Purification and characterization of alkaline phosphatase of Bacteroides gingivalis 381

Phosphorylation of major Porphyromonas gingivalis virulence factors is crucial for their processing and secretion

The main etiological agent of periodontitis is the anaerobic bacterium Porphyromonas gingivalis. Virulence of this pathogen is controlled by various mechanisms and executed by major virulence factors including the gingipain proteases, peptidylarginine deiminase (PPAD), and RagB, an outer membrane macromolecular transport component. Although the structures and functions of these proteins are well characterized, little is known about their posttranslational maturation. Here, we determined the phosphoproteome of P. gingivalis in which phosphorylated tyrosine residues constitute over 80% of all phosphoresidues. Multiple phosphotyrosines were found in gingipains, PPAD, and RagB. Although mutation of phosphorylated residues in PPAD and RagB had no effect on secretion or activity, site-directed mutagenesis showed that phosphorylation in hemagglutinin/adhesin domains of RgpA and Kgp, and in the catalytic domain of RgpB, had a strong influence on secretion, processing, and enzymatic activity. Moreover, preventing phosphorylation of one gingipain influenced the others, suggesting multiple phosphorylation-dependent pathways of gingipain maturation in P. gingivalis. Various candidate kinases including Ptk1 BY kinase and ubiquitous bacterial kinase 1 (UbK1) may be involved, but their contribution to gingipain processing and activation remains to be confirmed.

Characterization of Fusobacterium necrophorum isolated from llama and alpaca

Fusobacterium necrophorum, a Gram-negative, anaerobic bacterium, is an opportunistic animal and human pathogen that causes a variety of infections termed necrobacillosis. There are 2 subspecies of F. necrophorum (subsp. necrophorum and subsp. funduliforme) that differ morphologically and biochemically and in virulence. Leukotoxin, a secreted protein, is considered to be the major virulence factor. In camelids, F. necrophorum causes a variety of infections, generally involving the lips, tongue, pharynx, interdigital spaces, foot pad, larynx, mandible, or maxillary bones. The objective of the current study was to characterize the presumptive Fusobacterium isolates from a variety of necrotic infections in llama (Lama glama) and alpaca (Vicugna pacos) and determine whether the strains possess leukotoxin activities. A total of 7 isolates from alpaca and 2 isolates from llama were characterized. Based on growth characteristics in broth culture, and biochemical and polymerase chain reaction analyses, all 9 isolates belonged to subsp. necrophorum and possessed the putative hemagglutinin gene. Western blot analysis with antileukotoxin antibodies raised in rabbit showed the presence of leukotoxin protein in the culture supernatant of all isolates. Furthermore, flow cytometry of the culture supernatants demonstrated cytotoxicity to bovine and alpaca polymorphonuclear leukocytes (PMNs). The extent of cytotoxicity to either alpaca or bovine PMNs differed among camelid strains. The cytotoxicity of many of the camelid strains was higher (P < 0.05) toward alpaca PMNs compared to bovine PMNs. Fusobacterium necrophorum isolates from llama and alpaca are similar to bovine isolates, and leukotoxin may be a major virulence factor.

Detection, purification and characterisation of a secretory alkaline phosphatase from Onchocerca species

An Onchocerca secretory alkaline phosphatase (E.C. 3.1.3.1) of molecular weight 90 kDa when in crude extract, but which dimerises to about 180 kDa upon purification, was detected, purified and characterised. The enzyme was found to be secreted by both O. ochengi and O. volvulus worms. It was shown to be of Onchocerca origin by Western blotting with bovine onchocerciasis sera and by its time-dependent release in cultures. The O. ochengi enzyme was purified to near homogeneity by a combination of polyethylene glycol precipitation, DEAE-cellulose chromatography and preparative electrophoresis. About 0.96 mg of the active enzyme was purified from 48.4 mg of the crude parasite-released products, giving a purification fold of 71.45 and a yield of 8.7%. The purified enzyme exhibited a typical Michaelis-Menten kinetics with optimum activity on p-nitrophenylphosphate (p-NPP) at pH 10.2. Its apparent K(m) for p-NPP was 0.56+/-0.03 mM and it required Mg(2+) and dithiothreitol (DTT) for stability throughout its purification. Sodium dodecyl sulphate at 2% (w/v) did not inhibit the enzyme activity, but apparently stabilised it during freezing. Inorganic phosphate inhibited the enzyme competitively with an apparent inhibition constant (K(i)) of 3.33+/-0.04 mM, whereas l-phenylalanine inhibited it in a mixed way with a K(i) of 3.18+/-0.03 mM. While contributing to the understanding of metabolism in Onchocerca, the present apparently unique enzyme which is likely to serve in the nutrition of the parasite could be further characterised as a macrofilaricide target or diagnostic marker in onchocerciasis.

Trimeric structure of major outer membrane proteins homologous to OmpA in Porphyromonas gingivalis

The major outer membrane proteins Pgm6 (41 kDa) and Pgm7 (40 kDa) of Porphyromonas gingivalis ATCC 33277 are encoded by open reading frames pg0695 and pg0694, respectively, which form a single operon. Pgm6 and Pgm7 (Pgm6/7) have a high degree of similarity to Escherichia coli OmpA in the C-terminal region and are predicted to form eight-stranded beta-barrels in the N-terminal region. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Pgm6/7 appear as bands with apparent molecular masses of 40 and 120 kDa, with and without a reducing agent, suggesting a monomer and trimer, respectively. To verify the predicted trimeric structure and function of Pgm6/7, we constructed three mutants with pg0695, pg0694, or both deleted. The double mutant produced no Pgm6/7. The single-deletion mutants appeared to contain less Pgm7 and Pgm6 and to form homotrimers that migrated slightly faster (115 kDa) and slower (130 kDa), respectively, than wild-type Pgm6/7 under nonreducing conditions. N-terminal amino acid sequencing and mass spectrometry analysis of partially digested Pgm6/7 detected only fragments from Pgm6 and Pgm7. Two-dimensional, diagonal electrophoresis and chemical cross-linking experiments with or without a reducing agent clearly showed that Pgm6/7 mainly form stable heterotrimers via intermolecular disulfide bonds. Furthermore, growth retardation and arrest of the three mutants and increased permeability of their outer membranes indicated that Pgm6/7 play an important role in outer membrane integrity. Based on results of liposome swelling experiments, these proteins are likely to function as a stabilizer of the cell wall rather than as a major porin in this organism.

Inhibitory effects of green tea catechins on protein tyrosine phosphatase in Prevotella intermedia

Members of the Prevotella intermedia group possess protein tyrosine phosphatase (PTPase). The purpose of this study was to investigate the effects of catechin derivatives from Japanese green tea on the activity of PTPase in P. intermedia and related organisms. Multilocus enzyme electrophoresis of alkaline phosphatase derived from P. intermedia, Prevotella nigrescens, Prevotella pallens and Porphyromonas gingivalis revealed a species-specific migration pattern. Among the tea catechin derivatives tested, (-)-epigallocatechin gallate (EGCg), similar to orthovanadate, a specific inhibitor for PTPase, was effective in inhibiting the PTPase activity in P. intermedia at 0.5 microm, and related species at 5 microm. The results suggested that the inhibitory effect observed is due to the presence of galloyl moiety in the structure. In contrast, neither the green tea catechins nor orthovanadate inhibited the phosphatase activity in P. gingivalis, suggesting that this organism possessed a different family of alkaline phosphatase.

Purification and characterization of arginine carboxypeptidase produced by Porphyromonas gingivalis

Arginine carboxypeptidase was isolated from the cytoplasm of Porphyromonas gingivalis 381 and purified by DEAE-Sephacel column chromatography, followed by high-performance liquid chromatography on DEAE-5PW and TSK G2000SW(XL). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme revealed the presence of three major bands at 42, 33, and 32 kDa with identical N-terminal sequences. By Western blotting analysis and immunoelectron microscopy, the arginine carboxypeptidase was found to be widely distributed in the cytoplasm and on the surface of the outer membrane. The open reading frame corresponding to the N-terminal amino acids of the arginine carboxypeptidase was detected by a search of the sequence of the P. gingivalis W83 genome. This sequence showed homology with mammalian carboxypeptidases (M, N, and E/H) and included a zinc-binding region signature, suggesting that the enzyme is a member of the zinc carboxypeptidase family. The purified enzyme was inhibited by EGTA, o-phenanthroline, DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid, and some metal ions, such as Cu(2+), Zn(2+), and Cd(2+). On the other hand, Co(2+) activated the enzyme. The enzyme released arginine and/or lysine from biologically active peptides containing these amino acids at the C terminus but did not cleave substrates when proline was present at the penultimate position. These results indicate that the arginine carboxypeptidase produced by P. gingivalis is an exo type of metallocarboxypeptidase. This enzyme may function to release arginine in collaboration with an arginine aminopeptidase, e.g., Arg-gingipain, to obtain specific amino acids from host tissues during the growth of P. gingivalis.

Characterization of a highly thermostable alkaline phosphatase from the euryarchaeon Pyrococcus abyssi

This work reports the first isolation and characterization of an alkaline phosphatase (AP) from a hyperthermophilic archaeon. An AP gene from Pyrococcus abyssi, a euryarchaeon isolated from a deep-sea hydrothermal vent, was cloned and the enzyme expressed in Escherichia coli. Analysis of the sequence showed conservation of the active site and structural elements of the E. coli AP. The recombinant AP was purified and characterized. Monomeric and homodimeric active forms were detected, with a monomer molecular mass of 54 kDa. Apparent optimum pH and temperature were estimated at 11.0 and 70 degrees C, respectively. Thus far, P. abyssi AP has been demonstrated to be the most thermostable AP, with half-lives at 100 and 105 degrees C of 18 and 5 h, respectively. Enzyme activity was found to be dependent on divalent cations: metal ion chelators inhibited activity, whereas the addition of exogenous Mg(II), Zn(II), and Co(II) increased activity. The enzyme was inhibited by inorganic phosphate, but not by molybdate and vanadate. Strong inhibitory effects were observed in the presence of thiol-reducing agents, although cysteine residues of the P. abyssi AP were not found to be incorporated within intra- or interchain disulfide bonds. In addition, P. abyssi AP was demonstrated to dephosphorylate linear DNA fragments with dephosphorylation efficiencies of 93.8 and 84.1% with regard to cohesive and blunt ends, respectively.

Isolation, cloning, and expression of an acid phosphatase containing phosphotyrosyl phosphatase activity from Prevotella intermedia

A novel acid phosphatase containing phosphotyrosyl phosphatase (PTPase) activity, designated PiACP, from Prevotella intermedia ATCC 25611, an anaerobe implicated in progressive periodontal disease, has been purified and characterized. PiACP, a monomer with an apparent molecular mass of 30 kDa, did not require divalent metal cations for activity and was sensitive to orthovanadate but highly resistant to okadaic acid. The enzyme exhibited substantial activity against tyrosine phosphate-containing peptides derived from the epidermal growth factor receptor. On the basis of N-terminal and internal amino acid sequences of purified PiACP, the gene coding for PiACP was isolated and sequenced. The PiACP gene consisted of 792 bp and coded for a basic protein with an M(r) of 29,164. The deduced amino acid sequence exhibited striking similarity (25 to 64%) to those of members of class A bacterial acid phosphatases, including PhoC of Morganella morganii, and involved a conserved phosphatase sequence motif that is shared among several lipid phosphatases and the mammalian glucose-6-phosphatases. The highly conservative motif HCXAGXXR in the active domain of PTPase was not found in PiACP. Mutagenesis of recombinant PiACP showed that His-170 and His-209 were essential for activity. Thus, the class A bacterial acid phosphatases including PiACP may function as atypical PTPases, the biological functions of which remain to be determined.

Purification and characterization of alkaline phosphatase containing phosphotyrosyl phosphatase activity from the bacterium Prevotella intermedia

A novel alkaline phosphatase, designated PiALP, has been purified and characterized from Prevotella intermedia ATCC 25611, an anaerobe implicated in progressive periodontal disease. The enzyme was a homodimer of apparently identical subunits of Mr 54 kDa. Thiol-reducing agents completely inhibited the purified enzyme. The enzyme was highly stable even at 80 degrees C. It exhibited substantial activity against tyrosine-phosphate-containing Raytide. The phosphatase activity was sensitive to orthovanadate and Zn2+ but highly resistant to okadaic acid. The amino acid sequence of peptides derived from PiALP showed a high degree of identity (65%) with alkaline phosphatases from Zymomonas mobilis and Synechococcus. The present results imply that PiALP might represent a new family of alkaline phosphotyrosyl phosphatases which has not been described previously.

Cloning and expression of a neutral phosphatase gene from Treponema denticola

We have isolated and characterized a neutral phosphatase gene, phoN, from Treponema denticola ATCC 35405. The gene was isolated from a T. denticola clone bank constructed in the medium-copy-number plasmid vector pMCL19. Subcloning and nucleotide sequencing of the DNA insert from one phosphatase clone, pTph14, revealed that the activity corresponded to an open reading frame consisting of 1,027 bp coding for a 37.9-kDa protein. Hydrophobicity analysis indicated that the protein exhibits some hydrophobic regions. Indeed, partial purification of the phosphatase suggested that the enzyme was membrane associated both in T. denticola and in the Escherichia coli clone. The pH optimum of the enzyme, approximately pH 6.4, indicated that it corresponded to a neutral phosphatase activity from T. denticola. An examination of possible natural substrates for the enzyme suggested that this enzyme hydrolyzes nucleoside di- and triphosphates. Northern (RNA) blot analysis revealed that this phosphatase gene is not likely to be present in an operon structure.

Pathogenic mechanisms in periodontal disease

Periodontal diseases have been considered as "infections" in which micro-organisms initiate and maintain the destructive inflammatory response. Host-mediated tissue destruction occurs via complement activation and the release of lysosomal enzymes, and connective tissue matrix metalloproteinases. Microbial enzymes may damage connective tissues directly, and, together with toxic metabolites and structural materials, are thought to disrupt the reparative activities of fibroblasts and cells of the immune defenses. The significance and relative contributions of host and microbial factors to the disease process remain unresolved. Environmental changes in the gingival sulcus and periodontal pocket and tissues, the degree of the host response and nutrient availability, concomitant with disease progression, compromise tissue metabolism and repair, and allow for enhanced or de novo expression of microbial virulence factors, such as proteases, which alter microbial pathogenicity. Proteolytic destruction of specific antibodies and complement by both viable and non-viable bacterial cells may retard phagocytic killing and removal of pathogens, thus prolonging the inflammatory response. Bacterial products may indirectly mediate tissue destruction by stimulating release of matrix metalloproteinases or by proteolytically inactivating the specific inhibitors of these enzymes.

Characteristics of a protease inhibitor produced by Prevotella intermedia

The characterization of a protease inhibitor produced by a strain of Prevotella intermedia is reported in the present study. The protease inhibitor was secreted into the culture medium during the exponential growth phase and was also present in significant amounts in the periplasmic space. The inhibitor was active against a wide variety of proteolytic enzymes, including the trypsin-like activity of Porphyromonas gingivalis. The inhibitory compound, a heat labile protein, was isolated by non-denaturing preparative polyacrylamide gel electrophoresis, using concentrated culture supernatant as starting material. The exact functions and the ecological roles of the protease inhibitor produced by P. intermedia remain to be determined.

Effective method for discriminating between oral bacterial and human alkaline phosphatase activity

Alkaline phosphatase (ALPase) activity was quantitatively compared in various kinds of oral bacteria. High ALPase activity was detected in 3 species of periodontal bacteria, Porphyromonas gingivalis, Prevotella intermedia and Capnocytophaga sputigena. The ALPase activity detected in these bacteria was almost completely inhibited in the presence of 1% sodium dodecyl sulfate (SDS). By contrast, the activity of mammalian ALPase isoenzymes was not inhibited at all even in the presence of 1% SDS. These results indicate that the ALPase assay in combination with 1% SDS can identify the origin of ALPase detected in gingival crevicular fluid as being from bacteria or from a host response. Clinical examination with adult periodontitis revealed that ALPase activity in gingival crevicular fluid from the patients consisted of a combination of SDS-sensitive and SDS-resistant activities. These findings indicate that ALPase activity detected in gingival crevicular fluid originates not only from bacteria but also from a host response.

Effect of calcium ions on cell surface electrostatics of Bacteroides gingivalis and other oral bacteria

Surface electrostatics of Bacteroides gingivalis and other oral bacteria were examined. A polarization circuit was employed using platinum electrodes exposed in each bacterial suspension and the number of bacteria adsorbed to the anode and cathode were then estimated. In all bacteria (B. gingivalis, Streptococcus sobrinus, S. mutans, S. salivarius, S. sanguis and Actinomyces viscosus), the number of cells adsorbed to the anode were much greater than the number of cells adsorbed to the cathode. Treating these bacteria with calcium ions tended to decrease the ratio of the number of cells adsorbed to the anode to the number of cells adsorbed to the cathode in all bacteria examined. Moreover, in the case of B. gingivalis, the number of cells adsorbed to the anode and cathode was in an inverse relationship to the number counted before calcium ion treatment. These findings indicate that the cell surfaces of oral bacteria are generally negatively charged but only the cell surface electrostatics of B. gingivalis was dramatically affected by calcium ion treatment. Thus, divalent metal bridges such as calcium bridges contribute to the adherence of the periodontopathic bacterium, B. gingivalis rather than to that of other oral bacteria including cariogenic bacteria.