PDBsum entry 1xwc

Electron transport

PDB id: 1xwc

Contents

Protein chain

106 a.a. *

Waters ×42

* Residue conservation analysis

PDB id:

1xwc

Name:

Electron transport

Title:

Drosophila thioredoxin, reduced, p6522

Structure:

Thioredoxin. Chain: a. Engineered: yes

Source:

Drosophila melanogaster. Fruit fly. Organism_taxid: 7227. Gene: trx-2. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

Resolution:

2.30Å R-factor: 0.221 R-free: 0.249

Authors:

M.C.Wahl,A.Irmler,B.Hecker,R.H.Schirmer,K.Becker

Key ref:

M.C.Wahl et al. (2005). Comparative structural analysis of oxidized and reduced thioredoxin from Drosophila melanogaster. J Mol Biol, 345, 1119-1130. PubMed id: 15644209 DOI: 10.1016/j.jmb.2004.11.004

Date:

29-Oct-04 Release date: 16-Nov-04

Protein chain

Q9V429  (THIO2_DROME) -  Thioredoxin-2 from Drosophila melanogaster

Seq: 106 a.a.

Struc: 106 a.a.

DOI no: 10.1016/j.jmb.2004.11.004

J Mol Biol 345:1119-1130 (2005)

PubMed id: 15644209

Comparative structural analysis of oxidized and reduced thioredoxin from Drosophila melanogaster.

M.C.Wahl, A.Irmler, B.Hecker, R.H.Schirmer, K.Becker.

ABSTRACT

Thioredoxins (Trx) participate in essential antioxidant and redox-regulatory processes via a pair of conserved cysteine residues. In dipteran insects like Drosophila and Anopheles, which lack a genuine glutathione reductase (GR), thioredoxins fuel the glutathione system with reducing equivalents. Thus, characterizing Trxs from these organisms contributes to our understanding of redox control in GR-free systems and provides information on novel targets for insect control. Cytosolic Trx of Drosophila melanogaster (DmTrx) is the first thioredoxin that was crystallized for X-ray diffraction analysis in the reduced and in the oxidized form. Comparison of the resulting structures shows rearrangements in the active-site regions. Formation of the C32-C35 disulfide bridge leads to a rotation of the side-chain of C32 away from C35 in the reduced form. This is similar to the situation in human Trx and Trx m from spinach chloroplasts but differs from Escherichia coli Trx, where it is C35 that moves upon change of the redox state. In all four crystal forms that were analysed, DmTrx molecules are engaged in a non-covalent dimer interaction. However, as demonstrated by gel-filtration analyses, DmTrx does not dimerize under quasi in vivo conditions and there is no redox control of a putative monomer/dimer equilibrium. The dimer dissociation constants K(d) were found to be 2.2mM for reduced DmTrx and above 10mM for oxidized DmTrx as well as for the protein in the presence of reduced glutathione. In human Trx, oxidative dimerization has been demonstrated in vitro. Therefore, this finding may indicate a difference in redox control of GR-free and GR-containing organisms.

Selected figure(s)

Figure 1.
Figure 1. Structures of DmTrx. A, Stereo ribbon plot of oxidized DmTrx. a Helices are in red, b strands are in blue and coiled regions are in gold. Helices and strands are numbered from the N to the C terminus. The redox-active disulfide, formed by residues C32 and C35, is displayed with sticks (carbon, gray; sulfur, yellow). B, Stereo images of the final 2F[o] -F[c] electron densities (1s level) covering the redox-active region (ball-and-stick; redox-active cysteine residues are in red). Relevant residues are labeled. Top panel: oxidized form; bottom panel, reduced form. C, Sequence alignment of DmTrx, human thioredoxin and E. coli thioredoxin. Identical residues are shown on a red background, residues conserved in at least two of the molecules are coded yellow. The redox-active cysteine residues (C32 and C35) are shown in blue. The numbering is according to the DmTrx sequence. The secondary structure elements as observed in the present structures are indicated below the alignment. D, Stereo stick figures of the superimposed active-site regions of oxidized and reduced DmTrx. The molecules are color-coded by atom type. Carbon atoms of the reduced form are in a pinkish-gray, those of the oxidized form are in cyan. Arrows indicate possible side-chain and backbone rearrangements, which are observed upon transition from the oxidized to the reduced state.

Figure 2.
Figure 2. Phylogenetic comparisons. A, Stereo plot of the superimposed structures of oxidized DmTrx (yellow), human thioredoxin (red) and E. coli thioredoxin (blue). The molecules are oriented as in Figure 1A. The N and C termini and the active-site cysteine residues (sticks in lighter colors) are indicated. B, Electrostatic potential of DmTrx (top), human thioredoxin (center) and E. coli thioredoxin (bottom) mapped onto the protein surface. Red indicates negatively charged regions, blue denotes positively charged areas. The view in the left panels is the same as in A and in Figure 1A. The molecules in the right-hand panels are rotated by 180° as indicated. A region of strong negative potential surrounding helix a3 is highlighted. This negative region is present in the eukaryotic thioredoxins but not in the bacterial protein.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2005, 345, 1119-1130) copyright 2005.

Figures were selected by an automated process.