FPTA, THE FE(III)-PYOCHELIN RECEPTOR OF PSEUDOMONAS-AERUGINOSA - A PHENOLATE SIDEROPHORE RECEPTOR HOMOLOGOUS TO HYDROXAMATE SIDEROPHORE RECEPTORS

The Pseudomonas aeruginosa siderophore pyochelin is structurally uniqu e among siderophores and possesses neither hydroxamate- nor catecholat e-chelating groups. The structural gene encoding the 75-kDa outer memb rane Fe(III)-pyochelin receptor FptA has been isolated by plasmid resc ue techniques and sequenced. The N-terminal amino acid sequence of the isolated FptA protein corresponded to that deduced from the nucleotid e sequence of the fptA structural gene. The mature FptA protein has 68 2 amino acids and a molecular mass of 75,993 Da and has considerable o verall homology with the hydroxamate siderophore receptors FpvA of P. aeruginosa, PupA and PupB of Pseudomonas putida, and FhuE of Escherich ia coli. This observation indicates that homologies between siderophor e receptors are an unreliable predictor of siderophore ligand class re cognition by a given receptor. The fptA gene was strongly regulated by iron; fptA transcription was totally repressed by 30 muM FeCl3, as de termined by Northern (RNA) blotting. The promoter of the fptA gene con tained the sequence 5'-ATAATGATAAGCATTATC-3', which matches the consen sus E. coli Fur-binding site at 17 of 18 positions. The -10 promoter r egion and transcriptional start site of the fptA gene reside within th is Fur-binding site.