Cell Surface Localization of a 90-Kilodalton Heat Shock Protein on Porphyromonas Gingivalis and its Role in Periodontal Disease
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Heat shock proteins (stress proteins) have been implicated in many infectious diseases, although they are generally considered to be intracellular in location. This study demonstrates that a 90-kilodalton heat shock protein (hsp90) is probably localized on the surface of both stressed and unstressed bacterial cells. Recently, a hypothesis regarding the nature of periodontal disease was developed which concerns a protective mechanism whereby antibodies against hsp90 actually confer health as opposed to a diseased state. For this postulation to be valid, the protein must be on the bacterial cell surface in order for the antibody to bind and block adherence to the host tissue. This study was undertaken in an attempt to localize hsp90 on the outer membrane surface of Porphyromonas gingivalis by means of immunofluorescence and immunoelectron microscopy. Gel electrophoresis revealed that the bacterial samples were most likely not sufficiently stressed since there were no apparent differences in the protein bands between the stressed and the unstressed bacteria. A western immunoblot was unable to confirm the presence of hsp90 most likely due to a monoclonal antibody which only recognizes a conformational epitope that was destroyed during procedural protocol. Experiments with indirect immuno-fluorescence yielded a bright staining pattern when an anti-hsp90 monoclonal antibody was used on both stressed and unstressed bacterial cells. Moreover, immunogold labeling of the bacterial cells indicated that a protein recognized by the monoclonal antibody was specifically located on the outer membrane surface as well as on the extending fimbriae. The level of labeling, however, was substantially lower than expected and was most likely due to an inadequate heat shock treatment of the cells. Nevertheless, this probable localization of a 90-kD stress protein on the surface of virulent periodontal pathogens may have implications concerning the role of this molecule in the immune process of periodontal disease.