Abstract
Cytochromes c (cyts c), essential for respiration and photosynthesis in eukaryotes, confer bacteria respiratory versatility for survival and growth in natural environments. In bacteria having a cyt c maturation (CCM) system, DsbD is required to mediate electron transport from the cytoplasm to CcmG of the Ccm apparatus. Here with cyt c-rich Shewanella oneidensis as the research model, we identify NapB, a cyt c per se, that suppresses the CCM defect of a dsbD mutant during anaerobiosis, when NapB is produced at elevated levels, a result of activation by cAMP-Crp. Data are then presented to suggest that NapB reduces CcmG, leading to the suppression. We further show that NapB proteins capable of rescuing CCM in the dsbD mutant form a small distinct clade. The study sheds light on multifunctionality of cyts c, and more importantly, unravels a self-salvation strategy through which bacteria have evolved to better adjust to the natural world.
Highlights
Cytochromes c, essential for respiration and photosynthesis in eukaryotes, confer bacteria respiratory versatility for survival and growth in natural environments
Given that cyts c are responsible for the wellknown red-brown color of S. oneidensis colonies and cell-pellets and the color intensity is well correlated to the overall cyt c content[7,22], we took advantage of this feature for rapid assessment of the cyt c abundance in all strains used in this study (Fig. 2a, b and Supplementary Figs. 1, 2a)
As genetic complementation for both mutants was successful (Supplementary Fig. 2b), these data manifest that cyt c maturation (CCM) can occur independently of DsbD in S. oneidensis cells living in anaerobic environments
Summary
Cytochromes c (cyts c), essential for respiration and photosynthesis in eukaryotes, confer bacteria respiratory versatility for survival and growth in natural environments. 1234567890():,; Cytochromes c (cyts c), ubiquitous heme-containing proteins present in all domains of life, are primarily involved in energy transduction processes as electron carriers in respiration and photosynthesis[1]. After synthesis in the cytoplasm, apocyts c are exported into the periplasmic compartment via the classical Sec protein secretion apparatus, where the two cysteines of any HBM are promptly oxidized to form a disulfide bond[5] (Fig. 1) This process, catalyzed by the DsbA/DsbB oxidative folding system as well as other accessory proteins and/or small molecule oxidants, has to be promptly carried out as unoxidized apocyts c are degraded rapidly[6,7,8,9]. This DsbD-independent CCM can be promoted by small reducing agents, such as cysteine, reduced glutathione (GSH), and so on[7]
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