FptA, the Fe(III)-pyochelin receptor of Pseudomonas aeruginosa: a phenolate siderophore receptor homologous to hydroxamate siderophore receptors

Abstract

The Pseudomonas aeruginosa siderophore pyochelin is structurally unique among siderophores and possesses neither hydroxamate- nor catecholate-chelating groups. The structural gene encoding the 75-kDa outer membrane Fe(III)-pyochelin receptor FptA has been isolated by plasmid rescue techniques and sequenced. The N-terminal amino acid sequence of the isolated FptA protein corresponded to that deduced from the nucleotide sequence of the fptA structural gene. The mature FptA protein has 682 amino acids and a molecular mass of 75,993 Da and has considerable overall homology with the hydroxamate siderophore receptors FpvA of P. aeruginosa, PupA and PupB of Pseudomonas putida, and FhuE of Escherichia coli. This observation indicates that homologies between siderophore receptors are an unreliable predictor of siderophore ligand class recognition by a given receptor. The fptA gene was strongly regulated by iron; fptA transcription was totally repressed by 30 microM FeCl3, as determined by Northern (RNA) blotting. The promoter of the fptA gene contained the sequence 5'-ATAATGATAAGCATTATC-3', which matches the consensus E. coli Fur-binding site at 17 of 18 positions. The -10 promoter region and transcriptional start site of the fptA gene reside within this Fur-binding site.

Ferripyochelin uptake genes are involved in pyochelin-mediated signalling in Pseudomonas aeruginosa

“…3d) or fptX (PAO6397, Fig. 3f) strongly interfered with pyochelin-mediated growth promotion, thus confirming the proposed functions for FptA and FptX in pyochelinmediated iron uptake (Ankenbauer & Quan, 1994;Ó Cuív et al, 2004). Complementation of PAO6541 and PAO6397 with pME7036 (fptABCX) and pME7204 (fptX), respectively, fully restored pyochelin-mediated growth promotion (Fig.…”

“…1), originally described as ORF2 (Ankenbauer & Quan, 1994), seems to be translationally coupled to fptA as its predicted start codon overlaps with the fptA stop codon. The nucleotide sequence of PA4220 predicts a 93 amino acid cytoplasmic membrane protein of 9569 Da of unknown function.…”

“…The nucleotide sequence of PA4220 predicts a 93 amino acid cytoplasmic membrane protein of 9569 Da of unknown function. The following ORF, PA4219 [ORF 3 (Ankenbauer & Quan, 1994)], may be larger than originally proposed if translation initiates at a GTG codon located immediately downstream of PA4220. In this case, PA4219 would encode a protein of 501 amino acids with a molecular mass of 53 460 Da, predicted to be located in the cytoplasmic membrane as well.…”

“…Pyochelin sensing occurs in the cytoplasm of P. aeruginosa. We have shown recently that pyochelin, possibly in its ironloaded form (Michel et al, 2005), is the intracellular effector required by the AraC-type regulator PchR (Heinrichs & Poole, 1993 to activate the expression of the two pyochelin biosynthesis operons pchDCBA (Serino et al, 1997) and pchEFGHI (Reimmann et al, 1998(Reimmann et al, , 2001, and of the fptA gene, encoding the outer-membrane ferripyochelin receptor (Ankenbauer & Quan, 1994). (Note that until the iron status of the PchR effector has been confirmed by additional experiments, the more general term 'pyochelin' will be used here.)…”

Identification, isolation, and analysis of a gene cluster involved in iron acquisition by Pseudomonas mendocina ymp

“…Because fur has a high degree of conservation and single genomic copy, it was possible to develop degenerate primers from ClustalW alignments of several sequenced Pseudomonad fur homologs. The fpvA and fptA genes were previously cloned from P. aeruginosa and received as a kind gift from Prof. D. Castignetti (Loyola University of Chicago) (Ankenbauer and Quan 1994;Poole et al 1993). The fpvA gene was digested with BstXI and Bsu36I to produce a 1.7 kb DNA fragment and fptA was digested with SacII to produce a DNA fragment size of 1.8 kb.…”