Separation of the outer membrane and identification of major outer membrane proteins from Porphyromonas gingivalis

Structural and antigenic characterization of a novel genotype of Mfa1 fimbriae in Porphyromonas gingivalis

Background

Mfa1 fimbriae of the periodontal pathogen Porphyromonas gingivalis are responsible for biofilm formation and comprise five proteins: Mfa1-5. Two major genotypes, mfa170 and mfa153, encode major fimbrillin. The mfa170 genotype is further divided into the mfa170A and mfa170B subtypes. The properties of the novel mfa170B remain unclear.

Methods

Fimbriae were purified from P. gingivalis strains JI-1 (mfa170A), 1439 (mfa170B), and Ando (mfa153), and their components and their structures were analyzed. Protein expression and variability in the antigenic specificity of fimbrillins were compared using Coomassie staining and western blotting using polyclonal antibodies against Mfa170A, Mfa170B, and Mfa153 proteins. Cell surface expression levels of fimbriae were analyzed by filtration enzyme-linked immunosorbent assays.

Results

The composition and structures of the purified Mfa1 fimbriae of 1439 was similar to that of JI-1. However, each Mfa1 protein of differential subtype/genotype was specifically detected by western blotting. Mfa170B fimbriae were expressed in several strains such as 1439, JKG9, B42, 1436, and Kyudai-3. Differential protein expression and antigenic heterogeneities were detected in Mfa2-5 between strains.

Conclusion

Mfa1 fimbriae from the mfa170A and mfa170B genotypes indicated an antigenic difference suggesting the mfa170B, is to be utilized for the novel classification of P. gingivalis.

Outer membrane vesicles as biomimetic vaccine carriers against infections and cancers

In the last decade, nanoparticle-based therapeutic modalities have emerged as promising treatment options for cancer and infectious diseases. To improve prognosis, chemotherapeutic and antimicrobial drugs must be delivered selectively to the target sites. Researchers have increasingly focused their efforts on improving drug delivery, with a particular emphasis on cancer and infectious diseases. When drugs are administered systemically, they become diluted and can diffuse to all tissues but only until the immune system intervenes and quickly removes them from circulation. To enhance and prolong the systemic circulation of drugs, nanocarriers have been explored and used; however, nanocarriers have a major drawback in that they can trigger immune responses. Numerous nanocarriers for optimal drug delivery have been developed using innovative and effective biointerface technologies. Autologous cell-derived drug carriers, such as outer membrane vesicles (OMVs), have demonstrated improved bioavailability and reduced toxicity. Thus, this study investigates the use of biomimetic OMVs as biomimetic vaccine carriers against infections and cancers to improve our understanding in the field of nanotechnology. In addition, discussion on the advantages, disadvantages, and future prospects of OMVs will also be explored. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Dual Inhibitory Activity of Petroselinic Acid Enriched in Fennel Against Porphyromonas gingivalis

Increasing evidence has shown that a major periodontal pathobiont, Porphyromonas gingivalis, triggers oral dysbiosis leading to deterioration not only of periodontal health, but also of several systemic conditions. In the present study we identified remarkable anti-P. gingivalis activity of Foeniculum vulgare (fennel), an herbal plant used in Asian cuisine as well as in traditional medicine, by screening of 92 extracts prepared from 23 edible plants. The n-hexane-extracted fennel (HEF) showed a rapid lethal action toward P. gingivalis, while it was rather ineffective with a wide range of other oral commensal bacterial species. Morphological analysis using both high-speed atomic force microscopy and field emission scanning electron microscopy revealed that a low concentration of HEF (8 μg/mL) resulted in formation of protruding nanostructures composed of outer membrane vesicle (OMV)-like particles, while a high concentration of HEF (64 μg/mL) induced bacteriolysis with overproduction of OMVs with unusual surface properties. Interestingly, HEF treatment resulted in deprivation of two outer membrane transporter proteins, RagA and RagB, which is essential for nutrient acquisition in P. gingivalis, by extracellularly releasing RagA/RagB-enriched OMVs. Furthermore, HEF showed gingipain-inhibitory activity toward both arginine-specific (Rgps) and lysine-specific (Kgp) gingipains, resulting in blocking oral epithelial cell rounding and the subsequent detachment from culture dishes. Finally, we isolated petroselinic acid as a major bactericide as well as a gingipain inhibitor through a bioassay-guided fractionation of HEF. Taken together, our findings suggest clinical applicability of HEF and petroselinic acid for periodontitis therapy to eliminate P. gingivalis and its major virulence factors on the basis of the dual anti-P. gingivalis activity, i.e., rapid bacteriolysis and gingipain inhibition.

Extraction and Electrophoretic Analysis of Bacterial Lipopolysaccharides and Outer Membrane Proteins

Lipopolysaccharides (LPS) (or lipooligosaccharides [LOS], which lack the O-antigen side chains characteristic of LPS), and outer membrane proteins (OMP) are major cell-surface molecules in the outer membrane (OM) of gram-negative bacteria. The LPS is responsible for causing endotoxic shock in infected hosts and, in conjunction with some OMPs, provides protection to the bacterium against host innate immune defenses and attachment to host cells. Electrophoretic analysis can provide valuable information regarding the size, number, and variability of LPS/LOS and OMP components between bacterial strains and mutants, which aids in understanding the basic biology and virulence factors of a particular species. Furthermore, highly purified extracts are normally not required if only electrophoretic analysis is to be done, and various methods have been established for such procedures. Here, we review ameliorated procedures for fast and convenient extraction of LPS/LOS and protein-enriched outer membranes (PEOM) for optimal electrophoretic resolution. Specifically, we will describe the phenol-based micro-method for LPS/LOS extraction, a differential extraction procedure with sodium lauryl sarcosinate for PEOM, and gel preparation for electrophoretic analysis of LPS/LOS samples in detail. Graphic abstract: Workflow for the preparation and analysis of LPS/LOS and PEOM.

The RagA and RagB proteins of Porphyromonas gingivalis

RagA and RagB proteins are major components of the outer membrane of the oral pathogen Porphyromonas gingivalis and, while recently suggested to represent a novel peptide uptake system, their full function is still under investigation. Herein, we (a) discuss the evidence that the rag locus contributes to P. gingivalis virulence; (b) provide insight to Rag protein potential biological function in macromolecular transport and other aspects of bacterial physiology; (c) address the host response to Rag proteins which are immunodominant and immunomodulatory; and (d) review the potential of Rag-focused therapeutic strategies for the control of periodontal diseases.

Separation of Glycosylated OmpA-Like Proteins from Porphyromonas gingivalis and Tannerella forsythia

OmpA-like proteins located in the outer bacterial membrane are potential virulence factors from the major periodontal pathogens Porphyromonas gingivalis and Tannerella forsythia. Our previous studies have shown that OmpA-like proteins are glycosylated by O-linked N-acetylglucosamine (O-GlcNAc) and are strongly reactive to wheat germ agglutinin (WGA) lectin, which shows sugar specificity to GlcNAc. Utilizing this property, we have developed a separation method for OmpA-like proteins by affinity chromatography using WGA lectin-agarose. The purity of enriched native OmpA-like proteins were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie Brilliant Blue (CBB) staining. More importantly, the purified OmpA-like proteins formed a unique trimeric structure keeping their bioactivity intact. In this chapter, we describe a detailed procedure to separate OmpA-like proteins, which may be used to further progress the biological studies of OmpA-like proteins.

Involvement of PorK, a component of the type IX secretion system, in Prevotella melaninogenica pathogenicity

Prevotella melaninogenica is a gram-negative anaerobic commensal bacterium that resides in the human oral cavity and is isolated as a pathogen of suppurative diseases both inside and outside the mouth. However, little is known about the pathogenic factors of P. melaninogenica. The periodontal pathogens Porphyromonas gingivalis and Tanerella forsythia secrete virulence factors such as protease and bacterial cell surface proteins via a type IX secretion system (T9SS) that are involved in pathogenicity. P. melaninogenica also possesses all known orthologs of T9SS. In this study, a P. melaninogenica GAI 07411 mutant deficient in the orthologue of the T9SS-encoding gene, porK, was constructed. Hemagglutination and biofilm formation were decreased in the porK mutant. Furthermore, following growth on skim milk-containing medium, the diameters of the halos surrounding the porK mutant were smaller than those of the wild-type strain, suggesting a decrease in secretion of proteases outside the bacterium. To investigate this in detail, culture supernatants of wild-type and porK mutant strains were purified and compared by two-dimensional electrophoresis. In the mutant strain, fewer spots were detected, indicating fewer secreted proteins. In infection experiments, the mortality rate of mice inoculated with the porK mutant strain was significantly lower than in the wild-type strain. These results suggest that P. melaninogenica secretes potent virulence factors via the T9SS that contribute to its pathogenic ability.

OmpA-like proteins of Porphyromonas gingivalis contribute to serum resistance and prevent Toll-like receptor 4-mediated host cell activation

Porphyromonas gingivalis possesses various abilities to evade and disrupt host immune responses, by which it acts as an important periodontal pathogen. P. gingivalis produces outer membrane protein A (OmpA)-like proteins (OmpALPs), Pgm6 and Pgm7, as major O-linked glycoproteins, but their pathological roles in P. gingivalis infection are largely unknown. Here, we report that OmpALP-deficient strains of P. gingivalis show an enhanced stimulatory activity in coculture with host cells. Such an altered ability of the OmpALP-deficient strains was found to be due to their impaired survival in coculture and the release of LPS from dead bacterial cells to stimulate Toll-like receptor 4 (TLR4). Further analyses revealed that the OmpALP-deficient strains were inviable in serum-containing media although they grew normally in the bacterial medium. The wild-type strain was able to grow in 90% normal human serum, while the OmpALP-deficient strains did not survive even at 5%. The OmpALP-deficient strains did not survive in heat-inactivated serum, but they gained the ability to survive and grow in proteinase K-treated serum. Of note, the sensitivity of the OmpALP-deficient strains to the bactericidal activity of human β-defensin 3 was increased as compared with the WT. Thus, this study suggests that OmpALPs Pgm6 and Pgm7 are important for serum resistance of P. gingivalis. These proteins prevent bacterial cell destruction by serum and innate immune recognition by TLR4; this way, P. gingivalis may adeptly colonize serum-containing gingival crevicular fluids and subgingival environments.

Porphyromonas gingivalis gingipains cause defective macrophage migration towards apoptotic cells and inhibit phagocytosis of primary apoptotic neutrophils

Periodontal disease is a prevalent chronic inflammatory condition characterised by an aberrant host response to a pathogenic plaque biofilm resulting in local tissue damage and frustrated healing that can result in tooth loss. Cysteine proteases (gingipains) from the key periodontal pathogen Porphyromonas gingivalis have been implicated in periodontal disease pathogenesis by inhibiting inflammation resolution and are linked with systemic chronic inflammatory conditions such as rheumatoid arthritis. Efficient clearance of apoptotic cells is essential for the resolution of inflammation and tissue restoration. Here we sought to characterise the innate immune clearance of apoptotic cells and its modulation by gingipains. We examined the capacity of gingipain-treated macrophages to migrate towards and phagocytose apoptotic cells. Lysine gingipain treatment of macrophages impaired macrophage migration towards apoptotic neutrophils. Furthermore, lysine gingipain treatment reduced surface expression levels of CD14, a key macrophage receptor for apoptotic cells, which resulted in reduced macrophage interactions with apoptotic cells. Additionally, while apoptotic cells and their derived secretome were shown to inhibit TNF-α-induced expression by P. gingivalis lipopolysaccharide, we demonstrated that gingipain preparations induced a rapid inflammatory response in macrophages that was resistant to the anti-inflammatory effects of apoptotic cells or their secretome. Taken together, these data indicate that P. gingivalis may promote the chronic inflammation seen in periodontal disease patients by multiple mechanisms, including rapid, potent gingipain-mediated inflammation, coupled with receptor cleavage leading to defective clearance of apoptotic cells and reduced anti-inflammatory responses. Thus, gingipains represent a potential therapeutic target for intervention in the management of chronic periodontal disease.

PG1058 Is a Novel Multidomain Protein Component of the Bacterial Type IX Secretion System

Porphyromonas gingivalis utilises the Bacteroidetes-specific type IX secretion system (T9SS) to export proteins across the outer membrane (OM), including virulence factors such as the gingipains. The secreted proteins have a conserved carboxy-terminal domain essential for type IX secretion that is cleaved upon export. In P. gingivalis the T9SS substrates undergo glycosylation with anionic lipopolysaccharide (A-LPS) and are attached to the OM. In this study, comparative analyses of 24 Bacteroidetes genomes identified ten putative novel components of the T9SS in P. gingivalis, one of which was PG1058. Computer modelling of the PG1058 structure predicted a novel N- to C-terminal architecture comprising a tetratricopeptide repeat (TPR) domain, a β-propeller domain, a carboxypeptidase regulatory domain-like fold (CRD) and an OmpA_C-like putative peptidoglycan binding domain. Inactivation of pg1058 in P. gingivalis resulted in loss of both colonial pigmentation and surface-associated proteolytic activity; a phenotype common to T9SS mutants. Immunoblot and LC-MS/MS analyses of subcellular fractions revealed T9SS substrates accumulated within the pg1058 mutant periplasm whilst whole-cell ELISA showed the Kgp gingipain was absent from the cell surface, confirming perturbed T9SS function. Immunoblot, TEM and whole-cell ELISA analyses indicated A-LPS was produced and present on the pg1058 mutant cell surface although it was not linked to T9SS substrate proteins. This indicated that PG1058 is crucial for export of T9SS substrates but not for the translocation of A-LPS. PG1058 is a predicted lipoprotein and was localised to the periplasmic side of the OM using whole-cell ELISA, immunoblot and LC-MS/MS analyses of subcellular fractions. The structural prediction and localisation of PG1058 suggests that it may have a role as an essential scaffold linking the periplasmic and OM components of the T9SS.

Emerging facets of prokaryotic glycosylation

Glycosylation of proteins is one of the most prevalent post-translational modifications occurring in nature, with a wide repertoire of biological implications. Pathways for the main types of this modification, the N- and O-glycosylation, can be found in all three domains of life-the Eukarya, Bacteria and Archaea-thereby following common principles, which are valid also for lipopolysaccharides, lipooligosaccharides and glycopolymers. Thus, studies on any glycoconjugate can unravel novel facets of the still incompletely understood fundamentals of protein N- and O-glycosylation. While it is estimated that more than two-thirds of all eukaryotic proteins would be glycosylated, no such estimate is available for prokaryotic glycoproteins, whose understanding is lagging behind, mainly due to the enormous variability of their glycan structures and variations in the underlying glycosylation processes. Combining glycan structural information with bioinformatic, genetic, biochemical and enzymatic data has opened up an avenue for in-depth analyses of glycosylation processes as a basis for glycoengineering endeavours. Here, the common themes of glycosylation are conceptualised for the major classes of prokaryotic (i.e. bacterial and archaeal) glycoconjugates, with a special focus on glycosylated cell-surface proteins. We describe the current knowledge of biosynthesis and importance of these glycoconjugates in selected pathogenic and beneficial microbes.

Role of Mfa5 in Expression of Mfa1 Fimbriae in Porphyromonas gingivalis

Fimbriae are protein-based filamentous appendages that protrude from the bacterial cell surface and facilitate host adhesion. Two types of fimbriae, FimA and Mfa1, of the periodontal pathogen Porphyromonas gingivalis are responsible for adherence to other bacteria and to host cells in the oral cavity. Both fimbrial forms are composed of 5 proteins, but there is limited information about their polymerization mechanisms. Here, the authors evaluated the function of Mfa5, one of the Mfa1 fimbrial accessory proteins. Using mfa5 gene disruption and complementation studies, the authors revealed that Mfa5 affects the incorporation of other accessory proteins, Mfa3 and Mfa4, into fibers and the expression of fimbriae on the cell surface. Mfa5 is predicted to have a C-terminal domain (CTD) that uses the type IX secretion system (T9SS), which is limited to this organism and related Bacteroidetes species, for translocation across the outer membrane. To determine the relationship between the putative Mfa5 CTD and the T9SS, mutants were constructed with in-frame deletion of the CTD and deletion of porU, a C-terminal signal peptidase linked to T9SS-mediated secretion. The ∆CTD-expressing strain presented a similar phenotype to the mfa5 disruption mutant with reduced expression of fimbriae lacking all accessory proteins. The ∆porU mutants and the ∆CTD-expressing strain showed intracellular accumulation of Mfa5. These results indicate that Mfa5 function requires T9SS-mediated translocation across the outer membrane, which is dependent on the CTD, and subsequent incorporation into fibers. These findings suggest the presence of a novel polymerization mechanism of the P. gingivalis fimbriae.

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.

Characterization of wheat germ agglutinin lectin-reactive glycosylated OmpA-like proteins derived from Porphyromonas gingivalis

Glycosylation is one of the common posttranslational modifications in eukaryotes. Recently, glycosylated proteins have also been identified in prokaryotes. A few glycosylated proteins, including gingipains, have been identified in Porphyromonas gingivalis, a major pathogen associated with chronic periodontitis. However, no other glycosylated proteins have been found. The present study identified glycoproteins in P. gingivalis cell lysates by lectin blotting. Whole-cell lysates reacted with concanavalin A (ConA), Lens culinaris agglutinin (LCA), Phaseolus vulgaris erythroagglutinin (PHA-E4), and wheat germ agglutinin (WGA), suggesting the presence of mannose-, N-acetylgalactosamine-, or N-acetylglucosamine (GlcNAc)-modified proteins. Next, glycoproteins were isolated by ConA-, LCA-, PHA-E4-, or WGA-conjugated lectin affinity chromatography although specific proteins were enriched only by the WGA column. Mass spectrometry analysis showed that an OmpA-like, heterotrimeric complex formed by Pgm6 and Pgm7 (Pgm6/7) was the major glycoprotein isolated from P. gingivalis. Deglycosylation experiments and Western blotting with a specific antibody indicated that Pgm6/7 was modified with O-GlcNAc. When whole-cell lysates from P. gingivalis mutant strains with deletions of Pgm6 and Pgm7 were applied to a WGA column, homotrimeric Pgm7, but not Pgm6, was isolated. Heterotrimeric Pgm6/7 had the strongest affinity for fibronectin of all the extracellular proteins tested, whereas homotrimeric Pgm7 showed reduced binding activity. These findings suggest that the heterotrimeric structure is important for the biological activity of glycosylated WGA-binding OmpA-like proteins in P. gingivalis.

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 and characterization of prokaryotic dipeptidyl-peptidase 5 from Porphyromonas gingivalis

Porphyromonas gingivalis, a Gram-negative asaccharolytic anaerobe, is a major causative organism of chronic periodontitis. Because the bacterium utilizes amino acids as energy and carbon sources and incorporates them mainly as dipeptides, a wide variety of dipeptide production processes mediated by dipeptidyl-peptidases (DPPs) should be beneficial for the organism. In the present study, we identified the fourth P. gingivalis enzyme, DPP5. In a dpp4-7-11-disrupted P. gingivalis ATCC 33277, a DPP7-like activity still remained. PGN_0756 possessed an activity indistinguishable from that of the mutant, and was identified as a bacterial orthologue of fungal DPP5, because of its substrate specificity and 28.5% amino acid sequence identity with an Aspergillus fumigatus entity. P. gingivalis DPP5 was composed of 684 amino acids with a molecular mass of 77,453, and existed as a dimer while migrating at 66 kDa on SDS-PAGE. It preferred Ala and hydrophobic residues, had no activity toward Pro at the P1 position, and no preference for hydrophobic P2 residues, showed an optimal pH of 6.7 in the presence of NaCl, demonstrated Km and kcat/Km values for Lys-Ala-MCA of 688 μM and 11.02 μM(-1) s(-1), respectively, and was localized in the periplasm. DPP5 elaborately complemented DPP7 in liberation of dipeptides with hydrophobic P1 residues. Examinations of DPP- and gingipain gene-disrupted mutants indicated that DPP4, DPP5, DPP7, and DPP11 together with Arg- and Lys-gingipains cooperatively liberate most dipeptides from nutrient oligopeptides. This is the first study to report that DPP5 is expressed not only in eukaryotes, but also widely distributed in bacteria and archaea.

Major membrane protein TDE2508 regulates adhesive potency in Treponema denticola

The cultivation and genetic manipulation of Treponema denticola, a Gram-negative oral spirochaeta associated with periodontal diseases, is still challenging. In this study, we formulated a simple medium based on a commercially available one, and established a transformation method with high efficiency. We then analyzed proteins in a membrane fraction in T. denticola and identified 16 major membrane-associated proteins, and characterized one of them, TDE2508, whose biological function was not yet known. Although this protein, which exhibited a complex conformation, was presumably localized in the outer membrane, we did not find conclusive evidence that it was exposed on the cell surface. Intriguingly, a TDE2508-deficient mutant exhibited significantly increased biofilm formation and adherent activity on human gingival epithelial cells. However, the protein deficiency did not alter autoaggregation, coaggregation with Porphyromonas gingivalis, hemagglutination, cell surface hydrophobicity, motility, or expression of Msp which was reported to be an adherent molecule in this bacteria. In conclusion, the major membrane protein TDE2508 regulates biofilm formation and the adhesive potency of T. denticola, although the underlying mechanism remains unclear.

T helper cells from aggressive periodontitis patients produce higher levels of interleukin-1 beta and interleukin-6 in interaction with Porphyromonas gingivalis

OBJECTIVE

In this study, we analyzed the production of Interleukin-1 beta (IL-1β) and IL-6 by activated CD4+ cells obtained from aggressive periodontitis (AgP) patients in comparison with healthy subjects (HC).

MATERIALS AND METHODS

CD4+ cells were automatically separated from lymphocytes obtained from peripheral blood of patients with AgP and healthy controls. Cells were activated for 4, 8, and 24 h with three different stimuli: anti-CD3/anti-CD28, phytohemagglutinin (PHA), and Porphyromonas gingivalis (P. gingivalis) outer membrane protein (OMP). Protein levels were measured in supernatants of activated CD4+ cells by a bead-based immunoassay (CBA). In addition, serum antibodies against P. gingivalis were determined. Data were analyzed using U test (p < 0.05).

RESULTS

T helper cells of AgP patients activated with P. gingivalis OMP produced higher levels of IL-1β and IL-6 in comparison with healthy controls (p < 0.05). Neither the activation with anti-CD3/anti-CD28 nor the activation with PHA showed significantly different production of IL-1β and IL-6 by the cells 25 % of patients and 17 % of controls presented with high serum reactivity to P. gingivalis.

CONCLUSION

In view of these results, it is possible to conclude that P. gingivalis contributes to the pathogenesis of AgP by inducing high levels of pro-inflammatory cytokines such as IL-1β and IL-6 by peripheral CD4+ T helper cells.

CLINICAL RELEVANCE

In accordance with the clinical parameters and the immunological data, we suggest that full-mouth disinfection with adjunctive systemic antibiotics might be the anti-infectious non-surgical periodontal treatment of choice in this type of patients. Microbiological analyses at the beginning and at the end of the periodontal treatment are recommended. However, it is necessary to verify these data in longitudinal clinical studies.

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.

Analysis of Major Virulence Factors inPorphyromonas gingivalisunder Various Culture Temperatures Using Specific Antibodies

Porphyromonas gingivalis is implicated in the occurrence of adult periodontitis. We have previously identified major outer membrane proteins from P. gingivalis, which include representative virulence factors such as gingipains, a 75 kDa major protein, RagA, RagB, and putative porin. Fimbriae, another important virulence factor, exist on the cell surface. In this study, we identified major supernatant proteins. They were fimbrilin, the 75 kDa major protein, gingipains and their adhesin domains. Microscopic examination showed that supernatant proteins formed vesicle-like and fimbrial structures. To learn more about the character of this bacterium, we examined effects of growth temperature on localization and expression of these virulence factors. In general, localization of major virulence factors did not change at the various growth temperatures used. Most of the 75 kDa major protein, RagA, RagB, and putative porin were found in the envelope fraction, not in cell-free culture supernatant. Gingipains were found in both the envelope fraction and supernatant. More than 80% of fimbriae were associated with cells, less than 20% migrated to the supernatant. Most fimbriae existed in the whole cell lysate, although there was a small amount in the envelope fraction. When the growth temperature was increased, expression of fimbriae, gingipains, the 75 kDa major protein, RagA, and RagB decreased. However, temperature had almost no effect on expression of putative porin. The tendency for expression of major virulence factors to decrease at higher temperatures may enable P. gingivalis to survive under hostile conditions.

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.

Identification of an O-antigen chain length regulator, WzzP, in Porphyromonas gingivalis

The periodontal pathogen Porphyromonas gingivalis has two different lipopolysaccharides (LPSs) designated O-LPS and A-LPS, which are a conventional O-antigen polysaccharide and an anionic polysaccharide that are both linked to lipid A-cores, respectively. However, the precise mechanisms of LPS biosynthesis remain to be determined. In this study, we isolated a pigment-less mutant by transposon mutagenesis and identified that the transposon was inserted into the coding sequence PGN_2005, which encodes a hypothetical protein of P. gingivalis ATCC 33277. We found that (i) LPSs purified from the PGN_2005 mutant were shorter than those of the wild type; (ii) the PGN_2005 protein was located in the inner membrane fraction; and (iii) the PGN_2005 gene conferred Wzz activity upon an Escherichia coli wzz mutant. These results indicate that the PGN_2005 protein, which was designated WzzP, is a functional homolog of the Wzz protein in P. gingivalis. Comparison of amino acid sequences among WzzP and conventional Wzz proteins indicated that WzzP had an additional fragment at the C-terminal region. In addition, we determined that the PGN_1896 and PGN_1233 proteins and the PGN_1033 protein appear to be WbaP homolog proteins and a Wzx homolog protein involved in LPS biosynthesis, respectively.

Identification and characterization of Porphyromonas gingivalis client proteins that bind to Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase

Coaggregation of Porphyromonas gingivalis and oral streptococci is thought to play an important role in P. gingivalis colonization. Previously, we reported that P. gingivalis major fimbriae interacted with Streptococcus oralis glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and that amino acid residues 166 to 183 of GAPDH exhibited strong binding activity toward P. gingivalis fimbriae (H. Nagata, M. Iwasaki, K. Maeda, M. Kuboniwa, E. Hashino, M. Toe, N. Minamino, H. Kuwahara, and S. Shizukuishi, Infect. Immun. 77:5130-5138, 2009). The present study aimed to identify and characterize P. gingivalis components other than fimbriae that interact with S. oralis GAPDH. A pulldown assay was performed to detect potential interactions between P. gingivalis client proteins and S. oralis recombinant GAPDH with amino acid residues 166 to 183 deleted by site-directed mutagenesis. Seven proteins, namely, tonB-dependent receptor protein (RagA4), arginine-specific proteinase B, 4-hydroxybutyryl-coenzyme A dehydratase (AbfD), lysine-specific proteinase, GAPDH, NAD-dependent glutamate dehydrogenase (GDH), and malate dehydrogenase (MDH), were identified by two-dimensional gel electrophoresis followed by proteomic analysis using tandem mass spectrometry. Interactions between these client proteins and S. oralis GAPDH were analyzed with a biomolecular interaction analysis system. S. oralis GAPDH showed high affinity for five of the seven client proteins (RagA4, AbfD, GAPDH, GDH, and MDH). Interactions between P. gingivalis and S. oralis were measured by a turbidimetric method and fluorescence microscopy. RagA4, AbfD, and GDH enhanced coaggregation, whereas GAPDH and MDH inhibited coaggregation. Furthermore, the expression of luxS in P. gingivalis was upregulated by RagA4, AbfD, and GDH but was downregulated by MDH. These results indicate that the five P. gingivalis client proteins function as regulators in P. gingivalis biofilm formation with oral streptococci.

Porphyromonas gingivalis FimA fimbriae: fimbrial assembly by fimA alone in the fim gene cluster and differential antigenicity among fimA genotypes

The periodontal pathogen Porphyromonas gingivalis colonizes largely through FimA fimbriae, composed of polymerized FimA encoded by fimA. fimA exists as a single copy within the fim gene cluster (fim cluster), which consists of seven genes: fimX, pgmA and fimA-E. Using an expression vector, fimA alone was inserted into a mutant from which the whole fim cluster was deleted, and the resultant complement exhibited a fimbrial structure. Thus, the genes of the fim cluster other than fimA were not essential for the assembly of FimA fimbriae, although they were reported to influence FimA protein expression. It is known that there are various genotypes for fimA, and it was indicated that the genotype was related to the morphological features of FimA fimbriae, especially the length, and to the pathogenicity of the bacterium. We next complemented the fim cluster-deletion mutant with fimA genes cloned from P. gingivalis strains including genotypes I to V. All genotypes showed a long fimbrial structure, indicating that FimA itself had nothing to do with regulation of the fimbrial length. In FimA fimbriae purified from the complemented strains, types I, II, and III showed slightly higher thermostability than types IV and V. Antisera of mice immunized with each purified fimbria principally recognized the polymeric, structural conformation of the fimbriae, and showed low cross-reactivity among genotypes, indicating that FimA fimbriae of each genotype were antigenically different. Additionally, the activity of a macrophage cell line stimulated with the purified fimbriae was much lower than that induced by Escherichia coli lipopolysaccharide.

Identification and characterization of novel glycoproteins involved in growth and biofilm formation by Porphyromonas gingivalis

Porphyromonas gingivalis has been implicated as a major pathogen associated with chronic periodontitis. To extend our knowledge of post-translational protein glycosylation in P. gingivalis, a proteomic analysis involving two-dimensional polyacrylamide gel electrophoresis combined with carbohydrate staining and mass spectrometry was performed. Four novel glycoproteins, PGN0743, PGN0876, PGN1513 and PGN0729, in P. gingivalis ATCC 33277 were identified. These four identified glycoproteins possess a range of biochemical activities and cellular localization. PGN0743 contains a sequence motif identifying it as a FKBP-type cis-trans isomerase, which has activity usually associated with chaperone functions. PGN0876 and PGN1513 contain tetratricopeptide repeat domains that mediate protein-protein interactions. PGN0729 encodes the outer membrane protein 41 precursor, which was previously identified as Pgm6, and is homologous to the OmpA protein in Escherichia coli. Several different types of glycoprotein were identified, suggesting that P. gingivalis possesses a general mechanism for protein glycosylation. PGN0743-deficient and PGN0876-deficient mutants were constructed to examine the role(s) of the two identified glycoproteins. Both mutants showed a decreased growth rate under nutrient-limited conditions and reduced biofilm formation activity. These results suggest that the novel glycoproteins PGN0743 and PGN0876 play an important role in the growth and colonization of P. gingivalis.

E-selectin mediates Porphyromonas gingivalis adherence to human endothelial cells

Porphyromonas gingivalis, a major periodontal pathogen, may contribute to atherogenesis and other inflammatory cardiovascular diseases. However, little is known about interactions between P. gingivalis and endothelial cells. E-selectin is a membrane protein on endothelial cells that initiates recruitment of leukocytes to inflamed tissue, and it may also play a role in pathogen attachment. In the present study, we examined the role of E-selectin in P. gingivalis adherence to endothelial cells. Human umbilical vein endothelial cells (HUVECs) were stimulated with tumor necrosis factor alpha (TNF-α) to induce E-selectin expression. Adherence of P. gingivalis to HUVECs was measured by fluorescence microscopy. TNF-α increased adherence of wild-type P. gingivalis to HUVECs. Antibodies to E-selectin and sialyl Lewis X suppressed P. gingivalis adherence to stimulated HUVECs. P. gingivalis mutants lacking OmpA-like proteins Pgm6 and -7 had reduced adherence to stimulated HUVECs, but fimbria-deficient mutants were not affected. E-selectin-mediated P. gingivalis adherence activated endothelial exocytosis. These results suggest that the interaction between host E-selectin and pathogen Pgm6/7 mediates P. gingivalis adherence to endothelial cells and may trigger vascular inflammation.

OmpA-like protein influences cell shape and adhesive activity of Tannerella forsythia

Tannerella forsythia, a gram-negative fusiform rod, is implicated in several types of oral anaerobic infections. Most gram-negative bacteria have OmpA-like proteins that are homologous to the OmpA protein in Escherichia coli. We identified an OmpA-like protein in T. forsythia encoded by the tf1331 gene as one of the major proteins by mass spectrometric analysis. Two-dimensional, diagonal electrophoresis showed that the OmpA-like protein formed a dimeric or trimeric structure via intermolecular disulfide bonds. A biotin labeling experiment revealed that a portion of the protein was exposed on the cell surface, even though T. forsythia possesses an S-layer at the outermost cell surface. Using a tf1331-deletion mutant, we showed that the OmpA-like protein affected cell morphology. The length of the mutant cell was reduced almost by half. Cell swelling was observed in more than 40% of the mutant cells. Moreover, the mutant exhibited decreased adhesion to fibronectin, retarded autoaggregation, and reduced cell surface hydrophobicity. These results suggest that the OmpA-like protein in T. forsythia plays an important role in cellular integrity and adhesive function.

FimB regulates FimA fimbriation in Porphyromonas gingivalis

The periodontitis-associated pathogen Porphyromonas gingivalis colonizes and forms a biofilm in gingival crevices through fimbriae. It is known that the often-used strains ATCC 33277 and 381 produce long FimA fimbriae. We found a possible nonsense mutation within fimB, immediately downstream from fimA, coding a major subunit of FimA fimbriae of the strains. Indeed, P. gingivalis strains, except for ATCC 33277 and 381, universally expressed FimB, the gene product of fimB. Electron micrographs revealed that a FimB-restored strain had short and dense, "toothbrush"-like, FimA fimbriae. FimA overexpression elongated the fimbriae, whereas FimB overexpression shortened them. FimB restoration increased production of FimA and its accessory proteins. Thus, FimB regulates the length and expression of FimA fimbriae. Additionally, FimB restoration significantly reduced the release of FimA fimbriae from the cell surface, suggesting that FimB functions as an anchor of the fimbriae. The restoration enhanced adherent activity as well.

Characterization of hemin-binding protein 35 (HBP35) in Porphyromonas gingivalis: its cellular distribution, thioredoxin activity and role in heme utilization

Background

The periodontal pathogen Porphyromonas gingivalis is an obligate anaerobe that requires heme for growth. To understand its heme acquisition mechanism, we focused on a hemin-binding protein (HBP35 protein), possessing one thioredoxin-like motif and a conserved C-terminal domain, which are proposed to be involved in redox regulation and cell surface attachment, respectively.

Results

We observed that the hbp35 gene was transcribed as a 1.1-kb mRNA with subsequent translation resulting in three proteins with molecular masses of 40, 29 and 27 kDa in the cytoplasm, and one modified form of the 40-kDa protein on the cell surface. A recombinant 40-kDa HBP35 exhibited thioredoxin activity in vitro and mutation of the two putative active site cysteine residues abolished this activity. Both recombinant 40- and 27-kDa proteins had the ability to bind hemin, and growth of an hbp35 deletion mutant was substantially retarded under hemin-depleted conditions compared with growth of the wild type under the same conditions.

Conclusion

P. gingivalis HBP35 exhibits thioredoxin and hemin-binding activities and is essential for growth in hemin-depleted conditions suggesting that the protein plays a significant role in hemin acquisition.

Feasibility and therapeutic strategies of vaccines against Porphyromonas gingivalis

Periodontitis is a chronic infectious disease that is highly prevalent worldwide and is characterized by inflammation of the gums, and loss of connective tissue and bone support. The Gram-negative anerobic bacterium Porphyromonas gingivalis is generally accepted as the main etiological agent for chronic periodontitis. The objective of this paper is to elucidate the feasibility of achieving protection against periodontitis though immunization against P. gingivalis. Until now, animal studies have showed no complete protection against P. gingivalis. However, current knowledge about P. gingivalis structures could be applicable for further research to develop a successful licensed vaccine and alternative therapeutic strategies. This review reveals that a multicomponent vaccine against P. gingivalis, which includes structures shared among P. gingivalis serotypes, will be feasible to induce broad and complete protection.

Tetratricopeptide repeat protein-associated proteins contribute to the virulence of Porphyromonas gingivalis

Porphyromonas gingivalis is one of the most etiologically important microorganisms in periodontal disease. We found in a previous study that PG1385 (TprA) protein, a tetratricopeptide repeat (TPR) protein, was upregulated in P. gingivalis wild-type cells placed in a mouse subcutaneous chamber and that a tprA mutant was clearly less virulent in the mouse subcutaneous abscess model (M. Yoshimura et al., Oral Microbiol. Immunol. 23:413-418, 2008). In the present study, we investigated the gene expression profile of tprA mutant cells placed in a mouse subcutaneous chamber and found that 9 genes, including PG2102 (tapA), PG2101 (tapB), and PG2100 (tapC) genes, were downregulated in the tprA mutant compared with those in the wild type. Expression of a cluster of tapA, tapB, and tapC genes of the mutant was also downregulated in an in vitro culture with enriched brain heart infusion medium. The TprA protein has three TPR motifs known as a protein-protein interaction module. Yeast two-hybrid system analysis and in vitro protein binding assays with immunoprecipitation and surface plasmon resonance detection revealed that the TprA protein could bind to TapA and TapB proteins. TprA and TapB proteins were located in the periplasmic space, whereas TapA, which appeared to be one of the C-terminal domain family proteins, was located at the outer membrane. We constructed tapA, tapB, and tapC single mutants and a tapA-tapB-tapC deletion mutant. In the mouse subcutaneous infection experiment, all of the mutants were less virulent than the wild type. These results suggest that TprA, TapA, TapB, and TapC are cooperatively involved in P. gingivalis virulence.

Histidine kinase-mediated production and autoassembly of Porphyromonas gingivalis fimbriae

Porphyromonas gingivalis, a Gram-negative oral anaerobe, is strongly associated with chronic adult periodontitis, and it utilizes FimA fimbriae to persistently colonize and evade host defenses in the periodontal crevice. The FimA-related gene cluster (the fim gene cluster) is positively regulated by the FimS-FimR two-component system. In this study, comparative analyses between fimbriate type strain ATCC 33277 and fimbria-deficient strain W83 revealed differences in their fimS loci, which encode FimS histidine kinase. Using a reciprocal gene exchange system, we established that FimS from W83 is malfunctional. Complementation analysis with chimeric fimS constructs revealed that W83 FimS has a defective kinase domain due to a truncated conserved G3 box motif that provides an ATP-binding pocket. The introduction of the functional fimS from 33277 restored the production, but not polymerization, of endogenous FimA subunits in W83. Further analyses with a fimA-exchanged W83 isogenic strain showed that even the fimbria-deficient W83 retains the ability to polymerize FimA from 33277, indicating the assembly of mature FimA by a primary structure-dependent mechanism. It also was shown that the substantial expression of 33277-type FimA fimbriae in the W83 derivative requires the introduction and expression of the functional 33277 fimS. These findings indicate that FimSR is the unique and universal regulatory system that activates the fim gene cluster in a fimA genotype-independent manner.

Identification of a gingipain-sensitive surface ligand of Porphyromonas gingivalis that induces Toll-like receptor 2- and 4-independent NF-kappaB activation in CHO cells

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

Anchoring and length regulation of Porphyromonas gingivalis Mfa1 fimbriae by the downstream gene product Mfa2

Porphyromonas gingivalis, a causative agent of periodontitis, has at least two types of thin, single-stranded fimbriae, termed FimA and Mfa1 (according to the names of major subunits), which can be discriminated by filament length and by the size of their major fimbrilin subunits. FimA fimbriae are long filaments that are easily detached from cells, whereas Mfa1 fimbriae are short filaments that are tightly bound to cells. However, a P. gingivalis ATCC 33277-derived mutant deficient in mfa2, a gene downstream of mfa1, produced long filaments (10 times longer than those of the parent), easily detached from the cell surface, similar to FimA fimbriae. Longer Mfa1 fimbriae contributed to stronger autoaggregation of bacterial cells. Complementation of the mutant with the wild-type mfa2 allele in trans restored the parental phenotype. Mfa2 is present in the outer membrane of P. gingivalis, but does not co-purify with the Mfa1 fimbriae. However, co-immunoprecipitation demonstrated that Mfa2 and Mfa1 are associated with each other in whole P. gingivalis cells. Furthermore, immunogold microscopy, including double labelling, confirmed that Mfa2 was located on the cell surface and likely associated with Mfa1 fimbriae. Mfa2 may therefore play a role as an anchor for the Mfa1 fimbriae and also as a regulator of Mfa1 filament length. Two additional downstream genes (pgn0289 and pgn0290) are co-transcribed with mfa1 (pgn0287) and mfa2 (pgn0288), and proteins derived from pgn0289, pgn0290 and pgn0291 appear to be accessory fimbrial components.

Characteristics of Bacteroides fragilis lacking the major outer membrane protein, OmpA

OmpA1 is the major outer membrane protein of the Gram-negative anaerobic pathogen Bacteroides fragilis. We identified three additional conserved ompA homologues (ompA2-ompA4) and three less homologous ompA-like genes (ompAs 5, 6 and 7) in B. fragilis. We constructed an ompA1 disruption mutant in B. fragilis 638R (WAL6 OmegaompA1) using insertion-mediated mutagenesis. WAL6 OmegaompA1 formed much smaller colonies and had smaller, rounder forms on Gram stain analysis than the parental strain or other unrelated disruption mutants. SDS-PAGE and Western blot analysis (with anti-OmpA1 IgY) of the OMP patterns of WAL6 OmegaompA1 grown in both high- and low-salt media did not reveal any other OmpA proteins even under osmotic stress. An ompA1 deletant (WAL186DeltaompA1) was constructed using a two-step double-crossover technique, and an ompA 'reinsertant', WAL360+ompA1, was constructed by reinserting the ompA gene into WAL186DeltaompA1. WAL186DeltaompA1 was significantly more sensitive to exposure to SDS, high salt and oxygen than the parental (WAL108) or reinsertant (WAL360+ompA1) strain. No significant change was seen in MICs of a variety of antimicrobials for either WAL6 OmegaompA1 or WAL186DeltaompA1 compared to WAL108. RT-PCR revealed that all of the ompA genes are transcribed in the parental strain and in the disruption mutant, but, as expected, ompA1 is not transcribed in WAL186DeltaompA1. Unexpectedly, ompA4 is also not transcribed in WAL186DeltaompA1. A predicted structure indicated that among the four OmpA homologues, the barrel portion is more conserved than the loops, except for specific conserved patches on loop 1 and loop 3. The presence of multiple copies of such similar genes in one organism would suggest a critical role for this protein in B. fragilis.

Evaluation of procedures for outer membrane isolation from Campylobacter jejuni

Although infection with Campylobacter jejuni is one of the leading causes of gastroenteritis worldwide, relatively little is known about the factors that are required to elicit a protective immune response. The need for a vaccine against this pathogen is well recognized and a number of vaccine candidates have been tested with varying degrees of success; however, there is still a lack of a suitable vaccine. To gain a better understanding of the outer-membrane protein components of this organism, a 'gold standard' method to purify the outer membrane is needed. Therefore, we attempted to develop a robust and reliable method which resulted in a pure outer-membrane fraction. A total of nine methodologies were examined and analysed by SDS-PAGE and immunoblotting using subcellular markers for the cytoplasm, cytoplasmic membrane and outer membrane. We found that glycine extraction, differential detergent extraction using Triton X-100, serial extraction using 1 M Tris pH 7, spheroplasting by lysozyme and sonication, and carbonate extraction did not produce pure outer-membrane preparations. However, we identified three methods that provided outer-membrane fractions free from subcellular contamination. Isopycnic centrifugation using a 30-60 % sucrose gradient produced seven fractions free from cytoplasmic or cytoplasmic membrane contamination; however, these fractions did not correspond as well as expected with the typical outer-membrane-associated peak (e.g. Escherichia coli or Salmonella). The spheroplast method using lysozyme alone also resulted in pure outer-membrane fraction, as did carbonate washing of this sample. The extraction of outer membranes using N-lauroylsarcosine (Sarkosyl) produced the purest and most reproducible sample. These outer-membrane preparations will be useful for future studies aimed at identifying C. jejuni surface proteins as vaccine components.

Surface components of Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Research on Porphyromonas gingivalis, a periodontopathogen, has provided a tremendous amount of information over the last 20 years, which may exceed in part than that on other closely related members in terms of phylogenetic as well as proteomic criteria, including Bacteroides fragilis and B. thetaiotaomicron as major anaerobic, opportunistic pathogens in the medical field. In this minireview, we focused on recent research findings concerning surface components such as outer membrane proteins and fimbriae, of P. gingivalis.

MATERIAL AND METHODS

Elucidation of the surface components in P. gingivalis was especially difficult because outer membrane proteins are tightly bound to lipopolysaccharide and they are resistant to dissociation and separation from each other, even during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, unless samples are appropriately heated. In addition, P. gingivalis is asaccharolytic and therefore a potent proteolytic bacterium, another factor causing difficulty in research. The study of the surface components was carefully carried out considering these unique features in P. gingivalis when compared with other gram-negative bacteria, including Escherichia coli and Pseudomonas aeruginosa.

RESULTS

Separation of outer membrane proteins, and characterization of OmpA-like proteins and RagAB as major proteins, is described herein. Our recent findings on FimA and Mfa1 fimbriae, two unique appendages in this organism, and on their regulation of expression are also described briefly.

CONCLUSION

Surface components of P. gingivalis somehow have contact with host tissues and cells because of the outermost cell elements. Therefore, such bacterial components are potentially important in the occurrence of periodontal diseases.

LocateP: genome-scale subcellular-location predictor for bacterial proteins

Background

In the past decades, various protein subcellular-location (SCL) predictors have been developed. Most of these predictors, like TMHMM 2.0, SignalP 3.0, PrediSi and Phobius, aim at the identification of one or a few SCLs, whereas others such as CELLO and Psortb.v.2.0 aim at a broader classification. Although these tools and pipelines can achieve a high precision in the accurate prediction of signal peptides and transmembrane helices, they have a much lower accuracy when other sequence characteristics are concerned. For instance, it proved notoriously difficult to identify the fate of proteins carrying a putative type I signal peptidase (SPIase) cleavage site, as many of those proteins are retained in the cell membrane as N-terminally anchored membrane proteins. Moreover, most of the SCL classifiers are based on the classification of the Swiss-Prot database and consequently inherited the inconsistency of that SCL classification. As accurate and detailed SCL prediction on a genome scale is highly desired by experimental researchers, we decided to construct a new SCL prediction pipeline: LocateP.

Results

LocateP combines many of the existing high-precision SCL identifiers with our own newly developed identifiers for specific SCLs. The LocateP pipeline was designed such that it mimics protein targeting and secretion processes. It distinguishes 7 different SCLs within Gram-positive bacteria: intracellular, multi-transmembrane, N-terminally membrane anchored, C-terminally membrane anchored, lipid-anchored, LPxTG-type cell-wall anchored, and secreted/released proteins. Moreover, it distinguishes pathways for Sec- or Tat-dependent secretion and alternative secretion of bacteriocin-like proteins. The pipeline was tested on data sets extracted from literature, including experimental proteomics studies. The tests showed that LocateP performs as well as, or even slightly better than other SCL predictors for some locations and outperforms current tools especially where the N-terminally anchored and the SPIase-cleaved secreted proteins are concerned. Overall, the accuracy of LocateP was always higher than 90%. LocateP was then used to predict the SCLs of all proteins encoded by completed Gram-positive bacterial genomes. The results are stored in the database LocateP-DB [1].

Conclusion

LocateP is by far the most accurate and detailed protein SCL predictor for Gram-positive bacteria currently available.

Further evidence that major outer membrane proteins homologous to OmpA in Porphyromonas gingivalis stabilize bacterial cells

INTRODUCTION

Porphyromonas gingivalis is one of the most important bacteria in the progression of chronic periodontal disease. We hypothesized that the major outer membrane proteins Pgm6/7, which are homologous to the OmpA protein in Escherichia coli, might contribute to the stabilization of the cell surface. In this study, the effects of Pgm6/7 on the cell surface were examined morphologically.

METHODS

Deletion mutants of Pgm6/7 (Delta694, Delta695 and Delta695-694) were constructed using the polymerase chain reaction-based overlap extension method. Wild-type ATCC 33277 and Pgm6/7 mutants were grown under anaerobic conditions. Whole cells and thin sections of fixed cells were stained and examined by transmission electron microscopy.

RESULTS

Compared with the wild-type, numerous vesicles released from cells were observed in each deletion mutant. The outer membrane appeared wavy and irregular. Increased numbers of vesicles were confirmed after their preparation from the culture supernatant. Total gingipain activity in vesicles was increased five- to 10-fold in the deletion mutants.

CONCLUSION

This report provides further evidence that Pgm6/7 proteins in P. gingivalis play an important role in the maintenance of bacterial outer membrane integrity.

Characterization of RagA and RagB in Porphyromonas gingivalis: study using gene-deletion mutants

The major outer-membrane proteins RagA and RagB ofPorphyromonas gingivalisare considered to form a receptor complex functionally linked to TonB. In this study,P.gingivalismutants withragA,ragBor both deleted were constructed from strain W83 as the parent to examine the physiological and pathological functions of RagA and RagB. The double-deletion mutant completely lacked both RagA and RagB, whereas the ΔragAmutant reduced RagB expression considerably and the ΔragBmutant produced degraded RagA. Growth of the three mutants in a nutrient-rich medium and synthetic media containing digested protein as a unique nutrient source was similar to that of the parental strain; however, both the ΔragAand ΔragABmutants exhibited very slow growth in a synthetic medium containing undigested, native protein, and the two mutants tended to lose their viability during experiments, although gingipain (protease) activities were unchanged in the mutants. A mouse model showed that the ΔragBmutant had reduced virulence. Cell-surface labelling with biotin and dextran revealed that both RagA and RagB localized on the outermost cell surface. A cross-linking experiment using wild-typeP. gingivalisshowed that RagA and RagB were closely associated with each other. Furthermore, co-immunoprecipitation confirmed that RagA and RagB formed a protein–protein complex. These results suggest that physically associated RagA and RagB may stabilize themselves on the cell surface and function as active transporters of large degradation products of protein and in part as a virulence factor.

Loss of adherence ability to human gingival epithelial cells in S-layer protein-deficient mutants of Tannerella forsythensis

Tannerella forsythensis, one of the important pathogens in periodontal disease, has a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane. The S-layer in T. forsythensis is suggested to be associated with haemagglutinating activity, adhesion and invasion of host cells; however, its precise functions have been unknown. ORFs encoding the major S-layer proteins (230 and 270 kDa) of T. forsythensis ATCC 43037, tfsA and tfsB, respectively, following the names in a recent report [Lee, S.-W., Sabet, M., Um, H. S., Yang, L., Kim, H. C. & Zhu, W. (2006). Gene 371, 102-111] were determined. To verify the function of the S-layer proteins, three mutants with tfsA, tfsB, or both deleted were successfully constructed by a PCR-based overlapping method. S-layer proteins were completely lost in the double mutant. The single-deletion mutants appeared to lose one of the 230 and 270 kDa proteins. Thin-section microscopy clearly revealed that the 230 and 270 kDa proteins composed the S-layer. Although the S-layer proteins may be weakly related to haemagglutinating activity, these proteins were highly responsible for adherence to human gingival epithelial cells (Ca9-22) and KB cells. These results suggest that the S-layer proteins in T. forsythensis play an important role in the initiation stage of oral infection including periodontal disease.

Isolation and characterization of the Omp-PA porin from Porphyromonas asaccharolytica, determination of the omp-PA gene sequence and prediction of Omp-PA protein structure

A single monomeric porin, Omp-PA (37kDa), was isolated from the outer membrane of the gram-negative anaerobic rod Porphyromonas asaccharolytica. Further characterization revealed that this porin consists of two different fractions: a heat-modifiable fraction which in its denatured form migrated on SDS-PAGE as a protein with a molecular weight of 41kDa and a heat-resistant fraction which did not change its migration on SDS-PAGE after boiling. A liposome swelling assay revealed that only the heat-resistant fraction was able to transport sugars after its incorporation into the liposomes, although it did not discriminate between differently sized sugars. We hypothesize that the heat-modifiable fraction corresponds to the "closed" conformer of Omp-PA, whereas the heat-resistant fraction corresponds to the "open" conformer of the protein. Cloning of the omp-PA gene revealed an open reading frame of 1161 bases, with a predicted protein sequence of 387 amino acids. The mature protein consists of 366 amino acids with a calculated MW of 41,102Da and an estimated pI of 7.24. The C-terminal domain of Omp-PA is homologous to the characteristic OmpA signature domain (71% similarity with the OmpA consensus domain). Sequence comparison with other anaerobes from the Bacteroides family demonstrated homology across the entire ORF. Digestion of the P. asaccharolytica outer membrane analysis of trypsin-digested Omp-PA yielded two proteins migrating with apparent molecular weights of 37 and 27kDa. These data fully supported our hypothesis that the C-terminal domain of the two-domain "closed" conformer of Omp-PA was digested by trypsin, whereas the single domain beta-barrel "open" conformer was inaccessible to trypsin.

Effects of various growth conditions in a chemostat on expression of virulence factors in Porphyromonas gingivalis

Porphyromonas gingivalis, one of the gram-negative organisms associated with periodontal disease, possesses potential virulence factors, including fimbriae, proteases, and major outer membrane proteins (OMPs). In this study, P. gingivalis ATCC 33277 was cultured in a chemostat under hemin excess and presumably peptide-limiting conditions to better understand the mechanisms of expression of the virulence factors upon environmental changes. At higher growth rates, the amounts of FimA and the 75-kDa protein, forming long and short fimbriae, respectively, increased significantly, whereas gingipains decreased in amount and activity. In a nutrient-limited medium, lesser amounts of the above two fimbrial proteins were observed, whereas clear differences were not found in the amounts of gingipains. In addition, two-dimensional electrophoresis revealed that proteins in cells were generally fewer in number during nutrient-limited growth. Under aeration, a considerable reduction in gingipain activity was found, whereas several proteins associated with intact cells significantly increased. However, the expression of major OMPs, such as RagA, RagB, and the OmpA-like proteins, was almost constant under all conditions tested. These results suggest that P. gingivalis may actively control expression of several virulence factors to survive in the widely fluctuating oral environment.

Porphyromonas gingivalis-induced platelet aggregation in plasma depends on Hgp44 adhesin but not Rgp proteinase

Evidence from recent epidemiological studies suggests a link between periodontal infections and increased risk of atherosclerosis and related cardiovascular and cerebrovascular events in human subjects. One of the major pathogens of periodontitis, Porphyromonas gingivalis, has the ability to aggregate human platelets in platelet-rich plasma (PRP). Mechanism of P. gingivalis-induced platelet aggregation in PRP was investigated. Proteinase inhibitors toward Arg-gingipain (Rgp) and Lys-gingipain (Kgp) did not suppress P. gingivalis-induced platelet aggregation in PRP, whereas the Rgp inhibitor markedly inhibited P. gingivalis-induced platelet aggregation using washed platelets. Mutant analysis revealed that P. gingivalis-induced platelet aggregation in PRP depended on Rgp-, Kgp- and haemagglutinin A (HagA)-encoding genes that intragenically coded for adhesins such as Hgp44. Hgp44 adhesin on the bacterial cell surface, which was processed by Rgp and Kgp proteinases, was essential for P. gingivalis-induced platelet aggregation in PRP. P. gingivalis cell-reactive IgG in plasma, and FcgammaRIIa receptor and to a lesser extent GPIbalpha receptor on platelets were found to be a prerequisite for P. gingivalis-induced platelet aggregation in PRP. These results reveal a novel mechanism of platelet aggregation by P. gingivalis.

Assessing the precision of high-throughput computational and laboratory approaches for the genome-wide identification of protein subcellular localization in bacteria

BACKGROUND

Identification of a bacterial protein's subcellular localization (SCL) is important for genome annotation, function prediction and drug or vaccine target identification. Subcellular fractionation techniques combined with recent proteomics technology permits the identification of large numbers of proteins from distinct bacterial compartments. However, the fractionation of a complex structure like the cell into several subcellular compartments is not a trivial task. Contamination from other compartments may occur, and some proteins may reside in multiple localizations. New computational methods have been reported over the past few years that now permit much more accurate, genome-wide analysis of the SCL of protein sequences deduced from genomes. There is a need to compare such computational methods with laboratory proteomics approaches to identify the most effective current approach for genome-wide localization characterization and annotation.

RESULTS

In this study, ten subcellular proteome analyses of bacterial compartments were reviewed. PSORTb version 2.0 was used to computationally predict the localization of proteins reported in these publications, and these computational predictions were then compared to the localizations determined by the proteomics study. By using a combined approach, we were able to identify a number of contaminants and proteins with dual localizations, and were able to more accurately identify membrane subproteomes. Our results allowed us to estimate the precision level of laboratory subproteome studies and we show here that, on average, recent high-precision computational methods such as PSORTb now have a lower error rate than laboratory methods.

CONCLUSION

We have performed the first focused comparison of genome-wide proteomic and computational methods for subcellular localization identification, and show that computational methods have now attained a level of precision that is exceeding that of high-throughput laboratory approaches. We note that analysis of all cellular fractions collectively is required to effectively provide localization information from laboratory studies, and we propose an overall approach to genome-wide subcellular localization characterization that capitalizes on the complementary nature of current laboratory and computational methods.

Major outer membrane proteins from Porphyromonas gingivalis: strain variation, distribution, and clinical significance in periradicular lesions

Porphyromonas gingivalis has been implicated in both marginal periodontitis and periapical infection. This study examined the major outer membrane proteins, from P. gingivalis, which related to periradicular lesions. Outer membrane protein profiles of P. gingivalis ATCC 33277 and W83 were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and N-terminal amino acid analysis. Most outer membrane proteins, such as RagA, gingipains, and OmpA-like proteins, were found in both strains in a similar distribution pattern; however, the migration positions of Lys-gingipain and RagB were inverted in SDS-PAGE. Western blot analysis showed that RagA, RagB, and OmpA-like proteins were found in all of the P. gingivalis strains tested. The antiserum of W83 against RagB reacted poorly to some strains, such as ATCC 33277. When strains phylogenetically related to P. gingivalis were examined, RagA and OmpA homologs were immunologically detected in several strains. However, none of the RagB homologs were detected in any strain analyzed, suggesting that RagB is unique to P. gingivalis. To examine immunoreactive antigens in P. gingivalis, sera from patients with periradicular lesions were used. More than half of the sera showed strong reactions to P. gingivalis cell components, especially RagB. Our results indicate that a major outer membrane protein, RagB, is a possible virulence factor in periradicular lesions.

Expression of Arg-Gingipain RgpB is required for correct glycosylation and stability of monomeric Arg-gingipain RgpA from Porphyromonas gingivalis W50

Arg-gingipains are extracellular cysteine proteases produced by the gram-negative periodontal pathogen Porphyromonas gingivalis and are encoded by rgpA and rgpB. Three Arg-gingipains, heterodimeric high-molecular-mass Arg-gingipain HRgpA comprising the alpha-catalytic chain and the beta-adhesin chain, the monomeric soluble Arg-gingipain comprising only the alpha-catalytic chain (RgpA(cat)), and the monomeric membrane-type heavily glycosylated Arg-gingipain comprising the alpha-catalytic chain (mt-RgPA(cat)), are derived from rgpA. The monomeric enzymes contain between 14 and 30% carbohydrate by weight. rgpB encodes two monomeric enzymes, RgpB and mt-RgpB. Earlier work indicated that rgpB is involved in the glycosylation process, since inactivation of rgpB results in the loss of not only RgpB and mt-RgpB but also mt-RgpA(cat). This work aims to confirm the role of RgpB in the posttranslational modification of RgpA(cat) and the effect of aberrant glycosylation on the properties of this enzyme. Two-dimensional gel electrophoresis of cellular proteins from W50 and an inactivated rgpB strain (D7) showed few differences, suggesting that loss of RgpB has a specific effect on RgpA maturation. Inactivation of genes immediately upstream and downstream of rgpB had no effect on rgpA-derived enzymes, suggesting that the phenotype of the rgpB mutant is not due to a polar effect on transcription at this locus. Matrix-assisted laser desorption ionization-time of flight analysis of purified RgpA(cat) from W50 and D7 strains gave identical peptide mass fingerprints, suggesting that they have identical polypeptide chains. However, RgpA(cat) from D7 strain had a higher isoelectric point and a dramatic decrease in thermostability and did not cross-react with a monoclonal antibody which recognizes a glycan epitope on the parent strain enzyme. Although it had the same total sugar content as the parent strain enzyme, there were significant differences in the monosaccharide composition and linking sugars. These data suggest that RgpB is required for the normal posttranslational glycosylation of Arg-gingipains derived from rgpA and that this process is required for enzyme stabilization.