Identification of the ferrioxamine B receptor,FoxB, inEscherichia coli K12

The photoreactivep-azidobenzoyl analog of ferrioxamine B was used to show that ferrioxamine-B-mediated iron transport is separate and distinct from coprogen-mediated iron transport inEscherichia coli. Photolysis of this analog inhibited uptake of ⁵⁹Fe]ferrioxamine B but not ⁵⁹Fe]coprogen or ⁵⁹Fe]ferrichrome. Conversely, photolysis of thep-azidobenzoyl analog of coprogen B inhibited uptake of ⁵⁹Fe]coprogen but not ⁵⁹Fe]ferrioxamine B or ⁵⁹Fe]ferrichrome. Photolabeling of outer membranes withp-azidobenzoyl-⁵⁹Fe]ferrioxamine B resulted in the labeling of two iron-regulated peptides with molecular masses of about 66 and 26 kDa. Expression of these peptides was increased when ferrioxamine B was the sole iron source. Both peptides were present in outer membrane preparations of thefhuF mutant H1717, but the 66 kDa peptide was not inducible. These results are evidence for an outer membrane receptor inE. coli unique for linear ferrioxamines.