Differential Protein Expression by Porphyromonas gingivalis in Response to Secreted Epithelial Cell Components

Abstract

The human oral pathogen Porphyromonas gingivalis colonizes the gingival crevice and invades gingival epithelial cells. Multi-dimensional capillary HPLC coupled with tandem mass spectrometry and 2D gel electrophoresis were used to analyze the proteome of P. gingivalis as it adapts to a set of experimental conditions designed to reflect important features of an epithelial cell environment. 1014 proteins (46% of the total theoretical proteome) were identified in four independent analyses. 479 of these proteins showed evidence of differential expression after exposure of P. gingivalis to either conditioned epithelial cell growth medium or control conditions: i.e. they were only detected under one set of conditions. Moreover, 276 genes annotated as hypothetical were found to encode expressed proteins. Among the proteins upregulated in the presence of epithelial cell components were a homolog of the internalin proteins of Listeria monocytogenes and subunits of the ATP-dependent Clp protease complex. Insertional inactivation of clpP, encoding the Clp proteolytic subunit, resulted in an approximately 50% reduction in invasion of P. gingivalis. These results suggest that adaptation to an epithelial cell environment induces a major shift in the expressed proteome of the organism. Furthermore, ClpP, that is upregulated in this environment, is required for optimal invasive activity of P. gingivalis.