Localization and pathogenic role of the cysteine protease dentipain in Treponema denticola

The Msp protein complex and the serine protease dentilisin are the best-characterized virulence factors in Treponema denticola, the major etiological agent of chronic periodontitis. In addition to these outer sheath factors, the cysteine protease dentipain contributes to pathogenicity, but its secretion, processing, cellular localization, and role in T. denticola virulence are not fully understood. In this study, we found that full-sized dentipain (74-kDa) and the 52-kDa truncated form of the enzyme are located, respectively, in the outer sheath derived from T. denticola dentilisin- and the Msp-deficient mutants. Furthermore, dentipain was barely detected in the wild-type strain. These results suggest that dentilisin and Msp, the major outer sheath proteins, are involved in the secretion and maturation of dentipain. Inactivation of the dentipain gene slowed the growth of T. denticola, and the effect was more profound in serum-free medium than in serum-containing medium. Several genes, including those encoding transporters and methyl-accepting chemotaxis proteins, were differentially expressed in the dentipain-deficient mutant. Furthermore, the mutant strain was more hydrophobic than the wild-type strain. Finally, the mutant showed less autoaggregation activity and adhesion to IgG in a serum-free medium than the wild-type strain. These findings suggest that dentipain contributes to the virulence of T. denticola by facilitating adhesion and acquisition of nutrients essential for colonization and proliferation in the gingival crevice under serum-rich conditions.

Automated summary

The Msp protein complex and the serine protease dentilisin are the best-characterized virulence factors in Treponema denticola, the major etiological agent of chronic periodontitis. In addition, the cysteine protease dentipain also contributes to pathogenicity, but its secretion, processing, cellular localization, and role in T. denticola virulence are not fully understood. This study found that dentipain is located in the outer sheath derived from T. denticola dentilisin- and Msp-deficient mutants, suggesting that dentilisin and Msp are involved in the secretion and maturation of dentipain. Inactivation of the dentipain gene slowed the growth of T. denticola, and the mutant strain showed altered gene expression, increased hydrophobicity, reduced autoaggregation activity, and decreased adhesion to IgG.