Truncated mutants of human thioredoxin reductase 1 do not exhibit glutathione reductase activity.
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.
Urig
Sabine
S
Interdisciplinary Research Center (IFZ), Nutritional Biochemistry, Justus-Liebig-University, D-35392 Giessen, Germany.
Lieske
Johanna
J
Fritz-Wolf
Karin
K
Irmler
Angelika
A
Becker
Katja
K
D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D005980:Glutathione Reductase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013379:Substrate Specificity; D054481:Thioredoxin Reductase 1; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics* / Q000378:metabolism*
D005980:Glutathione Reductase; C516124:TXNRD1 protein, human; D054481:Thioredoxin Reductase 1; D013880:Thioredoxin-Disulfide Reductase