CHARACTERIZATION OF THE PASTEURELLA-HAEMOLYTICA TRANSFERRIN RECEPTOR GENES AND THE RECOMBINANT RECEPTOR PROTEINS

The tbpA and tbpB genes encoding the transferrin receptor proteins, Tb pA and TbpB, from Pasteurella haemolytica Al were cloned, sequenced an d expressed in Escherichia coli. The genes were organized in a putativ e operon arrangement of tbpB-tbpA. The tbpB gene was preceded by putat ive promoter and regulatory sequences, and followed by a 96 base pair intergenic sequence in which no promoter regions were found, suggestin g that the two genes are coordinately transcribed. The deduced amino a cid sequences of the TbpA and TbpB proteins had regions of homology wi th the corresponding Neisseria meningitidis, N. gonorrhoeae, Haemophil us influenzae and Actinobacillus pleuropneumoniae Tbp and Lbp proteins . The intact tbpB gene was expressed in a T7 expression system and the resulting recombinant TbpB protein retained the functional bovine tra nsferrin binding characteristics. The availability of the recombinant TbpB enabled us to demonstrate: its specificity for ruminant transferr ins, its ability to bind both the C-and N-terminal lobes of bovine tra nsferrin and its preference for the iron-loaded form of this protein. Several attempts at expressing the cloned tbpA gene were unsuccessful, suggesting that the product of the gene may be toxic to E. coli. (C) 1997 Academic Press Limited.