Biological characterization of major polypeptides on the surface of spotted fever group rickettsiae.

There are two major polypeptides on the surface of spotted fever group rickettsiae that play important roles as immunogens and possibly relate to the pathogenicity of rickettsial diseases. Digestion with trypsin and staphylococcal V-8 protease shows that the 115-kDa protein of Rickettsia conorii is a trypsin-sensitive, surface-exposed protein. The 135-kDa protein is relatively trypsin resistant. Both proteins resist heat treatment up to 52 degrees C and maintain their antigenic reactivity with monoclonal antibodies when the intact rickettsiae are heated. When rickettsiae are dissolved in SDS-containing sample buffer, these polypeptides lose their antigenic reactivity with monoclonal antibodies after incubation at 45 degrees C for 10 min. Staphylococcal V-8 protease does not appear to affect these polypeptides under the current experimental conditions. Monoclonal antibody to the 115-kDa protein reduces rickettsial attachment. The 115-kDa polypeptide may play a role in rickettsial adhesion to the host cell surface.