Bacteria use folding enzymes to produce functional virulence factors. These foldases include the Dsb family of proteins, which catalyse a key step in the protein-folding pathway, the introduction of disulfide bonds. The Dsb oxidative system, which includes an oxidative DsbA/DsbB pathway and an isomerase DsbC/DsbD pathway, is present in numerous bacterial species. However, many pathogens encode an extended arsenal of thiol oxidation pathways. For example, genomic analysis of the human pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) revealed a second Dsb-like system encoded by the scsABCD locus which has been associated with an increased tolerance to copper. This project focuses on the detailed characterisation of the Dsb-like systems in S. Typhimurium and their role in copper resistance. Using a combination of biochemical and biophysical approaches, we have shown that Salmonella contains separate Dsb and Scs electron transfer pathways, dedicated to the formation and reduction of disulfide bonds in different substrates. Furthermore, we have also dissected the molecular mechanism underlying Scs system mediated copper tolerance in Salmonella. Taken together, these data show that Scs proteins are novel reducing proteins involved in protection against copper ion toxicity by sequestering and transferring copper to periplasmic copper binding proteins. Our findings in Salmonella could have implications on establishing how other Gram-negative pathogens that contain similar Dsb-like redox enzymes, generate disulfide containing virulence proteins and resist the antibacterial action of copper.