Involvement of arginine-specific cysteine proteinase (Arg-gingipain) in fimbriation of Porphyromonas gingivalis

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.

Ingestion of Porphyromonas gingivalis exacerbates colitis via intestinal epithelial barrier disruption in mice

OBJECTIVE

This study aimed to evaluate the effects of ingested periodontal pathogens on experimental colitis in mice and to elucidate its underlying mechanisms.

BACKGROUND

Inflammatory bowel disease (IBD) is defined as a chronic intestinal inflammation that results in damage to the gastrointestinal tract. Epidemiological studies have shown an association between IBD and periodontitis. Although a large number of ingested oral bacteria reach gastrointestinal tract constantly, the effect of ingested periodontal pathogens on intestinal inflammation is still unknown.

METHODS

Experimental colitis was induced by inclusion of dextran sodium sulfate solution in drinking water of the mice. Major periodontal pathogens (Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum) were administered orally every day during the experiment. The severity of colitis between the groups was compared. In vitro studies of the intestinal epithelial cell line were conducted to explore the molecular mechanisms by which periodontal pathogens affect the development of colitis.

RESULTS

The oral administration of P. gingivalis significantly increased the severity of colitis when compared to other pathogens in the DSS-induced colitis model. The ingested P. gingivalis disrupted the colonic epithelial barrier by decreasing the expression of tight junction proteins in vivo. In vitro permeability assays using the intestinal epithelial cell line suggested the P. gingivalis-specific epithelial barrier disruption. The possible involvement of gingipains in the exacerbation of colitis was implied by using P. gingivalis lacking gingipains.

CONCLUSION

Porphyromonas gingivalis exacerbates gastrointestinal inflammation by directly interacting with the intestinal epithelial barrier in a susceptible host.

Transport and Polymerization of Porphyromonas gingivalis Type V Pili

Adhesive pili (or fimbriae) in bacteria are classified into five types, among which type V pili have been most recently described. Type V pili differ from other pili types with respect to transport mechanism, structure, and pilin synthesis. Genes of type V pili are restricted to the phylum Bacteroidetes. Protein subunits that compose type V pili are transported to the cell surface as lipoprotein precursors and then polymerized into a pilus through a strand-exchange mechanism, which is demonstrated by several experiments, including palmitic acid labeling and Cys-Cys cross-linking analysis. Here, we describe the use of these methods to analyze type V pili.

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.

Peptide-Based Inhibitors of Fimbrial Biogenesis in Porphyromonas gingivalis

Periodontitis is a progressive inflammatory disease that affects roughly half of American adults. Colonization of the oral cavity by the Gram-negative bacterial pathogen Porphyromonas gingivalis is a key event in the initiation and development of periodontal disease. Adhesive surface structures termed fimbriae (pili) mediate interactions of P. gingivalis with other bacteria and with host cells throughout the course of disease. The P. gingivalis fimbriae are assembled via a novel mechanism that involves proteolytic processing of lipidated precursor subunits and their subsequent polymerization on the bacterial surface. Given their extracellular assembly mechanism and central roles in pathogenesis, the P. gingivalis fimbriae are attractive targets for anti-infective therapeutics to prevent or treat periodontal disease. Here we confirm that conserved sequences in the N and C termini of the Mfa1 fimbrial subunit protein perform critical roles in subunit polymerization. We show that treatment of P. gingivalis with peptides corresponding to the conserved C-terminal region inhibits the extracellular assembly of Mfa fimbriae on the bacterial surface. We also show that peptide treatment interferes with the function of Mfa fimbriae by reducing P. gingivalis adhesion to Streptococcus gordonii in a dual-species biofilm model. Finally, we show that treatment of bacteria with similar peptides inhibits extracellular polymerization of the Fim fimbriae, which are also expressed by P. gingivalis These results support a donor strand-based assembly mechanism for the P. gingivalis fimbriae and demonstrate the feasibility of using extracellular peptides to disrupt the biogenesis and function of these critical periodontal disease virulence factors.

The Biosynthesis and Structures of Bacterial Pili

To interact with the external environments, bacteria often display long proteinaceous appendages on their cell surface, called pili or fimbriae. These non-flagellar thread-like structures are polymers composed of covalently or non-covalently interacting repeated pilin subunits. Distinct pilus classes can be identified on basis of their assembly pathways, including chaperone-usher pili, type V pili, type IV pili, curli and fap fibers, conjugative and type IV secretion pili, as well as sortase-mediated pili. Pili play versatile roles in bacterial physiology, and can be involved in adhesion and host cell invasion, DNA and protein secretion and uptake, biofilm formation, cell motility and more. Recent advances in structure determination of components involved in the various pilus systems has enabled a better molecular understanding of their mechanisms of assembly and function. In this chapter we describe the diversity in structure, biogenesis and function of the different pilus systems found in Gram-positive and Gram-negative bacteria, and review their potential as anti-microbial targets.

Maturation of the Mfa1 Fimbriae in the Oral Pathogen Porphyromonas gingivalis

The Mfa1 fimbriae of the periodontal pathogen Porphyromonas gingivalis are involved in adhesion, including binding to synergistic species in oral biofilms. Mfa1 fimbriae are comprised of 5 proteins: the structural component Mfa1, the anchor Mfa2, and Mfa3-5 which constitute the fimbrial tip complex. Interactions among the Mfa proteins and the polymerization mechanism for Mfa1 are poorly understood. Here we show that Mfa3 can bind to Mfa1, 2, 4, and 5 in vitro, and may function as an adaptor protein interlinking other fimbrial subunits. Polymerization of Mfa1 is independent of Mfa3-5 and requires proteolytic processing mediated by the RgpA/B arginine gingipains of P. gingivalis. Both the N- and C- terminal regions of Mfa1 are necessary for polymerization; however, potential β-strand disrupting amino acid substitutions in these regions do not impair Mfa1 polymerization. In contrast, substitution of hydrophobic amino acids with charged residues in either the N- or C- terminal domains yielded Mfa1 proteins that failed to polymerize. Collectively, these results indicate that Mfa3 serves as an adaptor protein between Mfa1 and other accessory fimbrial proteins. Mfa1 fimbrial polymerization is dependent on hydrophobicity in both the N- and C-terminal regions, indicative of an assembly mechanism involving the terminal regions forming a hydrophobic binding interface between Mfa1 subunits.

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.

Porphyromonas gingivalis suppresses invasion of Fusobacterium nucleatum into gingival epithelial cells

Invasion of periodontal pathogens into periodontal tissues is an important step that can cause tissue destruction in periodontal diseases. Porphyromonas gingivalis is a keystone pathogen and its gingipains are key virulence factors. Fusobacterium nucleatum is a bridge organism that mediates coadhesion of disease-causing late colonizers such as P. gingivalis and early colonizers during the development of dental biofilms. The aim of this study was to investigate how P. gingivalis, in particular its gingipains, influences the invasion of coinfecting F. nucleatum into gingival epithelial cells. When invasion of F. nucleatum was analyzed after 4 h of infection, invasion of F. nucleatum was suppressed in the presence of P. gingivalis compared with during monoinfection. However, coinfection with a gingipain-null mutant of P. gingivalis did not affect invasion of F. nucleatum. Inhibition of PI3K reduced invasion of F. nucleatum. P. gingivalis inactivated the PI3K/AKT pathway, which was also dependent on gingipains. Survival of intracellular F. nucleatum was promoted by P. gingivalis with Arg gingipain mutation. The results suggest that P. gingivalis, in particular its gingipains, can affect the invasion of coinfecting F. nucleatum through modulating intracellular signaling of the host cells.

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.

A comprehensive guide to pilus biogenesis in Gram-negative bacteria

Pili are crucial virulence factors for many Gram-negative pathogens. These surface structures provide bacteria with a link to their external environments by enabling them to interact with, and attach to, host cells, other surfaces or each other, or by providing a conduit for secretion. Recent high-resolution structures of pilus filaments and the machineries that produce them, namely chaperone-usher pili, type IV pili, conjugative type IV secretion pili and type V pili, are beginning to explain some of the intriguing biological properties that pili exhibit, such as the ability of chaperone-usher pili and type IV pili to stretch in response to external forces. By contrast, conjugative pili provide a conduit for the exchange of genetic information, and recent high-resolution structures have revealed an integral association between the pilin subunit and a phospholipid molecule, which may facilitate DNA transport. In addition, progress in the area of cryo-electron tomography has provided a glimpse of the overall architecture of the type IV pilus machinery. In this Review, we examine recent advances in our structural understanding of various Gram-negative pilus systems and discuss their functional implications.

[The type IX secretion system and the type V pilus in the phylum Bacteroidetes]

Many bacteria symbiotic and parasitic in humans are included in the genera Bacteroides, Prevotella, Porphyromonas and others, which belong to the phylum Bacteroidetes. We have been studying gingipain, a major secretory protease of Porphyromonas gingivalis which is a periodontopathogenic bacterium belonging to the genus Porphyromonas, and pili which contribute to host colonization in the bacterium. In the process, it was found that gingipain was secreted by a system not reported previously. Furthermore, this secretion system was found to exist widely in the Bacteroidetes phylum bacteria and closely related to the gliding motility of bacteroidete bacteria, and it was named the Por secretion system (later renamed the type IX secretion system). Regarding P. gingivalis pili, it was found that the pilus protein is transported as a lipoprotein to the cell surface, and the pilus formation occurs due to degradation by arginine-gingipain. Pili with this novel formation mechanism was found to be widely present in bacteria belonging to the class Bacteroidia in the phylum Bacteroidetes and was named the type V pili.

Contribution of cationic amino acids toward the inhibition of Arg-specific cysteine proteinase (Arg-gingipain) by the antimicrobial dodecapeptide, CL(14-25), from rice protein

CL(14-25), a dodecapeptide, exhibits antimicrobial activity against Porphyromonas gingivalis with the 50% growth-inhibitory concentration (IC50 ) value of 145 µM, and arginine-specific gingipain (Rgp)-inhibitory activity. Kinetic analysis revealed that CL(14-25) is a mixed-type inhibitor, with inhibition constants (Ki and Ki ' values) of 1.4 × 10(-6) M and 4.3 × 10(-6) M, respectively. To elucidate the contributions of four cationic amino acid residues at the N- and C-termini of CL(14-25) toward Rgp-inhibitory activity, we investigated the Rgp-inhibitory activities of truncated and alanine-substituted analogs of CL(14-25). Rgp-inhibitory activities significantly decreased by truncated analogs, CL(15-25) and CL(16-25), whereas those of CL(14-24) and CL(14-23) were almost as high as that of CL(14-25). Rgp-inhibitory activities of alanine-substituted analogs, CL(R14A) and CL(R14A, R15A) also significantly decreased, whereas those of CL(K25A) and CL(R24A, K25A) were higher than that of CL(14-25). These results suggest that the arginine residue at position 15 substantially contributes to the Rgp-inhibitory activity and that the arginine residue at position 14 plays important roles in exerting Rgp-inhibitory activity. In this study, we demonstrated that CL(K25A) was a potent, dual function, peptide inhibitor candidate, exhibiting Rgp-inhibitory activity with Ki and Ki ' of 9.6 × 10(-7) M and 1.9 × 10(-6) M, respectively, and antimicrobial activity against P. gingivalis with an IC50 value of 51 µM.

Effect of deletion of the rgpA gene on selected virulence of Porphyromonas gingivalis

Background/purpose

The most potent virulence factors of the periodontal pathogen Porphyromonas gingivalis are gingipains, three cysteine proteases (RgpA, RgpB, and Kgp) that bind and cleave a wide range of host proteins. Considerable proof indicates that RgpA contributes to the entire virulence of the organism and increases the risk of periodontal disease by disrupting the host immune defense and destroying the host tissue. However, the functional significance of this proteinase is incompletely understood. It is important to analyze the effect of arginine-specific gingipain A gene (rgpA) on selected virulence and physiological properties of P. gingivalis.

Materials and methods

Electroporation and homologous recombination were used to construct an rgpA mutant of P. gingivalis ATCC33277. The mutant was verified by polymerase chain reaction and sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Cell structures of the mutant were examined by transmission electron microscopy and homotypic biofilm formation was examined by confocal laser scanning microscopy.

Results

Gene analysis revealed that the rgpA gene was deleted and replaced by a drug resistance gene marker. The defect of the gene resulted in a complete loss of RgpA proteinase, a reduction of out membrane vesicles and hemagglutination, and an increase in homotypic biofilm formation.

Conclusion

Our data indicate that an rgpA gene deficient strain of P. gingivalis is successfully isolated. RgpA may have a variety of physiological and pathological roles in P. gingivalis.

Porphyromonas gingivalis Gingipain-Dependently Enhances IL-33 Production in Human Gingival Epithelial Cells

The cytokine IL-33 is constitutively expressed in epithelial cells and it augments Th2 cytokine-mediated inflammatory responses by regulating innate immune cells. We aimed to determine the role of the periodontal pathogen, Porphyromonas gingivalis, in the enhanced expression of IL-33 in human gingival epithelial cells. We detected IL-33 in inflamed gingival epithelium from patients with chronic periodontitis, and found that P. gingivalis increased IL-33 expression in the cytoplasm of human gingival epithelial cells in vitro. In contrast, lipopolysaccharide, lipopeptide, and fimbriae derived from P. gingivalis did not increase IL-33 expression. Specific inhibitors of P. gingivalis proteases (gingipains) suppressed IL-33 mRNA induction by P. gingivalis and the P. gingivalis gingipain-null mutant KDP136 did not induce IL-33 expression. A small interfering RNA for protease-activated receptor-2 (PAR-2) as well as inhibitors of phospholipase C, p38 and NF-κB inhibited the expression of IL-33 induced by P. gingivalis. These results indicate that the PAR-2/IL-33 axis is promoted by P. gingivalis infection in human gingival epithelial cells through a gingipain-dependent mechanism.

A Distinct Type of Pilus from the Human Microbiome

Pili are proteinaceous polymers of linked pilins that protrude from the cell surface of many bacteria and often mediate adherence and virulence. We investigated a set of 20 Bacteroidia pilins from the human microbiome whose structures and mechanism of assembly were unknown. Crystal structures and biochemical data revealed a diverse protein superfamily with a common Greek-key β sandwich fold with two transthyretin-like repeats that polymerize into a pilus through a strand-exchange mechanism. The assembly mechanism of the central, structural pilins involves proteinase-assisted removal of their N-terminal β strand, creating an extended hydrophobic groove that binds the C-terminal donor strands of the incoming pilin. Accessory pilins at the tip and base have unique structural features specific to their location, allowing initiation or termination of the assembly. The Bacteroidia pilus, therefore, has a biogenesis mechanism that is distinct from other known pili and likely represents a different type of bacterial pilus.

Varying hemin concentrations affect Porphyromonas gingivalis strains differently

Porphyromonas gingivalis requires heme to grow, however, heme availability and concentration in the periodontal pockets vary. Fluctuations in heme concentration may affect each P. gingivalis strain differently, however, this was never fully demonstrated. Here, we elucidated the effects of varying hemin concentrations in representative P. gingivalis strains. Throughout this study, representative P. gingivalis strains [FDC381 (type I), MPWIb-01 (type Ib), TDC60 (type II), ATCC49417 (type III), W83 (type IV), and HNA99 (type V)] were used and grown for 24 h in growth media under varying hemin concentrations (5 × , 1 × , 0.5 × , 0.1 × ). Samples were lysed and protein standardized. Arg-gingipain (Rgp), H2O2, and superoxide dismutase (SOD) levels were subsequently measured. We focused our study on 24 h-grown strains which excluded MPWIb-01 and HNA99. Rgp activity among the 4 remaining strains varied with Rgp peaking at: 1 × for FDC381, 5 × for TDC60, 0.5 × for ATCC49417, 5 × and 0.5 × for W83. With regards to H2O2 and SOD amounts: FDC381 had similar H2O2 amounts in all hemin concentrations while SOD levels varied; TDC60 had the lowest H2O2 amount at 1 × while SOD levels became higher in relation to hemin concentration; ATCC49417 also had similar H2O2 amounts in all hemin concentrations while SOD levels were higher at 1 × and 0.5 × ; and W83 had statistically similar H2O2 and SOD amounts regardless of hemin concentration. Our results show that variations in hemin concentration affect each P. gingivalis strain differently.

Mfa4, an Accessory Protein of Mfa1 Fimbriae, Modulates Fimbrial Biogenesis, Cell Auto-Aggregation, and Biofilm Formation in Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative obligate anaerobic bacterium, is considered to be a key pathogen in periodontal disease. The bacterium expresses Mfa1 fimbriae, which are composed of polymers of Mfa1. The minor accessory components Mfa3, Mfa4, and Mfa5 are incorporated into these fimbriae. In this study, we characterized Mfa4 using genetically modified strains. Deficiency in the mfa4 gene decreased, but did not eliminate, expression of Mfa1 fimbriae. However, Mfa3 and Mfa5 were not incorporated because of defects in posttranslational processing and leakage into the culture supernatant, respectively. Furthermore, the mfa4-deficient mutant had an increased tendency to auto-aggregate and form biofilms, reminiscent of a mutant completely lacking Mfa1. Notably, complementation of mfa4 restored expression of structurally intact and functional Mfa1 fimbriae. Taken together, these results indicate that the accessory proteins Mfa3, Mfa4, and Mfa5 are necessary for assembly of Mfa1 fimbriae and regulation of auto-aggregation and biofilm formation of P. gingivalis. In addition, we found that Mfa3 and Mfa4 are processed to maturity by the same RgpA/B protease that processes Mfa1 subunits prior to polymerization.

Extract from Rumex acetosa L. for prophylaxis of periodontitis: inhibition of bacterial in vitro adhesion and of gingipains of Porphyromonas gingivalis by epicatechin-3-O-(4β→8)-epicatechin-3-O-gallate (procyanidin-B2-Di-gallate)

BACKGROUND

The aerial parts of Rumex acetosa L. have been used in traditional European medicine for inflammatory diseases of the mouth epithelial tissue. The following study aimed to investigate the influence of a proanthocyanidin-enriched extract from R. acetosa extract against the adhesion of Porphyromonas gingivalis (P. gingivalis), a pathogen strongly involved in chronic and aggressive periodontitis. A further goal was to define the bioactive lead structures responsible for a potential antiadhesive activity and to characterize the underlying molecular mechanisms of the antiadhesive effects.

METHODOLOGY

An extract of R. acetosa (RA1) with a defined mixture of flavan-3-ols, oligomeric proanthocyanidins and flavonoids, was used. Its impact on P. gingivalis adhesion to KB cells was studied by flow cytometry, confocal laser scanning microscopy and in situ adhesion assay using murine buccal tissue. RA1 and its compounds 1 to 15 were further investigated for additional effects on gingipain activity, hemagglutination and gene expression by RT-PCR.

PRINCIPAL FINDINGS

RA1 (5 to 15 μg/mL) reduced P. gingivalis adhesion in a dose-dependent manner to about 90%. Galloylated proanthocyanidins were confirmed to be responsible for this antiadhesive effect with epicatechin-3-O-gallate-(4β,8)-epicatechin-3'-O-gallate (syn. procyanidin B2-di-gallate) being the lead compound. Ungalloylated flavan-3-ols and oligomeric proanthocyanidins were inactive. RA1 and the galloylated proanthocyanidins strongly interact with the bacterial virulence factor Arg-gingipain, while the corresponding Lys-gingipain was hardly influenced. RA1 inhibited also hemagglutination. In silico docking studies indicated that epicatechin-3-O-gallate-(4β,8)-epicatechin-3'-O-gallate interacts with the active side of Arg-gingipain and hemaglutinin from P. gingivalis; the galloylation of the molecule seems to be responsible for fixation of the ligand to the protein. In conclusion, the proanthocyanidin-enriched extract RA1 and its main active constituent procyanidin B2-di-gallate protect cells from P. gingivalis infection by inhibiting bacterial adhesion to the host cell. RA1 and procyanidin B2-di-gallate appear to be promising candidates for future cytoprotective preparations for oral mouth care products.

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.

Identification of a diguanylate cyclase and its role in Porphyromonas gingivalis virulence

Porphyromonas gingivalis is a Gram-negative obligate anaerobic bacterium and is considered a keystone pathogen in the initiation of periodontitis, one of the most widespread infectious diseases. Bacterial bis-(3'-5') cyclic GMP (cyclic di-GMP [c-di-GMP]) serves as a second messenger and is involved in modulating virulence factors in numerous bacteria. However, the role of this second messenger has not been investigated in P. gingivalis, mainly due to a lack of an annotation regarding diguanylate cyclases (DGCs) in this bacterium. Using bioinformatics tools, we found a protein, PGN_1932, containing a GGDEF domain. A deletion mutation in the pgn_1932 gene had a significant effect on the intracellular c-di-GMP level in P. gingivalis. Genetic analysis showed that expression of the fimA and rgpA genes, encoding the major protein subunit of fimbriae and an arginine-specific proteinase, respectively, was downregulated in the pgn_1932 mutant. Correspondingly, FimA protein production and the fimbrial display on the mutant were significantly reduced. Mutations in the pgn_1932 gene also had a significant impact on the adhesive and invasive capabilities of P. gingivalis, which are required for its pathogenicity. These findings provide evidence that the PGN_1932 protein is both responsible for synthesizing c-di-GMP and involved in biofilm formation and host cell invasion by P. gingivalis by controlling the expression and biosynthesis of FimA.

Gingipains Inactivate a Cell Surface Ligand onPorphyromonas gingivalisThat Induces TLR2- and TLR4-Independent Signaling

Arginine-specific gingipain and lysine-specific gingipain are two major cysteine proteinases produced by Porphyromonas gingivalis. To clarify the role of gingipains in the interaction between P. gingivalis and the innate immune system, CHO reporter cells expressing TLR2 or TLR4 were stimulated with wildtype or gingipain-deficient P. gingivalis cells and activation of nuclear factor-kappaB in these cells was examined. While CHO/CD14 cells and 7.19 cells, an MD-2-defective mutant derived from CHO/CD14 cells, failed to respond to wild-type P. gingivalis, they responded to gingipain-deficient P. gingivalis. On the other hand, CHO/CD14/TLR2 cells responded to both wild-type and gingipain-deficient P. gingivalis. These results suggested that gingipains have no effects on TLR2-dependent signaling from P. gingivalis but have inhibitory effects on TLR2-and TLR4-independent signaling in CHO cells. Indeed, the activity of gingipain-deficient P. gingivalis to induce the activation of 7.19 cells was diminished after treatment of the bacterial cells with gingipains. We next partially purified bacterial cell components activating 7.19 cells from gingipain-deficient P. gingivalis. The activity of the partially purified components was diminished by treatment with heat or gingipains. It is also noteworthy that anti-CD14 mAb inhibited the activation of 7.19 cells induced by the partially purified components. These results indicated that the components of P. gingivalis that were able to induce TLR2-and TLR4-independent signaling were inactivated by gingipains before being recognized by CD14. The inactivation of the components would be helpful for P. gingivalis to escape from the innate immune system.

Localization and function of the accessory protein Mfa3 in Porphyromonas gingivalis Mfa1 fimbriae

The fimbriae of Porphyromonas gingivalis, the causative agent of periodontitis, have been implicated in various aspects of pathogenicity, such as colonization, adhesion and aggregation. Porphyromonas gingivalis ATCC 33277 has two adhesins comprised of the FimA and Mfa1 fimbriae. We characterized the PGN0289 (Mfa3) protein, which is one of the three accessory proteins of Mfa1 fimbriae in P. gingivalis. The Mfa3 protein was present in two different sizes, 40 and 43 kDa, in the cell. The 43-kDa and 40-kDa Mfa3 were detected largely in the inner membrane and the outer membrane, respectively. Purified Mfa1 fimbriae contained the 40-kDa Mfa3 alone. Furthermore, the 40-kDa Mfa3 started with the Ala(44) residue of the deduced amino acid sequence, indicating that the N-terminal region of the nascent protein expressed from the mfa3 gene is processed in the transport step from the inner membrane into fimbriae. Immuno-electron microscopy revealed that Mfa3 localized at the tip of the fimbrial shaft. Interestingly, deletion of the mfa3 gene resulted in the absence of other accessory proteins, PGN0290 and PGN0291, in the purified Mfa1 fimbriae, suggesting that Mfa3 is required for integration of PGN0290 and PGN0291 into fimbriae. A double mutant of mfa3 and fimA genes (phenotype Mfa1 plus, FimA minus) showed increased auto-aggregation and biofilm formation similar to a double mutant of mfa1 and fimA genes (phenotype Mfa1(-) , FimA(-) ). These findings suggest that the tip protein Mfa3 of the Mfa1 fimbriae may function in the integration of accessory proteins and in the colonization of P. gingivalis.

Erythritol alters microstructure and metabolomic profiles of biofilm composed of Streptococcus gordonii and Porphyromonas gingivalis

The effects of sugar alcohols such as erythritol, xylitol, and sorbitol on periodontopathic biofilm are poorly understood, though they have often been reported to be non-cariogenic sweeteners. In the present study, we evaluated the efficacy of sugar alcohols for inhibiting periodontopathic biofilm formation using a heterotypic biofilm model composed of an oral inhabitant Streptococcus gordonii and a periodontal pathogen Porphyromonas gingivalis. Confocal microscopic observations showed that the most effective reagent to reduce P. gingivalis accumulation onto an S. gordonii substratum was erythritol, as compared with xylitol and sorbitol. In addition, erythritol moderately suppressed S. gordonii monotypic biofilm formation. To examine the inhibitory effects of erythritol, we analyzed the metabolomic profiles of erythritol-treated P. gingivalis and S. gordonii cells. Metabolome analyses using capillary electrophoresis time-of-flight mass spectrometry revealed that a number of nucleic intermediates and constituents of the extracellular matrix, such as nucleotide sugars, were decreased by erythritol in a dose-dependent manner. Next, comparative analyses of metabolites of erythritol- and sorbitol-treated cells were performed using both organisms to determine the erythritol-specific effects. In P. gingivalis, all detected dipeptides, including Glu-Glu, Ser-Glu, Tyr-Glu, Ala-Ala and Thr-Asp, were significantly decreased by erythritol, whereas they tended to be increased by sorbitol. Meanwhile, sorbitol promoted trehalose 6-phosphate accumulation in S. gordonii cells. These results suggest that erythritol has inhibitory effects on dual species biofilm development via several pathways, including suppression of growth resulting from DNA and RNA depletion, attenuated extracellular matrix production, and alterations of dipeptide acquisition and amino acid metabolism.

Propeptide-mediated inhibition of cognate gingipain proteinases

Porphyromonas gingivalis is a major pathogen associated with chronic periodontitis. The organism’s cell-surface cysteine proteinases, the Arg-specific proteinases (RgpA, RgpB) and the Lys-specific proteinase (Kgp), which are known as gingipains have been implicated as major virulence factors. All three gingipain precursors contain a propeptide of around 200 amino acids in length that is removed during maturation. The aim of this study was to characterize the inhibitory potential of the Kgp and RgpB propeptides against the mature cognate enzymes. Mature Kgp was obtained from P. gingivalis mutant ECR368, which produces a recombinant Kgp with an ABM1 motif deleted from the catalytic domain (rKgp) that enables the otherwise membrane bound enzyme to dissociate from adhesins and be released. Mature RgpB was obtained from P. gingivalis HG66. Recombinant propeptides of Kgp and RgpB were produced in Escherichia coli and purified using nickel-affinity chromatography. The Kgp and RgpB propeptides displayed non-competitive inhibition kinetics with K_i values of 2.04 µM and 12 nM, respectively. Both propeptides exhibited selectivity towards their cognate proteinase. The specificity of both propeptides was demonstrated by their inability to inhibit caspase-3, a closely related cysteine protease, and papain that also has a relatively long propeptide. Both propeptides at 100 mg/L caused a 50% reduction of P. gingivalis growth in a protein-based medium. In summary, this study demonstrates that gingipain propeptides are capable of inhibiting their mature cognate proteinases.

Inhibition of gingipains by their profragments as the mechanism protecting Porphyromonas gingivalis against premature activation of secreted proteases

BACKGROUND

Arginine-specific (RgpB and RgpA) and lysine-specific (Kgp) gingipains are secretory cysteine proteinases of Porphyromonas gingivalis that act as important virulence factors for the organism. They are translated as zymogens with both N- and C-terminal extensions, which are proteolytically cleaved during secretion. In this report, we describe and characterize inhibition of the gingipains by their N-terminal prodomains to maintain latency during their export through the cellular compartments.

METHODS

Recombinant forms of various prodomains (PD) were analyzed for their interaction with mature gingipains. The kinetics of their inhibition of proteolytic activity along with the formation of stable inhibitory complexes with native gingipains was studied by gel filtration, native PAGE and substrate hydrolysis.

RESULTS

PDRgpB and PDRgpA formed tight complexes with arginine-specific gingipains (Ki in the range from 6.2nM to 0.85nM). In contrast, PDKgp showed no inhibitory activity. A conserved Arg-102 residue in PDRgpB and PDRgpA was recognized as the P1 residue. Mutation of Arg-102 to Lys reduced inhibitory potency of PDRgpB by one order of magnitude while its substitutions with Ala, Gln or Gly totally abolished the PD inhibitory activity. Covalent modification of the catalytic cysteine with tosyl-l-Lys-chloromethylketone (TLCK) or H-D-Phe-Arg-chloromethylketone did not affect formation of the stable complex.

CONCLUSION

Latency of arginine-specific progingipains is efficiently exerted by N-terminal prodomains thus protecting the periplasm from potentially damaging effect of prematurely activated gingipains.

GENERAL SIGNIFICANCE

Blocking progingipain activation may offer an attractive strategy to attenuate P. gingivalis pathogenicity.

Identification of signaling pathways mediating cell cycle arrest and apoptosis induced by Porphyromonas gingivalis in human trophoblasts

Epidemiological and interventional studies of humans have revealed a close association between periodontal diseases and preterm delivery of low-birth-weight infants. Porphyromonas gingivalis, a periodontal pathogen, can translocate to gestational tissues following oral-hematogenous spread. We previously reported that P. gingivalis invades extravillous trophoblast cells (HTR-8) derived from the human placenta and inhibits proliferation through induction of arrest in the G(1) phase of the cell cycle. The purpose of the present study was to identify signaling pathways mediating cellular impairment caused by P. gingivalis. Following P. gingivalis infection, the expression of Fas was induced and p53 accumulated, responses consistent with response to DNA damage. Ataxia telangiectasia- and Rad3-related kinase (ATR), an essential regulator of DNA damage checkpoints, was shown to be activated together with its downstream signaling molecule Chk2, while the p53 degradation-related protein MDM2 was not induced. The inhibition of ATR prevented both G(1) arrest and apoptosis caused by P. gingivalis in HTR-8 cells. In addition, small interfering RNA (siRNA) knockdown of p53 abrogated both G(1) arrest and apoptosis. The regulation of apoptosis was associated with Ets1 activation. HTR-8 cells infected with P. gingivalis exhibited activation of Ets1, and knockdown of Ets1 with siRNA diminished both G(1) arrest and apoptosis. These results suggest that P. gingivalis activates cellular DNA damage signaling pathways that lead to G(1) arrest and apoptosis in trophoblasts.

Time course of gene expression during Porphyromonas gingivalis strain ATCC 33277 biofilm formation

Chronological gene expression patterns of biofilm-forming cells are important to understand bioactivity and pathogenicity of biofilms. For Porphyromonas gingivalis ATCC 33277 biofilm formation, the number of genes differentially regulated by more than 1.5-fold was highest during the growth stage (312/2,090 genes), and some pathogen-associated genes were time-dependently controlled.

Recombinant Porphyromonas gingivalis FimA preproprotein expressed in Escherichia coli is lipidated and the mature or processed recombinant FimA protein forms a short filament in vitro

The gram-negative anaerobic bacterium Porphyromonas gingivalis is an etiologically important pathogen for chronic periodontal diseases in adults. Our previous study suggested that the major structural components of both Fim and Mfa fimbriae in this organism are secreted through their lipidated precursors. In this study, we constructed Escherichia coli strains expressing various fimA genes with or without the 5'-terminal DNA region encoding the signal peptide, and we determined whether lipidation of recombinant FimA proteins occurred in E. coli. Lipidation occurred for a recombinant protein from the fimA gene with the 5'-terminal DNA region encoding the signal peptide but not for a recombinant protein from the fimA gene without the signal-peptide-encoding region, as revealed by [3H]palmitic acid labeling experiments. A TLR2-dependent signaling response was induced by the recombinant protein from the fimA gene with the signal-peptide-encoding region but not by a recombinant protein from the fimA gene with the signal-peptide-encoding region that had a base substitution causing an amino acid substitution (C19A). Electron microscopic analysis revealed that recombinant FimA (A-47 - W-383) protein was autopolymerized to form filamentous structures of about 80 nm in length in vitro. The results suggest that FimA protein, a major subunit of Fim fimbriae, is transported to the outer membrane by the lipoprotein sorting system, and a mature or processed FimA protein on the outer membrane is autopolymerized to form Fim fimbriae.

Collagenolytic activity in sonic extracts of Tannerella forsythia

OBJECTIVE

The purpose of the present study was to characterize the collagenolytic activity in a sonicated extract of Tannerella forsythia and to investigate the activation of proMMMP-2 and -9 by the T. forsythia extract.

METHODS

The T. forsythia extract was incubated with type I collagen. The cleaved products were then analyzed by SDS-PAGE using the method of Laemmli. We studied the effects of cysteine, DTT, CaCl(2), and various proteinase inhibitors on collagenolytic activity. A HT1080 cell culture supernatant containing proMMP-2 and -9 was incubated with the T. forsythia extract and analyzed for the activation of proMMP-2 and -9 by gelatin zymography.

RESULTS

The T. forsythia extract degraded type I collagen. Cysteine increased the collagenolytic activity of the extract, and 5mM CaCl(2) was required for this activity. The collagenolytic activity of T. forsythia was inhibited by N-ethylmaleimide, iodoacetamide, iodoacetic acid, EDTA, and leupeptin, but not by PMSF, E-64, TLCK, or TPCK. When proMMP-2 and -9 were incubated with the T. forsythia extract, gelatinases with the relative molecular masses of MMP-2 and -9 were produced.

CONCLUSION

The present study suggests that T. forsythia extract is able to degrade type I collagen and activate proMMP-2 and -9.

Putative respiratory chain of Porphyromonas gingivalis

The electron transfer chain in Porphyromonas gingivalis, or periodontopathogens, has not yet been characterized. P. gingivalis, a strict anaerobic bacteria and the second colonizer of the oral cavity, is considered to be a major causal agent involved in periodontal diseases. Primary colonizers create a favorable environment for P. gingivalis growth by decreasing oxygen pressure. Oxygen does not appear to be the final electron acceptor of the respiratory chain. Fumarate and cytochrome b have been implicated as major components of the respiratory activity. However, the P. gingivalis genome shows many other enzymes that could be implicated in aerobic or nitrite respiration. Using bioinformatic tools and literature studies of respiratory pathways, the ATP synthesis mechanism from the sodium cycle and nutrients metabolism, the putative respirasome of P. gingivalis has been proposed.

Identification of bistable populations of Porphyromonas gingivalis that differ in epithelial cell invasion

Bistable populations of bacteria give rise to two or more subtypes that exhibit different phenotypes. We have explored whether the periodontal pathogen Porphyromonas gingivalis exhibits bistable invasive phenotypes. Using a modified cell invasion assay, we show for the first time that there are two distinct subtypes within a population of P. gingivalis strains NCTC 11834 and W50 that display differences in their ability to invade oral epithelial cells. The highly invasive subtype invades cells at 10-30-fold higher levels than the poorly invasive subtype and remains highly invasive for approximately 12-16 generations. Analysis of the gingipain activity of these subtypes revealed that the highly invasive type had reduced cell-associated arginine-specific protease activity. The role of Arg-gingipain activity in invasion was verified by enhancement of invasion by rgpAB mutations and by inclusion of an Arg-gingipain inhibitor in invasion assays using wild-type bacteria. In addition, a population of ΔrgpAB bacteria did not contain a hyperinvasive subtype. Screening of the protease activity of wild-type populations of both strains identified high and low protease subtypes which also showed a corresponding reduction or enhancement, respectively, of invasive capabilities. Microarray analysis of these bistable populations revealed a putative signature set of genes that includes oxidative stress resistance and iron transport genes, and which might be critical to invasion of or survival within epithelial cells.

The native 67-kilodalton minor fimbria of Porphyromonas gingivalis is a novel glycoprotein with DC-SIGN-targeting motifs

We recently reported that the oral mucosal pathogen Porphyromonas gingivalis, through its 67-kDa Mfa1 (minor) fimbria, targets the C-type lectin receptor DC-SIGN for invasion and persistence within human monocyte-derived dendritic cells (DCs). The DCs respond by inducing an immunosuppressive and Th2-biased CD4(+) T-cell response. We have now purified the native minor fimbria by ion-exchange chromatography and sequenced the fimbria by tandem mass spectrometry (MS/MS), confirming its identity and revealing two putative N-glycosylation motifs as well as numerous putative O-glycosylation sites. We further show that the minor fimbria is glycosylated by ProQ staining and that glycosylation is partially removed by treatment with beta(1-4)-galactosidase, but not by classic N- and O-linked deglycosidases. Further monosaccharide analysis by gas chromatography-mass spectrometry (GC-MS) confirmed that the minor fimbria contains the DC-SIGN-targeting carbohydrates fucose (1.35 nmol/mg), mannose (2.68 nmol/mg), N-acetylglucosamine (2.27 nmol/mg), and N-acetylgalactosamine (0.652 nmol/mg). Analysis by transmission electron microscopy revealed that the minor fimbria forms fibers approximately 200 nm in length that could be involved in targeting or cross-linking DC-SIGN. These findings shed further light on molecular mechanisms of invasion and immunosuppression by this unique mucosal pathogen.