The FeoC Protein Leads to High Cellular Levels of the Fe(II) Transporter FeoB by Preventing FtsH Protease Regulation of FeoB in Salmonella enterica

In the gammaproteobacteria, the FeoA, FeoB, and FeoC proteins constitute the Feo system, which mediates ferrous iron [Fe(II)] import. Of these Feo proteins, FeoB is an inner membrane Fe(II) transporter that is aided by the small protein FeoA. However, the role of another small protein, FeoC, has remained unknown. Here we report that the FeoC protein is necessary for FeoB protein-mediated Fe(II) uptake in Salmonella experiencing low levels of oxygen and iron. The FeoC protein was found to directly bind to the FeoB transporter, leading to high cellular levels of FeoB. Depletion of the FtsH protease enabled high levels of FeoB in the absence of FeoC, suggesting that the FeoC protein protects the FeoB transporter from FtsH-mediated proteolysis. Our present study provides a singular example of bacteria that can control expression of iron uptake systems posttranslationally by employing a small iron transporter-binding protein.