Functional characterization of HgbB, a new hemoglobin binding protein of Pasteurella multocida

The biological function and role in pathogenesis of a Pasteurella multocida A:1 strain hemoglobin binding protein was investigated. The hgbB gene from the P. multocida A:1 strain, VP161, was cloned and characterized. hgbB was 2991 bp in length and encoded a mature length protein of 111 kDa. HgbB was predicted to be an outer membrane protein and shared 68 and 69% similarity to the hemoglobin/hemoglobin-haptoglobin binding protein, HI0712 from Haemophilus influenzae Rd and HgpC, from H. influenzae b, respectively. HgbB exhibited features typical of TonB dependent receptors, including seven conserved regions typical of these proteins, and conserved invariant residues. Escherichia coli expressing recombinant HgbB was found to bind hemoglobin in a solid phase dot blot binding assay. However, when a truncated form of the protein was expressed in E. coli, cells could no longer bind hemoglobin. Insertional inactivation of hgbB did not affect the ability of P. multocida to bind hemoglobin, nor its ability to produce disease in a mouse model. In addition, recombinant HgbB did not confer any protection against homologous or heterologous challenge.