Characterization of a fourth lipoprotein from Pasteurella haemolytica A1 and its homology to the OmpA family of outer membrane proteins

A fourth lipoprotein gene from Pasteurella haemolytica A1 was cloned and characterized. The plpD gene encodes a 31-kDa lipoprotein (Plp4) which could be recognized in Western immunoblot by sera from calves immunized with the culture supernatant vaccine Presponse. This suggests that Plp4 is one of the immunogenic molecules in the P. haemolytica A1 culture supernatant. The lipoprotein nature of Plp4 was confirmed by labelling with [3H]palmitate and inhibition of leader peptide cleavage with globomycin. A homology search with databanks showed extensive homology between Plp4 and a 31-kDa antigen from Haemophilus somnus and a 19.2-kDa antigen from Neisseria meningitidis. Additional homology of the distal half of Plp4 was identified with a number of bacterial outer membrane proteins belonging to the OmpA family. Plp4 appears to be a novel type of outer membrane protein that contains motifs typical of OmpA but which is also lipid modified.