The PorX/PorY system is a virulence factor of Porphyromonas gingivalis and mediates the activation of the type IX secretion system

Abstract

PorX/PorY is a two-component system (TCS) of Porphyromonas gingivalis that governs transcription of numerous genes including those encoding a type IX secretion system (T9SS) for gingipain secretion and heme accumulation. Here, an in vitro analysis showed that the response regulator PorX specifically bound to two regions in the promoter of porT , a known PorX-regulated T9SS gene, thus demonstrating that PorX/PorY can directly regulate specific target genes. A truncated PorX protein containing the N-terminal receiver and effector domains retained a wild-type ability in both transcription regulation and heme accumulation, ruling out the role of the C-terminal ALP domain in gene regulation. The PorX/PorY system was the only TCS essential for heme accumulation and concomitantly responded to hemin to stimulate transcription of several known PorX-dependent genes in a concentration-dependent manner. We found that PorX/PorY activated the sigH gene, which encodes a sigma factor known for P. gingivalis adaptation to hydrogen peroxide (H 2 O 2 ). Consistently, both Δ porX and Δ sigH mutants were susceptible to H 2 O 2 , suggesting a PorX/PorY-σ H regulatory cascade to confer resistance to oxidative stress. Furthermore, the Δ porX mutant became susceptible to high hemin levels that could induce oxidative stress. Therefore, a possible reason why hemin activates PorX/PorY is to confer resistance to hemin-induced oxidative stress. We also demonstrated that PorX/PorY was essential for P. gingivalis virulence because the Δ porX mutant was avirulent in a mouse model. Specifically, this TCS was required for the repression of proinflammatory cytokines secreted by dendritic cells and T cells in the P. gingivalis –infected mice.

Response regulator PorX coordinates oligonucleotide signalling and gene expression to control the secretion of virulence factors

“…The PglZ domain is often found in the RR proteins of TCSs ( 11 )—including PorX, which is required for the activation of the T9SS ( 18 ). In an apparently unrelated context, proteins containing a PglZ domain are necessary for the BREX anti-phage defence system ( 7 , 9 ).…”

“…In P. gingivalis , PorX has been associated with PorY ( 13 , 16 ), an orphan signalling HK with a periplasmic sensor domain. However, there is little phenotypic overlap between the Δ porX and Δ porY mutants ( 18 , 82 ), making it unlikely that a PorY/PorX TCS regulates the secretion of virulence factors. Even so, it is possible that PorX and PorY operate as a TCS that regulates T9SS activity in response to environmental cues in other Bacteroidetes.…”

“…First, an unknown stimulus is assumed to trigger the autophosphorylation of PorY, which transfers the phosphate to the conserved Asp residue in the RD of PorX, and the latter induces genes encoding components of the T9SS by binding to the extracytoplasmic function (ECF) sigma factor, SigP ( 13 , 17 ). Second, activated PorX has been shown to bind directly to the sigP and porT promoters, facilitating SigP-dependent transcription ( 15 , 18 ). However, this mechanism is controversial because PorX lacks a canonical DNA-binding motif ( 16 ).…”

Purification, crystallization and crystallographic analysis of the PorX response regulator associated with the type IX secretion system

“…To compensate for the lack of a DNA-binding domain, PorX interacts with and stabilizes the transcription factor SigP, which directly binds the promoter regions of T9SS genes (Fig. 1; Jiang et al, 2021;Yang et al, 2021;Kadowaki et al, 2016). While the precise signal triggering this pathway has yet to be identified, deletion of either porX or sigP in P. gingivalis, results in the downregulation of T9SS components and activity, and in impaired processing of gingipains, as well as decreased toxicity (Sato et al, 2010).…”

Hemin availability induces coordinated DNA methylation and gene expression changes in Porphyromonas gingivalis

“…However, the P. gingivalis ATCC33277– genome encodes seven two-component signal transduction system (TCS) pairs of a response regulator and a histidine kinase traditionally involved in gene regulation on other organisms (13). Recently it has been reported that one of these TCS, PorX/PorY, responds to environmental heme and through the co-ordinate action of porX and sigP regulates transcription of the T9SS and heme accumulation and mutants defective in either porX or porY are attenuated in a mouse model of virulence (14, 15). However, given the magnitude of changes in response to the concentration of heme, there may be other mechanisms of heme regulated gene expression in P. gingivalis.…”