Study of Desulfovibrio vulgaris DsrC, an essential protein in sulfate respiration
EMSL Project ID
31792
Abstract
The dissimilatory reduction of sulfur compounds is one of the earliest energy metabolisms detected on Earth, at ~3.5 billion years ago. A key enzyme in sulfur-based energy metabolism is the dissimilatory sulfite reductase (dSiR), which is present in organisms that reduce sulfate or other sulfur compounds and also found in some phototrophic and chemotrophic sulfur oxidisers, where it is proposed to operate in the reverse direction. The dSiR is minimally composed of two subunits, DsrA and DsrB, in an ï?¡2ï?¢2 arrangement. All organisms containing a dSiR include also the genes for the 11 kDa DsrC protein and the DsrMKJOP complex, both of which are proposed to be involved in the process of sulfite reduction. In sulfate reducers of the genus Desulfovibrio the dSiR is distinct from other dSiRs in that it forms a stable complex with DsrC, revealing a direct interaction between this protein and DsrAB. Interestingly, homologues of DsrC, like YccK, are also present in organisms that do not contain dSiRs such as Escherichia coli and Haemophillus influenzae. YccK (renamed as TusE) was recently shown to be involved in sulfur-transfer reactions as part of the biosynthesis of thio-modifications of bacterial tRNA wobble positions. This work provided the first functional assignment of a DsrC-like protein in sulfur metabolism, with important implications to the dissimilatory processes where the function of DsrC has not yet been elucidated.The functional part of DsrC seems to be a highly conserved, flexible C-terminal arm, which displays several strictly conserved residues including two cysteines. The penultimate residue, Cys104C in D. vulgaris, is strictly conserved in all family members (including YccK/TusE), whereas the previous one (Cys93C) is conserved only in DsrC proteins that are involved in dissimilatory sulfur metabolism. There is evidence for the possible involvement of a disulfide bridge between these two cysteines as a redox-active center in the sulfite reduction pathway, and one of the proposals is that DsrC could act as an electron donor for DsrAB. Following on recently published work (Cort et al., 2008) showing that reversible oxidation of DsrC from the sulphur oxidizing bacterium A. vinosum could be monitored by NMR spectroscopy, we propose to conduct similar experiments with DsrC from a sulphate reducer, Desulfovibrio vulgaris Hildenborough. This will require experiments for backbone and partial side chain assignment of the reduced and oxidized forms. The critical data are the 1H and 13C chemical shifts of the beta atoms of both cysteines; these values are well-known indicators of the oxidation state of cysteine. We also propose to conduct preliminary experiments that will establish whether a complete NMR structure determination of the oxidized DsrC monomer can be undertaken. This will entail collection of NOESY spectra to demonstrate the probable quality and quantity of extractable long range distance restraints.
Project Details
Project type
Limited Scope
Start Date
2008-10-13
End Date
2008-12-13
Status
Closed
Released Data Link
Team
Principal Investigator