Absence of Thiol-Disulfide Oxidoreductase DsbA Impairs -Type Cytochrome Oxidase Biogenesis in .

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 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 -type cytochrome oxidase (-Cox) on enriched medium. Availability of chemical oxidants (e.g., Cu or a mixture of cysteine and cystine) in the medium becomes critical for growth and -Cox production in the absence of DsbA. Indeed, addition of Cu to the enriched medium suppresses, and conversely, omission of Cu from the minimal medium induces, growth and -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 -Cox, especially in enriched medium where bioavailable Cu is scarce. This is the first report describing that DsbA activity is required for full respiratory capability of , and in particular, for proper biogenesis of its -Cox. We propose that absence of DsbA, besides impairing the maturation of the -type cytochrome subunits, also affects the incorporation of Cu into the catalytic subunit of -Cox. Defective high affinity Cu acquisition pathway, which includes the MFS-type Cu importer CcoA, and lower production of the -type cytochrome subunits lead together to improper assembly and degradation of -Cox.