Mechanism of NAD(P)H:quinone reductase:: Ab initio studies of reduced flavin
Mechanism of NAD(P)H:quinone reductase:: Ab initio studies of reduced flavin
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DOI：
10.1002/prot.1055
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发表时间：
2001-06-01
影响因子：
2.9
通讯作者：
Amzel, LM
中科院分区：
文献类型：
--
作者：
Cavelier, G;Amzel, LM
NAD(P)H：醌氧化还原酶1型（QR1, NQO1，原DT-diaphorase； EC 1.6.99.2）是一种含有fad的酶，催化烟酰胺核苷酸依赖性的醌，醌亚胺，偶氮染料和硝基的还原。QR1保护动物细胞免受醌类和其他亲电试剂的毒性和肿瘤作用。或者，在肿瘤细胞中，QR可以激活许多癌症化疗药物，如丝裂霉素和氮基苯醌。因此，保护机体免受醌类有害影响的同一种酶可以激活细胞毒性化疗前药并导致癌细胞死亡。QR的催化机理包括一个重要的初始步骤，即FAD被NAD(P)H还原。这种不利的电荷分离必须由蛋白质来稳定。这个电荷稳定步骤的细节无法通过简单的实验验证，但可以通过量子化学方法进行研究。在这里，我们报告从头算量子力学计算在酶的活性位点内和周围，提供有关蛋白质的贡献，以减少黄素的稳定性的细节信息。结果表明：(1)蛋白质相互作用提供约2 kcal/ mol来稳定x射线结构中黄素异alloxazine环的平面构象；(2)黄素还原平面形式中的电荷分离通过与蛋白质基团的相互作用而稳定；(3)即使在稳定后，辅因子的还原电位仍然比游离黄素负，使其成为更多种醌的较好还原剂；(4)负还原电位越大，醌还原步骤的动力学也越快。蛋白质2001;43:420 - 432。(C) 2001 Wiley-Liss, Inc。
NAD(P)H:quinone oxidoreductase type 1 (QR1, NQO1, formerly DT-diaphorase; EC 1.6.99.2) is an FAD-containing enzyme that catalyzes the nicotinamide nucleotide-dependent reduction of quinones, quinoneimines, azo dyes, and nitro groups. Animal cells are protected by QR1 from the toxic and neoplastic effects of quinones and other electrophiles. Alternatively, in tumor cells QR can activate a number of cancer chemotherapeutic agents such as mitomycins and aziridylbenzoquinones. Thus, the same enzyme that protects the organism from the deleterious effects of quinones can activate cytotoxic chemotherapeutic prodrugs and cause cancer cell death. The catalytic mechanism of QR includes an important initial step in which FAD is reduced by NAD(P)H. The unfavorable charge separation that results must be stabilized by the protein. The details of this charge stabilization step are inaccessible to easy experimental verification but can be studied by quantum chemistry methods. Here we report ab initio quantum mechanical calculations in and around the active site of the enzyme that provide information about the fine details of the contribution of the protein to the stabilization of the reduced flavin. The results show that (1) protein interactions provide approximately 2 kcal/ mol to stabilize the planar conformation of the reduced flavin isoalloxazine ring observed in the X-ray structure; (2) the charge separation present in the reduced planar form of the flavin is stabilized by interactions with groups of the protein; (3) even after stabilization, the reduction potential of the cofactor remains more negative than that of the free flavin, making it a better reductant for a larger variety of quinones; and (4) the more negative reduction potential may also result in faster kinetics for the quinone reduction step. Proteins 2001;43:420-432. (C) 2001 Wiley-Liss, Inc.