-氧代-GDP，但是8-氧代-GDP本身可以通过活性氧类氧化GDP而产生。由此形成的8-氧代-GDP可以转化为8-氧代-GTP，因为核苷二磷酸激酶和腺苷酸激酶（两者都催化GDP转化为GTP）不区分8-氧代-GDP与正常GDP。以这种方式和通过氧化GTP产生的8-氧代-GTP可用于RNA合成。MutT蛋白阻止了这种错误掺入，MutT蛋白具有将8-氧代-GTP以及8-氧代-GDP切割为8-氧代-GMP的潜力。当C-14标记的8-oxo-GTP应用于CaCl 2渗透的mutT（-）突变株细胞时，它可以以GTP的4%的速率掺入RNA中。大肠杆菌细胞似乎具有防止8-氧代-7，8-二氢鸟嘌呤错误掺入RNA的机制。
Reactive oxygen species are produced as side products of oxygen utilization and can lead to the oxidation of nucleic acids and their precursor nucleotides. Among the various oxidized bases, 8-oxo-7,8-dihydroguanine seems to be the most critical during the transfer of genetic information because it can pair with both cytosine and adenine. During the de novo synthesis of guanine nucleotides, GMP is formed first, and it is converted to GDP by guanylate kinase. This enzyme hardly acts on an oxidized form of GMP(8-oxo-GMP) formed by the oxidation of GMP or by the cleavage of 8-oxo-GDP and 8-oxo-GTP by MutT protein. Although the formation of 8-oxo-GDP from 8-oxo-GMP is thus prevented, 8-oxo-GDP itself may be produced by the oxidation of GDP by reactive oxygen species. The 8-oxo-GDP thus formed can be converted to 8-oxo-GTP because nucleoside-diphosphate kinase and adenylate kinase, both of which catalyze the conversion of GDP to GTP, do not discriminate 8-oxo-GDP from normal GDP. The 8-oxo-GTP produced in this way and by the oxidation of GTP can be used for RNA synthesis. This misincorporation is prevented by MutT protein, which has the potential to cleave 8-oxo-GTP as well as 8-oxo-GDP to 8-oxo-GMP. When C-14-labeled 8-oxo-GTP was applied to CaCl2-permeabilized cells of a mutT(-) mutant strain, it could be incorporated into RNA at 4% of the rate for GTP. Escherichia coli cells appear to possess mechanisms to prevent misincorporation of 8-oxo-7,8-dihydroguanine into RNA.