Mutagenesis of a novel gene in the prcA-prtP protease locus affects expression of Treponema denticola membrane complexes

Characterization of Treponema denticola Major Surface Protein (Msp) by Deletion Analysis and Advanced Molecular Modeling

Treponema denticola, a keystone pathogen in periodontitis, is a model organism for studying Treponema physiology and host-microbe interactions. Its major surface protein Msp forms an oligomeric outer membrane complex that binds fibronectin, has cytotoxic pore-forming activity, and disrupts several intracellular processes in host cells. T. denticola msp is an ortholog of the Treponema pallidum tprA to -K gene family that includes tprK, whose remarkable in vivo hypervariability is proposed to contribute to T. pallidum immune evasion. We recently identified the primary Msp surface-exposed epitope and proposed a model of the Msp protein as a β-barrel protein similar to Gram-negative bacterial porins. Here, we report fine-scale Msp mutagenesis demonstrating that both the N and C termini as well as the centrally located Msp surface epitope are required for native Msp oligomer expression. Removal of as few as three C-terminal amino acids abrogated Msp detection on the T. denticola cell surface, and deletion of four residues resulted in complete loss of detectable Msp. Substitution of a FLAG tag for either residues 6 to 13 of mature Msp or an 8-residue portion of the central Msp surface epitope resulted in expression of full-length Msp but absence of the oligomer, suggesting roles for both domains in oligomer formation. Consistent with previously reported Msp N-glycosylation, proteinase K treatment of intact cells released a 25 kDa polypeptide containing the Msp surface epitope into culture supernatants. Molecular modeling of Msp using novel metagenome-derived multiple sequence alignment (MSA) algorithms supports the hypothesis that Msp is a large-diameter, trimeric outer membrane porin-like protein whose potential transport substrate remains to be identified. IMPORTANCE The Treponema denticola gene encoding its major surface protein (Msp) is an ortholog of the T. pallidum tprA to -K gene family that includes tprK, whose remarkable in vivo hypervariability is proposed to contribute to T. pallidum immune evasion. Using a combined strategy of fine-scale mutagenesis and advanced predictive molecular modeling, we characterized the Msp protein and present a high-confidence model of its structure as an oligomer embedded in the outer membrane. This work adds to knowledge of Msp-like proteins in oral treponemes and may contribute to understanding the evolutionary and potential functional relationships between T. denticola Msp and the orthologous T. pallidum Tpr proteins.

Crawling motility of Treponema denticola modulated by outer sheath protein

Treponema denticola, a helically shaped motile microorganism, is a major pathogen of chronic periodontitis. Major surface protein (Msp) and dentilisin are virulence factors of T. denticola that are located on the outer sheath. The motility of T. denticola is deeply involved in colonization on and invasion into the host tissue. The outer sheath is located at the interface between the environment and T. denticola, and its components may also contribute to its motility via interaction with the materials outside the cells. The study aimed to clarify whether Msp or dentilisin contributes to the motility of T. denticola on solid surfaces, termed crawling, by investigating their effects using Msp-deficient and dentilisin-deficient T. denticola strains. Motility was analyzed by measuring the colony size in agar plates and velocity was analyzed using dark-field microscopy. The colony area of the mutant strains was smaller than that of the wild-type strain. The crawling velocity of the mutant strains was lower than that of the wild-type strain, with the lowest velocity observed in the dentilisin-deficient strain. Additionally, the ratio of the crawling distance by one revolution to the protoplasmic cylinder pitch (an indicator of the crawling efficiency) in the dentilisin mutant was significantly lower than that in the wild type strain and the Msp mutant. Together, these results indicate that dentilisin facilitates the crawling-dependent surface spreading of T. denticola.

Approaches to Understanding Mechanisms of Dentilisin Protease Complex Expression in Treponema denticola

The oral spirochete Treponema denticola is a keystone periodontal pathogen that, in association with members of a complex polymicrobial oral biofilm, contributes to tissue damage and alveolar bone loss in periodontal disease. Virulence-associated behaviors attributed to T. denticola include disruption of the host cell extracellular matrix, tissue penetration and disruption of host cell membranes accompanied by dysregulation of host immunoregulatory factors. T. denticola dentilisin is associated with several of these behaviors. Dentilisin is an outer membrane-associated complex of acylated subtilisin-family PrtP protease and two other lipoproteins, PrcB and PrcA, that are unique to oral spirochetes. Dentilisin is encoded in a single operon consisting of prcB-prcA-prtP. We employ multiple approaches to study mechanisms of dentilisin assembly and PrtP protease activity. To determine the role of each protein in the protease complex, we have made targeted mutations throughout the protease locus, including polar and nonpolar mutations in each gene (prcB, prcA, prtP) and deletions of specific PrtP domains, including single base mutagenesis of key PrtP residues. These will facilitate distinguishing between host cell responses to dentilisin protease activity and its acyl groups. The boundaries of the divergent promoter region and the relationship between dentilisin and the adjacent iron transport operon are being resolved by incremental deletions in the sequence immediately 5’ to the protease locus. Comparison of the predicted three-dimensional structure of PrtP to that of other subtilisin-like proteases shows a unique PrtP C-terminal domain of approximately 250 residues. A survey of global gene expression in the presence or absence of protease gene expression reveals potential links between dentilisin and iron uptake and homeostasis in T. denticola. Understanding the mechanisms of dentilisin transport, assembly and activity of this unique protease complex may lead to more effective prophylactic or therapeutic treatments for periodontal disease.

Characterization of the Treponema denticola Virulence Factor Dentilisin

Treponema denticola is a potent periodontal pathogen that forms a red complex with Porphyromonas gingivalis and Tannerella forsythia. It has many virulence factors, yet there are only a few reports detailing these factors. Among them, dentilisin is a well-documented surface protease. Dentilisin is reported to be involved in nutrient uptake, bacterial coaggregation, complement activation, evasion of the host immune system, inhibition of the hemostasis system, and cell invasion as a result of its action, in addition to its original proteolysis function. Therefore, characterization of dentilisin, and clarifying the relationship between T. denticola and the onset of periodontal disease will be important to better understanding this disease. In this chapter, we explain the methods for analysis of dentilisin activity and pathogenicity.

Investigation of the potential regulator proteins associated with the expression of major surface protein and dentilisin in Treponema denticola

ObjectiveTreponema denticola is involved in ‘chronic’ periodontitis pathogenesis. The mechanism underlying the regulation of the expression of its virulence factors, such as major surface protein (Msp) and prolyl-phenylalanine specific protease (dentilisin) is yet to be clarified. We determined the gene expression profiles of Msp- and dentilisin-deficient mutants of T. denticola to identify the regulation network of gene expression concomitant with the inactivation of these virulence genes.

Methods Gene expression profiles of T. denticola ATCC 35405 (wild type), dentilisin-deficient mutant K1, and msp-deficient mutant DMSP3 were determined using DNA microarray analysis and quantitative real-time reverse transcription PCR (qRT-PCR). Msp and dentilisin protein levels were determined by immunoblotting and proteolytic activity assays.

Results In addition to several differentially expressed genes, dentilisin expression was reduced in DMSP3; msp expression was significantly reduced in K1 (p < 0.05), both at the gene and protein levels. To identify the regulatory system involved, the expression levels of the potential regulators whose expression showed changes in the mutants were evaluated using qRT-PCR. Transcriptional regulators TDE_0127 and TDE_0814 were upregulated in K1, and the potential repressor, TDE_0344, was elevated in DMSP3.

Conclusions Dentilisin and Msp expression were interrelated, and gene expression regulators, such as TDE_0127, may be involved in their regulation.

Roles of TroA and TroR in Metalloregulated Growth and Gene Expression in Treponema denticola

The availability of divalent metal cations required as cofactors for microbial metabolism is severely limited in the host environment. Bacteria have evolved highly regulated uptake systems to maintain essential metal homeostasis to meet cellular demands while preventing toxicity. The Tro operon (troABCDR), present in all sequenced Treponema spp., is a member of a highly conserved family of ATP-binding cassette transporters involved in metal cation uptake whose expression is controlled by TroR, a DtxR-like cation-responsive regulatory protein. Transcription of troA responds to divalent manganese and iron (T. denticola) or manganese and zinc (T. pallidum), and metal-dependent TroR binding to the troA promoter represses troA transcription. We report here the construction and complementation of defined T. denticola ΔtroR and ΔtroA strains to characterize (i) the role of TroA in metal-dependent T. denticola growth and (ii) the role of TroR in T. denticola gene expression. We show that TroA expression is required for T. denticola growth under iron- and manganese-limited conditions. Furthermore, TroR is required for the transcriptional regulation of troA in response to iron or manganese, and deletion of troR results in significant differential expression of more than 800 T. denticola genes in addition to troA These results suggest that (i) TroA-mediated cation uptake is important in metal homeostasis in vitro and may be important for Treponema survival in the host environment and (ii) the absence of TroR results in significant dysregulation of nearly one-third of the T. denticola genome. These effects may be direct (as with troA) or indirect due to dysregulation of metal homeostasis.IMPORTANCE Treponema denticola is one of numerous host-associated spirochetes, a group including commensals, pathobionts, and at least one frank pathogen. While most T. denticola research concerns its role in periodontitis, its relative tractability for growth and genetic manipulation make it a useful model for studying Treponema physiology, metabolism, and host-microbe interactions. Metal micronutrient acquisition and homeostasis are highly regulated both in microbial cells and by host innate defense mechanisms that severely limit metal cation bioavailability. Here, we characterized the T. denticola troABCDR operon, the role of TroA-mediated iron and manganese uptake in growth, and the effects of TroR on global gene expression. This study contributes to our understanding of the mechanisms involved in cellular metal homeostasis required for survival in the host environment.

Immunotopological Analysis of the Treponema denticola Major Surface Protein (Msp)

Treponema denticola, one of several recognized periodontal pathogens, is a model organism for studying Treponema physiology and host-microbe interactions. Its major surface protein Msp (or MOSP) comprises an oligomeric outer membrane-associated complex that binds fibronectin, has cytotoxic pore-forming activity, and disrupts several intracellular responses. There are two hypotheses regarding native Msp structure and membrane topology. One hypothesis predicts that the entire Msp protein forms a β-barrel structure similar to that of well-studied outer membrane porins of Gram-negative bacteria. The second hypothesis predicts a bipartite Msp with distinct and separate periplasmic N-terminal and porin-like β-barrel C-terminal domains. The bipartite model, based on bioinformatic analysis of the orthologous Treponema pallidum Tpr proteins, is supported largely by studies of recombinant TprC and Msp polypeptides. The present study reports immunological studies in both T. denticola and Escherichia coli backgrounds to identify a prominent Msp surface epitope (residues 229 to 251 in ATCC 35405) in a domain that differs between strains with otherwise highly conserved Msps. These results were then used to evaluate a series of in silico structural models of representative T. denticola Msps. The data presented here are consistent with a model of Msp as a large-diameter β-barrel porin. This work adds to the knowledge regarding the diverse Msp-like proteins in oral treponemes and may contribute to an understanding of the evolutionary and potential functional relationships between Msps of oral Treponema and the orthologous group of Tpr proteins of T. pallidum. IMPORTANCE Treponema denticola is among a small subset of the oral microbiota contributing to severe periodontal disease. Due to its relative genetic tractability, T. denticola is a model organism for studying Treponema physiology and host-microbe interactions. T. denticola Msp is a highly expressed outer membrane-associated oligomeric protein that binds fibronectin, has cytotoxic pore-forming activity, and disrupts intracellular regulatory pathways. It shares homology with the orthologous group of T. pallidum Tpr proteins, one of which is implicated in T. pallidum in vivo antigenic variation. The outer membrane topologies of both Msp and the Tpr family proteins are unresolved, with conflicting reports on protein domain localization and function. In this study, we combined empirical immunological data derived both from diverse T. denticola strains and from recombinant Msp expression in E. coli with in silico predictive structural modeling of T. denticola Msp membrane topology, to move toward resolution of this important issue in Treponema biology.

The Treponema denticola FhbB Protein Is a Dominant Early Antigen That Elicits FhbB Variant-Specific Antibodies That Block Factor H Binding and Cleavage by Dentilisin

The Treponema denticola FhbB protein contributes to immune evasion by binding factor H (FH). Cleavage of FH by the T. denticola protease, dentilisin, may contribute to the local immune dysregulation that is characteristic of periodontal disease (PD). Although three FhbB phyletic types have been defined (FhbB1, FhbB2, and FhbB3), the in vivo expression patterns and antigenic heterogeneity of FhbB have not been assessed. Here, we demonstrate that FhbB is a dominant early antigen that elicits FhbB type-specific antibody (Ab) responses. Using the murine skin abscess model, we demonstrate that the presence or absence of FhbB or dentilisin significantly influences Ab responses to infection and skin abscess formation. Competitive binding analyses revealed that α-FhbB Ab can compete with FH for binding to T. denticola and block dentilisin-mediated FH cleavage. Lastly, we demonstrate that dentilisin cleavage sites reside within critical functional domains of FH, including the complement regulatory domain formed by CCPs 1 to 4. Analysis of the FH cleavage products revealed that they lack cofactor activity. The data presented here provide insight into the in vivo significance of dentilisin, FhbB and its antigenic diversity, and the potential impact of FH cleavage on the regulation of complement activation.

Kanamycin Resistance Cassette for Genetic Manipulation of Treponema denticola

Treponema denticola has been recognized as an important oral pathogen of the "red complex" bacterial consortium that is associated with the pathogenesis of endodontal and periodontal diseases. However, little is known about the virulence of T. denticola due to its recalcitrant genetic system. The difficulty in genetically manipulating oral spirochetes is partially due to the lack of antibiotic resistance cassettes that are useful for gene complementation following allelic replacement mutagenesis. In this study, a kanamycin resistance cassette was identified and developed for the genetic manipulation of T. denticola ATCC 35405. Compared to the widely used ermF-ermAM cassette, the kanamycin cassette used in the transformation experiments gave rise to additional antibiotic-resistant T. denticola colonies. The kanamycin cassette is effective for allelic replacement mutagenesis as demonstrated by inactivation of two open reading frames of T. denticola, TDE1430 and TDE0911. In addition, the cassette is also functional in trans-chromosomal complementation. This was determined by functional rescue of a periplasmic flagellum (PF)-deficient mutant that had the flgE gene coding for PF hook protein inactivated. The integration of the full-length flgE gene into the genome of the flgE mutant rescued all of the defects associated with the flgE mutant that included the lack of PF filament and spirochetal motility. Taken together, we demonstrate that the kanamycin resistance gene is a suitable cassette for the genetic manipulation of T. denticola that will facilitate the characterization of virulence factors attributed to this important oral pathogen.

Characterization of Treponema denticola mutants defective in the major antigenic proteins, Msp and TmpC

Treponema denticola, a gram-negative and anaerobic spirochete, is associated with advancing severity of chronic periodontitis. In this study, we confirmed that two major antigenic proteinswere Msp and TmpC, and examined their physiological and pathological roles using gene-deletion mutants. Msp formed a large complex that localized to the outer membrane, while TmpC existed as a monomer and largely localized to the inner membrane. However, TmpC was also detected in the outer membrane fraction, but its cell-surface exposure was not detected. Msp defects increased cell-surface hydrophobicity and secretion of TNF-α from macrophage-like cells, whereas TmpC defects decreased autoagglutination and chymotrypsin-like protease activities. Both mutants adhered to gingival epithelial cells similarly to the wild-type and showed slightly decreased motility. In addition, in Msp-defective mutants, the TDE1072 protein, which is a major membrane protein, was abolished; therefore, phenotypic changes in the mutant can be, at least in part, attributed to the loss of the TDE1072 protein. Thus, the major antigenic proteins, Msp and TmpC, have significant and diverse impacts on the characteristics of T. denticola, especially cell surface properties.

Treponema denticola upregulates MMP-2 activation in periodontal ligament cells: interplay between epigenetics and periodontal infection

OBJECTIVE

Periodontal pathogens initiate chronic dysregulation of inflammation and tissue homeostasis that characterize periodontal disease. To better understand oral microbe-host tissue interactions, we investigated expression and activation of MMP-2 in periodontal ligament cells following Treponema denticola challenge.

DESIGN

Cultured PDL cells were challenged with T. denticola, and bacterial adherence, internalization and survival were assayed by immunofluorescence microscopy and antibiotic protection assays, respectively. MMP-2 activation was detected by zymography. MMP-2, MT1/MMP and TIMP-2 expression following T. denticola challenge was determined by qRT-PCR. Promoter methylation of MMP-2 and MT1/MMP was screened by methylation-sensitive restriction analysis and by bisulfite DNA sequencing.

RESULTS

T. denticola adhered to and was internalized by PDL cells but did not survive intracellularly beyond 24h. Importantly, while dentilisin activity in PDL culture supernatants gradually decreased following T. denticola challenge, MMP-2 activation persisted for up to 5 days, suggesting involvement of other regulatory mechanisms. Transcription and expression of MT1/MMP and TIMP-2 increased in response to T. denticola challenge. However, consistent with previously reported constitutive pro-MMP-2 expression in PDL cells, the MMP-2 promoter was hypomethylated, independent of T. denticola challenge.

CONCLUSIONS

MMP-2 promoter hypomethylation is consistent with constitutive pro-MMP-2 expression in PDL cells. This, coupled with T. denticola-mediated upregulation of MMP-2-related genes and chronic activation of pro-MMP-2, mimics key in vivo mechanisms of periodontal disease chronicity, in particular MMP-2-dependent matrix degradation and bone resorption. Adherence and/or internalization of T. denticola may contribute to these processes by one or more regulatory mechanisms, including contact-dependent signal transduction or other epigenetic mechanisms.

Analysis of the complement sensitivity of oral treponemes and the potential influence of FH binding, FH cleavage and dentilisin activity on the pathogenesis of periodontal disease

Treponema denticola, a periopathogen, evades complement-mediated killing by binding the negative complement regulatory protein factor H (FH) to its surface via the FhbB protein. Paradoxically, bound FH is cleaved by T. denticola's dentilisin protease, a process hypothesized to trigger localized dysregulation of complement activation in periodontal pockets. The ability of other oral treponemes to evade complement-mediated killing and bind and cleave FH has not been assessed. In this report, we demonstrate that representative isolates of Treponema socranskii, Treponema medium, Treponema pectinovorum and Treponema maltophilum are also serum resistant, whereas Treponema vincentii and Treponema amylovorum are serum sensitive. Although T. denticola's ability to evade complement-mediated killing is strictly dependent on FH binding, other serum-resistant treponemal species lack FhbB and do not bind FH, indicating an FH-independent mechanism of complement evasion. To assess the influence of FhbB sequence variation on FH binding and cleavage by T. denticola, fhbB sequences were determined for 30 isolates. Three distinct phyletic types were identified. All T. denticola strains bound FH and were serum resistant, but differences in binding kinetics, dentilisin activity and FH cleavage ability were observed. Based on these analyses, we hypothesize that the composition of the T. denticola population is a determining factor that influences the progression and severity of periodontal disease.

Sequence divergence in the Treponema denticola FhbB protein and its impact on factor H binding

Treponema denticola is an anaerobic spirochete whose abundance in the subgingival crevice correlates with the development and severity of periodontal disease. The ability of T. denticola to survive and thrive in the hostile environment of the periodontal pocket is due, at least in part, to its ability to bind factor H (FH), a negative regulator of the alternative complement pathway. The FH binding protein of T. denticola has been identified as FhbB and its atomic structure has been determined. The interaction of FH with T. denticola is unique in that FH bound to the cell surface is cleaved by the T. denticola protease, dentilisin. It has been postulated that FH cleavage by T. denticola leads to immune dysregulation in periodontal pockets. In this study, we conduct a comparative assessment of the sequence, properties, structure and ligand binding kinetics of the FhbB proteins of strains 33521 and 35405. The biological outcome of the interaction of these strains with FH could differ significantly as 33521 lacks dentilisin activity. The data presented here offer insight into our understanding of the interactions of T. denticola with the host and its potential to influence disease progression.

A surface-exposed neuraminidase affects complement resistance and virulence of the oral spirochaete Treponema denticola

Neuraminidases (sialidases) catalyse the removal of terminal sialic acid from glycoconjugates. Bacterial pathogens often utilize neuraminidases to scavenge host sialic acid, which can be utilized either as a nutrient or as a decorating molecule to disguise themselves from host immune attacks. Herein, a putative neuraminidase (TDE0471) was identified in Treponema denticola, an oral spirochaete associated with human periodontitis. TDE0471 is a cell surface-exposed exo-neuraminidase that removes sialic acid from human serum proteins; it is required for T.denticola to grow in a medium that mimics gingival crevice fluid, suggesting that the spirochaete may use sialic acid as a nutrient in vivo. TDE0471 protects T.denticola from serum killing by preventing the deposition of membrane attack complexes on the bacterial cell surface. Animal studies revealed that a TDE0471-deficient mutant is less virulent than its parental wild-type strain in BALB/C mice. However, it causes a level of tissue damage similar to the wild type in complement-deficient B6.129S4-C3(tm1) (Crr) /J mice albeit the damage caused by both bacterial strains is more severe in these transgenic mice. Based on these results, we propose that T.denticola has evolved a strategy to scavenge host sialic acid using its neuraminidase, which allows the spirochaete to acquire nutrients and evade complement killing.

Conservation and revised annotation of the Treponema denticola prcB-prcA-prtP locus encoding the dentilisin (CTLP) protease complex

Interstrain differences in antigenic surface proteins may reflect immunological pressure or differences in receptor specificity of the antigen. Treponema denticola exhibits considerable interstrain variability in its major surface protein (Msp), but no studies have addressed this issue in dentilisin (CTLP), a surface protease complex that has a significant role in T. denticola-host interactions in periodontal disease. Furthermore, the genome annotation of the prcB-prcA-prtP operon encoding dentilisin contains apparent errors and lacks a deduced PrtP amino acid sequence. To address these issues we analysed the protease operon from diverse T. denticola strains, as well as clones of the ATCC 35405 Type strain from which the genome sequence and original GenBank prtP sequence were derived. 6xHis-tagging of the PrtP C-terminus in ATCC 35405 demonstrated absence of the 'authentic frameshift' in PrtP reported in the genome databases. We propose that T. denticola genome annotations be updated to reflect this new information. PrcB and the PrtP N-terminal region that includes the catalytic domain were highly conserved in common laboratory strains and clinical isolates of T. denticola. Dentilisin proteolytic activity varied considerably between strains. Antibodies against PrcB, PrcA and PrtP from the type strain recognized these proteins in most T. denticola strains. PrtP varied up to 20% over the C-terminal 270 residues between strains. The PrtP C-terminal eight-residues (DWFYVEYP) was present in all strains, with two strains containing an additional Y-residue preceding the stop codon. Such conserved PrtP domains may be required for interactions with PrcA and PrcB, or for substrate interactions.

Composition and localization of Treponema denticola outer membrane complexes

The Treponema denticola outer membrane lipoprotein-protease complex (dentilisin) contributes to periodontal disease by degrading extracellular matrix components and disrupting intercellular host signaling pathways. We recently demonstrated that prcB, located upstream of and cotranscribed with prcA and prtP, encodes a 22-kDa lipoprotein that interacts with PrtP and is required for its activity. Here we further characterize products of the protease locus and their roles in expression, formation, and localization of outer membrane complexes. PrcB migrates in native gels as part of a >400-kDa complex that includes PrtP and PrcA, as well as the major outer sheath protein Msp. PrcB is detectable as a minor constituent of the purified active protease complex, which was previously reported to consist of only PrtP and auxiliary polypeptides PrcA1 and PrcA2. Though it lacks the canonical ribosome binding site present upstream of both prcA and prtP, PrcB is present at levels similar to those of PrtP in whole-cell extracts. Immunofluorescence microscopy demonstrated cell surface exposure of the mature forms of PrtP, PrcA1, PrcB, and Msp. The 16-kDa N-terminal acylated fragment of PrtP (predicted to be released during activation of PrtP) was present in cell extracts but was detected neither in the purified active protease complex nor on the cell surface. PrcA2, detectable on the surface of Msp-deficient cells but not that of wild-type cells, coimmunoprecipitated with Msp. Our results indicate that PrcB is a component of the outer membrane lipoprotein protease complex and that Msp and PrcA2 interaction may mediate formation of a very-high-molecular-weight outer membrane complex.

Disruption of a type II endonuclease (TDE0911) enables Treponema denticola ATCC 35405 to accept an unmethylated shuttle vector

The oral spirochete Treponema denticola is associated with human periodontal disease. T. denticola ATCC 35405 and ATCC 33520 are two routinely used laboratory strains. Compared to T. denticola ATCC 33520, ATCC 35405 is more virulent but less accessible to genetic manipulations. For instance, the shuttle vectors of ATCC 33520 cannot be transformed into strain ATCC 35405. The lack of a shuttle vector has been a barrier to study the biology and virulence of T. denticola ATCC 35405. In this report, we hypothesize that T. denticola ATCC 35405 may have a unique DNA restriction-modification (R-M) system that prevents it from accepting the shuttle vectors of ATCC 33520 (e.g., the shuttle plasmid pBFC). To test this hypothesis, DNA restriction digestion, PCR, and Southern blot analyses were conducted to identify the differences between the R-M systems of these two strains. DNA restriction digestion analysis of these strains showed that only the cell extract from ATCC 35405 was able to digest pBFC. Consistently, PCR and Southern blot analyses revealed that the genome of T. denticola ATCC 35405 encodes three type II endonucleases that are absent in ATCC 33520. Among these three endonucleases, TDE0911 was predicted to cleave unmethylated double-stranded DNA and to be most likely responsible for the cleavage of unmethylated pBFC. In agreement with this prediction, the mutant of TDE0911 failed to cleave unmethylated pBFC plasmid, and it could accept the unmethylated shuttle vector. The study described here provides us with a new tool and strategy to genetically manipulate T. denticola, in particular ATCC 35405, and other strains that may carry similar endonucleases.

The Treponema denticola chymotrypsin-like protease dentilisin induces matrix metalloproteinase-2-dependent fibronectin fragmentation in periodontal ligament cells

Periodontal disease is a bacterially mediated chronic inflammatory disease that results in destruction of the periodontal ligament (PDL) and alveolar bone that surround and support the dentition. While their precise roles are not well understood, periodontal pathogens, including Treponema denticola, are believed to initiate the destructive inflammatory responses and dysregulation of tissue homeostasis that characterize the disease. These responses are believed to result from both proinflammatory effects of acylated bacterial membrane components (lipopolysaccharides and lipoproteins) and degradative effects of secreted bacterial proteases. Host-derived matrix metalloproteinases (MMPs) are key enzymes both in tissue homeostasis and tissue destruction. MMP expression is modulated in part by specific proteolytic fragments of fibronectin (FN), which are associated with periodontal disease. FN is a predominant extracellular matrix component in the periodontium. We examined the ability of Treponema denticola and its acylated outer membrane PrtP protease complex to induce both activation of MMP-2 and generation of FN fragments in human PDL cell culture supernatants. T. denticola parent and isogenic mutant strains, as well as MMP-2 small interfering RNA and specific inhibitors of MMP-2 and PrtP activity, were used to examine protein expression, gelatinolytic activity, and FN fragmentation in culture supernatants. T. denticola and its purified protease induced both MMP-2 activation and FN fragmentation. Here, we demonstrate that PrtP proteolytic activity induces the activation of MMP-2 and that active MMP-2 is required for FN fragmentation. These results suggest a specific mechanism by which the T. denticola protease may disrupt homeostatic processes required for the maintenance of periodontal health.

Identification of the primary mechanism of complement evasion by the periodontal pathogen, Treponema denticola

Treponema denticola, a periodontal pathogen, binds the complement regulatory protein Factor H (FH). Factor H binding protein B (FhbB) is the sole FH binding protein produced by T. denticola. The interaction of FhbB with FH is unique in that FH is bound to the cell and then cleaved by the T. denticola protease, dentilisin. A ∼ 50-kDa product generated by dentilisin cleavage is retained at the cell surface. Until this study, a direct role for the FhbB-FH interaction in complement evasion and serum sensitivity had not been demonstrated. Here we assess the serum resistance of T. denticola strain 35405 (Td35405wt) and isogenic mutants deficient in dentilisin (Td35405-CCE) and FhbB production (Td35405ΔfhbB), respectively. Both dentilisin and FhbB have been postulated to be key virulence factors that mediate complement evasion. Consistent with conditions in the subgingival crevice, an environment with a significant concentration of complement, Td35405wt was resistant to serum concentrations as high as 25%. Deletion of fhbB (Td35405ΔfhbB), which resulted in the complete loss of FH binding ability, but not inactivation of dentilisin activity (Td35405-CCE), rendered T. denticola highly sensitive to 25% human serum with 80% of the cells being disrupted after 4 h of incubation. Heat treatment of the serum to inactivate complement confirmed that killing was mediated by complement. These results indicate that the FH-FhbB interaction is required for serum resistance whereas dentilisin is not. This report provides new insight into the novel complement evasion mechanisms of T. denticola.

Virulence factors of the oral spirochete Treponema denticola

There is compelling evidence that treponemes are involved in the etiology of several chronic diseases, including chronic periodontitis as well as other forms of periodontal disease. There are interesting parallels with other chronic diseases caused by treponemes that may indicate similar virulence characteristics. Chronic periodontitis is a polymicrobial disease, and recent animal studies indicate that co-infection of Treponema denticola with other periodontal pathogens can enhance alveolar bone resorption. The bacterium has a suite of molecular determinants that could enable it to cause tissue damage and subvert the host immune response. In addition to this, it has several non-classic virulence determinants that enable it to interact with other pathogenic bacteria and the host in ways that are likely to promote disease progression. Recent advances, especially in molecular-based methodologies, have greatly improved our knowledge of this bacterium and its role in disease.

A simplified erythromycin resistance cassette for Treponema denticola mutagenesis

The primary selectable marker for the genetic studies of Treponema denticola is a hybrid gene cassette containing both ermF and ermAM (ermB) genes. ErmB functions in Escherichia coli, while ErmF has been assumed to confer resistance in T. denticola. We demonstrate here that ErmB is sufficient for erythromycin selection in T. denticola and that the native ermB promoter drives ErmB expression.

Treponema denticola PrcB is required for expression and activity of the PrcA-PrtP (dentilisin) complex

The Treponema denticola surface protease complex, consisting of PrtP protease (dentilisin) and two auxiliary polypeptides (PrcA1 and PrcA2), is believed to contribute to periodontal disease by degrading extracellular matrix components and disrupting host intercellular signaling. Previously, we showed that transcription of the protease operon initiates upstream of TDE0760 (herein designated prcB), the open reading frame immediately 5' of prcA-prtP. The prcB gene is conserved in T. denticola strains. PrcB localizes to the detergent phase of Triton X-114 cell surface extracts and migrates as a 22-kDa polypeptide, in contrast to the predicted 17-kDa cytoplasmic protein encoded in the annotated T. denticola genome. Consistent with this observation, the PrcB N terminus is unavailable for Edman sequencing, suggesting that it is acylated. Nonpolar deletion of prcB in T. denticola showed that PrcB is required for production of PrtP protease activity, including native PrtP cleavage of PrcA to PrcA1 and PrcA2. A 6xHis-tagged PrcB protein coimmunoprecipitates with native PrtP, using either anti-PrtP or anti-His-tag antibodies, and recombinant PrtP copurifies with PrcB-6xHis in nickel affinity chromatography. Taken together, these data are consistent with identification of PrcB as a PrtP-binding lipoprotein that likely stabilizes the PrtP polypeptide during localization to the outer membrane.

Analysis of a unique interaction between the complement regulatory protein factor H and the periodontal pathogen Treponema denticola

Treponema denticola, a spirochete associated with periodontitis, is abundant at the leading edge of subgingival plaque, where it interacts with gingival epithelia. T. denticola produces a number of virulence factors, including dentilisin, a protease which is cytopathic to host cells, and FhbB, a unique T. denticola lipoprotein that binds complement regulatory proteins. Earlier analyses suggested that FhbB specifically bound to factor H (FH)-like protein 1 (FHL-1). However, by using dentilisin-deficient mutants of T. denticola, we found that T. denticola preferentially binds FH and not FHL-1, and that FH is then cleaved by dentilisin to yield an FH subfragment of approximately 50 kDa. FH bound to dentilisin-deficient mutants but was not cleaved and retained its ability to serve as a cofactor for factor I in the cleavage of C3b. To assess the molecular basis of the interaction of FhbB with FH, mutational analyses were conducted. Replacement of specific residues in widely separated domains of FhbB and disruption of a central alpha helix with coiled-coil formation probability attenuated or eliminated FH binding. The data presented here are the first to demonstrate the retention at the cell surface of a proteolytic cleavage product of FH. The precise role of this FH fragment in the host-pathogen interaction remains to be determined.

Human serum antibodies recognize Treponema denticola Msp and PrtP protease complex proteins

BACKGROUND/AIMS

Treponema denticola outer membrane proteins are postulated to have key roles in microbe-host interactions in periodontitis. Because there are no reports of in vivo expression of these putative virulence factors, we examined several T. denticola strains to determine whether sera from human subjects recognized specific T. denticola outer membrane proteins.

METHODS

Soluble extracts were prepared from exponential phase cultures of T. denticola strains representing three serotypes, from defined T. denticola mutants defective in Msp (major surface protein) or PrtP lipoprotein protease complex (CTLP; dentilisin), and Escherichia coli strains expressing distinctly different T. denticola Msp. Extracts were subjected to Western immunoassays using archived human serum samples.

RESULTS

Human serum antibodies (immunoglobulin G class) recognized multiple protein bands in T. denticola strains. In the parent strain ATCC 35405, these included bands at 72-, 53-, 40-, and 30-kDa. Bands corresponding to Msp and the PrtP protease complex proteins were absent in isogenic msp and protease complex mutants, respectively. Individual human sera showed specificity for one or more Msp types.

CONCLUSIONS

This is the first definitive report of human serum antibody responses to specific T. denticola antigens. T. denticola Msp and the proteins comprising the PrtP lipoprotein protease complex are expressed in vivo and are immunogenic in humans. Human antibody recognition of Msp exhibits strain specificity and is consistent with strain serotyping. These results demonstrate the utility of T. denticola isogenic mutants in characterizing host immune responses to periodontal pathogens.

The chymotrypsin-like protease complex of Treponema denticola ATCC 35405 mediates fibrinogen adherence and degradation

Treponema denticola is an anaerobic spirochete strongly associated with human periodontal disease. T. denticola bacteria interact with a range of host tissue proteins, including fibronectin, laminin, and fibrinogen. The latter localizes in the extracellular matrix where tissue damage has occurred, and interactions with fibrinogen may play a key role in T. denticola colonization of the damaged sites. T. denticola ATCC 35405 showed saturable binding of fluid-phase fibrinogen to the cell surface and saturable adherence to immobilized fibrinogen. Levels of fibrinogen binding were enhanced in the presence of the serine protease inhibitor phenylmethylsulfonyl fluoride. The Aalpha and Bbeta chains of fibrinogen, but not the gamma chains, were specifically recognized by T. denticola. Following fibrinogen affinity chromatography analysis of cell surface extracts, a major fibrinogen-binding component (polypeptide molecular mass, approximately 100 kDa), which also degraded fibrinogen, was purified. Upon heating at 100 degrees C, the polypeptide was dissociated into three components (apparent molecular masses, 80, 48, and 45 kDa) that did not individually bind or degrade fibrinogen. The native 100-kDa polypeptide complex was identified as chymotrypsin-like protease (CTLP), or dentilisin. In an isogenic CTLP(-) mutant strain, CKE, chymotrypsin-like activity was reduced >90% compared to that in the wild type and fibrinogen binding and hydrolysis were ablated. Isogenic mutant strain MHE, deficient in the production of Msp (major surface protein), showed levels of CTLP reduced 40% relative to those in the wild type and exhibited correspondingly reduced levels of fibrinogen binding and proteolysis. Thrombin clotting times in the presence of wild-type T. denticola cells, but not strain CKE (CTLP(-)) cells, were extended. These results suggest that interactions of T. denticola with fibrinogen, which may promote colonization and modulate hemostasis, are mediated principally by CTLP.

Demonstration of factor H-like protein 1 binding to Treponema denticola, a pathogen associated with periodontal disease in humans

Treponema denticola is an important contributor to periodontal disease. In this study we investigated the ability of T. denticola to bind the complement regulatory proteins factor H and factor H-like protein 1 (FHL-1). The binding of these proteins has been demonstrated to facilitate evasion of the alternative complement cascade and/or to play a role in adherence and invasion. Here we demonstrate that T. denticola specifically binds FHL-1 via a 14-kDa, surface-exposed protein that we designated FhbB. Consistent with its FHL-1 binding specificity, FhbB binds only to factor H recombinant fragments spanning short consensus repeats (SCRs) 1 to 7 (H7 construct) and not to SCR constructs spanning SCRs 8 to 15 and 16 to 20. Binding of H7 to FhbB was inhibited by heparin. The specific involvement of SCR 7 in the interaction was demonstrated using an H7 mutant (H7AB) in which specific charged residues in SCR 7 were replaced by alanine. This construct lost FhbB binding ability. Analyses of the ability of FHL-1 bound to the surface of T. denticola to serve as a cofactor for factor I-mediated cleavage of C3b revealed that C3b is cleaved in an FHL-1/factor I-independent manner, perhaps by an unidentified protease. Based on the data presented here, we hypothesize that the primary function of FHL-1 binding by T. denticola might be to facilitate adherence to FHL-1 present on anchorage-dependent cells and in the extracellular matrix.