Absence of Thiol-Disulfide Oxidoreductase DsbA Impairs
cbb3-Type Cytochrome
c Oxidase Biogenesis in
Rhodobacter capsulatus.
Front Microbiol 2017;
8:2576. [PMID:
29312253 PMCID:
PMC5742617 DOI:
10.3389/fmicb.2017.02576]
[Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Accepted: 12/11/2017] [Indexed: 12/20/2022] Open
Abstract
The thiol-disulfide oxidoreductase DsbA carries out oxidative folding of extra-cytoplasmic proteins by catalyzing the formation of intramolecular disulfide bonds. It has an important role in various cellular functions, including cell division. The purple non-sulfur bacterium Rhodobacter capsulatus mutants lacking DsbA show severe temperature-sensitive and medium-dependent respiratory growth defects. In the presence of oxygen, at normal growth temperature (35°C), DsbA− mutants form colonies on minimal medium, but they do not grow on enriched medium where cells elongate and lyse. At lower temperatures (i.e., 25°C), cells lacking DsbA grow normally in both minimum and enriched media, however, they do not produce the cbb3-type cytochrome c oxidase (cbb3-Cox) on enriched medium. Availability of chemical oxidants (e.g., Cu2+ or a mixture of cysteine and cystine) in the medium becomes critical for growth and cbb3-Cox production in the absence of DsbA. Indeed, addition of Cu2+ to the enriched medium suppresses, and conversely, omission of Cu2+ from the minimal medium induces, growth and cbb3-Cox defects. Alleviation of these defects by addition of redox-active chemicals indicates that absence of DsbA perturbs cellular redox homeostasis required for the production of an active cbb3-Cox, especially in enriched medium where bioavailable Cu2+ is scarce. This is the first report describing that DsbA activity is required for full respiratory capability of R. capsulatus, and in particular, for proper biogenesis of its cbb3-Cox. We propose that absence of DsbA, besides impairing the maturation of the c-type cytochrome subunits, also affects the incorporation of Cu into the catalytic subunit of cbb3-Cox. Defective high affinity Cu acquisition pathway, which includes the MFS-type Cu importer CcoA, and lower production of the c-type cytochrome subunits lead together to improper assembly and degradation of cbb3-Cox.
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