title: Novel anion-independent iron coordination by members of a third class of bacterial periplasmic ferric ion-binding proteins.
abstract: The uptake of the element iron is vital for the survival of most organisms. Numerous pathogenic Gram-negative bacteria utilize a periplasm-to-cytosol ATP-binding cassette transport pathway to transport this essential atom in to the cell. In this study, we investigated the Yersinia enterocolitica (YfuA) and Serratia marcescens (SfuA) iron-binding periplasmic proteins. We have determined the 1.8-angstroms structures of iron-loaded (YfuA) and iron-free (SfuA) forms of this class of proteins. Although the sequence of these proteins varies considerably from the other members of the transferrin structural superfamily, they adopt the same three-dimensional fold. The iron-loaded YfuA structure illustrates the unique nature of this new class of proteins in that they are able to octahedrally coordinate the ferric ion in the absence of a bound anion. The iron-free SfuA structure contains a bound citrate anion in the iron-binding cleft that tethers the N- and C-terminal domains of the apo protein and stabilizes the partially open structure.
authors.affiliation: Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Shouldice
authors.forename: Duncan E
authors.initials: DE
authors.lastname: McRee
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Dougan
authors.forename: Leslie W
authors.initials: LW
authors.lastname: Tari
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Schryvers
mesh_terms: D000595:Amino Acid Sequence; D000838:Anions / Q000378:metabolism; D001419:Bacteria / Q000737:chemistry / Q000145:classification / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019897:Periplasm / Q000737:chemistry*; D010802:Phylogeny; D011487:Protein Conformation
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D005290:Ferric Compounds; D033862:Iron-Binding Proteins; D007501:Iron