A dimerization interface mediated by functionally critical residues creates interfacial disulfide bonds and copper sites in CueP

Evolution of Copper Homeostasis and Virulence in Salmonella

Salmonella enterica sv. Typhimurium modulates the expression of factors essential for virulence, contributing to its survival against the surge of copper (Cu) in the Salmonella-containing vacuole. This bactericidal host innate immune component primarily targets the bacterial envelope, where most cuproproteins are localized. While in most enteric species periplasmic Cu homeostasis is maintained by the CusR/CusS-controlled CusCFBA efflux system encoded in the cus locus, we noticed that these genes were lost from the Salmonella-core genome. At the same time, Salmonella acquired cueP, coding for a periplasmic Cu chaperone. As cus, cueP was shown to be essential for bacterial survival in a copper-rich environment under anaerobiosis, suggesting that it can functionally substitute the CusCFBA system. In the present study, the whole Escherichia coli cus locus was reintroduced to the chromosome of the Salmonella wild-type or the ΔcueP strain. While the integrated cus locus did not affect Cu resistance under aerobic conditions, it increases Cu tolerance under anaerobiosis, irrespective of the presence or absence of cueP. In contrast to the Cus system, CueP expression is higher at high copper concentrations and persisted over time, suggesting separate functions. Finally, we observed that, regardless of the presence or absence of cus, a mutant deleted of cueP shows a deficiency in replication inside macrophages compared to the wild-type strain. Our results demonstrate that CueP and CusCFBA exert redundant functions for metal resistance, but not for intracellular survival, and therefore for the virulence of this pathogen.

CpxR/CpxA Controls scsABCD Transcription To Counteract Copper and Oxidative Stress in Salmonella enterica Serovar Typhimurium

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 Salmonella genome, the system encoded by the scsABCD locus was shown to be required to cope with Cu and H₂O₂ stress. Here we report that this locus forms an operon whose transcription is driven by a promoter upstream of scsA and depends on CpxR/CpxA and on Cu. Furthermore, genes homologous to scsB, scsC, and scsD are always detected immediately downstream of scsA and in the same genetic arrangement in all scsA-harboring enterobacterial species. Also, a CpxR-binding site is detected upstream of scsA in most of those species, providing evidence of evolutionarily conserved function and regulation. Each individual scs gene shows a different role in copper and/or H₂O₂ resistance, indicating hierarchical contributions of these factors in the defense against these intoxicants. A protective effect of Cu preincubation against H₂O₂ toxicity and the increased Cu-mediated activation of cpxP in the ΔscsABCD 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 Salmonella envelope.IMPORTANCE Copper intoxication triggers both specific and nonspecific responses in Salmonella The scs 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 Escherichia coli Still, the conditions under which the scs 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 H₂O₂ and copper stress. We establish that the scs 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 database resources for biological macromolecules

This Briefing reviews the widely used, currently active, up-to-date databases derived from the worldwide Protein Data Bank (PDB) to facilitate browsing, finding and exploring its entries. These databases contain visualization and analysis tools tailored to specific kinds of molecules and interactions, often including also complex metrics precomputed by experts or external programs, and connections to sequence and functional annotation databases. Importantly, updates of most of these databases involves steps of curation and error checks based on specific expertise about the subject molecules or interactions, and removal of sequence redundancy, both leading to better data sets for mining studies compared with the full list of raw PDB entries. The article presents the databases in groups such as those aimed to facilitate browsing through PDB entries, their molecules and their general information, those built to link protein structure with sequence and dynamics, those specific for transmembrane proteins, nucleic acids, interactions of biomacromolecules with each other and with small molecules or metal ions, and those concerning specific structural features or specific protein families. A few webservers directly connected to active databases, and a few databases that have been discontinued but would be important to have back, are also briefly commented on. Along the Briefing, sample cases where these databases have been used to aid structural studies or advance our knowledge about biological macromolecules are referenced. A few specific examples are also given where using these databases is easier and more informative than using raw PDB data.

Compartment and signal-specific codependence in the transcriptional control of Salmonella periplasmic copper homeostasis

Copper homeostasis is essential for bacterial pathogen fitness and infection, and has been the focus of a number of recent studies. In Salmonella, envelope protection against copper overload and macrophage survival depends on CueP, a major copper-binding protein in the periplasm. This protein is also required to deliver the metal ion to the Cu/Zn superoxide dismutase SodCII. The Salmonella-specific CueP-coding gene was originally identified as part of the Cue regulon under the transcriptional control of the cytoplasmic copper sensor CueR, but its expression differs from the rest of CueR-regulated genes. Here we show that cueP expression is controlled by the concerted action of CueR, which detects the presence of copper in the cytoplasm, and by CpxR/CpxA, which monitors envelope stress. Copper-activated CueR is necessary for the appropriate spatial arrangement of the -10 and -35 elements of the cueP promoter, and CpxR is essential to recruit the RNA polymerase. The integration of two ancestral sensory systems-CueR, which provides signal specificity, and CpxR/CpxA, which detects stress in the bacterial envelope-restricts the expression of this periplasmic copper resistance protein solely to cells encountering surplus copper that disturbs envelope homeostasis, emulating the role of the CusR/CusS regulatory system present in other enteric bacteria.