title: Anion-independent iron coordination by the Campylobacter jejuni ferric binding protein.
abstract: Campylobacter jejuni, the leading cause of human gastroenteritis, expresses a ferric binding protein (cFbpA) that in many pathogenic bacteria functions to acquire iron as part of their virulence repertoire. Recombinant cFbpA is isolated with ferric iron bound from Escherichia coli. The crystal structure of cFbpA reveals unprecedented iron coordination by only five protein ligands. The histidine and one tyrosine are derived from the N-terminal domain, whereas the three remaining tyrosine ligands are from the C-terminal domain. Surprisingly, a synergistic anion present in all other characterized ferric transport proteins is not observed in the cFbpA iron-binding site, suggesting a novel role for this protein in iron uptake. Furthermore, cFbpA is shown to bind iron with high affinity similar to Neisserial FbpA and exhibits an unusual preference for ferrous iron (oxidized subsequently to the ferric form) or ferric iron chelated by oxalate. Sequence and structure analyses reveal that cFbpA is a member of a new class of ferric binding proteins that includes homologs from invasive and intracellular bacteria as well as cyanobacteria. Overall, six classes are defined based on clustering within the tree and by their putative iron coordination. The absence of a synergistic anion in the iron coordination sphere of cFbpA also suggests an alternative model of evolution for FbpA homologs involving an early iron-binding ancestor instead of a requirement for a preexisting anion-binding ancestor.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Stacey A L
authors.initials: SA
authors.lastname: Tom-Yew
authors.forename: Diana T
authors.initials: DT
authors.lastname: Cui
authors.forename: Elena G
authors.initials: EG
authors.lastname: Bekker
authors.forename: Michael E P
authors.initials: ME
authors.lastname: Murphy
mesh_terms: D000595:Amino Acid Sequence; D000838:Anions / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D016123:Campylobacter jejuni / Q000378:metabolism*; D017124:Conserved Sequence; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D033902:Periplasmic Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D033902:Periplasmic Binding Proteins; D011994:Recombinant Proteins; C499653:ferric binding protein, Campylobacter jejuni; D007501:Iron