The bdbDC Operon of Bacillus subtilisEncodes Thiol-disulfide Oxidoreductases Required for Competence Development

Abstract

The development of genetic competence in the Grampositive eubacterium Bacillus subtilis is a complex postexponential process. Here we describe a new bicistronic operon, bdbDC, required for competence development, which was identified by the B. subtilis Systematic Gene Function Analysis program. Inactivation of either the bdbC or bdbD genes of this operon results in the loss of transformability without affecting recombination or the synthesis of ComK, the competence transcription factor. BdbC and BdbD are orthologs of enzymes known to be involved in extracytoplasmic disulfide bond formation. Consistent with this, BdbC and BdbD are needed for the secretion of the Escherichia coli disulfide bond-containing alkaline phosphatase, PhoA, by B. subtilis. Similarly, the amount of the disulfide bond-containing competence protein ComGC is severely reduced in bdbC or bdbD mutants. In contrast, the amounts of the competence proteins ComGA and ComEA remain unaffected by bdbDC mutations. Taken together, these observations imply that in the absence of either BdbC or BdbD, ComGC is unstable and that BdbC and BdbD catalyze the formation of disulfide bonds that are essential for the DNA binding and uptake machinery.

Co-factor Insertion and Disulfide Bond Requirements for Twin-arginine Translocase-dependent Export of the Bacillus subtilis Rieske Protein QcrA

“…The fast degradation of the non-disulfide bonded QcrA-C123S protein is in line with the previously documented degradation of other extracytoplasmic proteins, such as ComEC and ComGC, lacking an essential disulfide bond (60,61). It should, however, be noted that, unlike ComEC or ComGC, the presence of QcrA was not affected by any of the bdb mutations that are known to interfere with oxidative protein folding in B. subtilis (51,(61)(62)(63). Specifically, we tested QcrA production directed from the chromosomal qcrA gene in previously analyzed bdbA-bdbB, bdbB-BdbC, or bdbC-bdbD mutant strains (Fig.…”

Staphylococcus aureus DsbA Does Not Have a Destabilizing Disulfide

“…3,58). Functional homologues of Dsb proteins have also been found in Gram-positive bacteria (15)(16)(17)(18)(19)(20)(21)(22); however our knowledge of the processes of oxidative folding in these organisms is scarce. Moreover, investigations of Gram-positive Dsb proteins indicate that we may not be able to directly extrapolate the mechanisms observed in E. coli to these organisms.…”

“…Functional orthologs of Dsb proteins in Gram-positive organisms include Bacillus brevis Bdb (a DsbA ortholog) (16), Bacillus subtilis BdbB and BdbC (orthologs of DsbB), B. subtilis BdbD (a DsbA ortholog) (17)(18)(19)(20)(21) and Mycobacterium tuberculosis DsbE (structurally a homolog of DsbE, but functionally an oxidant like DsbA) (22). Moreover, functional virulence factors produced by Gram-positive bacteria, such as the human pathogen Staphylococcus aureus, contain disulfide bonds that are introduced during folding (23)(24)(25).…”

Functional Analysis of Paralogous Thiol-disulfide Oxidoreductases in Streptococcus gordonii

“…Although Grampositive DsbA homologs have been identified, few have demonstrated functions, and those that do appear to perform specialized functions in the cell. For example, substrates of the DsbAB homologs in Bacillus subtilis, BdbDC, are limited to proteins required for genetic competence, such as the ComGC pseudopilus and ComEC channel protein (9,10). In Staphylococcus aureus, SaDsbA has also been shown to be required for the stable production of ComGC (11); however, no other substrates or phenotypes have been identified despite detailed functional and structural characterization (12,13).…”