Thioredoxin reductase

 

Thioredoxin reductase contains FAD and NADPH binding domains that are structurally similar to the corresponding domains of the related enzyme glutathione reductase. The relative orientation of these domains is, however, very different in the two enzymes: when the FAD domains of thioredoxin and glutathione reductases are superimposed, the NADPH domain of one is rotated by 66 degrees with respect to the other. The observed binding mode of NADP+ in thioredoxin reductase is non-productive in that the nicotinamide ring is more than 17 A from the flavin ring system. Thioredoxin reductase belongs to the class-II pyridine nucleotide-disulfide oxidoreductase family.

 

Reference Protein and Structure

Sequence
P0A9P4 UniProt (1.8.1.9) IPR005982 (Sequence Homologues) (PDB Homologues)
Biological species
Escherichia coli K-12 (Bacteria) Uniprot
PDB
1tde - CRYSTAL STRUCTURE OF ESCHERICHIA COLI THIOREDOXIN REDUCTASE REFINED AT 2 ANGSTROM RESOLUTION: IMPLICATIONS FOR A LARGE CONFORMATIONAL CHANGE DURING CATALYSIS (2.1 Å) PDBe PDBsum 1tde
Catalytic CATH Domains
3.50.50.60 CATHdb (see all for 1tde)
Cofactors
Fadh2(2-) (1)
Click To Show Structure

Enzyme Reaction (EC:1.8.1.9)

L-cysteine residue
CHEBI:29950ChEBI
+
NADP(3-)
CHEBI:58349ChEBI
→
L-cystine residue
CHEBI:50058ChEBI
+
hydron
CHEBI:15378ChEBI
+
NADPH(4-)
CHEBI:57783ChEBI
Alternative enzyme names: NADP--thioredoxin reductase, NADPH--thioredoxin reductase, NADPH(2):oxidized thioredoxin oxidoreductase, Thioredoxin reductase (NADPH), NADPH:oxidized thioredoxin oxidoreductase,

Enzyme Mechanism

Introduction

The most direct pathway for reducing equivalents in turnover would require a ternary complex in which the flavin is reduced by NADPH while thioredoxin is being reduced by the active site dithiol when the enzyme is in the proposed FR conformation (allows flavin reduction by pyridine nucleotide). Following the reversal of rotation, the nascent active site disulfide could be reduced by the newly reduced flavin.

Catalytic Residues Roles

UniProt PDB* (1tde)
Cys136, Cys139 Cys135A, Cys138A In the ground state of the protein is a disulfide bond that is cleaved during the course of the reaction to regenerate the thioredoxin molecule. covalent catalysis, proton shuttle (general acid/base)
Asp140 Asp139A Acts as a general acid/base. proton shuttle (general acid/base)
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

References

  1. Waksman G et al. (1994), J Mol Biol, 236, 800-816. Crystal Structure of Escherichia coli Thioredoxin Reductase Refined at 2 Å Resolution. DOI:10.1006/jmbi.1994.1190.
  2. Lennon BW (2000), Science, 289, 1190-1194. Twists in Catalysis: Alternating Conformations of Escherichia coli Thioredoxin Reductase. DOI:10.1126/science.289.5482.1190.
  3. Lennon BW et al. (1996), Biochemistry, 35, 4704-4712. Enzyme-monitored turnover of Escherichia coli thioredoxin reductase: insights for catalysis. DOI:10.1021/bi952521i. PMID:8664260.
  4. Williams CH Jr (1995), FASEB J, 9, 1267-1276. Mechanism and structure of thioredoxin reductase from Escherichia coli. PMID:7557016.

Step 1.

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Catalytic Residues Roles

Residue Roles
Cys135A proton shuttle (general acid/base)
Cys138A proton shuttle (general acid/base)
Cys135A covalent catalysis
Cys138A covalent catalysis
Asp139A proton shuttle (general acid/base)

Chemical Components

Step 1.

Contributors

Christian Drew, Craig Porter, Gemma L. Holliday