CHARACTERIZATION OF A LARGE TRANSFERRIN-BINDING PROTEIN FROM ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-7

The binding of transferrin at the surface of Actinobacillus pleuropneu moniae (A. pp) is mediated by two proteins of approximate to 60 and 10 0 kDa. The 60 kDa protein has been shown to be highly divergent among different serotypes and to induce a serotype-specific protective immun e response. In this study we have characterized the 100 kDa transferri n-binding protein of A. pp, serotype 7 and designated it as TfbB. The tfbB gene was found to be located immediately downstream of the tfbA g ene. It was cloned and sequenced, and antibodies raised against the is olated recombinant protein detected, with a constant intensity, a 100 kDa protein in A pp, serotypes 2, 4, 6, 7, 8, 9, 10 and 11, and a poly peptide of approximate to 103 kDa in serotypes 1, 3, 5A and 12. In add ition, comparative analysis of the deduced amino acid sequence showed more than 40% identity with the large transferrin-binding proteins of Neisseria meningitidis and Haemophilius influenzae. The TfbB protein w as expressed in E. coil outer membranes in a conformation eliciting po rcine transferrin-specific binding activity. Sera of pigs immunized wi th these TfbB-containing E. coli membranes recognized functional membr ane-associated TfbB protein whereas no such reaction was observed upon immunization with isolated recombinant TfbB protein. A preliminary an imal experiment showed that TfbB-containing outer membrane preparation s from recombinant E. roll can reduce significantly the mortality of a n A. pp. infection with the homologous strain.