Sialidase and Sialoglycoproteases Can Modulate Virulence in Porphyromonas gingivalis
ABSTRACTThePorphyromonas gingivalisrecombinant VimA can interact with the gingipains and several other proteins, including a sialidase. Sialylation can be involved in protein maturation; however, its role in virulence regulation inP. gingivalisis unknown. The three sialidase-related proteins inP. gingivalisshowed the characteristic sialidase Asp signature motif (SXDXGXTW) and other unique domains. To evaluate the roles of the associated genes, randomly chosenP. gingivalisisogenic mutants created by allelic exchange and designated FLL401 (PG0778::ermF), FLL402 (PG1724::ermF), and FLL403 (PG0352::ermF-ermAM) were characterized. Similar to the wild-type strain, FLL402 and FLL403 displayed a black-pigmented phenotype in contrast to FLL401, which was not black pigmented. Sialidase activity inP. gingivalisFLL401 was reduced by approximately 70% in comparison to those in FLL402 and FLL403, which were reduced by approximately 42% and 5%, respectively. Although there were no changes in the expression of the gingipain genes, their activities were reduced by 60 to 90% in all the isogenic mutants compared to that for the wild type. Immunoreactive bands representing the catalytic domains for RgpA, RgpB, and Kgp were present in FLL402 and FLL403 but were missing in FLL401. While adhesion was decreased, the capacity for invasion of epithelial cells by the isogenic mutants was increased by 11 to 16% over that of the wild-type strain. Isogenic mutants defective inPG0778andPG0352were more sensitive to hydrogen peroxide than the wild type. Taken together, these results suggest that theP. gingivalissialidase activity may be involved in regulating gingipain activity and other virulence factors and may be important in the pathogenesis of this organism.