Cleavage of Treponema denticola PrcA polypeptide to yield protease complex-associated proteins Prca1 and Prca2 is dependent on PrtP

Purification of Native Dentilisin Complex from Treponema denticola by Preparative Continuous Polyacrylamide Gel Electrophoresis and Functional Analysis by Gelatin Zymography

Periodontal disease is characterized by the destruction of the hard and soft tissues comprising the periodontium. This destruction translates to a degradation of the extracellular matrices (ECM), mediated by bacterial proteases, host-derived matrix metalloproteinases (MMPs), and other proteases released by host tissues and immune cells. Bacterial pathogens interact with host tissue, triggering adverse cellular functions, including a heightened immune response, tissue destruction, and tissue migration. The oral spirochete Treponema denticola is highly associated with periodontal disease. Dentilisin, a T. denticola outer membrane protein complex, contributes to the chronic activation of pro-MMP-2 in periodontal ligament (PDL) cells and triggers increased expression levels of activators and effectors of active MMP-2 in PDL cells. Despite these advances, no mechanism for dentilisin-induced MMP-2 activation or PDL cytopathic behaviors leading to disease is known. Here, we describe a method for purification of large amounts of the dentilisin protease complex from T. denticola and demonstrate its ability to activate MMP-2, a key regulator of periodontal tissue homeostasis. The T. denticola dentilisin and MMP-2 activation model presented here may provide new insights into the dentilisin protein and identify potential therapeutic targets for further research. Key features • This protocol builds upon a method described by Cunningham et al. [1] for selective release of Treponema outer membrane proteins. • We adapted the protocol for the purification of biologically active, detergent-stable outer membrane protein complexes from large batch cultures of T. denticola. • The protocol involves large-scale preparative electrophoresis using a Model 491 Prep Cell. • We then use gelatin zymography to demonstrate the activity of the purified dentilisin complex by its ability to activate matrix metalloproteinase 2 (MMP-2).

Molecular docking analysis of a virulence factor protein dentilisin from Treponema denticola with oxazole piperazine derivatives

Dentilisin is a surface protease synthesized by the cell wall of Treponema denticola. This protein aids in the invasion of the periodontal tissue by causing infection. To identify drug molecules that have better results, homology modeling of the dentilisin protein was constructed, and molecular docking was performed with the oxazole compounds (1-6) taken from previous studies that are not yet clinically used. Data shows that compounds 1, 2, 3 show better inhibiting properties.

Treponema denticola Induces Interleukin-36γ Expression in Human Oral Gingival Keratinocytes via the Parallel Activation of NF-κB and Mitogen-Activated Protein Kinase Pathways

The oral epithelial barrier acts as both a physical barrier to the abundant oral microbiome and a sentry for the immune system that, in health, constrains the accumulation of the polymicrobial plaque biofilm. The immune homeostasis during gingivitis that is largely protective becomes dysregulated, unproductive, and destructive to gingival tissue as periodontal disease progresses to periodontitis. The progression to periodontitis is associated with the dysbiosis of the oral microbiome, with increasing prevalences and abundances of periodontal pathogens such as Treponema denticola. Despite the association of T. denticola with a chronic inflammatory disease, relatively little is known about gingival epithelial cell responses to T. denticola infection. Here, we characterized the transcriptome of gingival keratinocytes following T. denticola challenge and identified interleukin-36γ (IL-36γ) as the most differentially expressed cytokine. IL-36γ expression is regulated by p65 NF-κB and the activation of both the Jun N-terminal protein kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) pathways downstream of Toll-like receptor 2 (TLR2). Finally, we demonstrate for the first time that mitogen- and stress-activated kinase 1 (MSK1) contributes to IL-36γ expression and may link the activation of MAPK and NF-κB signaling. These findings suggest that the interactions of T. denticola with the gingival epithelium lead to elevated IL-36γ expression, which may be a critical inducer and amplifier of gingival inflammation and subsequent alveolar bone loss.

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.

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

The major outer sheath protein forms distinct conformers and multimeric complexes in the outer membrane and periplasm of Treponema denticola

The major outer sheath protein (MOSP) is a prominent constituent of the cell envelope of Treponema denticola (TDE) and one of its principal virulence determinants. Bioinformatics predicts that MOSP consists of N- and C-terminal domains, MOSP^N and MOSP^C. Biophysical analysis of constructs refolded in vitro demonstrated that MOSP^C, previously shown to possess porin activity, forms amphiphilic trimers, while MOSP^N forms an extended hydrophilic monomer. In TDE and E. coli expressing MOSP with a PelB signal sequence (PelB-MOSP), MOSP^C is OM-embedded and surface-exposed, while MOSP^N resides in the periplasm. Immunofluorescence assay, surface proteolysis, and novel cell fractionation schemes revealed that MOSP in TDE exists as outer membrane (OM) and periplasmic trimeric conformers; PelB-MOSP, in contrast, formed only OM-MOSP trimers. Although both conformers form hetero-oligomeric complexes in TDE, only OM-MOSP associates with dentilisin. Mass spectrometry (MS) indicated that OM-MOSP interacts with proteins in addition to dentilisin, most notably, oligopeptide-binding proteins (OBPs) and the β-barrel of BamA. MS also identified candidate partners for periplasmic MOSP, including TDE1658, a spirochete-specific SurA/PrsA ortholog. Collectively, our data suggest that MOSP destined for the TDE OM follows the canonical BAM pathway, while formation of a stable periplasmic conformer involves an export-related, folding pathway not present in E. coli.

Oral treponeme major surface protein: Sequence diversity and distributions within periodontal niches

Treponema denticola and other species (phylotypes) of oral spirochetes are widely considered to play important etiological roles in periodontitis and other oral infections. The major surface protein (Msp) of T. denticola is directly implicated in several pathological mechanisms. Here, we have analyzed msp sequence diversity across 68 strains of oral phylogroup 1 and 2 treponemes; including reference strains of T. denticola, Treponema putidum, Treponema medium, 'Treponema vincentii', and 'Treponema sinensis'. All encoded Msp proteins contained highly conserved, taxon-specific signal peptides, and shared a predicted 'three-domain' structure. A clone-based strategy employing 'msp-specific' polymerase chain reaction primers was used to analyze msp gene sequence diversity present in subgingival plaque samples collected from a group of individuals with chronic periodontitis (n=10), vs periodontitis-free controls (n=10). We obtained 626 clinical msp gene sequences, which were assigned to 21 distinct 'clinical msp genotypes' (95% sequence identity cut-off). The most frequently detected clinical msp genotype corresponded to T. denticola ATCC 35405^T , but this was not correlated to disease status. UniFrac and libshuff analysis revealed that individuals with periodontitis and periodontitis-free controls harbored significantly different communities of treponeme clinical msp genotypes (P<.001). Patients with periodontitis had higher levels of clinical msp genotype diversity than periodontitis-free controls (Mann-Whitney U-test, P<.05). The relative proportions of 'T. vincentii' clinical msp genotypes were significantly higher in the control group than in the periodontitis group (P=.018). In conclusion, our data clearly show that both healthy and diseased individuals commonly harbor a wide diversity of Treponema clinical msp genotypes within their subgingival niches.

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.

Development of a modified gentamicin resistance cassette for genetic manipulation of the oral spirochete Treponema denticola

Herein, we report that a modified gentamicin cassette and a PCR-based method can be used for targeted mutagenesis of the oral spirochete Treponema denticola. This approach minimizes polar effects and spontaneous antibiotic resistance. Therefore, it can serve as a reliable tool for genetic manipulation of T. denticola.

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.

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.

Major proteins and antigens of Treponema denticola

Treponema denticola is a Gram-negative, motile, asaccharolytic, anaerobic spirochaete which along with Porphyromonas gingivalis and Tannerella forsythia has been shown to form a bacterial consortium called the Red Complex that is strongly associated with the clinical progression of chronic periodontitis. T. denticola was grown in continuous culture in a complex medium with a mean generation time of 15.75 h. Samples from two different membrane-enriched preparations and a cytoplasm-enriched preparation were separated by two-dimensional gel electrophoresis and the proteins identified by MALDI-TOF/TOF mass spectrometry. In total, 219 non-redundant proteins were identified including numerous virulence factors, lipoproteins, ABC transporter proteins and enzymes involved in the metabolism of nine different amino acids of which glycine seems to be of particular importance. Novel findings include the identification of several abundant peptide uptake systems, and the identification of three flagellar filament outer layer proteins. Two-dimensional Western blot analysis using sera from mice immunized with formalin-killed T. denticola cells suggested that Msp, PrcA, OppA, OppA10, MglB, TmpC and several flagellar filament proteins are antigenic.

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.

Characterization of Treponema denticola pyrF encoding orotidine-5'-monophosphate decarboxylase

The Treponema denticola ATCC 35405 genome annotation contains most of the genes for de novo pyrimidine biosynthesis. To initiate characterization of pyrimidine synthesis in Treponema, we focused on TDE2110 (the putative pyrF, encoding orotidine-5'-monophosphate decarboxlyase). Unlike the parent strain, an isogenic pyrF mutant was resistant to 5-fluoroorotic acid. In complex medium, growth of the pyrF mutant was independent of added uracil, indicating activity of a uracil uptake/salvage pathway. Transcription of pyrF was greatly reduced in T. denticola grown in excess uracil, demonstrating that de novo pyrimidine synthesis is regulated and suggesting a feedback mechanism. Treponema denticola PyrF complemented uracil auxotrophy in an Escherichia coli pyrF mutant. This study provides biochemical confirmation of T. denticola genome predictions of de novo and salvage pyrimidine pathways and provides proof of concept that pyrF has potential as a selectable marker in T. denticola.

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.

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

A novel gene was identified in the Treponema denticola prcA-prtP protease operon. Strains with mutations in either the prcA-prtP or the msp region showed altered expression of a product(s) of the other locus. Together, these results provide information on the assembly of outer membrane complexes involved in T. denticola interaction with host cells and tissue.

Outer membrane proteins of pathogenic spirochetes

Pathogenic spirochetes are the causative agents of several important diseases including syphilis, Lyme disease, leptospirosis, swine dysentery, periodontal disease and some forms of relapsing fever. Spirochetal bacteria possess two membranes and the proteins present in the outer membrane are at the site of interaction with host tissue and the immune system. This review describes the current knowledge in the field of spirochetal outer membrane protein (OMP) biology. What is known concerning biogenesis and structure of OMPs, with particular regard to the atypical signal peptide cleavage sites observed amongst the spirochetes, is discussed. We examine the functions that have been determined for several spirochetal OMPs including those that have been demonstrated to function as adhesins, porins or to have roles in complement resistance. A detailed description of the role of spirochetal OMPs in immunity, including those that stimulate protective immunity or that are involved in antigenic variation, is given. A final section is included which covers experimental considerations in spirochetal outer membrane biology. This section covers contentious issues concerning cellular localization of putative OMPs, including determination of surface exposure. A more detailed knowledge of spirochetal OMP biology will hopefully lead to the design of new vaccines and a better understanding of spirochetal pathogenesis.

A CDP-choline pathway for phosphatidylcholine biosynthesis in Treponema denticola

The genomes of Treponema denticola and Treponema pallidum contain a gene, licCA, which is predicted to encode a fusion protein containing choline kinase and CTP:phosphocholine cytidylyltransferase activities. Because both organisms have been reported to contain phosphatidylcholine, this raises the possibility that they use a CDP-choline pathway for the biosynthesis of phosphatidylcholine. This report shows that phosphatidylcholine is a major phospholipid in T. denticola, accounting for 35-40% of total phospholipid. This organism readily incorporated [14C]choline into phosphatidylcholine, indicating the presence of a choline-dependent biosynthetic pathway. The licCA gene was cloned, and recombinant LicCA had choline kinase and CTP:phosphocholine cytidylyltransferase activity. The licCA gene was disrupted in T. denticola by erythromycin cassette mutagenesis, resulting in a viable mutant. This disruption completely blocked incorporation of either [14C]choline or 32Pi into phosphatidylcholine. The rate of production of another phospholipid in T. denticola, phosphatidylethanolamine, was elevated considerably in the licCA mutant, suggesting that the elevated level of this lipid compensated for the loss of phosphatidylcholine in the membranes. Thus it appears that T. denticola does contain a licCA-dependent CDP-choline pathway for phosphatidylcholine biosynthesis.

A 43-kDa protein ofTreponema denticolais essential for dentilisin activity

A protease of Treponema denticola, dentilisin, is thought to be part of a complex with 43- and 38-kDa proteins. A sequence encoding a 43-kDa protein was located in the 3' region of the prcA gene upstream of the dentilisin gene (prtP). The 43-kDa protein was apparently generated from digestion of PrcA. To clarify the function of the protein, we constructed a mutant of the 43-kDa protein following homologous recombination. The mutant lacked detectable dentilisin activity. Immunoblot analysis demonstrated that the dentilisin protein was degraded in the mutant. The results of real-time polymerase chain reaction suggested that prtP mRNA expression in the mutant was somewhat decreased compared with the wild-type strain. These data suggest that the 43-kDa protein is involved in the stabilization of the dentilisin protein.

Two paralogous families of a two-gene subtilisin operon are widely distributed in oral treponemes

Certain oral treponemes express a highly proteolytic phenotype and have been associated with periodontal diseases. The periodontal pathogen Treponema denticola produces dentilisin, a serine protease of the subtilisin family. The two-gene operon prcA-prtP is required for expression of active dentilisin (PrtP), a putative lipoprotein attached to the treponeme's outer membrane or sheath. The purpose of this study was to examine the diversity and structure of treponemal subtilisin-like proteases in order to better understand their distribution and function. The complete sequences of five prcA-prtP operons were determined for Treponema lecithinolyticum, "Treponema vincentii," and two canine species. Partial operon sequences were obtained for T. socranskii subsp. 04 as well as 450- to 1,000-base fragments of prtP genes from four additional treponeme strains. Phylogenetic analysis demonstrated that the sequences fall into two paralogous families. The first family includes the sequence from T. denticola. Treponemes possessing this operon family express chymotrypsin-like protease activity and can cleave the substrate N-succinyl-alanyl-alanyl-prolyl-phenylalanine-p-nitroanilide (SAAPFNA). Treponemes possessing the second paralog family do not possess chymotrypsin-like activity or cleave SAAPFNA. Despite examination of a range of protein and peptide substrates, the specificity of the second protease family remains unknown. Each of the fully sequenced prcA and prtP genes contains a 5' hydrophobic leader sequence with a treponeme lipobox. The two paralogous families of treponeme subtilisins represent a new subgroup within the subtilisin family of proteases and are the only subtilisin lipoprotein family. The present study demonstrated that the subtilisin paralogs comprising a two-gene operon are widely distributed among treponemes.