Journal Article
Journal of Bacteriology, vol. 192, iss. 6, pp. 1652-1661, 2010
Authors
Frauke Grimm, John R. Cort, Christiane Dahl
Abstract
ABSTRACT
In the purple sulfur bacterium
Allochromatium vinosum
, the reverse-acting dissimilatory sulfite reductase (DsrAB) is the key enzyme responsible for the oxidation of intracellular sulfur globules. The genes
dsrAB
are the first and the gene
dsrR
is the penultimate of the 15 genes of the
dsr
operon in
A. vinosum
. Genes homologous to
dsrR
occur in a number of other environmentally important sulfur-oxidizing bacteria utilizing Dsr proteins. DsrR exhibits sequence similarities to A-type scaffolds, like IscA, that partake in the maturation of protein-bound iron-sulfur clusters. We used nuclear magnetic resonance (NMR) spectroscopy to solve the solution structure of DsrR and to show that the protein is indeed structurally highly similar to A-type scaffolds. However, DsrR does not retain the Fe-S- or the iron-binding ability of these proteins, which is due to the lack of all three highly conserved cysteine residues of IscA-like scaffolds. Taken together, these findings suggest a common function for DsrR and IscA-like proteins different from direct participation in iron-sulfur cluster maturation. An
A. vinosum
Δ
dsrR
deletion strain showed a significantly reduced sulfur oxidation rate that was fully restored upon complementation with
dsrR
in
trans
. Immunoblot analyses revealed a reduced level of DsrE and DsrL in the Δ
dsrR
strain. These proteins are absolutely essential for sulfur oxidation. Transcriptional and translational gene fusion experiments suggested the participation of DsrR in the posttranscriptional control of the
dsr
operon, similar to the alternative function of cyanobacterial IscA as part of the sense and/or response cascade set into action upon iron limitation.
