This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Deshmukh, M. Articles by Daldal, F. Search for Related Content PubMed PubMed Citation Articles by Deshmukh, M. Articles by Daldal, F.

The Dithiol:Disulfide Oxidoreductases DsbA and DsbB of Rhodobacter capsulatus Are Not Directly Involved in Cytochrome c Biogenesis, but Their Inactivation Restores the Cytochrome c Biogenesis Defect of CcdA-Null Mutants

Meenal Deshmukh, Serdar Turkarslan, Donniel Astor, Maria Valkova-Valchanova, and Fevzi Daldal^*

Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104

Received 3 December 2002/ Accepted 20 March 2003

The cytoplasmic membrane protein CcdA and its homologues in other species, such as DsbD of Escherichia coli, are thought to supply the reducing equivalents required for the biogenesis of c-type cytochromes that occurs in the periplasm of gram-negative bacteria. CcdA-null mutants of the facultative phototroph Rhodobacter capsulatus are unable to grow under photosynthetic conditions (Ps^-) and do not produce any active cytochrome c oxidase (Nadi^-) due to a pleiotropic cytochrome c deficiency. However, under photosynthetic or respiratory growth conditions, these mutants revert frequently to yield Ps⁺ Nadi⁺ colonies that produce c-type cytochromes despite the absence of CcdA. Complementation of a CcdA-null mutant for the Ps⁺ growth phenotype was attempted by using a genomic library constructed with chromosomal DNA from a revertant. No complementation was observed, but plasmids that rescued a CcdA-null mutant for photosynthetic growth by homologous recombination were recovered. Analysis of one such plasmid revealed that the rescue ability was mediated by open reading frame 3149, encoding the dithiol:disulfide oxidoreductase DsbA. DNA sequence data revealed that the dsbA allele on the rescuing plasmid contained a frameshift mutation expected to produce a truncated, nonfunctional DsbA. Indeed, a dsbA ccdA double mutant was shown to be Ps⁺ Nadi⁺, establishing that in R. capsulatus the inactivation of dsbA suppresses the c-type cytochrome deficiency due to the absence of ccdA. Next, the ability of the wild-type dsbA allele to suppress the Ps⁺ growth phenotype of the dsbA ccdA double mutant was exploited to isolate dsbA-independent ccdA revertants. Sequence analysis revealed that these revertants carried mutations in dsbB and that their Ps⁺ phenotypes could be suppressed by the wild-type allele of dsbB. As with dsbA, a dsbB ccdA double mutant was also Ps⁺ Nadi⁺ and produced c-type cytochromes. Therefore, the absence of either DsbA or DsbB restores c-type cytochrome biogenesis in the absence of CcdA. Finally, it was also found that the DsbA-null and DsbB-null single mutants of R. capsulatus are Ps⁺ and produce c-type cytochromes, unlike their E. coli counterparts, but are impaired for growth under respiratory conditions. This finding demonstrates that in R. capsulatus the dithiol:disulfide oxidoreductases DsbA and DsbB are not essential for cytochrome c biogenesis even though they are important for respiration under certain conditions.

Present address: Medarex, Inc., Bloomsbury, NJ 08804.

This article has been cited by other articles:

• Onder, O., Turkarslan, S., Sun, D., Daldal, F. (2008). Overproduction or Absence of the Periplasmic Protease DegP Severely Compromises Bacterial Growth in the Absence of the Dithiol: Disulfide Oxidoreductase DsbA. Mol. Cell. Proteomics 7: 875-890 [Abstract] [Full Text]  
• Borsetti, F., Francia, F., Turner, R. J., Zannoni, D. (2007). The Thiol:Disulfide Oxidoreductase DsbB Mediates the Oxidizing Effects of the Toxic Metalloid Tellurite (TeO32-) on the Plasma Membrane Redox System of the Facultative Phototroph Rhodobacter capsulatus. J. Bacteriol. 189: 851-859 [Abstract] [Full Text]  
• Feissner, R. E., Beckett, C. S., Loughman, J. A., Kranz, R. G. (2005). Mutations in Cytochrome Assembly and Periplasmic Redox Pathways in Bordetella pertussis. J. Bacteriol. 187: 3941-3949 [Abstract] [Full Text]  
• Sanders, C., Deshmukh, M., Astor, D., Kranz, R. G., Daldal, F. (2005). Overproduction of CcmG and CcmFHRc Fully Suppresses the c-Type Cytochrome Biogenesis Defect of Rhodobacter capsulatus CcmI-Null Mutants. J. Bacteriol. 187: 4245-4256 [Abstract] [Full Text]  
• Edeling, M. A., Ahuja, U., Heras, B., Thony-Meyer, L., Martin, J. L. (2004). The Acidic Nature of the CcmG Redox-Active Center Is Important for Cytochrome c Maturation in Escherichia coli. J. Bacteriol. 186: 4030-4033 [Abstract] [Full Text]  
• Allen, J. W. A., Barker, P. D., Ferguson, S. J. (2003). A Cytochrome b562 Variant with a c-Type Cytochrome CXXCH Heme-binding Motif as a Probe of the Escherichia coli Cytochrome c Maturation System. J. Biol. Chem. 278: 52075-52083 [Abstract] [Full Text]