Subcellular distribution of Plp-40, a lipoprotein in a serotype A strain of Pasteurella multocida

A 40-kDa lipoprotein (Plp-40) is expressed by serotype A strains of Pasteurella multocida in amounts which correlate with the amount of capsular material present. We hypothesized that Plp-40 is exposed at the outer surface of the outer membrane (OM) of the cell and is associated with the serotype A exopolysaccharide material. The objectives of the present study were to confirm the lipoprotein nature of Plp-40 and to determine its subcellular location. Plp-40 maturation was shown to be sensitive to globomycin, thereby confirming it to be a bacterial lipoprotein. Plp-40 was shown to be present in the OM fractions of P. multocida obtained by both sarkosyl extraction and sucrose density gradient centrifugation, as well as in capsule fractions obtained by either hyaluronidase treatment or warm buffer extraction. [(3)H]palmitic acid-labeled Plp-40 could be removed from the surface of whole cells by exposure to proteinase K. Autoradiography of (125)I-labeled cell surface proteins exhibited a 40-kDa band that was prominent in capsulated strains and greatly diminished in a noncapsulated strain. These results support the hypothesis that Plp-40 is a lipid-modified OM protein, which is exposed on the outer cell surface and is likely associated with serotype A extracellular polysaccharide.