耐辐射异常球菌黄嘌呤脱氢酶在氧化胁迫反应中的作用

黄嘌呤脱氢酶广泛分布在真核生物、细菌和古细菌中，是催化氧化嘌呤、蝶啶和醛类等多种杂环分子的氧化还原酶类，与氮同化、激素代谢、衰老的调控及活性氧产生等过程相关。耐辐射异常球菌（Deinococcus radiodurans R1）具有超强的氧化胁迫抗性和氧保护机制，其基因组含有完整的黄嘌呤脱氢酶编码基因xdhABC。为探究该酶的功能，构建了xdhA缺失突变株，通过比较分析突变株ΔxdhA与野生型菌株对嘌呤代谢及甲醛敏感性，确定xdhABC编码蛋白为黄嘌呤脱氢酶。氧化胁迫（60 mmol·L^-1 H₂O₂）条件下，菌株生存率以及氧保护相关基因表达的差异分析结果表明,ΔxdhA生存能力较野生型低2个数量级；氧化胁迫反应相关基因表达下调。另外，酶活分析也表明，H₂O₂冲击条件下xdhA突变导致细胞内总抗氧化能力下降。推测D. radiodurans R1黄嘌呤脱氢酶在氧化胁迫反应中发挥重要作用。

Role of Xanthine Dehydrogenase in Oxidative Stress Response of Deinococcus radiodurans R1

Xanthine dehydrogenase is widely distributed in eukaryotes, bacteria and archaea. It is a redox enzyme that catalyzes the oxidation of various heterocyclic molecules such as purine, pteridine and aldehydes, and is related to nitrogen assimilation, hormone metabolism, aging regulation and reactive oxygen species generation. Deinococcus radiodurans R1 has strong resistance to oxidative stress and oxygen protection mechanism, and has a complete set of xanthine dehydrogenase coding gene (xdhABC) in its genome. To explore the function of this enzyme, xdhA deleted mutant strain was constructed. Comparing the sensitivity of mutant strains ΔxdhA and wild type strain to purine metabolism and formaldehyde, determine xdhABC encoding protein of xanthine dehydrogenases. Compared with wild type strain, the viability of ΔxdhA was 2 orders of magnitude lower, and its survivability declined, and led to down-regulation of oxidative resistance genes after following exposure to 60 mmol·L^-1H₂O₂. The analysis of in vitro enzymatic activity further demonstrated that ΔxdhA mutant strain resulted in a decrease in total antioxidant capacity under shock conditions. Therefore, it was speculated that D. radiodurans R1 xanthine dehydrogenase played an important role in the oxidative stress response.