PorA, a conserved C-terminal domain-containing protein, impacts the PorXY-SigP signaling of the type IX secretion system

Abstract

Porphyromonas gingivalis, a periodontal pathogen, translocates many virulence factors including the cysteine proteases referred to as gingipains to the cell surface via the type IX secretion system (T9SS). Expression of the T9SS component proteins is regulated by the tandem signaling of the PorXY two-component system and the ECF sigma factor SigP. However, the details of this regulatory pathway are still unknown. We found that one of the T9SS conserved C-terminal domain-containing proteins, PGN_0123, which we have designated PorA, is involved in regulating expression of genes encoding T9SS structural proteins and that PorA can be translocated onto the cell surface without the T9SS translocation machinery. X-ray crystallography revealed that PorA has a domain similar to the mannose-binding domain of Escherichia coli FimH, the tip protein of Type 1 pilus. Mutations in the cytoplasmic domain of the sensor kinase PorY conferred phenotypic recovery on the ΔporA mutant. The SigP sigma factor, which is activated by the PorXY two-component system, markedly decreased in the ΔporA mutant. These results strongly support a potential role for PorA in relaying a signal from the cell surface to the PorXY-SigP signaling pathway.

The Type IX Secretion System and Its Role in Bacterial Function and Pathogenesis

“…The genes required for these processes fall into 2 broad groups (Table ). The first group of genes codes for components of the T9SS machinery, including IM proteins (PorL and PorM), OM associated proteins (PorE, PorF, PorG, PorK, PorN, PorP, PorQ, PorT, PorU, PorV, PorW, PorZ, and Sov) (Sato et al 2010;Naito et al 2019), and components involved in signal transduction and gene regulation (PorA, PorX, PorY, and SigP) (Yukitake et al 2020). Besides PorA, all of these proteins have orthologs in T. forsythia and P. intermedia (Table ).…”

Protein Interactome Analysis of the Type IX Secretion System Identifies PorW as the Missing Link between the PorK/N Ring Complex and the Sov Translocon

“…2A ), indicating that their presence in the pulldown assay was specific to the presence of Sov. PorA was recently demonstrated to be a component of the T9SS and is also known as a substrate of the T9SS ( 26 ). The specific enrichment of many T9SS components in the Sov coimmunoprecipitated material suggests a large T9SS interactome involving Sov.…”

“…In our study, PPI was not identified to interact with Sov; however, surprisingly, we found PorA to be part of the PorV-Sov complex in P. gingivalis . PorA was recently shown to be an essential component of the T9SS and shown to be involved in signal transduction as part of the PorXY-SigP regulatory system ( 26 ). PorA is also a cargo protein that, like other cargo, is secreted, binds to PorV, has its CTD signal removed, and is conjugated to A-LPS ( 31 , 32 ).…”

“…The PorA-PorV-Sov complex was also observed in T9SS mutants ( Table 1 ), and therefore the surface location of PorA in these strains is uncertain. Strangely, there could be an alternative secretion pathway for PorA since it was apparently exposed at the cell surface in both the sov and porV mutants ( 26 ).…”

Differential affinity chromatography reveals a link between Porphyromonas gingivalis–induced changes in vascular smooth muscle cell differentiation and the type 9 secretion system

“…PorX (PG0928), which is the cytoplasmic response regulator of T9SS expression detected in both proteomes, was not detected in the pull-down eluates. However, PorA (PG2172), the putative outer membrane relay protein of the PorXY-SigP signaling pathway ( Yukitake et al., 2020 , Gorasia et al, 2022 ) was detected in the pull-down eluate. PorX was enriched in the A7UF proteome, but PorA was enriched in the W83 proteome.…”