Conserved Interaction between Transferrin and Transferrin-binding Proteins from Porcine Pathogens

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.
Bacterial Metabolism, Iron, Mass Spectrometry (MS), Protein-Protein Interactions, Receptors, Mass Shift Analysis, Transferrin
Silva, L. P., Yu, R., Calmettes, C., Yang, X., Moraes, T. F., Schryvers, A. B., & Schriemer, D. C. (2011). Conserved interaction between transferrin and transferrin-binding proteins from porcine pathogens. Journal of Biological Chemistry, 286(24), 21353-21360. doi:10.1074/jbc.M111.226449