Atomic force spectroscopy evidence of non-specific adhesion of Aggregatibacter actinomycetemcomitans.

Aggregatibacter actinomycetemcomitans is a gram-negative periodontopathogen found within the subgingival plaque on the tooth surface. It is associated with localized aggressive periodontitis, a severe form of periodontitis in adolescents, and is the cause various extra-oral infections. The ability of this organism to tenaciously adhere to abiotic surfaces has been attributed to bundle-forming type IVb-like fimbriae whose major component is the fimbrial lower molecular weight protein (Flp). In this study the adhesion of purified Flp fimbriae isolated from A. actinomycetemcomitans to materials with different surface chemistries was measured using atomic force microscopy (AFM). The adhesion of Flp fimbriae to uncoated and saliva-coated tooth, hydroxylapatite, and glass surfaces was compared. Force data were used to quantify the magnitude of adhesion of the fimbriae and force-distance profiles were used to predict the mechanisms of adhesion. The results of this study confirm that non-specific interactions likely dominate the adhesion of these fimbriae to the surfaces used in this study. However, force data indicate that non-specific electrostatic interactions may be more significant under the conditions used in this study. Salivary coatings did affect both the hydrophobicity and adhesion of these fimbriae to the surfaces used in this study. Additionally, these data demonstrate the affect of salivary proteins on bacterial adhesion in the oral cavity.

Fibrinogen-neutrophil interactions in response to fMLP and Porphyromonas gingivalis fimbrial peptides.

Porphyromonas gingivalis (P.g) is the primary bacterial agent in many forms of chronic periodontitis. Since polymorphonuclear leukocytes (PMNs) are first-line responders to P.g.- induced inflammation, and fibrinogen is important for in vivo PMN in this disease, we have studied the effect of N-formyl-methionyl-leucyl-phenylalanine (fMLP) (an inflammatory stimulus), P.g. fimbriae and fimbrial peptides (based on FimA, the main structural protein of P.g. fimbriae) on PMN-fibrinogen interactions. Freshly isolated human PMNs were allowed to react with FITC-Fibrinogen and various fimbrial peptides (denoted as FimA followed by amino acid number within whole FimA protein), and FITC-Fibrinogen binding was measured using flow cytometry. Freshly isolated neutrophils were also challenged with Fibrinogen and/or fimbrial peptides to measure IL-8 secretion using ELISA. Our studies show that fibrinogen binding to PMNs is enhanced (p < 0.01) in response to fMLP as well as fimbrial peptides (FimA 61-80) containing the motif LTTE (p < 0.01) in a dose dependent manner but not in response to peptides without that motif. We also observed that fMLP and FimA 61-80 have an additive effect on fibrinogen binding to PMNs (p < 0.05), and fMLP and FimA 171-185 significantly inhibit fMLP-induced fibrinogen binding (p < 0.01). To determine of the role of inflammatory cytokines, we examined IL-8 release from PMNs in response to combinations of P. gingivalis fimbriae, fMLP and fibrinogen. In all cases, IL-8 release increased in a dose-dependent manner (p < 0.05). fMLP-fibrinogen effect on IL-8 release from PMNs was synergistic while fimbriae-fibrinogen effect was additive. In summary, PMN priming by fimbrial peptides facilitates fibrinogen-PMN interaction and may increase inflammation.

Porphyromonas gingivalis platelet aggregation activity: outer membrane vesicles are potent activators of murine platelets.

Recent evidence has established an association between chronic periodontitis and cardiovascular disease. Periodontitis is a chronic inflammatory disease caused by a small group of gram-negative bacteria, of which Porphyromonas gingivalis is considered an important causative agent. It has been proposed that dental plaque bacteria and their products can disseminate into the bloodstream from the site of infection and promote thromboembolic events associated with atherosclerosis and myocardial infarction. In this regard, Streptococcus sanguis and P. gingivalis have been shown to induce platelet aggregation in vitro. Here we report that P. gingivalis was able to induce platelet aggregation, and that oral strains of Actinobaillus actinomycetemcomitans, Bacteroides forsythus, Campylobacter rectus, Fusobacterium nucleatum, Prevotella intermedia and Trepenoma denticola failed to aggregate platelets when tested for platelet aggregation activity under similar conditions. Additionally, we show that vesicles (outer membrane evaginations that are shed into the environment by the bacteria) of P. gingivalis are potent inducers of mouse platelet aggregation in vitro. In summary, our data show that i) initial adherence of the bacterium to platelet may be facilitated by P. gingivalis fimbriae and ii) P. gingivalis vesicles possess platelet aggregation-inducing activity.

Role of the amino-terminal region of Porphyromonas gingivalis fimbriae in adherence to epithelial cells.

Porphyromonas gingivalis fimbriae elicit many responses in eukaryotic cells, including mitogenicity, cytokine production, epithelial cell invasion, and cellular immune response. Specific domains of the major fimbrial protein (FimA) have been shown to be important in triggering some of these functions. The goal of the present study was to identify the domain(s) of P. gingivalis FimA responsible for specific interaction with human mucosal epithelial cells. Fimbriated P. gingivalis strains have been shown to bind to buccal epithelial cells, whereas nonfimbriated strains bind at low levels or not at all. This and other studies provide evidence that FimA mediates the adherence of P. gingivalis to oral epithelial cells. To determine the specific region(s) of P. gingivalis FimA involved in epithelial cell binding, specific antipeptide antibodies were used to inhibit the binding of iodinated purified fimbriae as well as the binding of P. gingivalis cells to epithelial cells. Antibodies directed against peptides 49 to 68 (VVMANTAGAMELVGKTLAEVK) and 69 to 90 (ALTTELTAENQEAAGLIMTAEP) were found to highly inhibit both the binding of fimbriae and the binding of P. gingivalis cells to epithelial cells. The antibody against FimA peptides 69 to 90 also reacted with P. gingivalis fimbriae in immunogold labeling and immunoblot analysis, thereby indicating that this peptide domain is exposed on the surface of fimbriae. Our results suggest that the amino-terminal domain corresponding to amino acid residues 49 to 90 of the fimbrillin protein is a major epithelial cell binding domain of P. gingivalis fimbriae.

Expression of saliva-binding epitopes of the Porphyromonas gingivalis FimA protein on the surface of Streptococcus gordonii.

Porphyromonas gingivalis, a gram-negative oral anaerobic bacterium, has been implicated in the onset and development of periodontitis. The P. gingivalis fimbriae which mediate bacterial adherence to host oral sites and induce host inflammatory responses have been suggested as a potential antigen candidate. for vaccine development. This study was undertaken to generate Streptococcus gordonii vectors expressing the major subunit protein (FimA) of P. gingivalis fimbriae for testing as a potential live vaccine against periodontitis. We report here the expression of the C-terminal saliva-binding epitopes of P. gingivalis FimA on the surface of S. gordonii and demonstrate that domains containing free cysteine residues are poorly expressed on the surface of S. gordonii.

Cloning, expression, and sequencing of a cell surface antigen containing a leucine-rich repeat motif from Bacteroides forsythus ATCC 43037.

Bacteroides forsythus is a recently recognized human periodontopathogen associated with advanced, as well as recurrent, periodontitis. However, very little is known about the mechanism of pathogenesis of this organism. The present study was undertaken to identify the surface molecules of this bacterium that may play roles in its adherence to oral tissues or triggering of a host immune response(s). The gene (bspA) encoding a cell surface-associated protein of B. forsythus with an apparent molecular mass of 98 kDa was isolated by immunoscreening of a B. forsythus gene library constructed in a lambda ZAP II vector. The encoded 98-kDa protein (BspA) contains 14 complete repeats of 23 amino acid residues that show partial homology to leucine-rich repeat motifs. A recombinant protein containing the repeat region was expressed in Escherichia coli, purified, and utilized for antibody production, as well as in vitro binding studies. The purified recombinant protein bound strongly to fibronectin and fibrinogen in a dose-dependent manner and further inhibited the binding of B. forsythus cells to these extracellular matrix (ECM) components. In addition, adult patients with B. forsythus-associated periodontitis expressed specific antibodies against the BspA protein. We report here the cloning and expression of an immunogenic cell surface-associated protein (BspA) of B. forsythus and speculate that it mediates the binding of bacteria to ECM components and clotting factors (fibronectin and fibrinogen, respectively), which may be important in the colonization of the oral cavity by this bacterium and is also a target for the host immune response.

Structures involved in the interaction of Porphyromonas gingivalis fimbriae and human lactoferrin.

The ability of laboratory and clinical strains of Porphyromonas gingivalis to bind lactoferrin has been assessed (FEMS Immunology and Medical Microbiology, 1996, 14, 135-143). Relative binding for P. gingivalis to lactoferrin varies among strains from 3.78 to 26.62%. We also observed that fimbriated strains of P. gingivalis bind more strongly to lactoferrin as compared to nonfimbriated strains of P. gingivalis. This observation led us to study fimbrial interaction with human lactoferrin and the fine structure of these interactions. Binding of iodinated purified fimbriae was studied using an overlay assay. Iodinated fimbriae bind specifically and strongly to human lactoferrin. When various sugars were used to inhibit binding, only N-acetylgalactosamine and fucose were inhibitory. To confirm further that oligosaccharide of lactoferrin is involved in the interaction, lactoferrin was chemically deglycosylated, and fimbriae failed to bind deglycosylated lactoferrin. Antifimbriae, as well as four antipeptide antibodies against different regions of the P. gingivalis fimbrillin, were used to inhibit the interaction. Antipeptide E, directed against amino acids 81-98 (AAGLIMTAEPKTIVLKAG-C), was found to be the most effective inhibitor for the lactoferrin-fimbriae interaction. These results suggest that the binding of P. gingivalis cells to lactoferrin is lectin like, directed to a oligosaccharide of lactoferrin. Furthermore, these studies suggest that the region of fimbriae that binds to lactoferrin is the N-terminus of the molecule. It is likely that binding of lactoferrin to P. gingivalis cells results in antimicrobial activity directed against these cells by virtue of its ability to deprive the bacterial cell of needed iron.

Secretion of Porphyromonas gingivalis fimbrillin polypeptides by recombinant Streptococcus gordonii.

The fimbriae of Porphyromonas gingivalis plays an important role in the pathogenesis of periodontal disease. A structural subunit of the P. gingivalis fimbriae, fimbrillin, has been shown to promote adherence of the bacteria to host surfaces and also induce an immune response. Biologically active domains of fimbrillin responsible for adherence or eliciting immune responses have been determined. In a previous study, we engineered the human oral commensal organism Streptococcus gordonii to express such biologically active domains on the surface of the bacteria as a vaccine delivery system. In this study we report an alternative approach of secreting fimbrillin polypeptide domains into the medium by modification of the surface-expression system described earlier. Such recombinant S. gordonii, in addition to being a source for antigen presentation to trigger a protective immune response, may have the added advantage of directly blocking the fimbriae-mediated adherence of P. gingivalis to the oral cavity following implantation. This approach can also be utilized for secreting other biologically important therapeutic molecules on mucosal surfaces for modulating local microenvironments.

Expression and purification of recombinant human N-formyl-L-leucyl-L-phenylalanine (FMLP) receptor: generation of polyclonal antibody against FMLP receptor.

The recombinant formyl peptide receptor has been successfully expressed and purified, utilizing an Escherichia coli expression system. Purification of formyl peptide receptor was performed using gel filtration chromatography and affinity chromatography, and the purified protein migrated at an apparent molecular mass of 36,000 Da. The purified recombinant receptor retained functional activity as determined by a ligand binding assay. The yield of the recombinant purified receptor was approximately 1 mg/2 L of culture, and the binding activity was determined to be approximately 8 nM, which suggests the conclusion that glycosylation does not affect significantly ligand binding of the N-formyl-L-leucyl-L-phenylalanine (FMLP) receptor molecule. The recombinant receptor protein yield was found to be significantly higher than that obtained from neutrophils. The purified recombinant receptor was then utilized to generate antibody against the same. The reaction of the antibody against recombinant formylpeptide receptor and against native formylpeptide receptor on neutrophils was confirmed by western blot analysis and flow cytometric analysis, respectively. The antibody was also used successfully to detect recombinant formylpeptide receptor expression on transfected 293 cells. These results describe for the first time the expression, purification, and characterization of recombinant FMLP receptor with ligand binding activity and the generation of polyclonal antibody against the same. This work also provides a foundation for future biophysical studies of the FMLP receptor molecule, which have not been possible until now.

Isolation and characterization of fimbriae from a sparsely fimbriated strain of Porphyromonas gingivalis.

Porphyromonas gingivalis W50 (ATCC 53978) possesses the gene for fimbriae; however, the surface-expressed fimbriae are sparse and have not been previously isolated and characterized. We purified fimbriae from strain W50 to homogeneity by ammonium sulfate precipitation and reverse-phase high-performance liquid chromatography [H. T. Sojar, N. Hamada, and R. J. Genco, Protein Expr. Purif. 9(1):49-52, 1997]. Negative staining of purified fimbriae viewed by electron microscopy revealed that the fimbriae were identical in diameter to fimbriae of other P. gingivalis strains, such as 2561, but were shorter in length. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, the apparent molecular weight of isolated fimbrillin from strain W50 was found to be identical to that of the fimbrillin molecule of strain 2561. Unlike 2561 fimbriae, W50 fimbriae, under reducing condition, exhibited a monomeric structure on SDS-PAGE at room temperature. However, under nonreduced conditions, even at 100 degrees C, no monomer was observed. In immunoblot analysis as well as immunogold labeling of isolated fimbriae, polyclonal antibodies against 2561 fimbriae, as well as antibodies against peptide I (V-V-M-A-N-T-G-A-M-E-V-G-K-T-L-A-E-V-K-Cys) and peptide J (A-L-T-T-E-L-T-A-E-N-Q-E-A-A-G-L-I-M-T-A-E-P-Cys), reacted. However, antifimbrial antibodies against strain 2561 reacted very weakly compared to anti-peptide I and anti-peptide J. Negative staining of whole W50 cells, as well as immunogold electron microscopy with anti-peptide I and anti-peptide J, showed fimbriae shorter in length and very few in number compared to those of strain 2561. Purified fimbriae showed no hemagglutinating activity. Amino acid composition was very similar to that of previously reported fimbriae of the 2561 strain.

Interleukin-1 gene expression in macrophages induced by surface protein components of Porphyromonas gingivalis: role of tyrosine kinases in signal transduction.

We examined interleukin-beta (IL-1 beta) mRNA expression and protein tyrosine kinase activities induced by surface protein components of Porphyromonas gingivalis to gain insights into signaling pathways leading to macrophage responses. Reverse transcriptase-polymerase chain reaction analyses showed that native fimbriae, full-length recombinant fimbrillin, and a lectin-like 12-kDa antigen of P. gingivalis induced rapid expression of mRNA encoding IL-1 beta in BALB/c and lympopolysaccharide-hyporesponsive C3H/HeJ peritoneal macrophages. The antigens also specifically activated tyrosine kinase(s) in macrophages. The ability of the surface protein components to induce the cytokine mRNA accumulation was markedly abrogated by tyrosine kinase inhibitors. The findings reported here suggest that IL-1 beta expression in macrophages is a functional consequence of tyrosine kinase activation by the P. gingivalis surface protein components.

A role for fimbriae in Porphyromonas gingivalis invasion of oral epithelial cells.

Isogenic mutants of Porphyromonas gingivalis which differ in the expression of fimbriae were used to examine the contribution of fimbriae in invasion of a human oral epithelial cell line (KB). At a multiplicity of infection of 100, the wild-type P. gingivalis strains 33277, 381, and A7436 exhibited adherence efficiencies of 5.5, 0.11, and 5.0%, respectively, and invasion efficiencies of 0.15, 0.03, and 0.10%, respectively. However, adherence to and invasion of KB cells was not detected with the P. gingivalis fimA mutants, DPG3 and MPG1. Adherence of P. gingivalis wild-type strains to KB cells was completely inhibited by the addition of hyperimmune sera raised to the major fimbriae. Examination by electron microscopy of invasion of epithelial cells by the P. gingivalis wild-type strain 381 revealed microvillus-like extensions around adherent bacteria; this was not observed with P. gingivalis fim mutants. Taken together, these results indicate that the P. gingivalis major fimbriae are required for adherence to and invasion of oral epithelial cells.

Prophyromonas gingivalis fimbriae mediate coaggregation with Streptococcus oralis through specific domains.

Fimbriae are major adhesive components on the cell surface of Prophyromonas gingivalis. In this study, we evaluated the role of fimbriae in coaggregation with Streptococcus oralis. Fimbriae purified from P. gingivalis competitively inhibited the coaggregation by 100% at a concentration of 50 micrograms/mL. On the other hand, the same amount of lipopolysaccharide isolated from P. gingivalis was inhibited by only 25% of the level of the fimbriae. A fimA-inactivated mutant of P. gingivalis failed to show distinct coaggregation activity. Fimbriae added to a solution of various strains of streptococci caused their self-aggregation at a concentration of 10 to 30 micrograms/mL. The self-aggregation induced by fimbriae was inhibited by lambda-arginine (20 to 40 mM/L). Iodinated fimbriae reacted with S. oralis cells immobilized on the nitrocellulose membrane, and 100 degrees C heating of the cells diminished the binding abilities. Recombinant fimbrillin (r-Fim, corresponding to whole residues 1 to 337 of native fimbrillin) of P. gingivalis also showed 100% inhibition of the coaggregation. The r-Fim variant (residues 1 to 286) lacking the C-terminal 51 residues was as inhibitory as r-Fim. However, the variant (residues 1 to 265) without the C-terminal 72 residues lost 77% of the inhibitory activity. These findings suggested that residues 266 to 286 contain a domain involved in the coaggregation of P. gingivalis with S. oralis. Inhibition by three polypeptides corresponding to residues 266 to 286, 266 to 337, and 287 to 337 was studied. Peptides 266 to 286 and 266 to 337 inhibited by 96 and 100%, respectively, at a concentration of 1.5 nmol/mL. Peptide 287 to 337 also showed a significant inhibitory effect but to a slightly lesser extent than that of peptide 266 to 286. P. gingivalis fimbriae appear to be involved in coaggregation with streptococci, probably through an adhesive protein molecule(s) of the latter, and the fimbriae possess several domains in the C-terminal residues 266 to 337 for interaction with S. oralis.

Role of the carboxyl-terminal region of Porphyromonas gingivalis fimbrillin in binding to salivary proteins.

Porphyromonas gingivalis fimbriae are considered to play an important role in the adherence and colonization of the bacteria in the oral cavity. In this study, we generated and purified three carboxyl-terminal variants of recombinant fimbrillin (r-FimA 224-337, r-FimA 266-337, and r-FimA 287-337, corresponding to amino acid residues 224 to 337, 266 to 337, and 287 to 337, respectively, of the 43-kDa fimbrillin of P. gingivalis 2561). They were used as inhibitors of P. gingivalis cell binding to human salivary protein-coated hydroxyapatite (HAP) beads. All of the carboxyl-terminal region polypeptides inhibited binding in a dose-dependent manner; however, the inhibitory effect of r-FimA 287-337 was less than that of the other two polypeptides when HAP beads were coated with whole saliva or purified salivary proline-rich protein 1 (PRP1). Assays of binding of a synthetic peptide corresponding to amino acid residues 266 to 286 of P. gingivalis 2561 fimbrillin to salivary proteins showed that this peptide bound strongly to whole saliva or PRP1 but only weakly to statherin. These results suggest that the carboxyl-terminal region corresponding to amino acid residues 266 to 337 of P. gingivalis fimbrillin plays an important role in binding to salivary proteins and that the domain corresponding to amino acids 266 to 286 is likely a major binding site for PRP1s and the domain corresponding to amino acids 287 to 337 is likely a major binding site for statherin.

High-performance liquid chromatographic separation of Porphyromonas gingivalis fimbriae.

Fimbriae are responsible for the adherence of many bacterial species to the surfaces they eventually colonize. Porphyromonas gingivalis is an important pathogenic agent involved in periodontal disease. Fimbriae of P. gingivalis have been thought to mediate binding of the bacterium to oral surfaces. In order to study the role of fimbriae in microbial adhesion, it is important to purify fimbriae to homogeneity. A simple and rapid reverse-phase high-performance liquid chromatography (HPLC) method is developed to purify P. gingivalis fimbriae. The crude fimbriae were precipitated from sonic extract of P. gingivalis cells with the 40% ammonium sulfate precipitation. The dialyzed crude fimbriae preparation was subjected to reverse-phase HPLC separation. The purity and size of purified fimbrial proteins were confirmed by SDS-polyacrylamide gel electrophoresis(SDS-PAGE) followed by Western immunoblot using polyclonal antibodies against fimbriae. The purified major fimbrial protein from strain 33277 of P. gingivalis had apparent molecular mass of 41 kDa. The method is useful for analytical as well as preparative purification with 25% yields from the ammonium sulfate-precipitated crude fimbriae preparation, and represents increased speed and efficiency over earlier published methods.

Expression of functional Porphyromonas gingivalis fimbrillin polypeptide domains on the surface of Streptococcus gordonii.

Genetically engineering bacteria to express surface proteins which can antagonize the colonization of other microorganisms is a promising strategy for altering bacterial environments. The fimbriae of Porphyromonas gingivalis play an important role in the pathogenesis of periodontal diseases. A structural subunit of the P. gingivalis fimbriae, fimbrillin, has been shown to be an important virulence factor, which likely promotes adherence of the bacterium to saliva-coated oral surfaces and induces host responses. Immunization of gnotobiotic rats with synthetic peptides based on the predicted amino acid sequence of fimbrillin has also been shown to elicit a specific immune response and protection against P. gingivalis-associated periodontal destruction. In this study we engineered the human oral commensal organism Streptococcus gordonii to surface express subdomains of the fimbrillin polypeptide fused to the anchor region of streptococcal M6 protein. The resulting recombinant S. gordonii strains expressing P. gingivalis fimbrillin bound saliva-coated hydroxyapatite in a concentration-dependent manner and inhibited binding of P. gingivalis to saliva-coated hydroxyapatite. Moreover, the recombinant S. gordonii strains were capable of eliciting a P. gingivalis fimbrillin-specific immune response in rabbits. These results show that functional and immunologically reactive P. gingivalis fimbrillin polypeptides can be expressed on the surface of S. gordonii. The recombinant fimbrillin-expressing S. gordonii strains may provide an effective vaccine or a vehicle for replacement therapy against P. gingivalis. These experiments demonstrated the feasibility of expressing biologically active agents (antigens or adhesin molecules) by genetically engineered streptococci. Such genetically engineered organisms can be utilized to modulate the microenvironment of the oral cavity.

Isolation and characterization of a minor fimbria from Porphyromonas gingivalis.

We have discovered two distinctly different fimbriae expressed by the same Porphyromonas gingivalis strain. The construction of a fimA mutant of P. gingivalis ATCC 33277 has previously been reported by N. Hamada et al. (Infect. Immun. 62:1696-1704, 1994). Expression of fimbriae on the surface of the fimA mutant and the wild-type strain, ATCC 33277, were investigated by electron microscopy. The wild-type strain produced long fimbrial structures extending from the cell surface, whereas those structures were not observed on the fimA mutant. However, short fimbrial structures were seen on the surface of the fimA mutant. The short fimbrial protein was purified from the fimA mutant by selective protein precipitation and chromatography on DEAE Sepharose CL-6B. We have found that the second fimbrial structure of P. gingivalis ATCC 33277 is distinct from the 41-kDa (43-kDa) major fimbrial protein (FimA). We provisionally call this protein minor fimbriae. The molecular mass of the minor fimbriae is 67 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions after boiling at 100 degrees C. The component shows a ladder-like pattern at 80 degrees C under nonreducing conditions, suggesting a tendency to aggregate or polymerize. In immunoblotting analysis, anti-minor fimbria serum reacted with both the 100 degrees C- and the 80 degrees C-treated minor fimbriae. The anti-minor fimbria serum also reacts with the same-molecular-size fimbrial preparation from the wild-type strain. Immunogold electron microscopy showed that the anti-minor fimbria serum bound to the minor fimbria on the cell surface of the wild-type strain. This is the first report on the identification of the minor fimbria produced by P. gingivalis. These results suggest that the minor fimbriae appearing on the fimA mutant strain are produced together with numerous long major fimbriae on the wild-type strain. Moreover, the minor fimbriae are different in size and antigenicity from the earlier-reported FimA, a major 41-kDa fimbrial component of P. gingivalis.

Porphyromonas gingivalis surface components induce interleukin-1 release and tyrosine phosphorylation in macrophages.

The aim of the present study was to characterize the responses of macrophages to surface antigens of Porphyromonas gingivalis. Native fimbriae, full-length recombinant fimbrillin, and a lectin-like 12-kDa antigen all stimulated BALB/c peritoneal macrophages to secrete interleukin (IL)-1 beta. The antigens induced similar patterns of tyrosine phosphorylation; proteins in approximately 35-46 kDa range of undetermined identities were phosphorylated in the macrophages. The abilities of the surface antigens to induce IL-1 beta were markedly attenuated by tyrosine kinase inhibitors. This inhibition correlated with inhibition of the induced phosphorylation of specific macrophage proteins at tyrosine. The data suggest that tyrosine kinase(s) plays an important role in the regulatory intracellular signaling mechanisms by which P. gingivalis surface antigens can mediate certain responses in macrophages.

Structural domains of Porphyromonas gingivalis recombinant fimbrillin that mediate binding to salivary proline-rich protein and statherin.

Fimbriae (the oligomeric form of fimbrillin) are considered important in the adherence and colonization of Porphyromonas gingivalis in the oral cavity. In the present study, we have identified the structural domains of P. gingivalis fimbrillin that mediate the binding to salivary proline-rich protein 1 (PRP1) and statherin. A series of synthetic fimbrillin peptides were used to localize the active fimbrillin domains involved in the binding to PRP1 and statherin. The binding of 125I-labeled 41-r-Fim (whole-length recombinant fimbrillin, amino acid [aa] residues 1 to 337) to PRP1-coated hydroxyapatite beads (HAP) was strongly inhibited by the fimbrillin C-terminal peptides corresponding to aa residues 266 to 286 and 318 to 337 (peptides 266-286, and 318-337, respectively), while the binding to statherin was inhibited by C-terminal peptides 266-286, 293-306 and 307-326. Peptide 126-146 also showed a weak inhibitory effect, about half that of other active peptides, on the binding to both PRP1 and statherin. P. gingivalis whole-cell binding to PRP1- or statherin-coated HAP was inhibited by more than 80% by the same active peptides. To confirm that the C-terminal portion of fimbrillin includes domains responsible for the binding, two C-terminally truncated variants of recombinant fimbrillin were generated and purified. These were designated 34.5-r-Fim, corresponding to aa residues 1 to 286, and 32-r-Fim, corresponding to aa residues 1 to 265. 125I-34.5-r-Fim revealed 35 and 34% loss of binding ability to PRP1 and statherin, respectively. 125I-32-r-Fim had significantly less binding ability to PRP1 and statherin than 125I-34.5-r-Fim, which was reduced 78 and 73%, respectively. Whole-cell binding to PRP1-, statherin-, or whole saliva-coated HAP was inhibited up to 100% by 41-r-Fim, while 32-r-Fim also showed considerable inhibition, possibly due to the region of aa 126 to 146. Collectively, these results suggest that there are separate and multiple binding sites for PRP1 and statherin in the P. gingivalis fimbrillin, and the combination of all of these binding sites may be indispensable in establishing stable bacterial adherence to saliva-coated surfaces in the oral cavity.

Quantitative approach for detection and characterization of formyl peptide receptor in solution using a photoaffinity ligand.

In this paper we describe an assay method for the rapid detection and quantitation of human neutrophil FMLP (N-formyl-methionyl-leucyl-phenylalanine) receptor molecules. Although different assay methods are available to detect the receptor, none are rapid and at the same time allow quantitative detection of the binding affinity of the receptor molecule in solution. In our modified method, following a binding reaction using photoaffinity ligand, the amount of labeled ligand bound to the receptor is separated from the unbound one, thereby determining the binding affinity of the receptor protein. This simple procedure not only makes it possible to detect the recombinant FMLP receptor protein very rapidly, but also provides quantitative assessment of binding. This technique therefore allows a partial characterization (identification, determination of size and assessment of binding affinity) of receptor molecule in solution in less than 24 hours.