Bacterial suppressor-of-copper-sensitivity proteins exhibit diverse thiol-disulfide oxidoreductase cellular functions

Disulfide bond (Dsb) oxidoreductases involved in oxidative protein folding govern bacterial survival and virulence. Over the past decade, oligomerization has emerged as a potential factor that dictates oxidoreductase activities. To investigate the role of oligomerization, we studied three Dsb-like ScsC oxidoreductases involved in copper resistance: the monomeric <i>Salmonella enterica</i> StScsC, and the trimeric <i>Proteus mirabilis</i> PmScsC and <i>Caulobacter crescentus</i> CcScsC. For copper sequestration, ScsC proteins must remain in the reduced form. However, all three ScsC proteins exhibit both dithiol oxidation and disulfide reduction activity, despite structural differences and previously reported limited <i>in vitro</i> activity. Most ScsC reductase activity relies on interactions with <i>E. coli</i> DsbD reductase, while oxidase activity depends on environmental oxidation. Interestingly, engineered monomeric PmScsC interacts effectively with the <i>E. coli</i> DsbB oxidase, at the partial expense of its reductase activity. These findings highlight oligomerization of oxidoreductases as a steric hindrance strategy to block undesirable upstream oxidative interactions.