Identification of a Gingipain-Sensitive Surface Ligand of Porphyromonas gingivalis That Induces Toll-Like Receptor 2- and 4-Independent NF-κB Activation in CHO Cells

Abstract

ABSTRACT Porphyromonas gingivalis is a major periodontal pathogen that has the pathogenic proteinases Arg-specific gingipain and Lys-specific gingipain. We previously found that a cell surface component on P. gingivalis is able to induce Toll-like receptor 2 (TLR2)- and TLR4-independent signaling in 7.19 cells and that this component can be degraded by gingipains. In this study, we purified this component from the P. gingivalis gingipain-null mutant KDP136 and obtained two candidate proteins. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analysis showed that the proteins, with molecular masses of 123 and 43 kDa, were encoded by PGN_0748 and PGN_0728 ( pgm6 ), respectively, in the P. gingivalis ATCC 33277 genome sequence. The PGN_0748-encoded protein, which we refer to as g ingipain- s ensitive l igand A (GslA), reacted with antiserum that could effectively inhibit the activity of KDP136 to induce NF-κB activation in 7.19 cells, but Pgm6 did not. To further determine what protein is responsible for the NF-κB activation, we constructed gslA , pgm6 , and pgm6 pgm7 deletion mutants from KDP136. When 7.19 cells were exposed to those mutants, the gslA deletion mutant did not induce NF-κB activation, whereas the pgm6 and pgm6 pgm7 deletion mutants did. Furthermore, NF-κB activation in 7.19 cells induced by KDP136 was partially inhibited by antiserum against a recombinant protein expressed from the 5′-terminal third of gslA . These results indicate that GslA is one of the factors that induce NF-κB activation in 7.19 cells. Interestingly, the gslA gene was present in four of seven P. gingivalis strains tested. This restricted distribution might be associated with the virulence potential of each strain.