Why is mammalian thioredoxin reductase 1 so dependent upon the use of selenium?
Why is mammalian thioredoxin reductase 1 so dependent upon the use of selenium?
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DOI：
10.1021/bi400651x
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发表时间：
2014-01-28
期刊：
影响因子：
2.9
通讯作者：
Hondal, Robert J.
中科院分区：
文献类型：
--
作者：
Lothrop, Adam P.;Snider, Gregg W.;Ruggles, Erik L.;Hondal, Robert J.
胞质硫氧还蛋白还原酶 1 (TR1) 是一类高分子量 (Mr) 硫氧还蛋白还原酶 (TR) 中特征最鲜明的。 TR1 高度依赖稀有氨基酸硒代半胱氨酸 (Sec) 来还原硫氧还蛋白 (Trx) 和许多小分子底物，因为 Sec 突变为半胱氨酸 (Cys) 会导致所有底物类型的催化活性大幅下降。我们实验室和其他实验室之前的工作表明，线粒体 TR (TR3) 对使用 Sec 来还原小分子的依赖性要小得多。 TR1 的 Sec 依赖性底物利用行为可能是例外，而不是规则，因为我们表明，来自其他生物体（包括果蝇、秀丽隐杆线虫和恶性疟原虫）的各种高 Mr TRs 不需要 Sec 来减少小分子底物，包括 5,5'-二硫代双（2-硝基苯甲酸）、硫辛酸、亚硒酸盐和硒代胱氨酸。数据显示，根据底物利用模式，高 Mr TR 可以分为两组：TR1 组和 TR3 样组。我们已经从小鼠、黑腹果蝇、线虫和恶性疟原虫中构建了 TR3 样酶的突变体，这些突变体的动力学数据表明这些酶较少依赖于使用 Sec 来还原底物。我们认为，本研究中 TR1 和 TR3 类酶之间的机制差异是由于 TR1 中存在“引导杆”，即氨基酸 407-422，但 TR3 类酶中没有。由 Becker 及其同事提出的指导杆 [Fritz-Wolf, K.、Urig, S. 和 Becker, K. (2007) 人硫氧还蛋白还原酶 1 的结构提供了对催化过程中 C 末端重排的见解。 J.莫尔。生物。 370, 116–127]，限制含有C端Gly-Cys-Sec-Gly（氧化还原活性四肽）的C端尾部的运动，使得只有该C端氧化还原中心可以被N端氧化还原中心还原，而排除大多数其他底物。这使得 TR1 高度依赖于 Sec 的使用，因为在此模型中，硒原子负责从 N 端氧化还原中心接受电子并将其提供给底物。 TR1 的 Sec → Cys 突变体中 Se 亲电子性和 Se 亲核性的丧失大大降低了催化活性。相比之下，TR3 类酶对 Sec 的使用依赖性较小，因为这些酶中不存在导向杆，可以使底物更好地进入 N 末端氧化还原中心，并且因为它们可以利用 TR1 无法使用的替代机制途径。
Cytosolic thioredoxin reductase 1 (TR1) is the best characterized of the class of high-molecular weight (Mr) thioredoxin reductases (TRs). TR1 is highly dependent upon the rare amino acid selenocysteine (Sec) for the reduction of thioredoxin (Trx) and a host of small molecule substrates, as mutation of Sec to cysteine (Cys) results in a large decrease in catalytic activity for all substrate types. Previous work in our lab and others has shown that the mitochondrial TR (TR3) is much less dependent upon the use of Sec for the reduction of small molecules. The Sec-dependent substrate utilization behavior of TR1 may be the exception and not the rule as we show that a variety of high-Mr TRs from other organisms, including Drosophila melanogaster, Caenorhabditis elegans, and Plasmodium falciparum, do not require Sec to reduce small molecule substrates, including 5,5′-dithiobis(2-nitrobenzoic acid), lipoic acid, selenite, and selenocystine. The data show that high-Mr TRs can be divided into two groups based upon substrate utilization patterns: a TR1 group and a TR3-like group. We have constructed mutants of TR3-like enzymes from mouse, D. melanogaster, C. elegans, and P. falciparum, and the kinetic data from these mutants show that these enzymes are less dependent upon the use of Sec for the reduction of substrates. We posit that the mechanistic differences between TR1 and the TR3-like enzymes in this study are due to the presence of a “guiding bar”, amino acids 407–422, found in TR1, but not TR3-like enzymes. The guiding bar, proposed by Becker and co-workers [Fritz-Wolf, K., Urig, S., and Becker, K. (2007) The structure of human thioredoxin reductase 1 provides insights into C-terminal rearrangements during catalysis. J. Mol. Biol. 370, 116–127], restricts the motion of the C-terminal tail containing the C-terminal Gly-Cys-Sec-Gly, redox active tetrapeptide so that only this C-terminal redox center can be reduced by the N-terminal redox center, with the exclusion of most other substrates. This makes TR1 highly dependent upon the use of Sec because the selenium atom is responsible for both accepting electrons from the N-terminal redox center and donating them to the substrate in this model. Loss of both Se-electrophilicity and Se-nucleophilicity in the Sec → Cys mutant of TR1 greatly reduces catalytic activity. TR3-like enzymes, in contrast, are less dependent upon the use of Sec because the absence of the guiding bar in these enzymes allows for greater access of the substrate to the N-terminal redox center and because they can make use of alternative mechanistic pathways that are not available to TR1.
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影响因子：
3.7
作者：
Anestål K;Prast-Nielsen S;Cenas N;Arnér ES
通讯作者：
Arnér ES
DOI：
10.1093/protein/gzg088
发表时间：
2003-09-01
期刊：
PROTEIN ENGINEERING
影响因子：
--
作者：
Carugo, O;Cemazar, M;Pongor, S
通讯作者：
Pongor, S
DOI：
10.1073/pnas.2134510100
发表时间：
2003-10-28
影响因子：
11.1
作者：
Gromer, S;Johansson, L;Arnér, ESJ
通讯作者：
Arnér, ESJ
影响因子：
4.8
作者：
Cenas, N;Prast, S;Arnér, ESJ
通讯作者：
Arnér, ESJ
影响因子：
4.8
作者：
Cheng, Qing;Sandalova, Tatyana;Arner, Elias S. J.
通讯作者：
Arner, Elias S. J.