Proline iminopeptidase from the outer cell envelope of the human oral spirochete Treponema denticola ATCC 35405

Role of host cell-derived amino acids in nutrition of intracellular Salmonella enterica

The facultative intracellular pathogen Salmonella enterica resides in a specific membrane-bound compartment termed the Salmonella-containing vacuole (SCV). Despite being segregated from access to metabolites in the host cell cytosol, Salmonella is able to efficiently proliferate within the SCV. We set out to unravel the nutritional supply of Salmonella in the SCV with focus on amino acids. We studied the availability of amino acids by the generation of auxotrophic strains for alanine, asparagine, aspartate, glutamine, and proline in a macrophage cell line (RAW264.7) and an epithelial cell line (HeLa) and examined access to extracellular nutrients for nutrition. Auxotrophies for alanine, asparagine, or proline attenuated intracellular replication in HeLa cells, while aspartate, asparagine, or proline auxotrophies attenuated intracellular replication in RAW264.7 macrophages. The different patterns of intracellular attenuation of alanine- or aspartate-auxotrophic strains support distinct nutritional conditions in HeLa cells and RAW264.7 macrophages. Supplementation of medium with individual amino acids restored the intracellular replication of mutant strains auxotrophic for asparagine, proline, or glutamine. Similarly, a mutant strain deficient in succinate dehydrogenase was complemented by the extracellular addition of succinate. Complementation of the intracellular replication of auxotrophic Salmonella by external amino acids was possible if bacteria were proficient in the induction of Salmonella-induced filaments (SIFs) but failed in a SIF-deficient background. We propose that the ability of intracellular Salmonella to redirect host cell vesicular transport provides access of amino acids to auxotrophic strains and, more generally, is essential to continuously supply bacteria within the SCV with nutrients.

Studies on the molecular docking and amino Acid residues involving in recognition of substrate in proline iminopeptidase by site-directed mutagenesis

The proline iminopeptidase (PchPiPA) of Phanerochaete chrysosporium catalyze specifically hydrolysis of N-terminal proline from peptides. The substrate Pro-pNA was docked into the catalytic pocket and several amino acid residues were identified to interact or associate with the substrate. Eight residues were selected for site-directed mutagenesis. The wild-type and mutant proteins were expressed in Escherichia coli and purified. Kinetic parameters were calculated by hydrolyzing Pro-pNA for these enzymes. Substitution of two Glu residues (Glu198 and Glu227) which interact with the substrate via formation of hydrogen bond, led to deleterious effect on catalytic efficiency (k(cat)/K(m)) due to decrease of k(cat) and increase of K(m). Four Phe residues consisting of catalytic pocket and surrounding the docked substrate, were substituted with Ala, resulting in decrease in k(cat)/K(m) to various extents. Substitution of two residues (Val267 and Cys267) localized at the deep end of the catalytic pocket also yielded negative influence on the substrate hydrolysis. Besides, all the mutants except E227Q exhibited lower thermostability than the wild-type did, indicating that these mutations may modulate the local structure. In conclusion, these amino acid residues may play an important role in maintaining local environment of the impacted catalytic pocket and be involved in recognizing or positioning the substrate.

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.

Effect of salt on the activity of Streptomyces prolyl aminopeptidase

A salt-tolerant prolyl aminopeptidase from Streptomyces aureofaciens TH-3 (TH-3PAP) was purified from a culture supernatant. The gene encoding TH-3PAP was cloned and sequenced. The primary structure of TH-3PAP showed 65% identity with that of PAP from Streptomyces lividans (SLPAP) and possessed a conserved catalytic motif, GxSxGG, which is conserved in the alpha/beta hydrolase fold family. The characterization of the recombinants TH-3PAP and SLPAP indicated a difference: in 4.0 M NaCl, TH-3PAP showed enzyme activity, whereas SLPAP was inactive. Next, we constructed chimeras between TH-3PAP and SLPAP using an in vivo DNA shuffling system and a sandwich chimera (sc-PAP), whose region from 63 to 78 amino acids of TH-3PAP was substituted with that of SLPAP. Comparison of the biochemical properties between TH-3PAP and the salt-sensitive sc-PAP suggested that the fine tuning of the N-terminal conformation of TH-3PAP by hydrophobic interaction is important for the salt tolerance mechanism of the enzyme.

An Aneurinibacillus sp. strain AM-1 produces a proline-specific aminopeptidase useful for collagen degradation

AIMS

We have been for a species of thermophilic bacteria that can effectively decompose collagen and collagen peptides that tend to be hard-to-degrade proteins because of their high content of proline residues. This study focused upon the enzymatic degradation of prolyl peptides by thermophilic bacteria.

METHODS AND RESULTS

A strain, AM-1, producing a proline-specific aminopeptidase was isolated using a medium containing gelatin that was taken from soil samples collected at Arima Hot Spring located near Kobe, Japan. The strain showed the strongest level of hydrolysing activity toward prolyl-p-nitroanilide, and the activity proved to be thermostable. Phylogenetic analysis based on 16S rDNA sequences revealed that the isolated strain AM-1 was closest to Aneurinibacillus thermoaerophilus DSM10154T in its characteristics. Analysis of the purified proline-specific aminopeptidase suggested that the enzyme is an aminopeptidase containing metal that includes important disulphide bond(s). The strain AM-1 aminopeptidase has more similarities with leucyl aminopeptidases, but its activity level differs greatly with prolyl peptides.

CONCLUSIONS

The proline-specific aminopeptidase from strain AM-1 is the first from the genus Aneurinibacillus and may be a new type of aminopeptidase for hydrolysing prolyl peptide. This enzyme also contributed to the degradation of collagen when used in combination with another collagenolytic protease.

SIGNIFICANCE AND IMPACT OF THE STUDY

The proline-specific aminopeptidase obtained from strain AM-1 may be used in the treatment of wastewater containing collagen that is encountered in the meat industries, and for decreasing bitter peptides in milk products.

Characterization and expression of adjacent proline iminopeptidase and aspartase genes from Eikenella corrodens

Two adjacent genes involved in nitrogen metabolism from Eikenella corrodens, with a potential role in pathogenesis, were studied. Proline iminopeptidase (Pip) activity, which may be essential for energy production and protection against host immune mechanisms, is exhibited by E. corrodens. Analysis of Pip-expressing clones revealed an ORF of 939 bases with a predicted amino acid sequence identity of 67% to the Pip of Neisseria gonorrhoea. 200 bp downstream from pip, an ORF of 1395 bases, encoding a protein with 87% identity to a putative aspartase from the Neisseria meningitidis genome sequence, was identified. Enzymatic function was confirmed with a complemented Escherichia coli aspartase deficient mutant. The E. corrodens aspartase was found to be 77% identical to the Haemophilus influenzae aspartase sequence, which was originally identified on the basis of its ability to bind plasminogen. However, the E. corrodens aspartase had no such activity. Southern hybridization indicated both genes to be single copy and conserved within the genomes of a diverse panel of E. corrodens isolates from health and disease.

Enzymatic degradation of collagen-guided tissue regeneration membranes by periodontal bacteria

Bacterial infection in the vicinity of guided tissue regeneration barrier membranes was shown to have a negative effect on the clinical outcomes of this increasingly used technique. Several oral and specifically periodontal bacteria were shown to adhere to such membranes in vivo and in vitro with a higher affinity to membranes constructed from collagen. The present study examined the role of periodontal bacteria and their enzymes in the degradation of commercially used collagen membranes. Degradation of two collagen membranes [Biomend (Calcitek, Colla-Tec Inc., Plainsboro, NJ) and Bio-Gide (Geistlich Biomaterials, Wolhousen, Switzerland)] labeled by fluorescein isothiocyanate was examined by measuring soluble fluorescence. Porphyromonas gingivalis, Treponema denticola and Actinobacillus actinomycetemcomitans and their enzymes were evaluated. Collagenase from Clostridium hystolyticum was used as a positive control. While whole cells of P. gingivalis were able to degrade both types of membranes, T. denticola could degrade Bio-Gide membranes only and A. actinomycetemcomitans whole cells could degrade none of the membranes. Fractionation of P. gingivalis cells revealed that cell membrane associated proteases were responsible for the degradation of the two collagen membranes. In T. denticola, the purified major phenylalanine protease was found to be responsible for the degradation of Bio-Gide membranes. These results suggest that proteolytic bacterial enzymes may take part in the degradation of collagen barrier membranes used for guided tissue regeneration.

Genetic relatedness and phenotypic characteristics of Treponema associated with human periodontal tissues and ruminant foot disease

Treponema have been implicated recently in the pathogenesis of digital dermatitis (DD) and contagious ovine digital dermatitis (CODD) that are infectious diseases of bovine and ovine foot tissues, respectively. Previous analyses of treponemal 16S rDNA sequences, PCR-amplified directly from DD or CODD lesions, have suggested relatedness of animal Treponema to some human oral Treponema species isolated from periodontal tissues. In this study a range of adhesion and virulence-related properties of three animal Treponema isolates have been compared with representative human oral strains of Treponema denticola and Treponema vincentii. In adhesion assays using biotinylated treponemal cells, T. denticola cells bound in consistently higher numbers to fibronectin, laminin, collagen type I, gelatin, keratin and lactoferrin than did T. vincentii or animal Treponema isolates. However, animal DD strains adhered to fibrinogen at equivalent or greater levels than T. denticola. All Treponema strains bound to the amino-terminal heparin I/fibrin I domain of fibronectin. 16S rDNA sequence analyses placed ovine strain UB1090 and bovine strain UB1467 within a cluster that was phylogenetically related to T. vincentii, while ovine strain UB1466 appeared more closely related to T. denticola. These observations correlated with phenotypic properties. Thus, T. denticola ATCC 35405, GM-1, and Treponema UB1466 had similar outer-membrane protein profiles, produced chymotrypsin-like protease (CTLP), trypsin-like protease and high levels of proline iminopeptidase, and co-aggregated with human oral bacteria Porphyromonas gingivalis and Streptococcus crista. Conversely, T. vincentii ATCC 35580, D2A-2, and animal strains UB1090 and UB1467 did not express CTLP or trypsin-like protease and did not co-aggregate with P. gingivalis or S. crista. Taken collectively, these results suggest that human oral-related Treponema have broad host specificity and that similar control or preventive strategies might be developed for human and animal Treponema-associated infections.

Role of Treponema denticola in periodontal diseases

Among periodontal anaerobic pathogens, the oral spirochetes, and especially Treponema denticola, have been associated with periodontal diseases such as early-onset periodontitis, necrotizing ulcerative gingivitis, and acute pericoronitis. Basic research as well as clinical evidence suggest that the prevalence of T denticola, together with other proteolytic gram-negative bacteria in high numbers in periodontal pockets, may play an important role in the progression of periodontal disease. The accumulation of these bacteria and their products in the pocket may render the surface lining periodontal cells highly susceptible to lysis and damage. T. denticola has been shown to adhere to fibroblasts and epithelial cells, as well as to extracellular matrix components present in periodontal tissues, and to produce several deleterious factors that may contribute to the virulence of the bacteria. These bacterial components include outer-sheath-associated peptidases, chymotrypsin-like and trypsin-like proteinases, hemolytic and hemagglutinating activities, adhesins that bind to matrix proteins and cells, and an outer-sheath protein with pore-forming properties. The effects of T. denticola whole cells and their products on a variety of host mucosal and immunological cells has been studied extensively (Fig. 1). The clinical data regarding the presence of T. denticola in periodontal health and disease, together with the basic research results involving the role of T. denticola factors and products in relation to periodontal diseases, are reviewed and discussed in this article.

Cloning and expression of two novel hemin binding protein genes from Treponema denticola

Treponema denticola does not appear to produce siderophores, so it must acquire iron by other pathways. Indeed, T. denticola has been shown to have an iron-regulated 44-kDa outer membrane protein (HbpA) with hemin binding ability. To characterize the HbpA protein, its gene was cloned from genomic DNA libraries of T. denticola. Sequence analysis of the hbpA open reading frame indicated that it encoded a 42.8-kDa protein with a 23-amino-acid signal peptide. HbpA has no significant homology to any proteins in the databases. Southern blot analysis demonstrated that hbpA is present in several T. denticola ATCC strains and clinical isolates, but not in Treponema pectinovorum, Treponema socranskii, or Escherichia coli. HbpA, expressed as a recombinant protein in E. coli and purified by antibody affinity chromatography, has hemin binding activity as determined by lithium dodecyl sulfate-polyacrylamide gel electrophoresis with tetramethylbenzidine staining. Northern blot analysis showed that there were two hbpA-containing transcripts, of approximately 1.3 and 2.6 kb, and that the RNA levels were low-iron induced. Interestingly, the 2.6-kb mRNA also encoded a second protein with significant homology to hbpA. This downstream gene, called hbpB, was cloned and sequenced and its product was expressed as a fusion protein in E. coli. The hbpB gene product is 49% identical to HbpA and binds hemin. Thus, T. denticola has two novel hemin binding proteins which may be part of a previously unrecognized iron acquisition pathway.

Taxonomy and virulence of oral spirochetes

All oral spirochetes are classified in the genus Treponema. This genus is in the family Spirochaetaceae as in Bergey's manual of systematic bacteriology. Other generic members of the family include Spirochaeta, Cristispira and Borrelia. This conventional classification is in accord with phylogenetic analysis of the spirochetes based on 16S rRNA cataloguing. The oral spirochetes fall naturally within the grouping of Treponema. Only four species of Treponema have been cultivated and maintained reliably: Treponema denticola, Treponema pectinovorum, Treponema socranskii and Treponema vincentii. These species have valid names according to the rules of nomenclature except for Treponema vincentii, which only has had effective publication. The virulence factors of the oral spirochetes updated in this mini-review have been discussed within the following broad confines: adherence, cytotoxic effects, iron sequestration and locomotion. T. denticola has been shown to attach to human gingival fibroblasts, basement membrane proteins, as well as other substrates by specific attachment mechanisms. The binding of the spirochete to human gingival fibroblasts resulted in cytotoxicity and cell death due to enzymes and other proteins. Binding of the spirochete to erythrocytes was accompanied by agglutination and lysis. Hemolysis releases hemin, which is sequestered by an outer membrane sheath receptor protein of the spirochete. The ability to locomote through viscous environments enables spirochetes to migrate within gingival crevicular fluid and to penetrate sulcular epithelial linings and gingival connective tissue. The virulence factors of the oral spirochetes proven in vitro underscore the important role they play in the periodontal disease process. This role has been evaluated in vivo by use of a murine model.

Dentilisin activity affects the organization of the outer sheath of Treponema denticola

Prolyl-phenylalanine-specific serine protease (dentilisin) is a major extracellular protease produced by Treponema denticola. The gene, prtP, coding for the protease was recently cloned and sequenced (K. Ishihara, T. Miura, H. K. Kuramitsu, and K. Okuda, Infect. Immun. 64:5178-5186, 1996). In order to determine the role of this protease in the physiology and virulence of T. denticola, a dentilisin-deficient mutant, K1, was constructed following electroporation with a prtP-inactivated DNA fragment. No chymotrypsin-like protease activity was detected in the dentilisin-deficient mutant. In addition, the high-molecular-mass oligomeric protein characteristic of the outer sheath of the organism decreased in the mutant. Furthermore, the hydrophobicity of the mutant was decreased, and coaggregation of the mutant with Fusobacterium nucleatum was enhanced compared to that of the wild-type organism. The results obtained with a mouse abscess model system indicated that the virulence of the mutant was attenuated relative to that of the wild-type organism. These results suggest that dentilisin activity plays a major role in the structural organization of the outer sheath of T. denticola. The loss of dentilsin activity and the structural change in the outer sheath affect the pathogenicity of T. denticola.

Cytopathic effects of the major surface protein and the chymotrypsinlike protease of Treponema denticola

Prominent antigens of Treponema denticola have been suggested to be mediators of the cytopathic effects typically seen in periodontal disease. In the present study of the T. denticola major surface protein (Msp) and the surface-expressed chymotrypsinlike protease complex (CTLP), we characterized the ability of these proteins to adhere to and lyse epithelial cells. Msp and CTLP were closely associated in spirochete outer membranes. Purified Msp, both native and recombinant, and CTLP bound to glutaraldehyde-fixed periodontal ligament epithelial cells. Adherence of Msp was partially blocked by specific antibodies. Adherence of CTLP was partially blocked by serine protease inhibitors and was further inhibited by specific antibodies. Both native Msp and CTLP were cytotoxic toward periodontal ligament epithelial cells, and their cytotoxicity was inhibited by the same treatments that inhibited adherence. Msp, but not CTLP, lysed erythrocytes. Msp complex (partially purified outer membranes free of protease activity) was cytotoxic toward a variety of different cell types. Pore-forming activities of recombinant Msp in black lipid model membrane assays and in HeLa cell membranes were similar to those reported for the native protein, supporting the hypothesis that Msp cytotoxicity was due to its pore-forming activity.

Activation of the interleukin-1beta precursor by Treponema denticola: a potential role in chronic inflammatory periodontal diseases

There are several indications suggesting that interleukin-1beta (IL-1beta) may play an important role in inflammatory periodontal diseases. We hypothesized that periodontal sites would represent a unique combination of both cellular sources of IL-1beta precursor (pro-IL-1beta) and microbial proteases and proposed that Treponema denticola, a suspected periodontal pathogen, would play a critical role in the inflammatory nature of adult chronic periodontitis by activating pro-IL-1beta. The aim of this study was thus to demonstrate the proteolytic cleavage and activation of the inactive precursor pro-IL-1beta by T. denticola. After incubation of bacterial cells with recombinant pro-IL-1beta, proteolytic cleavage was monitored by Western immunoblotting, and the biological activity of the digestion products was tested in a bioassay. We report here that T. denticola can cleave pro-IL-1beta to yield two fragments with molecular masses of 18 and 19 kDa. Cleavage products showed a dose-dependent biological activity in the thymocyte proliferation bioassay, and this activity was inhibited by anti-IL-1beta neutralizing antibodies. These results suggest that T. denticola may have a proinflammatory role in periodontal diseases.

gamma-Glutamyltransferase from the outer cell envelope of Treponema denticola ATCC 35405

The human oral spirochete Treponema denticola ATCC 35405 was shown to exhibit relatively high enzyme activity toward the gamma-glutamyl amide bond present in N-gamma-L-glutamyl-4-nitroaniline. The enzyme responsible for this catalysis (gamma-glutamyltransferase [GGT]; EC 2.3.2.2) was purified by means of fast protein liquid chromatography to two sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-pure forms from a mild (0.1%) Triton X-100 extract of washed cells. The GGT was studied primarily with regard to its hydrolytic activity by using N-gamma-L-glutamyl-4-nitroaniline as a substrate, although the GGT was shown to catalyze transpeptidation reactions. The high-molecular-mass form of the GGT gave a value of about 213 kDa by SDS-PAGE when heat treatment was omitted and one of 26 kDa after heat treatment; mass spectrometry gave a value of 26.877. The larger form may represent an aggregate with nonprotein structures (possibly of a carbohydrate nature). The preliminary N-terminal sequence of the GGT is MKKPLIGITGSXLYETSQXXF. The enzyme was highly active on glutathione, transferring its Glu residue either to a water molecule or to the Gly-L-Leu dipeptide. The GGT stability was absolutely dependent on the presence of free thiol(s), while no evidence of metalloenzyme nature was obtained. The proposed location of the GGT in the outer cell envelope and its high activity on glutathione, a major nonprotein thiol present in virtually all cells, suggest that the GGT may play a role in the propagation of T. denticola within inflamed periodontal tissues.