Summary: In a previous investigation, a 35 kDa iron-regulated protein was identified from total cellular proteins of grown under iron-depleted conditions. This study reports identification of the gene encoding the 35 kDa protein based on complementation of an strain transformed with a plasmid derived from a lambda ZAP II library. Cross-reactivity was demonstrated between an anti-35 kDa mAb and a 35 kDa protein expressed in this strain. Furthermore, a translated ORF identified on the recombinant plasmid corresponded with the N-terminal amino acid sequence of the intact and a CNBr-cleaved fragment of the 35 kDa iron-regulated protein. Nucleotide sequence analysis of the gene encoding the 35 kDa protein demonstrated homology with the cluster 1 group of extracellular solute-binding proteins, especially to the iron-binding proteins of this family. Complete sequence analysis of the recombinant plasmid insert identified three other predominant ORFs, two of which appeared to be in an operonic organization with These latter components ( and ) showed homology to the transmembrane and ATPase components of ATP-binding cassette (ABC)-type uptake systems, respectively. Based on amino acid/DNA sequencing, citrate competition assay of iron affinity and visible wavelength spectra, it was concluded that the 35 kDa protein functions as an FbpA homologue (referred to as PFbpA) and that the gene encoding this protein is part of an operon comprising a member of the FbpABC family of iron uptake systems. Primary sequence analysis revealed rather surprisingly that PFbpA is more closely related to the intracellular Mn/Febinding protein IdiA found in cyanobacteria than to any of the homologous FbpA proteins currently known in commensal or pathogenic members of the or .


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