Spore photoproduct lyase catalyzes specific repair of the 5R but not the 5S spore photoproduct.
Spore photoproduct lyase catalyzes specific repair of the 5R but not the 5S spore photoproduct.
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DOI：
10.1021/ja807375c
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发表时间：
2009-02-25
影响因子：
15
通讯作者：
Broderick JB
中科院分区：
文献类型：
--
作者：
Chandra T;Silver SC;Zilinskas E;Shepard EM;Broderick WE;Broderick JB
细菌孢子在抵抗化学和物理压力方面非常出色，包括暴露在紫外线辐射下。细菌孢子对紫外线的异常抗性是孢子DNA独特的光化学作用的结果，它导致5-胸腺嘧啶-5，6-二氢胸腺嘧啶(孢子光产物或SP)的积累，并通过孢子光产物裂解酶(SPL)有效地修复积累的损伤。Sp1是自由基ADOMet超家族的成员之一，它利用铁−硫簇和腺苷蛋氨酸通过从胸腺嘧啶二聚体的C-6中提取H原子的直接逆转机制来修复SP。虽然紫外线照射细菌孢子原则上可以形成SP的两个不同的非对映异构体(5R或5S)，但由于DNA结构的限制，在双螺旋DNA中由相邻胸腺嘧啶形成的SP只可能形成5R构型；5S构型可能在较不明确的DNA结构中或作为链间交联物。在此，我们报告了在立体化学定义的SP底物上进行的体外酶分析中的高效液相和质谱学分析结果，表明SPL仅特异性地修复SP的5个异构体。观察到5R-SP而不是5S-SP是SPL的底物，这与5R是细菌孢子DNA在紫外线照射下产生的SP异构体的预期一致。
Bacterial spores are remarkable in their resistance to chemical and physical stresses, including exposure to UV radiation. The unusual UV resistance of bacterial spores is a result of the unique photochemistry of spore DNA, which results in accumulation of 5-thyminyl-5,6-dihydrothymine (spore photoproduct, or SP), coupled with the efficient repair of accumulated damage by the enzyme spore photoproduct lyase (SPL). SPL is a member of the radical AdoMet superfamily of enzymes, and utilizes an iron−sulfur cluster andS-adenosylmethionine to repair SP by a direct reversal mechanism initiated by H atom abstraction from C-6 of the thymine dimer. While two distinct diastereomers of SP (5Ror 5S) could in principle be formed upon UV irradiation of bacterial spores, only the 5Rconfiguration is possible for SP formed from adjacent thymines in double helical DNA, due to the constraints imposed by the DNA structure; the 5Sconfiguration is possible in less well-defined DNA structures or as an interstrand cross-link. We report here results from HPLC and MS analysis ofin vitroenzymatic assays on stereochemically defined SP substrates demonstrating that SPL specifically repairs only the 5Risomer of SP. The observation that 5R-SP, but not 5S-SP, is a substrate for SPL is consistent with the expectation that 5Ris the SP isomer producedin vivoupon UV irradiation of bacterial spore DNA.
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