Ferric enterobactin binding and utilization by Neisseria gonorrhoeae

FetA, formerly designated FrpB, an iron-regulated, 76-kDa neisserial outer membrane protein, shows sequence homology to the TonB-dependent family of r eceptors that transport iron into gram-negative bacteria. Although FetA is commonly expressed by most neisserial strains and is a potential vaccine ca ndidate for both Neisseria gonorrhoeae and Neisseria meningitidis, its func tion in cell physiology was previously undefined. We now report that FetA f unctions as an enterobactin receptor. N.gonorrhoeae FA1090 utilized ferric enterobactin as the sole iron source when supplied with ferric enterobactin at approximately 10 mu M but growth stimulation was abolished when an omeg a (Omega) cassette was inserted within fetA or when tonB was insertionally interrupted. FA1090 FetA specifically bound Fe-59-enterobactin, with a K-d of approximately 5 mu M. Monoclonal antibodies raised against the Escherich ia coli enterobactin receptor, FepA, recognized FetA in Western blots, and amino acid sequence comparisons revealed that residues previously implicate d in ferric enterobactin binding by FepA were partially conserved in FetA. An open reading frame downstream of fetA, designated fetB, predicted a prot ein with sequence similarity to the family of periplasmic binding proteins necessary for transporting siderophores through the periplasmic space of gr am-negative bacteria. An Omega insertion within fetB abolished ferric enter obactin utilization without causing a loss of ferric enterobactin binding. These data show that FetA is a functional homolog of FepA that binds ferric enterobactin and may be part of a system responsible for transporting the siderophore into the cell.