CpxR/CpxA ControlsscsABCDTranscription To Counteract Copper and Oxidative Stress in Salmonella enterica Serovar Typhimurium

Abstract

Periplasmic thiol/disulfide oxidoreductases participate in the formation and isomerization of disulfide bonds and contribute to the virulence of pathogenic microorganisms. Among the systems encoded in the genome, the system encoded by the locus was shown to be required to cope with Cu and HO stress. Here we report that this locus forms an operon whose transcription is driven by a promoter upstream of and depends on CpxR/CpxA and on Cu. Furthermore, genes homologous to, , and are always detected immediately downstream of and in the same genetic arrangement in all-harboring enterobacterial species. Also, a CpxR-binding site is detected upstream of in most of those species, providing evidence of evolutionarily conserved function and regulation. Each individual gene shows a different role in copper and/or HO resistance, indicating hierarchical contributions of these factors in the defense against these intoxicants. A protective effect of Cu preincubation against HO toxicity and the increased Cu-mediated activation of in the Δ mutant suggest that the CpxR/CpxA-controlled transcription of the ScsABCD system contributes to prevent Cu toxicity and to restore the redox balance at the envelope. Copper intoxication triggers both specific and nonspecific responses in The locus, which codes for periplasmic thiol/disulfide-oxidoreductase/isomerase-like proteins, has been the focus of attention because it is necessary for copper resistance, oxidative stress responses, and virulence and because it is not present in nonpathogenic Still, the conditions under which the locus is expressed and the roles of its individual components remain unknown. In this report, we examine the contribution of each Scs factor to survival under HO and copper stress. We establish that the genes form a copper-activated operon controlled by the CpxR/CpxA signal transduction system, and we provide evidence of its conserved gene arrangement and regulation in other bacterial pathogens.

Structural and functional studies of suppressor of copper sensitivity proteins from Proteus mirabilis

“…Studies of the suppressor of copper sensitivity (Scs) proteins have shown that they are involved in the bacterial response to copper and oxidative stress, but their specific cellular role is unknown. Typhimurium, was shown to be upregulated in the presence of copper and dependent on the transcription factor CpxR (112). CpxR, in concert with CpxA, senses misfolded periplasmic proteins and allows the transcription of the Cu(II) binding protein CueP and other proteins under copper stress (113)(114)(115)(116).…”

“…Typhimiurium results in reduced growth of the bacterial pathogen under copper stress (112,117). However, one study found that the Δscs strain had increased invasiveness in vitro and in a mouse model of infection (117).…”

“…The four proteins encoded in the S. Typhimurium scs locus, ScsA, ScsB, ScsC and ScsD, all contain cysteine residues predicted to form redox-active pairs and three harbour predicted thioredoxin folds (111). The Scs proteins are encoded in a number of pathogenic bacteria (112,118), though little is known about these proteins. Most of the published work has focused on the Scs systems in S. Typhimurium and, to a lesser extent, Caulobacter crescentus.…”

“…No biochemical or structural analyses have been performed on any ScsA protein to date, however, genetic analysis has provided some insight into its biological function. Deletion of scsA (ΔscsA) in S. Typhimurium does not increase the sensitivity of the bacteria to copper, revealing that the encoded protein does not play a role in the response to copper stress (112,117). Two studies have found that scsA deletion mutants are sensitive to H 2 O 2 (which generates reactive oxygen species) suggesting that ScsA plays a role in the response to oxidative stress (112,117).…”

“…Deletion of scsA (ΔscsA) in S. Typhimurium does not increase the sensitivity of the bacteria to copper, revealing that the encoded protein does not play a role in the response to copper stress (112,117). Two studies have found that scsA deletion mutants are sensitive to H 2 O 2 (which generates reactive oxygen species) suggesting that ScsA plays a role in the response to oxidative stress (112,117). When exposed to 6 mM H 2 O 2 the ΔscsABCD S. Typhimurium strain displays the same phenotype as the ΔscsA strain (112).…”