Hemagglutinin activity and heterogeneity of related Porphyromonas gingivalis proteinases

Selective bacterial degradation of the extracellular matrix attaching the gingiva to the tooth

The junctional epithelium (JE) is a specialized portion of the gingiva that seals off the tooth‐supporting tissues from the oral environment. This relationship is achieved via a unique adhesive extracellular matrix that is, in fact, a specialized basal lamina (sBL). Three unique proteins – amelotin (AMTN), odontogenic ameloblast‐associated (ODAM), and secretory calcium‐binding phosphoprotein proline‐glutamine rich 1 (SCPPPQ1) – together with laminin‐332 structure the supramolecular organization of this sBL and determine its adhesive capacity. Despite the constant challenge of the JE by the oral microbiome, little is known of the susceptibility of the sBL to bacterial degradation. Assays with trypsin‐like proteases, as well as incubation with Porphyromonas gingivalis, Prevotella intermedia, and Treponema denticola, revealed that all constituents, except SCPPPQ1, were rapidly degraded. Porphyromonas gingivalis was also shown to alter the supramolecular network of reconstituted and native sBLs. These results provide evidence that proteolytic enzymes and selected gram‐negative periodontopathogenic bacteria can attack this adhesive extracellular matrix, intimating that its degradation could contribute to progression of periodontal diseases.

Structural properties of a haemophore facilitate targeted elimination of the pathogen Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone bacterial pathogen of chronic periodontitis. P. gingivalis is unable to synthesise the porphyrin macrocycle and relies on exogenous porphyrin, including haem or haem biosynthesis intermediates from host sources. We show that under the iron-limited conditions prevailing in tissue environments, P. gingivalis expresses a haemophore-like protein, HusA, to mediate the uptake of essential porphyrin and support pathogen survival within epithelial cells. The structure of HusA, together with titration studies, mutagenesis and in silico docking, show that haem binds in a hydrophobic groove on the α-helical structure without the typical iron coordination seen in other haemophores. This mode of interaction allows HusA to bind to a variety of abiotic and metal-free porphyrins with higher affinities than to haem. We exploit this unusual porphyrin-binding activity of HusA to target a prototypic deuteroporphyrin-metronidazole conjugate with restricted antimicrobial specificity in a Trojan horse strategy that effectively kills intracellular P. gingivalis.

Porphyromonas gingivalis-epithelial cell interactions in periodontitis

Emerging data on the consequences of the interactions between invasive oral bacteria and host cells have provided new insights into the pathogenesis of periodontal disease. Indeed, modulation of the mucosal epithelial barrier by pathogenic bacteria appears to be a critical step in the initiation and progression of periodontal disease. Periodontopathogens such as Porphyromonas gingivalis have developed different strategies to perturb the structural and functional integrity of the gingival epithelium. P. gingivalis adheres to, invades, and replicates within human epithelial cells. Adhesion of P. gingivalis to host cells is multimodal and involves the interaction of bacterial cell-surface adhesins with receptors expressed on the surfaces of epithelial cells. Internalization of P. gingivalis within host cells is rapid and requires both bacterial contact-dependent components and host-induced signaling pathways. P. gingivalis also subverts host responses to bacterial challenges by inactivating immune cells and molecules and by activating host processes leading to tissue destruction. The adaptive ability of these pathogens that allows them to survive within host cells and degrade periodontal tissue constituents may contribute to the initiation and progression of periodontitis. In this paper, we review current knowledge on the molecular cross-talk between P. gingivalis and gingival epithelial cells in the development of periodontitis.

Porphyromonas gingivalis affects host collagen degradation by affecting expression, activation, and inhibition of matrix metalloproteinases

OBJECTIVE

Studies have shown that Porphyromonas gingivalis and host matrix metalloproteinases (MMPs) play important roles in the tissue destruction associated with periodontal disease. It is still unclear which MMPs or their inhibitors are regulated by P. gingivalis at the transcriptional and/or at the protein levels. Therefore, this study was conducted to determine what effects P. gingivalis supernatant has on the collagen degrading ability of human gingival fibroblasts (HGFs) and how it regulates the activation, mRNA expression, and inhibition of MMPs.

METHODS

Culture supernatant from P. gingivalis ATCC 33277 was added to HGFs cultured in six-well plates coated with Type I collagen. At certain time intervals, the cell conditioned media was collected for zymography and/or western blot analyses to determine the MMP and tissue inhibitor of MMPs (TIMP) protein levels. The cells were then removed and the collagen cleavage visualized by Coomassie blue staining. The mRNA expression of multiple MMPs and TIMPs by the treated and untreated HGFs was determined by reverse transcription-polymerase chain reaction.

RESULTS

The collagen in the six-well plates was degraded more rapidly by the HGFs treated with 10% v/v P. gingivalis supernatant. More active MMP-1, MMP-2, MMP-3, and MMP-14 were detected in the conditioned media from the HGFs treated with the P. gingivalis supernatant. TIMP-1, but not TIMP-2, was decreased in the presence of the P. gingivalis supernatant. MMP-1 mRNA expression by the treated HGFs increased more than two-fold over the untreated HGFs. MMP-3 mRNA was unchanged, MMP-2 mRNA had a slight increase, MMP-14 mRNA decreased, and MMP-15 increased. MMP-12 mRNA was induced in the P. gingivalis treated HGFs. TIMP-1 and TIMP-2 mRNA had a slight increase with P. gingivalis treatment.

CONCLUSION

Porphyromonas gingivalis increased the collagen degrading ability of HGFs, in part, by increasing MMP activation and by lowering the TIMP-1 protein level, as well as by affecting the mRNA expression of multiple MMPs and TIMPs.

Construction of novel human monoclonal antibodies neutralizing Porphyromonas gingivalis hemagglutination activity using transgenic mice expressing human Ig loci

Porphyromonas gingivalis has been implicated as an important pathogen in the development of adult periodontitis, and its colonization of subgingival sites is critical in the pathogenic process. One potential virulence factor, hemagglutinin, may mediate bacteria attachment onto and penetration into host cells, as well as agglutinate and lyses erythrocytes to intake heme, an absolute requirement for growth. Toward the development of passive immunotherapy, the construction of a human type monoclonal antibody, which is capable of inhibiting the hemagglutinating ability, will be significant and important. The human mAbs, both exhibiting a high degree of specificity and affinity against the recombinant 130 kDa hemagglutinin domain protein have been prepared using XenoMouse technology. The constructed Xeno-mAbs, IgG2 subclass, significantly inhibited hemagglutination of P. gingivalis and its vesicles. The newly constructed Xeno-mAbs may prove to be useful for the development of passive immunization against periodontal diseases caused by P. gingivalis infection, pending the results of fertility study in disease mode.

Humoral responses to Porphyromonas gingivalis gingipain adhesin domains in subjects with chronic periodontitis

The gingipains have been implicated in the pathogenicity of Porphyromonas gingivalis, a major etiologic agent of chronic periodontitis. Mature gingipains often present as a membrane-bound glycosylated proteinase-adhesin complex comprising multiple adhesin domains (HA1 to -4) and a catalytic domain. Using recombinant adhesin domains, we were able to show that patients with chronic periodontitis produce significantly more immunoglobulin G reactive with gingipain domains than a corresponding group with healthy periodontium. Titers were predominantly directed toward the carbohydrate epitopes shared between the gingipains and the lipopolysaccharide of P. gingivalis with little recognition of the peptide backbone of the catalytic domains. Distribution of titers to peptide epitopes of the adhesin domains was as follows: HA4 approximately HA1 > HA3 >> HA2. No correlation was observed between markers of disease severity and titers to individual adhesins within the disease group. Posttreatment titers showed no change or a decrease in titers for the majority of patients except for titers to the HA2 domain which showed marked increases in a few responding patients. Since the HA2 domain is important in hemoglobin binding and acquisition of essential porphyrin, boosting titers of antibodies to this domain may have the potential to control the growth of this organism.

Adhesins encoded by the gingipain genes of Porphyromonas gingivalis are responsible for co-aggregation with Prevotella intermedia

Co-aggregation among bacterial cells caused by the adherence of one bacterial species to another is a potential colonization mechanism. Several putative aggregation factors for co-aggregation between Porphyromonas (Por.) gingivalis and Prevotella (Pre.) intermedia were partially purified from Por. gingivalis vesicles by gel filtration and affinity chromatography. Antisera against the aggregation factors were made. Analysis using these antisera revealed that 18 and 44 kDa proteins might be responsible for Por. gingivalis vesicle-mediated aggregation of Pre. intermedia. Using antiserum against the 18 kDa protein, the DNA region encoding it was cloned from Por. gingivalis genomic DNA. Sequence analysis revealed that the DNA region was located within the rgpA and kgp genes, encoding Arg-gingipain (Rgp) and Lys-gingipain (Kgp), respectively, and it encoded non-catalytic adhesin domain regions, namely a C-terminal portion of HGP15, the entire HGP17 sequence and an N-terminal portion of HGP27. A portion of the DNA sequence was also found in the haemagglutinin A (hagA) gene. A recombinant glutathione S-transferase (GST)-HGP17 fusion protein reacted to antiserum against the 18 kDa protein and Pre. intermedia cells could adhere to GST-HGP17-conjugated Sepharose 4B beads, indicating that the HGP17 domain protein is responsible for Por. gingivalis vesicle-mediated aggregation of Pre. intermedia.

Porphyrin-mediated cell surface heme capture from hemoglobin by Porphyromonas gingivalis

The porphyrin requirements for growth recovery of Porphyromonas gingivalis in heme-depleted cultures are investigated. In addition to physiologically relevant sources of heme, growth recovery is stimulated by a number of noniron porphyrins. These data demonstrate that, as for Haemophilus influenzae, reliance on captured iron and on exogenous porphyrin is manifest as an absolute growth requirement for heme. A number of outer membrane proteins including some gingipains contain the hemoglobin receptor (HA2) domain. In cell surface extracts, polypeptides derived from HA2-containing proteins predominated in hemoglobin binding. The in vitro porphyrin-binding properties of a recombinant HA2 domain were investigated and found to be iron independent. Porphyrins that differ from protoporphyrin IX in only the vinyl aspect of the tetrapyrrole ring show comparable effects in competing with hemoglobin for HA2 and facilitate growth recovery. For some porphyrins which differ from protoporphyrin IX at both propionic acid side chains, the modification is detrimental in both these assays. Correlations of porphyrin competition and growth recovery imply that the HA2 domain acts as a high-affinity hemophore at the cell surface to capture porphyrin from hemoglobin. While some proteins involved with heme capture bind directly to the iron center, the HA2 domain of P. gingivalis recognizes heme by a mechanism that is solely porphyrin mediated.

Human monoclonal antibody inhibits Porphyromonas gingivalis hemagglutinin activity

BACKGROUND

Porphyromonas gingivalis has been implicated as an important pathogen in the development of chronic periodontitis, and its colonization of subgingival sites is critical in the pathogenic process. One potential virulence factor, hemagglutinin, may mediate bacteria attachment onto and penetration into host cells, as well as agglutinate and lyse erythrocytes to intake heme, an absolute requirement for growth. We previously cloned the gene encoding the 130 kDa hemagglutinin domain (130k HMGD) and identified its functional domain. The construction of a human monoclonal antibody that is capable of inhibiting the hemagglutinating ability is significant and important toward the development of passive immunotherapy.

METHODS

Human lymphocytes isolated from a donor, who had high antibody titer against the recombinant 130k HMGD (r130k HMGD), were immortalized by Epstein-Barr virus, and specific antibody-producing B cells were established by panning using the r130k HMGD.

RESULTS

The constructed HuMAb-HMGD1, IgG subclass, recognized the r130k HMGD as well as the 43 and 49 kDa major bands in P. gingivalis cells and vesicles. The HuMAb-HMGD1 significantly inhibited hemagglutinating activity of P. gingivalis vesicles in a dose-dependent manner. Furthermore, the HuMAb-HMGD1 recognized the synthetic peptide, EGSNEFAPVQNLTGSSVG, which contains the functional domain of 130k HMGD.

CONCLUSION

The newly constructed HuMAb-HMGD1 may prove to be useful for the development of passive immunization against periodontal diseases caused by P. gingivalis infection, pending the results of fertility study in disease mode.

Feasibility of an HA2 domain-based periodontitis vaccine

In a rat periodontitis model, preinoculation with the Porphyromonas gingivalis HA2 binding domain for hemoglobin provided protection from disease. Protection was associated with induced anti-HA2 immunoglobulin G (IgG) humoral antibodies. The IgG subclass ratios suggested that relatively lower Th2/Th1-driven responses were directly associated with protection when rHA2 was administered in saline.

Modulation of an interleukin-12 and gamma interferon synergistic feedback regulatory cycle of T-cell and monocyte cocultures by Porphyromonas gingivalis lipopolysaccharide in the absence or presence of cysteine proteinases

Interleukin 12 (IL-12) is an efficient inducer and enhancer of gamma interferon (IFN-gamma) production by both resting and activated T cells. There is evidence that human monocytes exposed to IFN-gamma have enhanced ability to produce IL-12 when stimulated with lipopolysaccharide (LPS). In this study, it was demonstrated that LPS from the oral periodontal pathogen Porphyromonas gingivalis stimulated monocytes primed with IFN-gamma to release IL-12, thereby enhancing IFN-gamma accumulation in T-cell populations. P. gingivalis LPS was shown to enhance IL-12 induction of IFN-gamma in T cells in a manner independent from TNF-alpha contribution. The levels of T-cell IL-12 receptors were not affected by P. gingivalis LPS and played only a minor role in the magnitude of the IFN-gamma response. These data suggest that LPS from P. gingivalis establishes an activation loop with IL-12 and IFN-gamma with potential to augment the production of inflammatory cytokines in relation to the immunopathology of periodontitis. We previously reported that the major cysteine proteinases (gingipains) copurifying with LPS in this organism were responsible for reduced IFN-gamma accumulation in the presence of IL-12. However, the addition of the gingipains in the presence of LPS resulted in partial restoration of the IFN-gamma levels. In the destructive periodontitis lesion, release of gingipains from the outer membrane (OM) of P. gingivalis could lead to the downregulation of Th1 responses, while gingipain associated with LPS in the OM or in OM vesicles released from the organism could have net stimulatory effects.

Passive immunization against dental caries and periodontal disease: development of recombinant and human monoclonal antibodies

Indigenous micro-organisms in the oral cavity can cause two major diseases, dental caries and periodontal diseases. There is neither agreement nor consensus as to the actual mechanisms of pathogenesis of the specific virulence factors of these micro-organisms. The complexity of the bacterial community in dental plaque has made it difficult for the single bacterial agent of dental caries to be determined. However, there is considerable evidence that Streptococcus mutans is implicated as the primary causative organism of dental caries, and the cell-surface protein antigen (SA I/II) as well as glucosyltransferases (GTFs) produced by S. mutans appear to be major colonization factors. Various forms of periodontal diseases are closely associated with specific subgingival bacteria. Porphyromonas gingivalis has been implicated as an important etiological agent of adult periodontitis. Adherence of bacteria to host tissues is a prerequisite for colonization and one of the important steps in the disease process. Bacterial coaggregation factors and hemagglutinins likely play major roles in colonization in the subgingival area. Emerging evidence suggests that inhibition of these virulence factors may protect the host against caries and periodontal disease. Active and passive immunization approaches have been developed for immunotherapy of these diseases. Recent advances in mucosal immunology and the introduction of novel strategies for inducing mucosal immune responses now raise the possibility that effective and safe vaccines can be constructed. In this regard, some successful results have been reported in animal experimental models. Nevertheless, since the public at large might be skeptical about the seriousness of oral diseases, immunotherapy must be carried out with absolute safety. For this goal to be achieved, the development of safe antibodies for passive immunization is significant and important. In this review, salient advances in passive immunization against caries and periodontal diseases are summarized, and the biotechnological approaches for developing recombinant and human-type antibodies are introduced. Furthermore, our own attempts to construct single-chain variable fragments (ScFv) and human-type antibodies capable of neutralizing virulence factors are discussed.

Human lactoferrin binds and removes the hemoglobin receptor protein of the periodontopathogen Porphyromonas gingivalis

Porphyromonas gingivalis possesses a hemoglobin receptor (HbR) protein on the cell surface as one of the major components of the hemoglobin utilization system in this periodontopathogenic bacterium. HbR is intragenically encoded by the genes of an arginine-specific cysteine proteinase (rgpA), lysine-specific cysteine proteinase (kgp), and a hemagglutinin (hagA). Here, we have demonstrated that human lactoferrin as well as hemoglobin have the abilities to bind purified HbR and the cell surface of P. gingivalis through HbR. The interaction of lactoferrin with HbR led to the release of HbR from the cell surface of P. gingivalis. This lactoferrin-mediated HbR release was inhibited by the cysteine proteinase inhibitors effective to the cysteine proteinases of P. gingivalis. P. gingivalis could not utilize lactoferrin for its growth as an iron source and, in contrast, lactoferrin inhibited the growth of the bacterium in a rich medium containing hemoglobin as the sole iron source. Lactoferricin B, a 25-amino acid-long peptide located at the N-lobe of bovine lactoferrin, caused the same effects on P. gingivalis cells as human lactoferrin, indicating that the effects of lactoferrin might be attributable to the lactoferricin region. These results suggest that lactoferrin has a bacteriostatic action on P. gingivalis by binding HbR, removing it from the cell surface, and consequently disrupting the iron uptake system from hemoglobin.

Porphyrin-mediated binding to hemoglobin by the HA2 domain of cysteine proteinases (gingipains) and hemagglutinins from the periodontal pathogen Porphyromonas gingivalis

Heme binding and uptake are considered fundamental to the growth and virulence of the gram-negative periodontal pathogen Porphyromonas gingivalis. We therefore examined the potential role of the dominant P. gingivalis cysteine proteinases (gingipains) in the acquisition of heme from the environment. A recombinant hemoglobin-binding domain that is conserved between two predominant gingipains (domain HA2) demonstrated tight binding to hemin (Kd = 16 nM), and binding was inhibited by iron-free protoporphyrin IX (Ki = 2.5 microM). Hemoglobin binding to the gingipains and the recombinant HA2 (rHA2) domain (Kd = 2.1 nM) was also inhibited by protoporphyrin IX (Ki = 10 microM), demonstrating an essential interaction between the HA2 domain and the heme moiety in hemoglobin binding. Binding of rHA2 with either hemin, protoporphyrin IX, or hematoporphyrin was abolished by establishing covalent linkage of the protoporphyrin propionic acid side chains to fixed amines, demonstrating specific and directed binding of rHA2 to these protoporphyrins. A monoclonal antibody which recognizes a peptide epitope within the HA2 domain was employed to demonstrate that HA2-associated hemoglobin-binding activity was expressed and released by P. gingivalis cells in a batch culture, in parallel with proteinase activity. Cysteine proteinases from P. gingivalis appear to be multidomain proteins with functions for hemagglutination, erythrocyte lysis, proteolysis, and heme binding, as demonstrated here. Detailed understanding of the biochemical pathways for heme acquisition in P. gingivalis may allow precise targeting of this critical metabolic aspect for periodontal disease prevention.

Antigenic variation in Porphyromonas gingivalis ribotypes recognized by serum immunoglobulin G of adult periodontitis patients

We obtained clinical isolates of Porphyromonas gingivalis of known ribotype from patients diagnosed with adult periodontitis and used Western blot methodology to evaluate profiles of antigens recognized by IgG in heterologous and homologous patient sera. Our aims were to identify isolates belonging to different serogroups, to learn if serogroup membership is related to ribotype to assess variation in IgG responses of patients to antigens is homologous and heterologous ribotypes, and to determine the frequency of shared and variable antigens in different biochemical classes recognized across different serogroups and ribotypes. Blots of separation patterns of 28 isolates were developed in sera from patients and bound IgG was quantified by digital image densitometry. The membership of isolates in different serogroups was determined by correlation and hierarchical cluster analysis of isolate whole-cell IgG binding profiles. Two major isolate clusters, each with two subclusters, were found. Isolates within the same ribotype clustered together in some cases but not others. Homologous isolates ranked high in IgG binding levels relative to those from different patients irrespective of ribotype. Patient subgroups with IgG responses dominant for different ribotypes and serogroups were revealed by correlation analysis. The IgG binding profiles observed for individual protein and proteinase-resistant antigens across both homologous and heterologous isolates were very dissimilar. Furthermore, the frequency of antigens both shared across all ribotypes and recognized by IgG in patient sera was unexpectedly low. Only two protein antigens (Mr 44 kDa and 27 kDa) were strongly recognized across all ribotypes by different sera. We conclude that the IgG response of patients infected with a particular P. gingivalis serotype or ribotype is directed mainly against antigens that are not shared by other potentially infective clonal types.

Life below the gum line: pathogenic mechanisms of Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative anaerobe, is a major etiological agent in the initiation and progression of severe forms of periodontal disease. An opportunistic pathogen, P. gingivalis can also exist in commensal harmony with the host, with disease episodes ensuing from a shift in the ecological balance within the complex periodontal microenvironment. Colonization of the subgingival region is facilitated by the ability to adhere to available substrates such as adsorbed salivary molecules, matrix proteins, epithelial cells, and bacteria that are already established as a biofilm on tooth and epithelial surfaces. Binding to all of these substrates may be mediated by various regions of P. gingivalis fimbrillin, the structural subunit of the major fimbriae. P. gingivalis is an asaccharolytic organism, with a requirement for hemin (as a source of iron) and peptides for growth. At least three hemagglutinins and five proteinases are produced to satisfy these requirements. The hemagglutinin and proteinase genes contain extensive regions of highly conserved sequences, with posttranslational processing of proteinase gene products contributing to the formation of multimeric surface protein-adhesin complexes. Many of the virulence properties of P. gingivalis appear to be consequent to its adaptations to obtain hemin and peptides. Thus, hemagglutinins participate in adherence interactions with host cells, while proteinases contribute to inactivation of the effector molecules of the immune response and to tissue destruction. In addition to direct assault on the periodontal tissues, P. gingivalis can modulate eucaryotic cell signal transduction pathways, directing its uptake by gingival epithelial cells. Within this privileged site, P. gingivalis can replicate and impinge upon components of the innate host defense. Although a variety of surface molecules stimulate production of cytokines and other participants in the immune response, P. gingivalis may also undertake a stealth role whereby pivotal immune mediators are selectively inactivated. In keeping with its strict metabolic requirements, regulation of gene expression in P. gingivalis can be controlled at the transcriptional level. Finally, although periodontal disease is localized to the tissues surrounding the tooth, evidence is accumulating that infection with P. gingivalis may predispose to more serious systemic conditions such as cardiovascular disease and to delivery of preterm infants.

Induction of matrix metalloproteinases and a collagen-degrading phenotype in fibroblasts and epithelial cells by secreted Porphyromonas gingivalis proteinase

Periodontitis is characterized by advancement of a narrow band of epithelium (1-10 cells wide) through the collagenous periodontal ligament in response to bacterial accumulation and infection. A modulating role by epithelial cells in the progression of periodontitis was hypothesized due to the close proximity of the advancing epithelium to both the etiological bacteria and to the collagen fibers of the ligament. We demonstrate that rat mucosal epithelial cells and human fibroblasts are similarly stimulated to degrade a collagen type I cellular substrate by thiol-dependent activity released by the major periodontal pathogen Porphyromonas gingivalis. A purified, extracellular bacterial thiol-proteinase from P. gingivalis ATCC 33277 stimulated mucosal epithelial cells to upregulate expression of collagenase and stromelysin, and to degrade a collagen type I fibril matrix. Stimulation of the epithelial cells with this purified proteinase was associated with morphological changes in the cells and with accumulation of secreted latent procollagenase throughout the culture medium. Release of active collagenase was minimal and collagen degradation by the epithelial cells was discreet and localized subcellularly suggesting the possibility that activation of secreted procollagenase was cell-associated. We conclude that a collagen-degrading phenotype can be stimulated in relatively quiescent mucosal epithelial cells and fibroblasts by the presence of bacterial proteinase. These experiments suggest roles for the P. gingivalis thiol-proteinase and the epithelial cell in the pathogenesis of periodontal disease and demonstrate the potential for dysregulation of extracellular matrix remodeling events during healing of other bacterially infected wounds.

Construction of a functional single-chain variable fragment antibody against hemagglutinin from Porphyromonas gingivalis

Hemagglutinin is a major glycoprotein of Porphyromonas gingivalis vesicles and likely confers the ability to adsorb and penetrate into host tissue cells. To protect this bacterial invasion, murine monoclonal antibody (MAb) Pg-vc, which inhibited the hemagglutinating activity, was prepared by using P. gingivalis vesicles as an antigen. Western blot analysis revealed that when both MAb Pg-vc and anti-HA-Ag2 antibody raised against the P. gingivalis hemagglutinin adhesin (M. Deslauriers and C. Mouton, Infect. Immun. 60:2791-2799, 1992) were allowed to react with protein blots from P. gingivalis vesicles, a superimposable profile was observed. To obtain a recombinant antibody, cDNAs coding for the variable domains of the L and H chains of MAb Pg-vc were cloned by PCR, and a plasmid specifying a single-chain variable fragment (ScFv) was constructed. Following transformation of Escherichia coli cells, a recombinant ScFv protein was successfully expressed. The immunological properties of this protein were identical to those of the parental murine MAb, specifically recognizing the two proteins (43 and 49 kDa) originating from P. gingivalis vesicles. In addition, the ScFv antibody inhibited the P. gingivalis vesicle-associated hemagglutinating activity. The amino acid sequences deduced from nucleotide sequencing experiments confirmed that variable heavy-chain and variable light-chain regions belonged to VH1 and Vkappa12/13 families, respectively. Since the expression system used in this study can readily provide large quantities of single-chain recombinant antibody, it may be a useful in developing a therapeutic agent for passive immunization in humans.

Haemoglobin receptor protein is intragenically encoded by the cysteine proteinase-encoding genes and the haemagglutinin-encoding gene of Porphyromonas gingivalis

The obligately anaerobic bacterium Porphyromonas gingivalis produces characteristic black-pigmented colonies on blood agar. It is thought that the black pigmentation is caused by haem accumulation and is related to virulence of the microorganism. P. gingivalis cells expressed a prominent 19 kDa protein when grown on blood agar plates. Analysis of its N-terminal amino acid sequence indicated that the 19 kDa protein was encoded by an internal region (HGP15 domain) of an arginine-specific cysteine proteinase (Arg-gingipain, RGP)-encoding gene (rgp1) and was also present in genes for lysine-specific cysteine proteinases (prtP and kgp) and a haemagglutinin (hagA) of P. gingivalis. The HGP15 domain protein was purified from an HGP15-overproducing Escherichia coli and was found to have the ability to bind to haemoglobin in a pH-dependent manner. The anti-HGP15 antiserum reacted with the 19 kDa haemoglobin-binding protein in the envelope of P. gingivalis. P. gingivalis wild-type strain showed pH-dependent haemoglobin adsorption, whereas its non-pigmented mutants that produced no HGP15-related proteins showed deficiency in haemoglobin adsorption. These results strongly indicate a close relationship among HGP15 production, haemoglobin adsorption and haem accumulation of P. gingivalis.

Activation and novel processing of matrix metalloproteinases by a thiol-proteinase from the oral anaerobe Porphyromonas gingivalis

A critical outcome of periodontal disease is degradation of the collagenous periodontal ligament that connects teeth to bone in the dental arch. Periodontal diseases occur in response to bacterial colonization of the teeth, but their molecular pathogenesis is still speculative. One family of enzymes, known as the matrix metalloproteinases (MMPs), has been implicated in the degradation of the periodontal ligament. MMPs, which are also suspected to play a role in many other physiologic and pathologic remodeling processes, can be secreted by epithelial cells surrounding the teeth and are found in relative abundance in tissues and fluids near periodontally diseased sites. Since most MMPs are secreted as inactive zymogens which may be activated by limited proteolysis, it has been suggested that proteinases expressed by the infecting periodontal pathogens might activate latent host MMPs to initiate or accelerate degradation of the collegenous periodontal ligament. The aim of this work was to examine interactions between purified host MMPs and bacterial proteinase. In this article, we demonstrate that a proteinase isolated from the periodontopathogen Porphyromonas gingivalis can activate MMP-1, MMP-3, and MMP-9 and can catalyze the superactivation of MMP-1 by MMP-3. Activation of these MMPs is demonstrated to result from initial hydrolysis within their propeptide. Also, for MMP-1 and MMP-9, the P. gingivalis proteinase cleaves the MMP propeptide following a lysine residue at a previously unreported site which, for both MMPs, is one residue NH2-terminal to the known autocatalytic cleavage site. These data describe a mode of virulence for the periodontopathogen Porphyromonas gingivalis that involves activation of host-degradative enzymes.