Urig Sabine, Lieske Johanna, Fritz-Wolf Karin, Irmler Angelika, Becker Katja
Interdisciplinary Research Center (IFZ), Nutritional Biochemistry, Justus-Liebig-University, D-35392 Giessen, Germany.
FEBS Lett. 2006 Jun 26;580(15):3595-600. doi: 10.1016/j.febslet.2006.05.038. Epub 2006 May 23.
The substrate spectrum of human thioredoxin reductase (hTrxR) is attributed to its C-terminal extension of 16 amino acids carrying a selenocysteine residue. The concept of an evolutionary link between thioredoxin reductase and glutathione reductase (GR) is presently discussed and supported by the fact that almost all residues at catalytic and substrate recognition sites are identical. Here, we addressed the question if a deletion of the C-terminal part of TrxR leads to recognition of glutathione disulfide (GSSG), the substrate of GR. We introduced mutations at the putative substrate binding site to enhance GSSG binding and turnover. However, none of these enzyme species accepted GSSG as substrate better than the full length cysteine mutant of TrxR, excluding a role of the C-terminal extension in preventing GSSG binding. Furthermore, we show that GSSG binding at the N-terminal active site of TrxR is electrostatically disfavoured.
人硫氧还蛋白还原酶（hTrxR）的底物谱归因于其携带硒代半胱氨酸残基的16个氨基酸的C末端延伸。硫氧还蛋白还原酶与谷胱甘肽还原酶（GR）之间进化联系的概念目前正在讨论中，并且几乎所有催化和底物识别位点的残基都相同这一事实也支持了这一概念。在此，我们探讨了TrxR的C末端部分缺失是否会导致对GR的底物谷胱甘肽二硫化物（GSSG）的识别这一问题。我们在假定的底物结合位点引入突变以增强GSSG结合和周转。然而，这些酶种类中没有一种比TrxR的全长半胱氨酸突变体更能接受GSSG作为底物，这排除了C末端延伸在防止GSSG结合中的作用。此外，我们表明TrxR的N末端活性位点处的GSSG结合在静电方面是不利的。
