Characterization of heat-inducible expression and cloning of HtpG (Hsp90 homologue) of Porphyromonas gingivalis

Porphyromonas gingivalis is implicated in the etiology of periodontal disea se. Associations between microbial,virulence and stress protein expression have been identified in other infections. For example, Hsp90 homologues in several microbial species have been shown to contribute to virulence. We pr eviously reported that P. gingivalis possessed an Hsp90 homologue (HtpG) wh ich cross-reacts with human Hsp90. In addition, we found that elevated leve ls of serum antibody to Hsp90 stress protein in individuals colonized with this microorganism were associated with periodontal health. However, the ro le of HtpG in P. gingivalis has not been explored. Therefore, we cloned the htpG gene and investigated the characteristics of HtpG localization and ex pression in P. gingivalis. htpG exists as a single gene of 2,052 bp from wh ich a single message encoding a mature protein of approximately 68 kDa is t ranscribed. Western blot analysis revealed that the 68-kDa polypeptide was stress inducible and that a major band at 44 kDa and a minor band at 40 kDa were present at constitutive levels. Cellular localization studies reveale d that the 44- and 40-kDa species were associated with membrane and vesicle fractions, while the 68-kDa polypeptide aas localized to the cystosolic fr actions.