A Bacterial Stress Response Regulates Respiratory Protein Complexes To Control Envelope Stress Adaptation

Abstract

The Cpx envelope stress response mediates adaptation to stresses that affect protein folding within the envelope of Gram-negative bacteria. Recent transcriptome analyses revealed that the Cpx response impacts genes that affect multiple cellular functions predominantly associated with the cytoplasmic membrane. In this study, we examined the connection between the Cpx response and the respiratory complexes NADH dehydrogenase I and cytochrome bo 3 in enteropathogenic Escherichia coli. We found that the Cpx response directly represses the transcription of the nuo and cyo operons and that Cpx-mediated repression of these complexes confers adaptation to stresses that compromise envelope integrity. Furthermore, we found that the activity of the aerobic electron transport chain is reduced in E. coli lacking a functional Cpx response despite no change in the transcription of either the nuo or the cyo operon. Finally, we show that expression of NADH dehydrogenase I and cytochrome bo 3 contributes to basal Cpx pathway activity and that overproduction of individual subunits can influence pathway activation. Our results demonstrate that the Cpx response gauges and adjusts the expression, and possibly the function, of inner membrane protein complexes to enable adaptation to envelope stress.IMPORTANCE Bacterial stress responses allow microbes to survive environmental transitions and conditions, such as those encountered during infection and colonization, that would otherwise kill them. Enteric microbes that inhabit or infect the gut are exposed to a plethora of stresses, including changes in pH, nutrient composition, and the presence of other bacteria and toxic compounds. Bacteria detect and adapt to many of these conditions by using envelope stress responses that measure the presence of stressors in the outermost compartment of the bacterium by monitoring its physiology. The Cpx envelope stress response plays a role in antibiotic resistance and host colonization, and we have shown that it regulates many functions at the bacterial inner membrane. In this report, we describe a novel role for the Cpx response in sensing and controlling the expression of large, multiprotein respiratory complexes at the cytoplasmic membrane of Escherichia coli. The significance of our research is that it will increase our understanding of how these stress responses are involved in antibiotic resistance and the mechanisms used by bacteria to colonize the gut.KEYWORDS envelope stress response, NADH dehydrogenase I, cytochrome bo 3 , membrane protein biogenesis, Cpx envelope stress response, NADH dehydrogenase, cytochrome oxidase, inner membrane, protein complex, protein folding, protein localization, respiration, two-component regulatory systems G ram-negative bacteria are characterized by the structure of their cell envelope, which consists of the inner membrane (IM), the outer membrane, and the peptidoglycan layer within the periplasmic space. Of these, the IM contains the greatest protein diversity (1). Proteins that reside within the IM...

Stress Reduction, Bacterial Style

“…If it is true that the targets of downregulation are proteins that cause the stress in the first place, deletion of these genes might relieve the stress; that is what Raivio and coworkers find. Thus, in a cpxR mutant, when the cell cannot properly mount a Cpx response, cells are killed by treatment with sublethal doses of the antibiotic amikacin or high pH, but deletion of either the nuo or the cyo gene relieves this lethality (5). Strikingly, deletion of these gene clusters also significantly lowers the induction of a Cpx reporter normally induced as cells enter stationary phase.…”

Metabolism of long-chain fatty acids affects disulfide bond formation inEscherichia coliand activates envelope stress response pathways as a combat strategy

“…Several lipoproteins, misfolded pilin subunits of uropathogenic E. coli , and inner membrane respiratory complexes are known inducers of the Cpx pathway [33, 35, 47, 48]. Although the details of Cpx activation by these envelope components remains largely elusive, there are two suggested mechanisms.…”

Impaired Efflux of the Siderophore Enterobactin Induces Envelope Stress inEscherichia coli

“…The second 275 possibility is that activation of the Cpx response, or another regulatory system, by deleting tolC 276 reduces expression of NDH-I or NDH-II. In support of this hypothesis, CpxR has been shown to 277 directly repress the transcription of the operon encoding NDH-I(Guest et al, 2017). At this 278 point, we are unable to distinguish between these two possibilities.…”

“…Under 171 aerobic conditions, electrons released from β-NADH by NDH-I or NDH-II are first transferred to 172 ubiquinone and then to a terminal oxidase, such as cytochrome bo 3 . Given that activity of the 173 NADH oxidation arm of the aerobic respiratory chain is impaired in the tolC mutant (figure 3), 174 and that NDH-I and cytochrome bo 3 contribute to Cpx pathway activity in enteropathogenic E. 175 coli(Guest et al, 2017), we next asked whether NDH-I, NDH-II, or cytochrome bo 3 are required 176 for activation of the Cpx response in the tolC mutant. To test this hypothesis, we mutated each 177 of these electron transport chain components in E. coli containing or lacking tolC and measured 178Cpx pathway activity using the cpxP-lacZ transcriptional reporter.…”