title: Conserved interaction between transferrin and transferrin-binding proteins from porcine pathogens.
abstract: Gram-negative porcine pathogens from the Pasteurellaceae family possess a surface receptor complex capable of acquiring iron from porcine transferrin (pTf). This receptor consists of transferrin-binding protein A (TbpA), a transmembrane iron transporter, and TbpB, a surface-exposed lipoprotein. Questions remain as to how the receptor complex engages pTf in such a way that iron is positioned for release, and whether divergent strains present distinct recognition sites on Tf. In this study, the TbpB-pTf interface was mapped using a combination of mass shift analysis and molecular docking simulations, localizing binding uniquely to the pTf C lobe for multiple divergent strains of Actinobacillus plueropneumoniae and suis. The interface was further characterized and validated with site-directed mutagenesis. Although targeting a common lobe, variants differ in preference for the two sublobes comprising the iron coordination site. Sublobes C1 and C2 participate in high affinity binding, but sublobe C1 contributes in a minor fashion to the overall affinity. Further, the TbpB-pTf complex does not release iron independent of other mediators, based on competitive iron binding studies. Together, our findings support a model whereby TbpB efficiently captures and presents iron-loaded pTf to other elements of the uptake pathway, even under low iron conditions.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Leslie P
authors.initials: LP
authors.lastname: Silva
authors.forename: Ronghua
authors.initials: R
authors.lastname: Yu
authors.forename: Charles
authors.initials: C
authors.lastname: Calmettes
authors.forename: Xue
authors.initials: X
authors.lastname: Yang
authors.forename: Trevor F
authors.initials: TF
authors.lastname: Moraes
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Schryvers
authors.forename: David C
authors.initials: DC
authors.lastname: Schriemer
mesh_terms: D000188:Actinobacillus / Q000378:metabolism; D044132:Actinobacillus suis / Q000378:metabolism; D000818:Animals; D004252:DNA Mutational Analysis; D006193:Haemophilus influenzae / Q000378:metabolism; D007501:Iron / Q000737:chemistry; D008074:Lipoproteins / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods; D008968:Molecular Conformation; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020349:Surface Plasmon Resonance; D013552:Swine; D014168:Transferrin / Q000737:chemistry*; D033863:Transferrin-Binding Proteins / Q000737:chemistry*
chemical_list: D008074:Lipoproteins; D014168:Transferrin; D033863:Transferrin-Binding Proteins; D007501:Iron