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Truncated mutants of human thioredoxin reductase 1 do not exhibit glutathione reductase activity
Author(s) -
Urig Sabine,
Lieske Johanna,
Fritz-Wolf Karin,
Irmler Angelika,
Becker Katja
Publication year - 2006
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2006.05.038
Subject(s) - thioredoxin reductase , selenocysteine , glutathione reductase , biochemistry , thioredoxin , cysteine , reductase , mutant , glutathione , chemistry , active site , binding site , glutaredoxin , ferredoxin thioredoxin reductase , enzyme , substrate (aquarium) , selenoprotein , biology , glutathione peroxidase , gene , ecology
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.