Purification and partial characterization of a dipeptidyl peptidase from Prevotella intermedia

Prevotella: An insight into its characteristics and associated virulence factors

Prevotella species, a gram-negative obligate anaerobe, is commonly associated with human infections such as dental caries and periodontitis, as well as other conditions such as chronic osteomyelitis, bite-related infections, rheumatoid arthritis and intestinal diseases like ulcerative colitis. This generally harmless commensal possesses virulence factors such as adhesins, hemolysins, secretion systems exopolysaccharide, LPS, proteases, quorum sensing molecules and antibiotic resistance to evolve into a well-adapted pathogen capable of causing successful infection and proliferation in the host tissue. This review describes several of these virulence factors and their advantage to Prevotella spp. in causing inflammatory diseases like periodontitis. In addition, using genome analysis of Prevotella reference strains, we examined other putative virulence determinants which can provide insights as biomarkers and be the targets for effective interventions in Prevotella related diseases like periodontitis.

Characterization of substrate specificity and novel autoprocessing mechanism of dipeptidase A from Prevotella intermedia

Prevotella intermedia, a Gram-negative anaerobic rod, is frequently observed in subgingival polymicrobial biofilms from adults with chronic periodontitis. Peptidases in periodontopathic bacteria are considered to function as etiological reagents. Prevotella intermedia OMA14 cells abundantly express an unidentified cysteine peptidase specific for Arg-4-methycoumaryl-7-amide (MCA). BAU17746 (locus tag, PIOMA14_I_1238) and BAU18827 (locus tag, PIOMA14_II_0322) emerged as candidates of this peptidase from the substrate specificity and sequence similarity with C69-family Streptococcus gordonii Arg-aminopeptidase. The recombinant form of the former solely exhibited hydrolyzing activity toward Arg-MCA, and BAU17746 possesses a 26.6% amino acid identity with the C69-family Lactobacillus helveticus dipeptidase A. It was found that BAU17746 as well as L. helveticus dipeptidase A was a P1-position Arg-specific dipeptidase A, although the L. helveticus entity, a representative of the C69 family, had been reported to be specific for Leu and Phe. The full-length form of BAU17746 was intramolecularly processed to a mature form carrying the N-terminus of Cys15. In conclusion, the marked Arg-MCA-hydrolyzing activity in Pre. intermedia was mediated by BAU17746 belonging to the C69-family dipeptidase A, in which the mature form carries an essential cysteine at the N-terminus.

Potential Contributions of Anaerobes in Cystic Fibrosis Airways

Cystic fibrosis (CF) is the most common, lethal genetic disease among the Caucasian population. The leading cause of mortality is recurrent acute exacerbations resulting in chronic airway inflammation and subsequent downward progression of pulmonary function. Traditionally, these periods of clinical deterioration have been associated with several principal pathogens. However, a growing body of literature has demonstrated a polymicrobial lower respiratory community compromised of facultative and obligate anaerobes. Despite the understanding of a complex bacterial milieu in CF patient airways, specific roles of anaerobes in disease progression have not been established. In this paper, we first present a brief review of the anaerobic microorganisms that have been identified within CF lower respiratory airways. Next, we discuss the potential contribution of these organisms to CF disease progression, in part by pathogenic potential and also through synergistic interaction with principal pathogens. Finally, we propose a variety of clinical scenarios in which these anaerobic organisms indirectly facilitate principal CF pathogens by modulating host defense and contribute to treatment failure by antibiotic inactivation. These mechanisms may affect patient clinical outcomes and contribute to further disease progression.

The Potential Role of the Dipeptidyl Peptidase-4-Like Activity From the Gut Microbiota on the Host Health

The Dipeptidyl peptidase-4 (DPP-4) activity influences metabolic, behavioral and intestinal disorders through the cleavage of key hormones and peptides. Some studies describe the existence of human DPP-4 homologs in commensal bacteria, for instance in Prevotella or Lactobacillus. However, the role of the gut microbiota as a source of DPP-4-like activity has never been investigated. Through the comparison of the DPP-4 activity in the cecal content of germ-free mice (GFM) and gnotobiotic mice colonized with the gut microbiota of a healthy subject, we bring the proof of concept that a significant DPP-4-like activity occurs in the microbiota. By analyzing the existing literature, we propose that DPP-4-like activity encoded by the intestinal microbiome could constitute a novel mechanism to modulate protein digestion as well as host metabolism and behavior.

Crystal structures of a bacterial dipeptidyl peptidase IV reveal a novel substrate recognition mechanism distinct from that of mammalian orthologues

Dipeptidyl peptidase IV (DPP IV, DPP4, or DAP IV) preferentially cleaves substrate peptides with Pro or Ala at the P1 position. The substrate recognition mechanism has been fully elucidated for mammalian DPP IV by crystal structure analyses but not for bacterial orthologues. Here, we report the crystal structures of a bacterial DPP IV (PmDAP IV) in its free form and in complexes with two kinds of dipeptides as well as with a non-peptidyl inhibitor at 1.90 to 2.47 Å resolution. Acyl-enzyme intermediates were observed for the dipeptide complexes of PmDAP IV, whereas tetrahedral intermediates were reported for the oligopeptide complexes of mammalian DPP IVs. This variation reflects the different structural environments of the active site Arg residues, which are involved in the recognition of a substrate carbonyl group, of mammalian and bacterial enzymes. A phylogenetic analysis revealed that PmDAP IV is a closer relative of dipeptidyl peptidases 8 and 9 (DPP8 and DPP9, DPP IV-family enzymes) than DPP IV. These results provide new insights into the substrate recognition mechanism of bacterial DAP IVs and may assist in the development of selective inhibitors for DAP IVs from pathogenic asaccharolytic bacteria, which utilise proteins or peptides as an energy source.

Dipeptidyl peptidase IV and quorum sensing signaling in biofilm-related virulence of Prevotella aurantiaca

Biofilm formation and dipeptidyl peptidase IV (DPPIV) enzyme activity contribute to the virulence of oral bacteria, and these virulence factors are partly regulated by quorum sensing signaling system. We recently demonstrated that estradiol regulates growth properties and DPPIV activity of Prevotella intermedia, Prevotella nigrescens, and Prevotella pallens. Here, we examined the DPPIV dependency of biofilm formation of Prevotella aurantiaca. Three strains (two clinical strains AHN 37505 and 37552 and the type strain CCUG 57723) were incubated in three estradiol concentrations (30, 90, and 120 nmol/L). Regulation of DPPIV activity, biofilm and fimbria formation, and coaggregation of bacterial strains were analyzed after incubation with four concentrations (10 nM, 100 nM, 1 μM, 10 μM) of dihydroxy-2,3-pentaedione (DPD), the universal precursor of autoinducer -2 (AI-2), and analogs (ethyl-DPD, butyl-DPD, and isobutyl-DPD) for 24 h. Estradiol enhanced the planktonic growth, coaggregation, and biofilm formation of P. aurantiaca strains. The whole cell extract of AHN 37505 had the highest DPPIV activity, followed by CCUG 57723 and AHN 37552. Inhibition of DPPIV activity with di-isopropylfluorophosphate suppressed the effect of estradiol on biofilm formation. At 100 nM and 10 μM concentrations of DPD, butyl DPD, and isobutyl DPD, biofilm formation of P. aurantiaca was significantly inhibited. Fimbriae formation was enhanced up to concentrations of 100 nM and 1 μM followed by a significant inhibition at higher concentrations of DPD and all analogs. A slight but significant inhibitory effect of DPD and analogs on DPPIV activity was observed. Our results indicate that DPPIV plays a key role in the estradiol-regulated biofilm formation of P. aurantiaca. Quorum sensing autoinducer DPD and C1-alkyl analogs could inhibit biofilm-related virulence of P. aurantiaca.

PAI-2/SerpinB2 inhibits proteolytic activity in a P. gingivalis-dominated multispecies bacterial consortium

OBJECTIVE

The aim of this study was to investigate the ability of the serine protease inhibitor plasminogen activator inhibitor type 2 (PAI-2/Serpin B2) to inhibit proteases produced by a multispecies bacterial consortium in vitro.

BACKGROUND

Gingival and periodontal inflammation is associated with an increased flow of protein-rich gingival fluid. This nutritional change in the microenvironment favors bacteria with a proteolytic phenotype, triggering inflammation and associated tissue breakdown. PAI-2 is produced by macrophages and keratinocytes and is present in very high concentrations in gingival crevicular fluid; the highest level in the body.

DESIGN

A multispecies bacterial consortium comprising nine bacterial strains, resembling the conditions in a periodontal pocket, was grown planktonically and as a biofilm. After seven days PAI-2 was added to the consortium and the proteolytic activity was assayed with fluorogenic protease substrates; FITC-labeled casein to detect global protease activity, fluorescent H-Gly-Pro-AMC for serine protease activity and fluorescent BIKKAM-10 for Porphyromonas gingivalis-associated protease activity. Protease activity associated with biofilm cells was examined by confocal scanning laser microscopy.

RESULTS

PAI-2 inhibited proteolytic activity of the bacterial consortium, as seen by decreased fluorescence of all substrates. PAI-2 specifically inhibited P. gingivalis proteolytic activity.

CONCLUSION

To our knowledge, this is the first time that PAI-2 has been shown to inhibit bacterial proteases. Given the high concentration of PAI-2 in the gingival region, our results indicate that PAI-2 might play a role for the integrity of the epithelial barrier.

Comparative genome analysis of Prevotella intermedia strain isolated from infected root canal reveals features related to pathogenicity and adaptation

Background

Many species of the genus Prevotella are pathogens that cause oral diseases. Prevotella intermedia is known to cause various oral disorders e.g. periodontal disease, periapical periodontitis and noma as well as colonize in the respiratory tract and be associated with cystic fibrosis and chronic bronchitis. It is of clinical significance to identify the main drive of its various adaptation and pathogenicity. In order to explore the intra-species genetic differences among strains of Prevotella intermedia of different niches, we isolated a strain Prevotella intermedia ZT from the infected root canal of a Chinese patient with periapical periodontitis and gained a draft genome sequence. We annotated the genome and compared it with the genomes of other taxa in the genus Prevotella.

Results

The raw data set, consisting of approximately 65X-coverage reads, was trimmed and assembled into contigs from which 2165 ORFs were predicted. The comparison of the Prevotella intermedia ZT genome sequence with the published genome sequence of Prevotella intermedia 17 and Prevotella intermedia ATCC25611 revealed that ~14% of the genes were strain-specific. The Preveotella intermedia strains share a set of conserved genes contributing to its adaptation and pathogenic and possess strain-specific genes especially those involved in adhesion and secreting bacteriocin. The Prevotella intermedia ZT shares similar gene content with other taxa of genus Prevotella. The genomes of the genus Prevotella is highly dynamic with relative conserved parts: on average, about half of the genes in one Prevotella genome were not included in another genome of the different Prevotella species. The degree of conservation varied with different pathways: the ability of amino acid biosynthesis varied greatly with species but the pathway of cell wall components biosynthesis were nearly constant. Phylogenetic tree shows that the taxa from different niches are scarcely distributed among clades.

Conclusions

Prevotella intermedia ZT belongs to a genus marked with highly dynamic genomes. The specific genes of Prevotella intermedia indicate that adhesion, competing with surrounding microbes and horizontal gene transfer are the main drive of the evolution of Prevotella intermedia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1272-3) contains supplementary material, which is available to authorized users.

Physiological adaptations of key oral bacteria

Oral colonising bacteria are highly adapted to the various environmental niches harboured within the mouth, whether that means while contributing to one of the major oral diseases of caries, pulp infections, or gingival/periodontal disease or as part of a commensal lifestyle. Key to these infections is the ability to adhere to surfaces via a range of specialised adhesins targeted at both salivary and epithelial proteins, their glycans and to form biofilm. They must also resist the various physical stressors they are subjected to, including pH and oxidative stress. Possibly most strikingly, they have developed the ability to harvest both nutrient sources provided by the diet and those derived from the host, such as protein and surface glycans. We have attempted to review recent developments that have revealed much about the molecular mechanisms at work in shaping the physiology of oral bacteria and how we might use this information to design and implement new treatment strategies.

Role of the cysteine protease interpain A of Prevotella intermedia in breakdown and release of haem from haemoglobin

The gram-negative oral anaerobe Prevotella intermedia forms an iron(III) protoporphyrin IX pigment from haemoglobin. The bacterium expresses a 90 kDa cysteine protease, InpA (interpain A), a homologue of Streptococcus pyogenes streptopain (SpeB). The role of InpA in haemoglobin breakdown and haem release was investigated. At pH 7.5, InpA mediated oxidation of oxyhaemoglobin to hydroxymethaemoglobin [in which the haem iron is oxidized to the Fe(III) state and which carries OH- as the sixth co-ordinate ligand] by limited proteolysis of globin chains as indicated by SDS/PAGE and MALDI (matrix-assisted laser-desorption ionization)-TOF (time-of-flight) analysis. Prolonged incubation at pH 7.5 did not result in further haemoglobin protein breakdown, but in the formation of a haemoglobin haemichrome (where the haem Fe atom is co-ordinated by another amino acid ligand in addition to the proximal histidine residue) resistant to degradation by InpA. InpA-mediated haem release from hydroxymethaemoglobin-agarose was minimal compared with trypsin at pH 7.5. At pH 6.0, InpA increased oxidation at a rate greater than auto-oxidation, producing aquomethaemoglobin (with water as sixth co-ordinate ligand), and resulted in its complete breakdown and haem loss. Aquomethaemoglobin proteolysis and haem release was prevented by blocking haem dissociation by ligation with azide, whereas InpA proteolysis of haem-free globin was rapid, even at pH 7.5. Both oxidation of oxyhaemoglobin and breakdown of methaemoglobin by InpA were inhibited by the cysteine protease inhibitor E-64 [trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane]. In summary, we conclude that InpA may play a central role in haem acquisition by mediating oxyhaemoglobin oxidation, and by degrading aquomethaemoglobin in which haem-globin affinity is weakened under acidic conditions.

Interpain A, a cysteine proteinase from Prevotella intermedia, inhibits complement by degrading complement factor C3

Periodontitis is an inflammatory disease of the supporting structures of the teeth caused by, among other pathogens, Prevotella intermedia. Many strains of P. intermedia are resistant to killing by the human complement system, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with recombinant cysteine protease of P. intermedia (interpain A) resulted in a drastic decrease in bactericidal activity of the serum. Furthermore, a clinical strain 59 expressing interpain A was more serum-resistant than another clinical strain 57, which did not express interpain A, as determined by Western blotting. Moreover, in the presence of the cysteine protease inhibitor E64, the killing of strain 59 by human serum was enhanced. Importantly, we found that the majority of P. intermedia strains isolated from chronic and aggressive periodontitis carry and express the interpain A gene. The protective effect of interpain A against serum bactericidal activity was found to be attributable to its ability to inhibit all three complement pathways through the efficient degradation of the alpha-chain of C3 -- the major complement factor common to all three pathways. P. intermedia has been known to co-aggregate with P. gingivalis, which produce gingipains to efficiently degrade complement factors. Here, interpain A was found to have a synergistic effect with gingipains on complement degradation. In addition, interpain A was able to activate the C1 complex in serum, causing deposition of C1q on inert and bacterial surfaces, which may be important at initial stages of infection when local inflammatory reaction may be beneficial for a pathogen. Taken together, the newly characterized interpain A proteinase appears to be an important virulence factor of P. intermedia.

Dipeptidyl aminopeptidase IV from Stenotrophomonas maltophilia exhibits activity against a substrate containing a 4-hydroxyproline residue

The crystal structure of dipeptidyl aminopeptidase IV from Stenotrophomonas maltophilia was determined at 2.8-A resolution by the multiple isomorphous replacement method, using platinum and selenomethionine derivatives. The crystals belong to space group P4(3)2(1)2, with unit cell parameters a = b = 105.9 A and c = 161.9 A. Dipeptidyl aminopeptidase IV is a homodimer, and the subunit structure is composed of two domains, namely, N-terminal beta-propeller and C-terminal catalytic domains. At the active site, a hydrophobic pocket to accommodate a proline residue of the substrate is conserved as well as those of mammalian enzymes. Stenotrophomonas dipeptidyl aminopeptidase IV exhibited activity toward a substrate containing a 4-hydroxyproline residue at the second position from the N terminus. In the Stenotrophomonas enzyme, one of the residues composing the hydrophobic pocket at the active site is changed to Asn611 from the corresponding residue of Tyr631 in the porcine enzyme, which showed very low activity against the substrate containing 4-hydroxyproline. The N611Y mutant enzyme was generated by site-directed mutagenesis. The activity of this mutant enzyme toward a substrate containing 4-hydroxyproline decreased to 30.6% of that of the wild-type enzyme. Accordingly, it was considered that Asn611 would be one of the major factors involved in the recognition of substrates containing 4-hydroxyproline.

A new autocatalytic activation mechanism for cysteine proteases revealed by Prevotella intermedia interpain A

Prevotella intermedia is a major periodontopathogen contributing to human gingivitis and periodontitis. Such pathogens release proteases as virulence factors that cause deterrence of host defenses and tissue destruction. A new cysteine protease from the cysteine-histidine-dyad class, interpain A, was studied in its zymogenic and self-processed mature forms. The latter consists of a bivalved moiety made up by two subdomains. In the structure of a catalytic cysteine-to-alanine zymogen variant, the right subdomain interacts with an unusual prodomain, thus contributing to latency. Unlike the catalytic cysteine residue, already in its competent conformation in the zymogen, the catalytic histidine is swung out from its active conformation and trapped in a cage shaped by a backing helix, a zymogenic hairpin, and a latency flap in the zymogen. Dramatic rearrangement of up to 20A of these elements triggered by a tryptophan switch occurs during activation and accounts for a new activation mechanism for proteolytic enzymes. These findings can be extrapolated to related potentially pathogenic cysteine proteases such as Streprococcus pyogenes SpeB and Porphyromonas gingivalis periodontain.