Molecular genetics and nomenclature of proteases of Porphyromonas gingivalis

Arginine-specific gingipains (RgpA/RgpB) knockdown modulates neutrophil machinery

Background

Gingipains are important virulence factors present in Porphyromonas gingivalis. Arginine-specific gingipains (RgpA and RgpB) are critically associated with increased proteolytic activity and immune system dysfunction, including neutrophilic activity. In this study, we assessed the impact of gingipains (RgpA and RgpB) on neutrophil function.

Methods

Peripheral blood samples were obtained; neutrophils were isolated and incubated with P. gingivalis A7436, W50, and the double RgpA/RgpB double knockout mutant E8 at MOI 20 for 2 hours. Neutrophil viability was assessed by Sytox staining. Phagocytic capacity and apoptosis were measured by flow cytometry. Superoxide release was measured by superoxide dismutase and cytochrome c reduction assay. Gene expression of TLR2, p47-phox, p67-phox, and P2 × 7was measured by qPCR. Inflammatory cytokine and chemokine production was measured by IL-1β, IL-8, RANTES, and TNF-α in cell supernatants.

Results

Neutrophil TLR2 gene expression was reduced in the absence of RgpA/RgpB (p < 0.05), while superoxide production was not significantly impacted. RgpA/RgpB-/- significantly impaired neutrophil phagocytic function (p < 0.05) and increased TNF-α production when compared with the wild-type control (p < 0.05). Neutrophil apoptosis was not altered when exposed to RgpA/RgpB-/- E8 (p > 0.05).

Conclusion

These data suggest that arginine-specific gingipains (RgpA/RgpB) can modulate neutrophil responses against P. gingivalis infection.

Production and properties of adhesin-free gingipain proteinase RgpA

The Arg-specific gingipains of Porphyromonas gingivalis RgpA and RgpB have 97% identical sequences in their catalytic domains yet their propeptides are only 76% identical. RgpA isolates as a proteinase-adhesin complex (HRgpA) which hinders direct kinetic comparison of RgpA_cat as a monomer with monomeric RgpB. We tested modifications of rgpA identifying a variant that enabled us to isolate histidine-tagged monomeric RgpA (rRgpAH). Kinetic comparisons between rRgpAH and RgpB used benzoyl-L-Arg-4-nitroanilide with and without cysteine and glycylglycine acceptor molecules. With no glycylglycine, values of K_m, V_max, k_cat and k_cat/K_m for each enzyme were similar, but with glycylglycine K_m decreased, V_max increased and k_cat increased ~ twofold for RgpB but ~ sixfold for rRgpAH. The k_cat/K_m for rRgpAH was unchanged whereas that of RgpB more than halved. Recombinant RgpA propeptide inhibited rRgpAH and RgpB with K_i 13 nM and 15 nM K_i respectively slightly more effectively than RgpB propeptide which inhibited rRgpAH and RgpB with K_i 22 nM and 29 nM respectively (p < 0.0001); a result that may be attributable to the divergent propeptide sequences. Overall, the data for rRgpAH reflected observations previously made by others using HRgpA, indicating rRgpAH fidelity and confirming the first production and isolation of functional affinity tagged RgpA.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Porphyromonas gingivalis-Helicobacter pylori co-incubation enhances Porphyromonas gingivalis virulence and increases migration of infected human oral keratinocytes

Background

Porphyromonas gingivalis is part of the subgingival biofilm and a keystone species in the development of periodontitis. Interactions between P.gingivalis and other bacteria in biofilms have been shown to affect bacterial virulence. Helicobacter pylori also inhabits the subgingival biofilm, but the consequences of interactions there with P.gingivalis remain unknown. Here, we investigated how the pre-incubation of P.gingivalis with H.pylori affects P.gingivalis virulence.

Methods

We assayed P.gingivalis internalization by oral keratinocytes (OKs), hemagglutination and biofilm formation to identify alterations in virulence after pre-incubation with H. pylori. Also, we evaluated viability and migration of OKs infected with P. gingivalis, as well as the role of toll-like receptor 4 (TLR4).   In addition, we quantified the mRNA of genes associated with P.gingivalis virulence.

Results

Pre-incubation of P.gingivalis with H.pylori enhanced P.gingivalis biofilm formation, bacterial internalization into OKs and hemagglutination. Infection with pre-incubated P.gingivalis increased OK migration in a manner dependent on the O-antigen and linked to  increased expression of the gingipain RgpB. Also, OK TLR4 participates in these events, because upon TLR4 knock-down, pre-incubated P.gingivalis no longer stimulated OK migration.

Discussion

We provide here for the first time insight to the consequences of direct interaction between P.gingivalis and H.pylori. In doing so, we shed light on the mechanism by which H. pylori presence in the oral cavity increases the severity or progression of periodontitis.

Purification of RgpA from external outer membrane vesicles of Porphyromonas gingivalis

INTRODUCTION

Purification of native gingipains is challenging because these proteases are frequently associated with the cell surface, which affects yield. This study aimed to purify native Arg-gingipain (RgpA) from Porphyromonas gingivalis Outer Membrane Vesicles (OMV).

METHODS

Native RgpA was purified from P. gingivalis strain ATCC33277 OMV using a strategy including ultracentrifugation, sonication, and successive anionic and cationic fast protein liquid chromatography (FPLC). The presence and purity of the protease were confirmed by SDS-PAGE and detection of protease activity using fluorogenic substrates. Rat antibodies produced against the unique adhesin hemagglutinin (H1) domain of RgpA (amino acids 719-865) were titrated by ELISA at a 1:100 dilution using whole P. gingivalis lysate as an antigen and western blotting to detect a 75 kDa band corresponding to RgpA.

RESULTS

Double anionic-cationic FLPC yielded prominent peaks with evident amidolytic gingipain activity of the appropriate molecular weight, as confirmed by western blotting. The final RgpA yield from 1 L of bacterial culture with colony forming unit (CFU) (Log₁₀) 7.4 ± 0.08/mL was of 12.6% (2 mg/mL), with 3.2 FU/μg of amidolytic activity.

CONCLUSIONS

This protocol allows purification of native RgpA from OMV that retains protease activity.

Calcium ions and vitamin B12 are growth factors for Porphyromonas gingivalis

BACKGROUND

Porphyromonas gingivalis is a causative agent of chronic periodontitis. Standard strains of P. gingivalis, such as W83 and ATCC 33277, proliferate in minimal medium when protein is added as the energy source and hemin and menadione are added as growth factors. Nevertheless, minimal medium containing bovine serum albumin sometimes fails to support growth.

HIGHLIGHTS

The proliferation of two W83 strains and seven ATCC 33277 strains in various minimal media was investigated. Previously, we determined that calcium chloride (CaCl₂) was a growth factor for W83NM, a W83 strain. In this study, we found that vitamin B₁₂ enhanced the proliferation of W83NM in a minimal medium with cultures from the fourth passage but not from the first to the third passage. Therefore, using fourth-passage cultures, we assessed the proliferation of two W83 and seven ATCC 33277 strains in minimal media and the effects of CaCl₂ and vitamin B₁₂. Surprisingly, the nine P. gingivalis strains all differed with respect to their proliferation in minimal media, and protein products used as energy sources showed product-to-product and lot-to-lot heterogeneity. Even though strains or protein products were different, we found CaCl₂-dependent growth in nine strains and vitamin B₁₂-dependent growth in seven strains.

CONCLUSION

These results suggest that calcium ions and vitamin B₁₂ are novel growth factors for P. gingivalis.

A common oral pathogen Porphyromonas gingivalis induces myocarditis in rats

AIM

To evaluate whether Porphyromonas gingivalis (P. gingivalis) inoculation could induce cardiac remodelling in rats.

MATERIALS AND METHODS

The study was conducted on 33 Wistar rats, which were distributed in the following experimental groups: not inoculated; inoculated with 1 × 10⁸ CFU/ml of bacteria; inoculated with 3 × 10⁸ CFU/ml of bacteria. The animals were inoculated at baseline and on the 15th day of follow-up. Blood collection was performed at baseline and 60 min after each inoculation. At 29 days, the animals were subjected to echocardiography and at 30 days to haemodynamic studies before sacrificing them.

RESULTS

Impact of the bacteria was more evident in rats that received higher P. gingivalis concentration. Thus, 3 × 10⁸ CFU/ml of bacteria increased the rectal temperature and water content in the lung as well as myocardial necrosis and fibrosis. P. gingivalis induced the intensification of DNA fragmentation and increased the levels of malondialdehyde, oxidized proteins, and macrophage expression in the myocardium. These findings were associated with lower LV isovolumetric relaxation time, +dP/dt, -dP/dt, and higher end-diastolic pressure.

CONCLUSIONS

P. gingivalis bacteraemia is significantly associated with adverse cardiac remodelling and may play a biological role in the genesis of heart failure.

Human Oral Keratinocytes Challenged by Streptococcus sanguinis and Porphyromonas gingivalis Differentially Affect the Chemotactic Activity of THP-1 Monocytes

Periodontal diseases are initiated by the shift from microbe-host symbiosis to dysbiosis, and the disrupted host response predominantly contributes to tissue destruction. This study investigated whether and to what extent human oral keratinocytes (HOKs) challenged by a periodontal commensal or pathogen could differentially affect the chemotactic activity of THP-1 monocytes. A selected periodontal commensal (Streptococcus sanguinis ATCC 10556) and a pathogen (Porphyromonas gingivalis ATCC 33277) were cultured and inoculated, respectively, into the lower chamber of Transwell® Permeable Supports with HOKs and incubated for 2 h or 18 h at 37°C under appropriate cell growth conditions. HOKs alone served as the control for the transwell migration assay. Well-stained THP-1 monocytes were seeded in the top chamber of the device, incubated for 2 h and then collected from the lower well for quantitation of the migrated fluorescence-labeled cells by the FACSCalibur™ flow cytometer. The statistical significance was determined using one-way ANOVA. The HOKs challenged by S. sanguinis attracted a significantly higher number of THP-1 cell migration as compared with the control after 2 h or 18 h interaction ( $p<0.01$ ). By contrast, P. gingivalis-treated HOKs exhibited a markedly reduced chemotactic effect on THP-1 cells ( $p<0.01$ , 2 h; $p<0.05$ , 18 h). There was no significant difference in THP-1 cell migration among the groups with either S. sanguinis or P. gingivalis alone. The current findings on P. gingivalis-HOKs interactions with resultant paralysis of THP-1 cell chemotaxis provide further evidence that the keystone periodontopathogen P. gingivalis can evade innate defense and contribute to periodontal pathogenesis.

Porphyromonas gingivalis in oral squamous cell carcinoma: A review

Oral cancer contributes significantly to the global cancer burden. Oral bacteria play an important role in the spread of oral cancer, according to mounting evidence. The most proven instance is the carcinogenic implications of Porphyromonas gingivalis, a key pathogen in chronic periodontitis. It is imperative to understand the pathogenesis of P. gingivalis in OSCC. This review aims to gather and assess scientific shreds of evidence on the involvement of Porphyromonas gingivalis in the molecular mechanism of oral squamous cell carcinoma.

Unrevealing the Proteolytic Activity of RgpB Gingipain from Computational Simulations

Alzheimer's disease represents one of the greatest medical concerns for today's population and health services. Its multifactorial inherent nature represents a challenge for its treatment and requires the development of a broad spectrum of drugs. Recently, the cysteine protease gingipain RgpB has been related to neurodegenerative diseases, including Alzheimer's disease, and its inhibition appears to be a promising neuroprotective strategy. Given these features, a computational study that integrates molecular dynamics (MD) simulations with classical and hybrid quantum mechanics/molecular mechanics (QM/MM) potentials was carried out to unravel the atomistic details of RgpB activity. First, a preliminary study based on principal component analysis (PCA), determined the protonation state of the Cys/His catalytic dyad, as well as the crucial role of a flexible loop that favors reactive interactions of the catalytic residues and the peptide in the precatalytic state in its closed conformation. Then, different mechanisms were explored by means of QM/MM MD simulations. The most favorable mechanism consists of two stages. First is an acylation stage that takes place in two steps where, initially, the sulfur atom of the C244 residue attacks the carbonylic carbon of the peptide and the proton of the C244 residue is transferred to the amino group of the peptide in a concerted manner. Subsequently, the peptide bond is broken, and a fragment of the peptide is released. After that, the deacylation stage takes place in a single step where a water molecule attacks the carbonylic carbon of the peptide and a proton of the water is transferred to the C244 residue. The free energy barrier of the rate limiting step is in very good agreement with available experimental data. The mechanism exhibits an unusual role of H211 residue compared with other cysteine proteases but a crucial role of the peptide in triggering the catalysis. Notably, the atomic and energetic particularities found represent a significant contribution to the comprehension of the reaction mechanism and a great opportunity for the design of efficient inhibitors of gingipain RgpB.

Outer membrane vesicles of Porphyromonas gingivalis: Novel communication tool and strategy

Extracellular vesicles (EVs) have been recognized as a universal method of cellular communications and are reportedly produced in bacteria, archaea, and eukaryotes. Bacterial EVs are often called “Outer Membrane Vesicles” (OMVs) as they were the result of a controlled blebbing of the outer membrane of gram-negative bacteria such as Porphyromonas gingivalis (P. gingivalis). Bacterial EVs are natural messengers, implicated in intra- and inter-species cell-to-cell communication among microorganism populations present in microbiota. Bacteria can incorporate their pathogens into OMVs; the content of OMVs differs, depending on the type of bacteria. The production of distinct types of OMVs can be mediated by different factors and routes. A recent study highlighted OMVs ability to carry crucial molecules implicated in immune modulation, and, nowadays, they are considered as a way to communicate and transfer messages from the bacteria to the host and vice versa. This review article focuses on the current understanding of OMVs produced from major oral bacteria, P. gingivalis: generation, characteristics, and contents as well as the involvement in signal transduction of host cells and systemic diseases. Our recent study regarding the action of P. gingivalis OMVs in the living body is also summarized.

Construction and characterization of the PGN_0296 mutant of Porphyromonas gingivalis

The periodontal pathogen Porphyromonas gingivalis produces gingipains (Kgp, RgpA, and RgpB), cysteine proteases involved in the organism's virulence, and pigmentation. We previously showed that deletion of the PGN_0297 and PGN_0300 genes reduced the proteolytic activity of gingipains. The role of the PGN_0296 gene, consisting of an operon with the PGN_0297 and PGN_0300 genes, is unclear. Herein, we examined the effect of PGN_0296 gene deletion on the proteolytic activity. Although the proteolytic activity of the gingipains did not decrease in the culture supernatant of a PGN_0296 gene deletion mutant (ΔPGN_0296), the growth was delayed.

Reassessment of minimal media reveals differences in growth among Porphyromonas gingivalis standard strains

OBJECTIVES

Porphyromonas gingivalis is one of the etiologic agents of chronic periodontitis. Our previous study showed that the use of minimal media for P. gingivalis allowed to isolate novel inhibitors of P. gingivalis growth. However, growth of P. gingivalis in minimal media was not always reproducible.

METHODS

To explain this phenomenon, we analyzed the growth of seven wild-type ATCC 33277 strains and two wild-type W83 strains in 10 minimal media and three complex media.

RESULTS

All nine strains grew in LF (Lactalbumin-Ferric chloride), GC (bovine γ-immunoglobulin G-Calcium chloride), and newly developed mC (milk-Casein) minimal media. Therefore, LF, GC, and mC could be used as minimal media for P. gingivalis. In contrast, other six minimal media containing bovine serum albumin (BSA) supported the growth of several less strains; among these, two media also showed lack of reproducibility in growth among ATCC 33277 strains. On the other hand, four ATCC 33277 strains grew similarly in all 13 media, but two W83 and other three ATCC 33277 strains grew differently in at least one medium.

CONCLUSIONS

These results suggest that the lack of reproducibility of P. gingivalis growth on minimal media is caused by the presence of BSA, and by differences among the standard strains of P. gingivalis.

Argeloside I inhibits the pathogenicity of Porphyromonas gingivalis TDC60

Porphyromonas gingivalis, a major pathogen associated with chronic periodontitis, produces several virulence agents in the outer cell membrane, including gingipains and hemagglutinins. These virulence factors enable the bacteria to adhere to periodontal tissue and degrade host proteins to obtain the nutrients needed for dental plaque formation. P. gingivalis TDC60 was recently identified as the most aggressive P. gingivalis strain to dates. In this study, we isolated a known pregnane glycoside, argeloside I, from the aqueous extract of Solenostemma argel leaves. Argeloside I completely hindered the growth of P. gingivalis TDC60 and inhibited the production of hemagglutinins as well as Arg- and Lys-specific gingipains. Our results demonstrate a new function of pregnane glycosides. Argeloside I may be a candidate for reducing the risk associated with P. gingivalis TDC60 and its adhesion factors.

Inflammatory response of uric acid produced by Porphyromonas gingivalis gingipains

Uric acid is a potential metabolite that serves as a danger-associated molecular pattern (DAMP) and induces inflammatory responses in sterile environments. Porphyromonas gingivalis is a keystone periodontopathogen, and its gingipain proteases play a critical role in the pathogenesis of periodontitis. In this study, we demonstrate that P. gingivalis gingipains play a role in THP-1 macrophage uric acid production by increasing the expression and activity of xanthine oxidoreductase (XOR). Uric acid sodium salt induces caspase-1 activation, cell death, and the expression of proinflammatory cytokines, including IL-1α, IL-6, and IL-8, in the human keratinocyte HOK-16B cell line. Our results suggest that gingipain-induced uric acid can mediate inflammation in periodontal tissue cells.

The Use of Antimicrobial and Antiviral Drugs in Alzheimer's Disease

The aggregation and accumulation of amyloid-β plaques and tau proteins in the brain have been central characteristics in the pathophysiology of Alzheimer's disease (AD), making them the focus of most of the research exploring potential therapeutics for this neurodegenerative disease. With success in interventions aimed at depleting amyloid-β peptides being limited at best, a greater understanding of the physiological role of amyloid-β peptides is needed. The development of amyloid-β plaques has been determined to occur 10-20 years prior to AD symptom manifestation, hence earlier interventions might be necessary to address presymptomatic AD. Furthermore, recent studies have suggested that amyloid-β peptides may play a role in innate immunity as an antimicrobial peptide. These findings, coupled with the evidence of pathogens such as viruses and bacteria in AD brains, suggests that the buildup of amyloid-β plaques could be a response to the presence of viruses and bacteria. This has led to the foundation of the antimicrobial hypothesis for AD. The present review will highlight the current understanding of amyloid-β, and the role of bacteria and viruses in AD, and will also explore the therapeutic potential of antimicrobial and antiviral drugs in Alzheimer's disease.

Proteolysis of Gingival Keratinocyte Cell Surface Proteins by Gingipains Secreted From Porphyromonas gingivalis - Proteomic Insights Into Mechanisms Behind Tissue Damage in the Diseased Gingiva

Porphyromonas gingivalis, the main etiologic agent of periodontitis, secretes cysteine proteases named gingipains. HRgpA and RgpB gingipains have Arg-specificity, while Kgp gingipain is Lys-specific. Together they can cleave an array of proteins and importantly contribute to the development of periodontitis. In this study we focused on gingipain-exerted proteolysis at the cell surface of human gingival epithelial cells [telomerase immortalized gingival keratinocytes (TIGK)] in order to better understand the molecular mechanisms behind tissue destruction in periodontitis. Using mass spectrometry, we investigated the whole sheddome/degradome of TIGK cell surface proteins by P. gingivalis strains differing in gingipain expression and by purified gingipains, and performed the first global proteomic analysis of gignpain proteolysis at the membrane. Incubation of TIGK cells with P. gingivalis resulted in massive degradation of proteins already at low multiplicity of infection, whereas incubating cells with purified gingipains resulted in more discrete patterns, indicative of a combination of complete degradation and shedding of membrane proteins. Most of the identified gingipain substrates were molecules involved in adhesion, suggesting that gingipains may cause tissue damage through cleavage of cell contacts, resulting in cell detachment and rounding, and consequently leading to anoikis. However, HRgpA and RgpB gingipains differ in their mechanism of action. While RgpB rapidly degraded the proteins, HRgpA exhibited a much slower proteolysis indicative of ectodomain shedding, as demonstrated for the transferrin receptor protein 1 (TFRC). These results reveal a molecular underpinning to P. gingivalis-induced tissue destruction and enhance our knowledge of the role of P. gingivalis proteases in the pathobiology of periodontitis. Proteomics data are available via ProteomeXchange with identifier PXD015679.

Protease-activated receptor signaling in intestinal permeability regulation

Protease-activated receptors (PARs) are a unique class of G-protein-coupled transmembrane receptors, which revolutionized the perception of proteases from degradative enzymes to context-specific signaling factors. Although PARs are traditionally known to affect several vascular responses, recent investigations have started to pinpoint the functional role of PAR signaling in the gastrointestinal (GI) tract. This organ is exposed to the highest number of proteases, either from the gut lumen or from the mucosa. Luminal proteases include the host's digestive enzymes and the proteases released by the commensal microbiota, while mucosal proteases entail extravascular clotting factors and the enzymes released from resident and infiltrating immune cells. Active proteases and, in case of a disrupted gut barrier, even entire microorganisms are capable to translocate the intestinal epithelium, particularly under inflammatory conditions. Especially PAR-1 and PAR-2, expressed throughout the GI tract, impact gut permeability regulation, a major factor affecting intestinal physiology and metabolic inflammation. In addition, PARs are critically involved in the onset of inflammatory bowel diseases, irritable bowel syndrome, and tumor progression. Due to the number of proteases involved and the multiple cell types affected, selective regulation of intestinal PARs represents an interesting therapeutic strategy. The analysis of tissue/cell-specific knockout animal models will be of crucial importance to unravel the intrinsic complexity of this signaling network. Here, we provide an overview on the implication of PARs in intestinal permeability regulation under physiologic and disease conditions.

Fragment-based discovery of the first nonpeptidyl inhibitor of an S46 family peptidase

Antimicrobial resistance is a global public threat and raises the need for development of new antibiotics with a novel mode of action. The dipeptidyl peptidase 11 from Porphyromonas gingivalis (PgDPP11) belongs to a new class of serine peptidases, family S46. Because S46 peptidases are not found in mammals, these enzymes are attractive targets for novel antibiotics. However, potent and selective inhibitors of these peptidases have not been developed to date. In this study, a high-resolution crystal structure analysis of PgDPP11 using a space-grown crystal enabled us to identify the binding of citrate ion, which could be regarded as a lead fragment mimicking the binding of a substrate peptide with acidic amino acids, in the S1 subsite. The citrate-based pharmacophore was utilized for in silico inhibitor screening. The screening resulted in an active compound SH-5, the first nonpeptidyl inhibitor of S46 peptidases. SH-5 and a lipophilic analog of SH-5 showed a dose-dependent inhibitory effect against the growth of P. gingivalis. The binding mode of SH-5 was confirmed by crystal structure analysis. Thus, these compounds could be lead structures for the development of selective inhibitors of PgDPP11.

A screening system using minimal media identifies a flavin-competing inhibitor of Porphyromonas gingivalis growth

Chronic periodontitis is caused by dysbiosis of human oral commensals and especially by increase in Porphyromonas gingivalis. Inhibitors of P. gingivalis growth are expected to serve as effective drugs for the periodontal therapy. In the present study, we isolated new growth inhibitors of P. gingivalis using minimal media for P. gingivalis. The minimal media included the previously reported Globulin-Albumin (GA) and the newly developed Lactalbumin-Ferric chloride (LF) and Globulin-Calcium chloride (GC); all supported growth of the wild-type strain of P. gingivalis but did not support the growth of a mutant defective for a type IX secretion system. GC contains CaCl2, indicating that P. gingivalis requires a calcium ion for growth. Using LF and GA, we screened about 100 000 compounds and identified 73 that strongly inhibited the growth of P. gingivalis. More than half of these candidates would not have been obtained if these minimal media had not been used in our screen. One of our candidate inhibitors was diphenyleneiodonium chloride (DPIC), which showed strong bactericidal activity against P. gingivalis. Excess amounts of flavin adenine dinucleotide or flavin mononucleotide suppressed the inhibitory activity of DPIC, suggesting that DPIC would be a novel potent growth inhibitor.

Triggering NETosis via protease-activated receptor (PAR)-2 signaling as a mechanism of hijacking neutrophils function for pathogen benefits

Neutrophil-derived networks of DNA-composed extracellular fibers covered with antimicrobial molecules, referred to as neutrophil extracellular traps (NETs), are recognized as a physiological microbicidal mechanism of innate immunity. The formation of NETs is also classified as a model of a cell death called NETosis. Despite intensive research on the NETs formation in response to pathogens, the role of specific bacteria-derived virulence factors in this process, although postulated, is still poorly understood. The aim of our study was to determine the role of gingipains, cysteine proteases responsible for the virulence of P. gingivalis, on the NETosis process induced by this major periodontopathogen. We showed that NETosis triggered by P. gingivalis is gingipain dependent since in the stark contrast to the wild-type strain (W83) the gingipain-null mutant strain only slightly induced the NETs formation. Furthermore, the direct effect of proteases on NETosis was documented using purified gingipains. Notably, the induction of NETosis was dependent on the catalytic activity of gingipains, since proteolytically inactive forms of enzymes showed reduced ability to trigger the NETs formation. Mechanistically, gingipain-induced NETosis was dependent on proteolytic activation of protease-activated receptor-2 (PAR-2). Intriguingly, both P. gingivalis and purified Arg-specific gingipains (Rgp) induced NETs that not only lacked bactericidal activity but instead stimulated the growth of bacteria species otherwise susceptible to killing in NETs. This protection was executed by proteolysis of bactericidal components of NETs. Taken together, gingipains play a dual role in NETosis: they are the potent direct inducers of NETs formation but in the same time, their activity prevents P. gingivalis entrapment and subsequent killing. This may explain a paradox that despite the massive accumulation of neutrophils and NETs formation in periodontal pockets periodontal pathogens and associated pathobionts thrive in this environment.

Periodontitis, or gum disease, is characterized by chronic inflammation and erosion of the tooth-supporting tissues. The condition is fuelled by bacterial accumulation on the tooth surface below the gum line that resists the host innate immune response, including massive accumulation of neutrophils. Despite possessing a formidable array of bactericidal machineries, including neutrophil extracellular traps (NETs) formation whereby neutrophils release DNA-composed fibers decorated with bactericidal proteins and peptides to efficiently trap and kill bacteria. Nevertheless, neutrophils in periodontitis are unable to clear the infection due to the presence of key periodontal pathogens, including Porphyromonas gingivalis. This bacterium secretes a variety of virulence factors, including proteases (gingipains) that allow the organism to manipulate the host immune response to benefit the entire dysbiotic microbial community. Here, we describe a unique strategy whereby P. gingivalis trigger NET formation through gingipain-dependent cleavage of Protease Activated Receptor (PAR)-2 on the neutrophil surface. Importantly, NETs formed in this way are deficient in antibacterial activity but instead, supports bacterial growth due to degradation of bactericidal components by gingipains. This finding may explain a paradox that dysbiotic bacteria flourished in periodontal pockets in spite of massive accumulation of neutrophils and abundant NETs formation.

Characterization and development of SAPP as a specific peptidic inhibitor that targets Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone bacterium in the oral microbial communities that elicits a dysbiosis between the microbiota and the host. Therefore, inhibition of this organism in dental plaques has been one of the strategies for preventing and treating chronic periodontitis. We previously identified a Streptococcal ArcA derived Anti-P gingivalils Peptide (SAPP) that in vitro, is capable of repressing the expression of several virulence genes in the organism. This leads to a significant reduction in P gingivalis virulence potential, including its ability to colonize on the surface of Streptococcus gordonii, to invade human oral epithelial cells, and to produce gingipains. In this study, we showed that SAPP had minimal cytotoxicity to human oral keratinocytes and gingival fibroblasts. We observed that SAPP directly bound to the cell surface of P gingivalis, and that alterations in the sequence at the N-terminus of SAPP diminished its abilities to interact with P gingivalis cells and repressed the expression of virulence genes. Most strikingly, we demonstrated using an ex-vivo assay that besides its inhibitory activity against P gingivalis colonization, SAPP could also reduce the levels of several other oral Gram-negative bacteria strongly associated with periodontitis in multispecies biofilms. Our results provide a platform for the development of SAPP-targeted therapeutics against chronic periodontitis.

The contribution of Tannerella forsythia dipeptidyl aminopeptidase IV in the breakdown of collagen

In this study, we characterized a serine protease from Tannerella forsythia that degrades gelatin, type I, and III collagen. Tannerella forsythia is associated with periodontitis progression and severity. The primary goal of this research was to understand the mechanisms by which T. forsythia contributes to periodontitis progression. One of our previous metatranscriptomic analysis revealed that during periodontitis progression T. forsythia highly expressed the bfor_1659 ORF. The N-terminal end is homologous to dipeptidyl aminopeptidase IV (DPP IV). DPP IV is a serine protease that cleaves X-Pro or X-Ala dipeptide from the N-terminal end of proteins. Collagen type I is rich in X-Pro and X-Ala sequences, and it is the primary constituent of the periodontium. This work assessed the collagenolytic and gelatinolytic properties of BFOR_1659. To that end, the complete BFOR_1659 and its domains were purified as His-tagged recombinant proteins, and their collagenolytic activity was tested on collagen-like substrates, collagen type I and III combined, and on the extracellular matrix (ECM) formed on human gingival fibroblasts culture HGF-1. BFOR_1659 was only found in T. forsythia supernatants, highlighting its potential role on the pathogenicity of T. forsythia. We also found that BFOR_1659 efficiently degrades all tested substrates but the individual domains were inactive. Given that BFOR_1659 is highly expressed in the periodontal pocket, its clinical relevance is suggested to periodontitis progression.

Gingipains disrupt F-actin and cause osteoblast apoptosis via integrin β1

BACKGROUND AND OBJECTIVE

The aim of this study was to explore the cellular mechanisms underlying gingipain-caused changes in cell morphology and apoptosis of osteoblasts.

MATERIAL AND METHODS

Human calvarial osteoblasts and mouse osteoblasts MC3T3-E1 were treated with gingipain extracts from Porphyromonas gingivalis stain W83. Apoptosis was detected with annexin V and propidium iodide flow cytometry analysis or terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling staining. F-actin was determined by immunostaining. Western blotting was used to detect protein expression. Knocking down and overexpressing approaches were used to determine the role of integrin β1.

RESULTS

Osteoblasts exposed to gingipain extracts displayed increased apoptosis, accompanied by loss of F-actin integrity and cell shrinkage. The effects of gingipain extracts were abolished by the cysteine protease inhibitor N-tosyl-l-lysyl chloromethyl-ketone. Notably, gingipain extracts resulted in reduction of integrin β1, accompanied by diminished active RhoA whereas without effect on the total RhoA. Knockdown of integrin β1 resembled those seen in gingipain-treated osteoblasts. By contrast, the effects of gingipain extracts were abrogated by either overexpression of integrin β1 or presence of RhoA agonist CN03.

CONCLUSION

Gingipain-induced F-actin disruption and apoptosis are mediated by the degradation of integrin β1 and inhibition of RhoA activity, which account for osteoblast apoptosis.

Type IX secretion system PorM and gliding machinery GldM form arches spanning the periplasmic space

Type IX secretion system (T9SS), exclusively present in the Bacteroidetes phylum, has been studied mainly in Flavobacterium johnsoniae and Porphyromonas gingivalis. Among the 18 genes, essential for T9SS function, a group of four, porK-N (P. gingivalis) or gldK-N (F. johnsoniae) belongs to a co-transcribed operon that expresses the T9SS core membrane complex. The central component of this complex, PorM (or GldM), is anchored in the inner membrane by a trans-membrane helix and interacts through the outer membrane PorK-N complex. There is a complete lack of available atomic structures for any component of T9SS, including the PorKLMN complex. Here we report the crystal structure of the GldM and PorM periplasmic domains. Dimeric GldM and PorM, each contain four domains of ~180-Å length that span most of the periplasmic space. These and previously reported results allow us to propose a model of the T9SS core membrane complex as well as its functional behavior.

A novel peptidic inhibitor derived from Streptococcus cristatus ArcA attenuates virulence potential of Porphyromonas gingivalis

Periodontitis is a global health problem and the 6th most common infectious disease worldwide. Porphyromonas gingivalis is considered a keystone pathogen in the disease and is capable of elevating the virulence potential of the periodontal microbial community. Strategies that interfere with P. gingivalis colonization and expression of virulence factor are therefore attractive approaches for preventing and treating periodontitis. We have previously reported that an 11-mer peptide (SAPP) derived from Streptococcus cristatus arginine deiminase (ArcA) was able to repress the expression and production of several well-known P. gingivalis virulence factors including fimbrial proteins and gingipains. Herein we expand and develop these studies to ascertain the impact of this peptide on phenotypic properties of P. gingivalis related to virulence potential. We found that growth rate was not altered by exposure of P. gingivalis to SAPP, while monospecies and heterotypic biofilm formation, and invasion of oral epithelial cells were inhibited. Additionally, SAPP was able to impinge the ability of P. gingivalis to dysregulate innate immunity by repressing gingipain-associated degradation of interleukin-8 (IL8). Hence, SAPP has characteristics that could be exploited for the manipulation of P. gingivalis levels in oral communities and preventing realization of virulence potential.

The Type IX Secretion System (T9SS): Highlights and Recent Insights into Its Structure and Function

Protein secretion systems are vital for prokaryotic life, as they enable bacteria to acquire nutrients, communicate with other species, defend against biological and chemical agents, and facilitate disease through the delivery of virulence factors. In this review, we will focus on the recently discovered type IX secretion system (T9SS), a complex translocon found only in some species of the Bacteroidetes phylum. T9SS plays two roles, depending on the lifestyle of the bacteria. It provides either a means of movement (called gliding motility) for peace-loving environmental bacteria or a weapon for pathogens. The best-studied members of these two groups are Flavobacterium johnsoniae, a commensal microorganism often found in water and soil, and Porphyromonas gingivalis, a human oral pathogen that is a major causative agent of periodontitis. In P. gingivalis and some other periodontopathogens, T9SS translocates proteins, especially virulence factors, across the outer membrane (OM). Proteins destined for secretion bear a conserved C-terminal domain (CTD) that directs the cargo to the OM translocon. At least 18 proteins are involved in this still enigmatic process, with some engaged in the post-translational modification of T9SS cargo proteins. Upon translocation across the OM, the CTD is removed by a protease with sortase-like activity and an anionic LPS is attached to the newly formed C-terminus. As a result, a cargo protein could be secreted into the extracellular milieu or covalently attached to the bacterial surface. T9SS is regulated by a two-component system; however, the precise environmental signal that triggers it has not been identified. Exploring unknown systems contributing to bacterial virulence is exciting, as it may eventually lead to new therapeutic strategies. During the past decade, the major components of T9SS were identified, as well as hints suggesting the possible mechanism of action. In addition, the list of characterized cargo proteins is constantly growing. The actual structure of the translocon, situated in the OM of bacteria, remains the least explored area; however, new technical approaches and increasing scientific attention have resulted in a growing body of data. Therefore, we present a compact up-to-date review of this topic.

Mucosal immunization with a flagellin-adjuvanted Hgp44 vaccine enhances protective immune responses in a murine Porphyromonas gingivalis infection model

Chronic periodontitis is caused by interactions between the oral polymicrobial community and host factors. Periodontal diseases are associated with dysbiotic shift in oral microbiota. Vaccination against periodontopathic bacteria could be a fundamental therapeutic to modulate polymicrobial biofilms. Because oral cavity is the site of periodontopathic bacterial colonization, mucosal vaccines should provide better protection than vaccines administered systemically. We previously reported that bacterial flagellin is an excellent mucosal adjuvant. In this study, we investigated whether mucosal immunization with a flagellin-adjuvanted polypeptide vaccine induces protective immune responses using a Porphyromonas gingivalis infection model. We used the Hgp44 domain polypeptide of Arg-gingipain A (RgpA) as a mucosal antigen. Intranasal (IN) immunization induced a significantly higher Hgp44-specific IgG titer in the serum of mice than sublingual (SL) administration. The co-administration of flagellin potentiated serum IgG responses for both the IN and SL vaccinations. On the other hand, the anti-Hgp44-specific IgA titer in the saliva was comparable between IN and SL vaccinations, suggesting SL administration as more compliant vaccination route for periodontal vaccines. The co-administration of flagellin significantly potentiated the secretory IgA response in saliva also. Furthermore, mice administered a mixture of Hgp44 and flagellin via the IN and SL routes exhibited significant reductions in alveolar bone loss induced by live P. gingivalis infections. An intranasally administered Hgp44-flagellin fusion protein induced a comparable level of Hgp44-specific antibody responses to the mixture of Hgp44 and flagellin. Overall, a flagellin-adjuvanted Hgp44 antigen would serve an important component for a multivalent mucosal vaccine against polymicrobial periodontitis.

The Type IX Secretion System (T9SS): Highlights and Recent Insights into Its Structure and Function

Protein secretion systems are vital for prokaryotic life, as they enable bacteria to acquire nutrients, communicate with other species, defend against biological and chemical agents, and facilitate disease through the delivery of virulence factors. In this review, we will focus on the recently discovered type IX secretion system (T9SS), a complex translocon found only in some species of the Bacteroidetes phylum. T9SS plays two roles, depending on the lifestyle of the bacteria. It provides either a means of movement (called gliding motility) for peace-loving environmental bacteria or a weapon for pathogens. The best-studied members of these two groups are Flavobacterium johnsoniae, a commensal microorganism often found in water and soil, and Porphyromonas gingivalis, a human oral pathogen that is a major causative agent of periodontitis. In P. gingivalis and some other periodontopathogens, T9SS translocates proteins, especially virulence factors, across the outer membrane (OM). Proteins destined for secretion bear a conserved C-terminal domain (CTD) that directs the cargo to the OM translocon. At least 18 proteins are involved in this still enigmatic process, with some engaged in the post-translational modification of T9SS cargo proteins. Upon translocation across the OM, the CTD is removed by a protease with sortase-like activity and an anionic LPS is attached to the newly formed C-terminus. As a result, a cargo protein could be secreted into the extracellular milieu or covalently attached to the bacterial surface. T9SS is regulated by a two-component system; however, the precise environmental signal that triggers it has not been identified. Exploring unknown systems contributing to bacterial virulence is exciting, as it may eventually lead to new therapeutic strategies. During the past decade, the major components of T9SS were identified, as well as hints suggesting the possible mechanism of action. In addition, the list of characterized cargo proteins is constantly growing. The actual structure of the translocon, situated in the OM of bacteria, remains the least explored area; however, new technical approaches and increasing scientific attention have resulted in a growing body of data. Therefore, we present a compact up-to-date review of this topic.

Identification of Streptococcus cristatus peptides that repress expression of virulence genes in Porphyromonas gingivalis

Dental plaque is a complex multispecies biofilm, and is a direct precursor of periodontal disease. The virulence of periodontal pathogens, such as Porphyromonas gingivalis, is expressed in the context of this polymicrobial community. Previously, we reported an antagonistic relationship between Streptococcus cristatus and P. gingivalis, and identified arginine deiminase (ArcA) of S. cristatus as the signaling molecule to which P. gingivalis responds by repressing the expression and production of FimA protein. Here we demonstrate that direct interaction between P. gingivalis and S. cristatus is necessary for the cell-cell communication. Two surface proteins of P. gingivalis, PGN_0294 and PGN_0806, were found to interact with S. cristatus ArcA. Using a peptide array analysis, we identified several P. gingivalis-binding sites of ArcA, which led to the discovery of an 11-mer peptide with the native sequence of ArcA that repressed expression of fimbriae and of gingipains. These data indicate that a functional motif of ArcA is sufficient to selectively alter virulence gene expression in P. gingivalis, and PGN_0294 and PGN_0806 may serve as receptors for ArcA. Our findings provide a molecular basis for future rational design of agents that interfere with the initiation and formation of a P. gingivalis-induced pathogenic community.

Porphyromonas gingivalis Uses Specific Domain Rearrangements and Allelic Exchange to Generate Diversity in Surface Virulence Factors

Porphyromonas gingivalis is a keystone pathogen of chronic periodontitis. The virulence of P. gingivalis is reported to be strain related and there are currently a number of strain typing schemes based on variation in capsular polysaccharide, the major and minor fimbriae and adhesin domains of Lys-gingipain (Kgp), amongst other surface proteins. P. gingivalis can exchange chromosomal DNA between strains by natural competence and conjugation. The aim of this study was to determine the genetic variability of P. gingivalis strains sourced from international locations over a 25-year period and to determine if variability in surface virulence factors has a phylogenetic basis. Whole genome sequencing was performed on 13 strains and comparison made to 10 previously sequenced strains. A single nucleotide polymorphism-based phylogenetic analysis demonstrated a shallow tri-lobed phylogeny. There was a high level of reticulation in the phylogenetic network, demonstrating extensive horizontal gene transfer between the strains. Two highly conserved variants of the catalytic domain of the major virulence factor the Kgp proteinase (Kgp_catI and Kgp_catII) were found. There were three variants of the fourth Kgp C-terminal cleaved adhesin domain. Specific variants of the cell surface proteins FimA, FimCDE, MfaI, RagAB, Tpr, and PrtT were also identified. The occurrence of all these variants in the P. gingivalis strains formed a mosaic that was not related to the SNP-based phylogeny. In conclusion P. gingivalis uses domain rearrangements and genetic exchange to generate diversity in specific surface virulence factors.

Synthesis of Sphingolipids Impacts Survival of Porphyromonas gingivalis and the Presentation of Surface Polysaccharides

Bacteria alter the biophysical properties of their membrane lipids in response to environmental cues, such as shifts in pH or temperature. In essence, lipid composition determines membrane structure, which in turn influences many basic functions, such as transport, secretion, and signaling. Like other members of the phylum Bacteroidetes, the oral anaerobe Porphyromonas gingivalis possesses the ability to synthesize a variety of novel membrane lipids, including species of dihydroceramides that are distinct, yet similar in structure to sphingolipids produced by the human host. The role of dihydroceramides in the physiology and pathogenic potential of the human microbiota is only beginning to be explored; yet there is increasing data indicating that these lipids play a role in human diseases, such as periodontitis and multiple sclerosis. Here, we report on the identification of a gene (PG1780) in the chromosome of P. gingivalis strain W83 encoding a putative serine palmitoyltransferase, the enzyme that catalyzes the first step in sphingolipid biosynthesis. While we were able to detect dihydroceramides in whole lipid extracts of P. gingivalis cells as well as crude preparations of outer membrane vesicles, sphingolipids were absent in the PG1780 mutant strain. Moreover, we show that the synthesis of sphingolipids plays an essential role in the long-term survival of the organism as well as its resistance to oxidative stress. Further, a PG1780 mutant displayed much lower activity of cell-associated arginine and lysine gingipains, yet slightly higher activity in the corresponding culture supernates, which we hypothesize is due to altered membrane properties and anchoring of these proteases to the cell surface. In addition, we determined that sphingolipid production is critical to the presentation of surface polysaccharides, with the mutant strain displaying less K-antigen capsule and more anionic polysaccharide (APS). Overall, we have discovered that, in addition to their role in pathogenicity, the synthesis of sphingolipids is critical to the cellular homeostasis and persistence of this important dental pathogen.

A two-component system regulates gene expression of the type IX secretion component proteins via an ECF sigma factor

The periodontopathogen Porphyromonas gingivalis secretes potent pathogenic proteases, gingipains, via the type IX secretion system (T9SS). This system comprises at least 11 components; however, the regulatory mechanism of their expression has not yet been elucidated. Here, we found that the PorY (PGN_2001)-PorX (PGN_1019)-SigP (PGN_0274) cascade is involved in the regulation of T9SS. Surface plasmon resonance (SPR) analysis revealed a direct interaction between a recombinant PorY (rPorY) and a recombinant PorX (rPorX). rPorY autophosphorylated and transferred a phosphoryl group to rPorX in the presence of Mn²⁺. These results demonstrate that PorX and PorY act as a response regulator and a histidine kinase, respectively, of a two component system (TCS), although they are separately encoded on the chromosome. T9SS component-encoding genes were down-regulated in a mutant deficient in a putative extracytoplasmic function (ECF) sigma factor, PGN_0274 (SigP), similar to the porX mutant. Electrophoretic gel shift assays showed that rSigP bound to the putative promoter regions of T9SS component-encoding genes. The SigP protein was lacking in the porX mutant. Co-immunoprecipitation and SPR analysis revealed the direct interaction between SigP and PorX. Together, these results indicate that the PorXY TCS regulates T9SS-mediated protein secretion via the SigP ECF sigma factor.

Relationship between invasion of the periodontium by periodontal pathogens and periodontal disease: a systematic review

Bacterial invasion of the periodontal tissues has been suggested as a relevant step in the etiopathogenesis of periodontal disease. However, its exact importance remains to be defined. The present systematic review assessed the scientific evidence concerning the relationship between the quality or quantity of periodontal microbiota in periodontal tissues and development of periodontal disease. The databases Medline-PubMed, Cochrane-CENTRAL, ISI Web of Knowledge and SCOPUS were searched, up to January 2014. Studies that reported evaluation of periodontal pathogens invasion on human tissues were selected. The screening of 440 title/abstracts elected 26 papers for full-text reading. Twenty three papers were subsequently excluded because of insufficient data or a study protocol not related to the objectives of this systematic review. All included studies were case-control studies that evaluated intracellular or adherent bacteria to epithelial cells from periodontal pockets versus healthy sulci. Study protocols presented heterogeneity regarding case and control definitions and methodological approaches for microbial identification. No consistent significant differences were found related to the presence/absence or proportion of specific periopathogens across the studies, as only one study found statistically significant differences regarding the presence of A. actinomycetemcomitans (p = 0.043), T. forsythia (P < 0.001), P. intermedia (P < 0.001), C. ochracea (P < 0.001) and C. rectus (P = 0.003) in epithelial cells from periodontal pockets vs. healthy sulci. All studies reported a larger unspecific bacterial load in or on the epithelial cells taken from a diseased site compared to a healthy sulcus. The current available data is of low to moderate quality and inconsistent mainly due to study design, poor reporting and methodological diversity. As so, there is insufficient evidence to support or exclude the invasion by periodontal pathogens as a key step in the etiopathogenesis of periodontal disease. Further research is needed.

Involvement of an Skp-Like Protein, PGN_0300, in the Type IX Secretion System of Porphyromonas gingivalis

The oral Gram-negative anaerobic bacterium Porphyromonas gingivalis is an important pathogen involved in chronic periodontitis. Among its virulence factors, the major extracellular proteinases, Arg-gingipain and Lys-gingipain, are of interest given their abilities to degrade host proteins and process other virulence factors. Gingipains possess C-terminal domains (CTDs) and are translocated to the cell surface or into the extracellular milieu by the type IX secretion system (T9SS). Gingipains contribute to the colonial pigmentation of the bacterium on blood agar. In this study, Omp17, the PGN_0300 gene product, was found in the outer membrane fraction. A mutant lacking Omp17 did not show pigmentation on blood agar and showed reduced proteolytic activity of the gingipains. CTD-containing proteins were released from bacterial cells without cleavage of the CTDs in the omp17 mutant. Although synthesis of the anionic polysaccharide (A-LPS) was not affected in the omp17 mutant, the processing of and A-LPS modification of CTD-containing proteins was defective. PorU, a C-terminal signal peptidase that cleaves the CTDs of other CTD-containing proteins, was not detected in any membrane fraction of the omp17 mutant, suggesting that the defective maturation of CTD-containing proteins by impairment of Omp17 is partly due to loss of function of PorU. In the mouse subcutaneous infection experiment, the omp17 mutant was less virulent than the wild type. These results suggested that Omp17 is involved in P. gingivalis virulence.

Porphyromonas gingivalis and related bacteria: from colonial pigmentation to the type IX secretion system and gliding motility

Porphyromonas gingivalis is a gram-negative, non-motile, anaerobic bacterium implicated as a major pathogen in periodontal disease. P. gingivalis grows as black-pigmented colonies on blood agar, and many bacteriologists have shown interest in this property. Studies of colonial pigmentation have revealed a number of important findings, including an association with the highly active extracellular and surface proteinases called gingipains that are found in P. gingivalis. The Por secretion system, a novel type IX secretion system (T9SS), has been implicated in gingipain secretion in studies using non-pigmented mutants. In addition, many potent virulence proteins, including the metallocarboxypeptidase CPG70, 35 kDa hemin-binding protein HBP35, peptidylarginine deiminase PAD and Lys-specific serine endopeptidase PepK, are secreted through the T9SS. These findings have not been limited to P. gingivalis but have been extended to other bacteria belonging to the phylum Bacteroidetes. Many Bacteroidetes species possess the T9SS, which is associated with gliding motility for some of these bacteria.

Structure of the lysine specific protease Kgp from Porphyromonas gingivalis, a target for improved oral health

The oral pathogen Porphyromonas gingivalis is a keystone pathogen in the development of chronic periodontitis. Gingipains, the principle virulence factors of P. gingivalis are multidomain, cell-surface proteins containing a cysteine protease domain. The lysine specific gingipain, Kgp, is a critical virulence factor of P. gingivalis. We have determined the X-ray crystal structure of the lysine-specific protease domain of Kgp to 1.6 Å resolution. The structure provides insights into the mechanism of substrate specificity and catalysis.

Gingipains from Porphyromonas gingivalis play a significant role in induction and regulation of CXCL8 in THP-1 cells

Background

Porphyromonas gingivalis is an important bacterial etiological agent involved in periodontitis. The bacterium expresses two kinds of cysteine proteases called gingipains: arginine gingipains (RgpA/B) and lysine gingipain (Kgp). This study evaluated the interaction between P. gingivalis and THP-1 cells, a widely used monocytic cell line, in vitro with a focus on CXCL8 at the gene and protein levels and its fate thereafter in cell culture supernatants. THP-1 cells were stimulated with viable and heat-killed wild-type strains ATCC 33277 or W50 or viable isogenic gingipain mutants of W50, E8 (Rgp mutant) or K1A (Kgp mutant), for 24 hours.

Results

ELISA and qPCR results show an elevated CXCL8 expression and secretion in THP-1 cells in response to P. gingivalis, where the heat-killed ATCC33277 and W50 induced higher levels of CXCL8 in comparison to their viable counterparts. Furthermore, the Kgp-deficient mutant K1A caused a higher CXCL8 response compared to the Rgp-deficient E8. Chromogenic quantification of lipopolysaccharide (LPS) in supernatant showed no significant differences between viable and heat killed bacteria except that W50 shed highest levels of LPS. The wild-type strains secreted relatively more Rgp during the co-culture with THP-1 cells. The CXCL8 degradation assay of filter-sterilized supernatant from heat-killed W50 treated cells showed that Rgp was most efficient at CXCL8 hydrolysis. Of all tested P. gingivalis strains, adhesion and internalization in THP-1 cells was least conspicuous by Rgp-deficient P. gingivalis (E8), as demonstrated by confocal imaging.

Conclusions

W50 and its Kgp mutant K1A exhibit a higher immunogenic and proteolytic function in comparison to the Rgp mutant E8. Since K1A differs from E8 in the expression of Rgp, it is rational to conclude that Rgp contributes to immunomodulation in a more dynamic manner in comparison to Kgp. Also, W50 is a more virulent strain when compared to the laboratory strain ATCC33277.

Gingipains from Porphyromonas gingivalis - Complex domain structures confer diverse functions

Gingipains, a group of arginine or lysine specific cysteine proteinases (also known as RgpA, RgpB and Kgp), have been recognized as major virulence factors in Porphyromonas gingivalis. This bacterium is one of a handful of pathogens that cause chronic periodontitis. Gingipains are involved in adherence to and colonization of epithelial cells, haemagglutination and haemolysis of erythrocytes, disruption and manipulation of the inflammatory response, and the degradation of host proteins and tissues. RgpA and Kgp are multi-domain proteins composed of catalytic domains and haemagglutinin/adhesin (HA) regions. The structure of the HA regions have previously been defined by a gingipain domain structure hypothesis which is a set of putative domain boundaries derived from the sequences of fragments of these proteins extracted from the cell surface. However, multiple sequence alignments and hidden Markov models predict an alternative domain architecture for the HA regions of gingipains. In this alternate model, two or three repeats of the so-called "cleaved adhesin" domains (and one other undefined domain in some strains) are the modules which constitute the substructure of the HA regions. Recombinant forms of these putative cleaved adhesin domains are indeed stable folded protein modules and recently determined crystal structures support the hypothesis of a modular organisation of the HA region. Based on the observed K2 and K3 structures as well as multiple sequence alignments, it is proposed that all the cleaved adhesin domains in gingipains will share the same β-sandwich jelly roll fold. The new domain model of the structure for gingipains and the haemagglutinin (HagA) proteins of P. gingivalis will guide future functional studies of these virulence factors.

kgp, rgpA, and rgpB DNA vaccines induce antibody responses in experimental peri-implantitis

BACKGROUND

Peri-implantitis is the key factor for implant failure. This study aims to evaluate kgp, rgpA, and rgpB DNA vaccines to induce an immune response and prevent peri-implantitis.

METHODS

The kgp, rgpA, and rgpB genes were amplified by polymerase chain reaction (PCR) from Porphyromonas gingivalis (Pg) ATCC 33277 and cloned into the pVAX1 vector. Titanium implants were placed into the mandibular bone of dogs. Three months later, the animals were divided into four groups, immunized with pVAX1-kgp, pVAX1-rgpA, pVAX1-rgpB, or pVAX1. Cotton ligatures infiltrated with Pg were tied around the neck of the implants. Immunoglobulin (Ig)G and IgA antibodies were detected by enzyme-linked immunosorbent assay before and after immunization.

RESULTS

The kgp, rgpA, and rgpB genes were successfully cloned into the pVAX1 plasmid. Animals immunized with pVAX1-kgp and pVAX1-rgpA showed higher titers of IgG and IgA antibodies compared to those before immunization (P <0.05) and compared to those that were immunized with pVAX1 and pVAX1-rgpB, whereas there were no significant differences in the animals treated with pVAX1 and pVAX1-rgpB. Furthermore, among these, the kgp DNA vaccine was more effective. The bone losses of the groups with pVAX1-kgp and pVAX1-rgpA were significantly attenuated.

CONCLUSION

pVAX1-kgp and pVAX1-rgpA DNA vaccines enhanced immunity responses and significantly retarded bone loss in experimental peri-implantitis animal models, whereas pVAX1-rgpB was ineffective.

Analysis of a Lys-specific serine endopeptidase secreted via the type IX secretion system in Porphyromonas gingivalis

Porphyromonas gingivalis, a significant causative agent of adult periodontitis, possesses a novel secretion system called the type IX secretion system (T9SS). A number of virulence factors, such as Arg-gingipain (Rgp), are translocated onto the cell surface and into the extracellular milieu via the T9SS. In this study, we found that the PGN_1416 90- to 120-kDa diffuse protein bands were located in the outer membrane fraction and that the presence of the bands was dependent on genes involved in the T9SS and the formation of anionic lipopolysaccharide (A-LPS). These data strongly suggest that the PGN_1416 protein is secreted by the T9SS and anchored onto the cell surface by binding to A-LPS. Enzymatic analysis using outer membrane fractions suggested that the PGN_1416 protein has a Lys-specific serine endopeptidase activity and that its activation requires processing by Rgp. Homologues of the gene encoding PGN_1416, which is referred to as pepK, were found in bacteria belonging to the phyla Bacteroidetes and Proteobacteria, whereas homologues encoding the C-terminal domain, which is essential for T9SS-mediated secretion, and the catalytic domain were only observed in bacteria belonging to the Bacteroidetes phylum.

Porphyromonas gingivalis gingipain is involved in the detachment and aggregation of Aggregatibacter actinomycetemcomitans biofilm

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are major periodontal pathogens that cause several types of periodontal disease. Our previous study suggested that P. gingivalis gingipains secreted in the subgingival environment are related to the detachment of A.actinomycetemcomitans biofilms. However, it remains unclear whether arginine-specific cysteine proteinase (Rgp) and lysine-specific proteinase (Kgp) play different roles in the detachment of A. actinomycetemcomitans biofilm. The aim of this study was to investigate possible disruptive roles of Kgp and Rgp in the aggregation and attachment of A. actinomycetemcomitans. While P. gingivalis ATCC33277 culture supernatant has an ability to decrease autoaggregation and coaggregation of A. actinomycetemcomitans cells, neither the boiled culture supernatant of ATCC33277 nor the culture supernatant of KDP136 showed this ability. The addition of KYT-1 and KYT-36, specific inhibitors of Rgp and Kgp, respectively, showed no influence on the ability of P. gingivalis culture supernatant. The result of gelatin zymography suggested that other proteases processed by gingipains mediated the decrease of A. actinomycetemcomitans aggregations. We also examined the biofilm-destructive effect of gingipains by assessing the detachment of A. actinomycetemcomitans from polystyrene surfaces. Scanning electron microscope analysis indicated that A. actinomycetemcomitans cells were detached by P. gingivalis Kgp. The quantity of A. actinomycetemcomitans in biofilm was decreased in co-culture with P. gingivalis. However, this was not found after the addition of KYT-36. These findings suggest that Kgp is a critical component for the detachment and decrease of A. actinomycetemcomitans biofilms.