TRANSFERRIN RECEPTORS ON RUMINANT PATHOGENS VARY IN THEIR INTERACTIONWITH 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, Haemo philus somnus, Pasteurella multocida, Haemophilus agnii, and Moraxella bovis was evaluated by a combination of binding assays and affinity i solation procedures. Membranes isolated from P. haemolytica, P. multoc ida, and H. agnii were capable of binding sheep, goat, and cattle tran sferrins whereas binding by membranes from H. somnus and M. bovis was specific for bovine transferrin. Proteolytically derived bovine transf errin C-lobe was capable of inhibiting the interaction between bovine transferrin and both Tbp1 and Tbp2 from P. haemolytica and M. bovis bu t only Tbp1 from H. somnus and P. multocida. Proteolytically derived N -lobe inhibited the binding of P. multocida and H. somnus Tbp2 to bovi ne transferrin and the binding of bovine transferrin to the single rec eptor protein identified in H. agnii. The implications of these result s regarding the nature of the ligand-receptor interaction and similari ties of this interaction with ligand-receptor interactions in differen t species are discussed.