TRANSFERRIN RECEPTORS ON RUMINANT PATHOGENS VARY IN THEIR INTERACTION WITH THE C-LOBE AND N-LOBE OF RUMINANT TRANSFERRINS

The interaction between ruminant transferrins and receptor proteins on the surface of the ruminant pathogens Pasteuerella haemolytica, Haemophilus somnus, Pasteurella multocida, Haemophilus agnii, and Moraxella bovis was evaluated by a combination of binding assays and affinity isolation procedures. Membranes isolated from P. haemolytica, P. multocida, and H. agnii were capable of binding sheep, goat, and cattle transferrins whereas binding by membranes from H. somnus and M. bovis was specific for bovine transferrin. Proteolytically derived bovine transferrin C-lobe was capable of inhibiting the interaction between bovine transferrin and both Tbp1 and Tbp2 from P. haemolytica and M. bovis but only Tbp1 from H. somnus and P. multocida. Proteolytically derived N-lobe inhibited the binding of P. multocida and H. somnus Tbp2 to bovine transferrin and the binding of bovine transferrin to the single receptor protein identified in H. agnii. The implications of these results regarding the nature of the ligand-receptor interaction and similarities of this interaction with ligand-receptor interactions in different species are discussed.