The copper-responsive ScsC protein of Salmonella promotes intramacrophage survival and interacts with the arginine sensor ArtI

The scsABCD (suppressor of copper sensitivity) locus of Salmonella encodes four proteins that resemble the disulphide-folding machinery of other bacteria. Previous work has shown that Salmonella encounters toxic levels of copper during infection and the Scs system provides protection against this copper-mediated toxicity. The current work reports that expression of the soluble periplasmic protein StScsC is induced by copper, and that intramacrophage survival in the presence of copper is diminished by the loss of StScsC. Using a combination of genetic and proteomics approaches, the abundance of various cysteine-containing periplasmic proteins were found to be elevated by StScsC in the Salmonella periplasm, implicating StScsC in the disulphide folding of superoxide dismutases and proteins involved in amino acid sensing and import. Co-purification and mass spectrometry approaches confirmed that the arginine-sensing periplasmic protein ArtI associates with StScsC via a disulphide interaction, and purified ArtI was shown to alter the thiol redox state of purified StScsC. This work reports the first demonstration of a redox partner for the Scs system of Salmonella, and provides insights into how this bacterial pathogen responds to copper stress during infection.