PDBsum entry: 1tdf

Oxidoreductase(flavoenzyme)

PDB id: 1tdf

Contents

Protein chain

316 a.a. *

Ligands

FAD

NAP

Waters ×474

* Residue conservation analysis

PDB id:

1tdf

Name:

Oxidoreductase(flavoenzyme)

Title:

Crystal structure of escherichia coli thioredoxin reductase 2 angstrom resolution: implications for a large conformatio during catalysis

Structure:

Thioredoxin reductase. Chain: a. Engineered: yes

Source:

Escherichia coli. Organism_taxid: 562

Biol. unit:

Dimer (from PQS)

Resolution:

2.30Å R-factor: 0.179

Authors:

G.Waksman,T.S.R.Krishna,C.H.Williams Junior,J.Kuriyan

Key ref:

G.Waksman et al. (1994). Crystal structure of Escherichia coli thioredoxin reductase refined at 2 A resolution. Implications for a large conformational change during catalysis. J Mol Biol, 236, 800-816. PubMed id: 8114095 DOI: 10.1006/jmbi.1994.1190

Date:

14-Jan-94 Release date: 30-Nov-94

Protein chain

P0A9P4  (TRXB_ECOLI) -  Thioredoxin reductase

Seq: 321 a.a.

Struc: 316 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

Enzyme reactions

• Enzyme class: E.C.1.8.1.9 - Thioredoxin-disulfide reductase.
• Reaction: Thioredoxin + NADP⁺ = thioredoxin disulfide + NADPH

Thioredoxin + NADP(+) (Bound ligand (Het Group name = NAP) corresponds exactly) = thioredoxin disulfide + NADPH

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

 Gene Ontology (GO) functional annotation 

• Cellular component: cytoplasm (1 term)
• Biological process: oxidation-reduction process (2 terms)
• Biochemical function: protein binding (4 terms)

reference

DOI no: 10.1006/jmbi.1994.1190

J Mol Biol 236:800-816 (1994)

PubMed id: 8114095

Crystal structure of Escherichia coli thioredoxin reductase refined at 2 A resolution. Implications for a large conformational change during catalysis.

G.Waksman, T.S.Krishna, C.H.Williams, J.Kuriyan.

ABSTRACT

The crystal structures of three forms of Escherichia coli thioredoxin reductase have been refined: the oxidized form of the wild-type enzyme at 2.1 A resolution, a variant containing a cysteine to serine mutation at the active site (Cys138Ser) at 2.0 A resolution, and a complex of this variant with nicotinamide adenine dinucleotide phosphate (NADP+) at 2.3 A resolution. The enzyme mechanism involves the transfer of reducing equivalents from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to a disulfide bond in the enzyme, via a flavin adenine dinucleotide (FAD). 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. While in glutathione reductase the redox active disulfide is located in the FAD domain, in thioredoxin reductase it is in the NADPH domain and is part of a four-residue sequence (Cys-Ala-Thr-Cys) that is close in structure to the corresponding region of thioredoxin (Cys-Gly-Pro-Cys), with a root-mean-square deviation of 0.22 A for atoms in the disulfide bonded ring. There are no significant conformational differences between the structure of the wild-type enzyme and that of the Cys138Ser mutant, except that a disulfide bond is not present in the latter. The disulfide bond is positioned productively in this conformation of the enzyme, i.e. it stacks against the flavin ring system in a position that would facilitate its reduction by the flavin. However, the cysteine residues are relatively inaccessible for interaction with the substrate, thioredoxin. These results suggest that thioredoxin reductase must undergo conformational changes during enzyme catalysis. All three structures reported here are for the same conformation of the enzyme and no direct evidence is available as yet for such conformational changes. The simplest possibility is that the NADPH domain rotates between the conformation observed here and an orientation similar to that seen in glutathione reductase. This would alternately place the nicotinamide ring and the disulfide bond near the flavin ring, and expose the cysteine residues for reaction with thioredoxin in the hypothetical conformation.(ABSTRACT TRUNCATED AT 400 WORDS)