Complete nucleotide sequence of the structural gene for alkaline proteinase from Pseudomonas aeruginosa IFO 3455

Effect of Pseudomonas colonisation on lower limb venous ulcer healing: a systematic review

OBJECTIVE

Pseudomonas aeruginosa is a Gram-negative bacillus that commonly colonises lower limb venous ulcers. Its effects on venous ulcer healing are widely debated. It produces exotoxins and elastase, as well as forming biofilms in hard-to-heal wounds. It is postulated that these virulence factors lead to slower healing times in patients with lower limb venous ulcers colonised with Pseudomonas. This review aimed to summarise the available evidence pertaining to this topic.

METHOD

A systematic review was performed in August 2019, where the Pubmed, Cochrane and Embase databases were searched for relevant literature according to PRISMA guidelines. Retrospective and prospective studies examining the effect of Pseudomonas colonisation on any measure of ulcer healing were included.

RESULTS

Some 282 articles were screened, of which seven studies including 491 patients were ultimately included for analysis. Of these, no study demonstrated a significant association between Pseudomonas colonisation and delayed healing of venous ulcers. In five of the seven studies, the effect of Pseudomonas aeruginosa on initial ulcer size at presentation was recorded.

CONCLUSION

All the studies demonstrated an association between ulcer size and the presence of Pseudomonas aeruginosa. While Pseudomonas aeruginosa may colonise larger ulcers or those with a worse prognosis, no evidence was found to support the hypothesis that this colonisation had a negative impact on lower limb venous ulcer healing.

Molecular investigation of a gene encoding organic solvent-tolerant alkaline protease from Pseudomonas aeruginosa strain K

A gene encoding an organic solvent-stable protease was amplified from Pseudomonas aeruginosa strain K by polymerase chain reaction using consensus primers based on multiple sequence alignment of alkaline and metalloprotease genes from Pseudomonas species. The gene, which consisted of 1440 bp nucleotides and deduced 479 amino acid residues, was successfully expressed in pGEX-4T-1 expression system in the presence of 1.0 mM IPTG, after an incubation of 6 h at 37 degrees C. Under these conditions, the recombinant strain K protease was, subsequently, released into the periplasm of E. coli BL21 (DE3) with an optimum proteolytic activity detected at 1.0112 U/ml. To date, this is the first reported expression of alkaline protease (aprA) with such remarkable property in Escherichia coli.

Heterogeneity of heat-resistant proteases from milk Pseudomonas species

Pseudomonas fragi, Pseudomonas lundensis and members of the Pseudomonas fluorescens group may spoil Ultra High Temperature (UHT) treated milk and dairy products, due to the production of heat-stable proteases in the cold chain of raw milk. Since the aprX gene codes for a heat-resistant protease in P. fluorescens, the presence of this gene has also been investigated in other members of the genus. For this purpose an aprX-screening PCR test has been developed. Twenty-nine representatives of important milk Pseudomonas species and thirty-five reference strains were screened. In 42 out of 55 investigated Pseudomonas strains, the aprX gene was detected, which proves the potential of the aprX-PCR test as a screening tool for potentially proteolytic Pseudomonas strains in milk samples. An extensive study of the obtained aprX-sequences on the DNA and the amino acid level, however, revealed a large heterogeneity within the investigated milk isolates. Although this heterogeneity sets limitations to a general detection method for all proteolytic Pseudomonas strains in milk, it offers a great potential for the development of a multiplex PCR screening test targeting individual aprX-genes. Furthermore, our data illustrated the potential use of the aprX gene as a taxonomic marker, which may help in resolving the current taxonomic deadlock in the P. fluorescens group.

Cloning, expression, and purification of insecticidal protein Pr596 from locust pathogen Serratia marcescens HR-3

A novel insecticidal protein (Pr596) produced by Serratia marcescens HR-3 was found be a metalloprotease and responsible for insecticidal activity toward locusts. Two pairs of primers were designed to amplify Pr596, a putative open reading frame (ORF) by similarity search and the N-terminal amino-acid sequence of insecticidal protein. The results revealed that the ORF consisted of 1464 nucleotides encoding a protein of 487 amino-acid residues. Pr596 was cloned into expression vector pET32a(+) and was expressed in Escherichia coli BL21 (DE3)/pLysS strain with isopropyl-beta-D-thiogalactopyranoside induction. The Pr596 was found to be highly expressed as inclusion bodies by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Pr596 inclusion bodies were isolated and subjected to Ni-NTA His Bind Resins (Pharmacia, Germany). Pr596 purified and refolded was revealed by SDS-PAGE and had proteolytic activity and insecticidal activity. Results suggested that there is a potential to develop this protein to be used as an alternative locus control agent.

Reliable enzyme-linked immunosorbent assay systems for pathogenic factors of Pseudomonas aeruginosa alkaline proteinase, elastase, and exotoxin A: a comparison of methods for labeling detection antibodies with horseradish peroxidase

Sensitive sandwich enzyme-linked immunosorbent assay (ELISA) systems for the quantification of 3 pathogenic factors of Pseudomonas aeruginosa-alkaline proteinase (aeruginolysin), elastase (pseudolysin ), and exotoxin A-were developed. The maleimide-pyridyl disulfide method was applied for the labeling of rabbit anti-each antigen IgG with horseradish peroxidase (HRP) and the conjugates were used as secondary antibodies (detection antibodies) in the ELISA systems. The EDTA, a chelating agent, was added to the buffers for sample and detection antibody, which inhibited the degradation of IgG by elastase derived from P. aeruginosa for improving the assay precision. The ELISA systems using the HRP-labeled detection antibodies produced by the maleimide-pyridyl disulfide method exhibited higher sensitivity than previously reported methods. The detection limits for alkaline proteinase, elastase, and exotoxin A were 18 pg/ml, 34 pg/ml, and 22 pg/ml, respectively. The intra-assay coefficients of variation for alkaline proteinase, elastase, and exotoxin A were 3.4%-5.0%, 1.9%-3.5%, and 1.3%-5.4%, respectively. These ELISA systems exhibited good inter-assay precision, non-cross-reactivity, dilution linearity, and recovery . Employing these ELISA systems, we revealed that pathogenic factor concentrations were different among the P. aeruginosa strains tested, which may relate to the different pathogenicity of each strain.

Interaction of a novel form of Pseudomonas aeruginosa alkaline protease (aeruginolysin) with interleukin-6 and interleukin-8

Pseudomonas aeruginosa secretes several proteases considered as important virulence factors. In this report we present data indicating that two key proinflammatory cytokines, interleukin-6 (IL-6) and IL-8, are substrates for pseudolysin (elastase) and aeruginolysin (alkaline protease). While IL-6 was totally digested by both proteases, a long form of IL-8 (IL-8-77) was first rapidly processed into a 72-residue form with enhanced chemokine activity, then very slowly degraded. Interestingly, aeruginolysin bearing two additional residues at the N-terminus (Leu-Lys-aeruginolysin) in the absence of calcium degraded both IL-6 and IL-8-72 far more efficiently than the shorter form of the enzyme.

Nonnatural amino acid incorporation into the methionine 214 position of the metzincin Pseudomonas aeruginosa alkaline protease

Background

The alkaline protease from Pseudomonas aeruginosa (AprA) is a member of the metzincin superfamily of metalloendoproteases. A key feature of these proteases is a conserved methionine-containing 1,4-tight β turn at the base of the active site zinc binding region.

Results

To explore the invariant methionine position in this class of protease, incorporation of a nonnatural fluorinated methionine, L-difluoromethionine (DFM), into this site was accomplished. Although overproduction of the N-terminal catalytic fragment of AprA resulted in protein aggregates which could not be resolved, successful heterologous production of the entire AprA was accomplished in the presence and absence of the nonnatural amino acid. DFM incorporation was found to only slightly alter the enzyme kinetics of AprA. In addition, differential scanning calorimetry indicated no significant alteration in the thermal stability of the modified enzyme.

Conclusion

Although invariant in all metzincin proteases, the methionine 214 position in AprA can be successfully replaced by the nonnatural amino acid DFM resulting in little effect on protein structure and function. This study indicates that the increased size of the methyl group by the introduction of two fluorines is still sufficiently non-sterically demanding, and bodes well for the application of DFM to biophysical studies of protein structure and function in this class of protease.

Elastase-producing Pseudomonas aeruginosa degrade plasma proteins and extracellular products of human skin and fibroblasts, and inhibit fibroblast growth

Leg ulcers of venous origin represent a disease affecting 0.1-0.2% of the population. It is known that almost all chronic ulcers are colonized by different bacteria, such as staphylococci, enterococci and Pseudomonas aeruginosa. We here report that P. aeruginosa, expressing the major metalloproteinase elastase, induces degradation of complement C3, various antiproteinases, kininogens, fibroblast proteins, and proteoglycans (PG) in vitro, thus mimicking proteolytic activity previously identified in chronic ulcer fluid in vivo. Elastase-producing P. aeruginosa isolates were shown to significantly degrade human wound fluid as well as human skin proteins ex vivo. Elastase-containing conditioned P. aeruginosa medium and purified elastase inhibited fibroblast cell growth. These effects, in conjunction with the finding that proteinase production was detected in wound fluid ex vivo, suggest that bacterial proteinases play a pathogenic role in chronic ulcers.

Proteinases of common pathogenic bacteria degrade and inactivate the antibacterial peptide LL-37

Effectors of the innate immune system, the anti-bacterial peptides, have pivotal roles in preventing infection at epithelial surfaces. Here we show that proteinases of the significant human pathogens Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and Streptococcus pyogenes, degrade the antibacterial peptide LL-37. Analysis by mass spectrometry of fragments generated by P. aeruginosa elastase in vitro revealed that the initial cleavages occurred at Asn-Leu and Asp-Phe, followed by two breaks at Arg-Ile, thus inactivating the peptide. Proteinases of the other pathogens also degraded LL-37 as determined by SDS-PAGE. Ex vivo, P. aeruginosa elastase induced LL-37 degradation in human wound fluid, leading to enhanced bacterial survival. The degradation was blocked by the metalloproteinase inhibitors GM6001 and 1, 10-phenantroline (both of which inhibited P. aeruginosa elastase, P. mirabilis proteinase, and E. faecalis gelatinase), or the inhibitor E64 (which inhibited S. pyogenes cysteine proteinase). Additional experiments demonstrated that dermatan sulphate and disaccharides of the structure [DeltaUA(2S)-GalNAc(4,6S)], or sucroseoctasulphate, inhibited the degradation of LL-37. The results indicate that proteolytic degradation of LL-37 is a common virulence mechanism and that molecules which block this degradation could have therapeutic potential.

Arylamidase activity of neutral proteinase from Saccharomonospora canescens. Comparison with other Zn-proteinases that exhibit the same activity

The arylamidase activity of Zn-proteinase from Saccharomonospora canescens (NPS) was studied with series of peptide nitroanilides of varying amino acid sequence and N-acyl blocking groups. The partial mapping of the enzyme S(1), S(2), S(3), S(4) subsites shows that variations in all positions P(1) to P(4) in the substrate structure affect the catalytic efficiency. The importance of P(4)-S(4) and P(1)-S(1) interactions, which is a characteristic feature of the serine proteinases, is evidenced for the studied Zn-proteinases NPS and serralysin too. The presence of arylamidase activity in the case of Zn-proteinases-astacin EC 3.4.24.21 and serralysin EC 3.4.24.40 is correlated with some specific characteristics of their active site structure: penta-coordinated Zn(2+) and a tyrosyl residue as a fifth ligand to the Zn(2+). It is assumed that this tyrosyl residue plays a role in the productive binding and stabilization of the tetrahedral adduct formed during the reaction of enzyme-catalysed hydrolysis of peptide arylamides of corresponding length and sequence.

Caulobacter crescentus synthesizes an S-layer-editing metalloprotease possessing a domain sharing sequence similarity with its paracrystalline S-layer protein

Strains of Caulobacter crescentus elaborate an S-layer, a two-dimensional protein latticework which covers the cell surface. The S-layer protein (RsaA) is secreted by a type I mechanism (relying on a C-terminal signal) and is unusual among type I secreted proteins because high levels of protein are produced continuously. In efforts to adapt the S-layer for display of foreign peptides and proteins, we noted a proteolytic activity that affected S-layer monomers with foreign inserts. The cleavage was precise, resulting in fragments with an unambiguous N-terminal sequence. We developed an assay to screen for loss of this activity (i.e., presentation of foreign peptides without degradation), using transposon and traditional mutagenesis. A metalloprotease gene designated sap (S-layer-associated protease) was identified which could complement the protease-negative mutants. The N-terminal half of Sap possessed significant similarity to other type I secreted proteases (e.g., alkaline protease of Pseudomonas aeruginosa), including the characteristic RTX repeat sequences, but the C-terminal half which normally includes the type I secretion signal exhibited no such similarity. Instead, there was a region of significant similarity to the N-terminal region of RsaA. We hypothesize that Sap evolved by combining the catalytic portion of a type I secreted protease with an S-layer-like protein, perhaps to associate with nascent S-layer monomers to "scan" for modifications.

Iron-Mediated regulation of alkaline proteinase production in Pseudomonas aeruginosa

We analyzed the regulation by iron of alkaline proteinase (AP) production in Pseudomonas aeruginosa. Extracellular AP production was detected from the mid-logarithmic to the stationary phase by an antibody-based assay system, and was strongly repressed by iron in the medium. This repression was shown by Northern hybridization and primer extension to occur at the level of transcription. The primer extension analysis revealed that the start point of transcription of AP gene was the nucleotide position -84 from the start point of translation. Furthermore, we investigated whether this transcriptional repression involved PvdS protein. Using the mutant strain of pvdS, the alternative sigma factor gene revealed that the PvdS protein is required for the full expression of AP, and a previous study showed that expression of pvdS is also repressed by iron. Therefore, we thought that one mechanism of repression of AP production operated through reduction of the PvdS protein level. Purified AP decomposed the transferrin, and released iron from it. Purified AP added to the medium containing transferrin as the only iron source enhanced the growth of P. aeruginosa. Moreover, mutation in the AP gene decreased the growth rate in the medium containing the transferrin as the only iron source. These results clearly indicated that AP expression should occur in a free-iron-deficient environment and emphasized the importance of AP to iron acquisition in the infection site.

Epidemic population structure of Pseudomonas aeruginosa: evidence for a clone that is pathogenic to the eye and that has a distinct combination of virulence factors

The genetic structure of a population of Pseudomonas aeruginosa, isolated from patients with keratitis, endophthalmitis, and contact lens-associated red eye, contact lens storage cases, urine, ear, blood, lungs, wounds, feces, and the environment was determined by multilocus enzyme electrophoresis. The presence and characteristics of virulence factors were determined by restriction fragment length polymorphism analysis with DNA probes for lasA, lasB, aprA, exoS, exoT, exoU, and ctx and by zymography of staphylolysin, elastase, and alkaline protease. These analyses revealed an epidemic population structure of P. aeruginosa, characterized by frequent recombination in which a particular successful clone may increase, predominate for a time, and then disappear as a result of recombination. Epidemic clones were found among isolates from patients with keratitis. They were characterized by high activity of a hitherto-unrecognized size variant of elastase, high alkaline protease activity, and possession of the exoU gene encoding the cytotoxic exoenzyme U. These virulence determinants are not exclusive traits in strains causing keratitis, as strains with other properties may cause keratitis in the presence of predisposing conditions. There were no uniform patterns of characteristics of isolates from other types of infection; however, all strains from urinary tract infections possessed the exoS gene, all strains from environment and feces and the major part of keratitis and wound isolates exhibited high elastase and alkaline protease activity, and all strains from feces showed high staphylolysin activity, indicating that these virulence factors may be important in the pathogenesis of these infectious diseases.

Dermatan sulphate is released by proteinases of common pathogenic bacteria and inactivates antibacterial alpha-defensin

Defensins represent an evolutionarily conserved group of small peptides with potent antibacterial activities. We report here that extracellular proteinases secreted by the human pathogens Pseudomonas aeruginosa, Enterococcus faecalis and Streptococcus pyogenes release dermatan sulphate by degrading dermatan sulphate-containing proteoglycans, such as decorin. Dermatan sulphate was found to bind to neutrophil-derived alpha-defensin, and this binding completely neutralized its bactericidal activity. During infection, proteoglycan degradation and release of dermatan sulphate may therefore represent a previously unknown virulence mechanism, which could serve as a target for novel antibacterial strategies.

Cloning and sequencing of a gene of organic solvent-stable protease secreted from Pseudomonas aeruginosa PST-01 and its expression in Escherichia coli

A gene of organic solvent-stable protease (PST-01 protease) secreted by Pseudomonas aeruginosa PST-01 was cloned and its nucleotide was sequenced. The nucleotide sequence analysis revealed that the PST-01 protease was a pseudolysin, which was an elastase produced by P. aeruginosa and was well characterized by the previous investigators. The PST-01 protease produced in recombinant Escherichia coli was not secreted into the extracellular medium, but its proenzyme was released by the lysis of the cells and became a 33.1kDa mature enzyme autoproteolytically. Its characteristics including organic solvent stability were as same as those of the PST-01 protease secreted by P. aeruginosa PST-01.

Molecular characterization of a protease secreted by Erwinia amylovora

A protease with a molecular mass of 48 kDa is secreted by the fire blight pathogen Erwinia amylovora in minimal medium. We characterized this activity as a metalloprotease, since the enzyme was inhibited by EDTA and o -phenanthroline. A gene cluster was determined to encode four genes connected to protease expression, including a structural gene (prtA) and three genes (prtD, prtE, prtF) for secretion of the protease, which are transcribed in the same direction. The organization of the protease gene cluster in E. amylovora is different from that in other Gram-negative bacteria, such as Erwinia chrysanthemi, Pseudomonas aeruginosa and Serratia marcescens. On the basis of the conservative motif of metalloproteases, PrtA was identified to be a member of the metzincin subfamily of zinc-binding metalloproteases, and was confirmed to be the 48 kDa protease on gels by sequencing of tryptic peptide fragments derived from the protein. The protease is apparently secreted into the external medium through the type I secretion pathway via PrtD, PrtE and PrtF which share more than 90% identity with the secretion apparatus for lipase of S. marcescens. A protease mutant was created by Tn 5 -insertions, and the mutation localized in the prtD gene. The lack of protease reduced colonization of an E. amylovora secretion mutant labelled with the gene for the green fluorescent protein (gfp) in the parenchyma of apple leaves.

Identification of neutralizing epitopes on Pseudomonas aeruginosa elastase and effects of cross-reactions on other thermolysin-like proteases

Monoclonal antibodies (MAbs) to a Burkholderia (Pseudomonas) cepacia 36-kDa protease (PSCP) which neutralize PSCP and Pseudomonas aeruginosa elastase but not P. aeruginosa alkaline protease have been isolated (C. Kooi et al., Infect. Immun. 62:2811-2817, 1994). These MAbs, designated 36-6-6 and 36-6-8, react with N-chlorosuccinimide cleavage products of P. aeruginosa elastase, consistent with the recognition of a 13.9-kDa fragment which contains the active site. Overlapping 9-mer peptides that span this region were synthesized. Neutralizing MAbs to PSCP reacted strongly with two peptides (341HGFTEQNSG349 and 395RYM DQPSRD403). Peptide 341HGFTEQNSG349 overlaps the motif 337HEXXH341, which has been found in many zinc-dependent endopeptidases. Peptide 395RYMDQPSRD403 lies between E361, which binds a zinc atom, and H420, which acts as a proton donor at the active site. Polyclonal rabbit sera raised against these peptides reacted with elastase on Western immunoblots and by enzyme-linked immunosorbent assay. With hide powder azure as the substrate, antisera to either HGFTEQNG and RYMDQPSRD completely neutralized the activities of elastase, thermolysin, Vibrio cholerae hemagglutinin/protease, and PSCP but had no effect on P. aeruginosa alkaline protease or the Serratia marcescens major protease. These results suggest that the MAbs recognize two different epitopes on P. aeruginosa elastase and that antibodies raised against synthetic peptides corresponding to either of these epitopes neutralize proteolytic activity.

Structural features of a superfamily of zinc-endopeptidases: the metzincins

A large number of zinc endopeptidases contain an HEXXHXXGXXH consensus motif in their catalytic site (single letter code; X is any amino acid residue). These enzymes can be grouped into four distinct families, the astacins, the adamalysins, the serralysins and the matrix metalloproteinases (matrixins). Despite a low degree of sequence similarity, their catalytic modules are topologically similar. A topology derived sequence alignment suggests that the four families form a superfamily, called the metzincins because of a perfectly superimposable methionine residue close to the zinc-binding active site. Topological similarity to the thermolysin-like enzymes indicates that these enzymes may have had a common ancestor.

The metzincins--topological and sequential relations between the astacins, adamalysins, serralysins, and matrixins (collagenases) define a superfamily of zinc-peptidases

The three-dimensional structures of the zinc endopeptidases human neutrophil collagenase, adamalysin II from rattle snake venom, alkaline proteinase from Pseudomonas aeruginosa, and astacin from crayfish are topologically similar, with respect to a five-stranded beta-sheet and three alpha-helices arranged in typical sequential order. The four proteins exhibit the characteristic consensus motif HEXXHXXGXXH, whose three histidine residues are involved in binding of the catalytically essential zinc ion. Moreover, they all share a conserved methionine residue beneath the active site metal as part of a superimposable "Met-turn." This structural relationship is supported by a sequence alignment performed on the basis of topological equivalence showing faint but distinct sequential similarity. The alkaline proteinase is about equally distant (26% sequence identity) to both human neutrophil collagenase and astacin and a little further away from adamalysin II (17% identity). The pairs astacin/adamalysin II, astacin/human neutrophil collagenase, and adamalysin II/human neutrophil collagenase exhibit sequence identities of 16%, 14%, and 13%, respectively. Therefore, the corresponding four distinct families of zinc peptidases, the astacins, the matrix metalloproteinases (matrixins, collagenases), the adamalysins/reprolysins (snake venom proteinases/reproductive tract proteins), and the serralysins (large bacterial proteases from Serratia, Erwinia, and Pseudomonas) appear to have originated by divergent evolution from a common ancestor and form a superfamily of proteolytic enzymes for which the designation "metzincins" has been proposed. There is also a faint but significant structural relationship of the metzincins to the thermolysin-like enzymes, which share the truncated zinc-binding motif HEXXH and, moreover, similar topologies in their N-terminal domains.

Anthrax toxin lethal factor contains a zinc metalloprotease consensus sequence which is required for lethal toxin activity

Comparison of the anthrax toxin lethal factor (LF) amino acid sequence with sequences in the Swiss protein database revealed short regions of similarity with the consensus zinc-binding site, HEXXH, that is characteristic of metalloproteases. Several protease inhibitors, including bestatin and captopril, prevented intoxication of macrophages by lethal toxin. LF was fully inactivated by site-directed mutagenesis that substituted Ala for either of the residues (H-686 and H-690) implicated in zinc binding. Similarly, LF was inactivated by substitution of Cys for E-687, which is thought to be an essential part of the catalytic site. In contrast, replacement of E-720 and E-721 with Ala had no effect on LF activity. LF bound 65Zn both in solution and on protein blots. The 65Zn binding was reduced for several of the LF mutants. These data suggest that anthrax toxin LF is a zinc metallopeptidase, the catalytic function of which is responsible for the lethal activity observed in cultured cells and in animals.

lasA and lasB genes of Pseudomonas aeruginosa: analysis of transcription and gene product activity

The lasA gene was the first of the Pseudomonas aeruginosa genes involved in proteolysis and elastolysis to be cloned and sequenced. Its function and significance have been studied by genetic approaches (D. S. Toder, M. J. Gambello, and B. H. Iglewski, Mol. Microbiol. 5:2003-2010, 1991) and by attempts to purify an active fragment of the protein (J. E. Peters and D. R. Galloway, J. Bacteriol. 172:2236-2240, 1990). To further study LasA in vivo, we have constructed and characterized an insertional mutant in the lasA gene in strain PAO1 (PAO-A1) and in the lasB insertional mutant, PAO-B1. Analysis of these isogenic strains demonstrates that the lasA lesion diminished elastolysis more than proteolysis and that LasA is required for staphylolytic activity. Despite previous suggestions that lasB elastase cleaves the LasA protein, the size of the LasA protein was the same whether or not lasB elastase was present. Expression of lasA in a lasR-negative mutant, PAO-R1, demonstrated that the LasA protein is produced in an active form in the absence of (lasB) elastase or alkaline protease and is itself a protease with elastolytic activity. We also observed that PAO-A1 was closer to the parental phenotype, with respect to elastolytic and proteolytic activities, than the previously characterized, chemically induced lasA mutant PAO-E64. Quantification of promoter activity with lasA::lacZ and lasB::lacZ fusions suggests that PAO-E64 harbors a mutation in a gene which regulates expression of both lasA and lasB.

Genetic and biochemical properties of an extracellular neutral metalloprotease from Staphylococcus hyicus subsp. hyicus

The gene encoding the extracellular neutral metalloprotease ShpI from Staphylococcus hyicus subsp. hyicus was cloned. DNA sequencing revealed an ORF of 1317 nucleotides encoding a 438 amino acid protein with Mr of 49,698. When the cloned gene was expressed in Staphylococcus carnosus, a 42 kDa protease was found in the culture medium. The protease was purified from both S. carnosus (pCAshp1) and S. hyicus subsp. hyicus. The N-terminal amino acid sequences of the two proteases revealed that ShpI is organized as a pre-pro-enzyme with a proposed 26 amino acid signal peptide, a 75 amino acid hydrophilic pro-region, and a 337 amino acid extracellular mature form with a calculated Mr of 38,394. The N-termini showed microheterogeneity in both host strains. ShpI had a maximum proteolytic activity at 55 degrees C and pH 7.4-8.5. The protease, which had a low substrate specificity, could be inhibited by metal- and zinc-specific inhibitors, such as EDTA and 1,10-phenanthroline. Insensitivity to phosphoramidon separates ShpI from the thermolysin-like family. The conserved Zn2+ binding motif, the only homology to other proteases, and the reactivation of the apoenzyme by Zn2+, indicated that Zn2+ is the catalytic ion. Ca2+ very probably acts as a stabilizer. We also demonstrated the presence of a second extracellular protease in S. hyicus subsp. hyicus.

Bacterial extracellular zinc-containing metalloproteases

Extracellular zinc-containing metalloproteases are widely distributed in the bacterial world. The most extensively studied are those which are associated with pathogenic bacteria or bacteria which have industrial significance. They are found practically wherever they are sought in both gram-negative and gram-positive microorganisms, be they aerobic or anaerobic. This ubiquity in itself implies that these enzymes serve important functions for the organisms which produce them. Because of the importance of zinc to enzymatic activity, it is not surprising that there is a pervasive amino acid sequence homology in the primary structure of this family of enzymes regardless of their source. The evidence suggests that both convergent and divergent evolutionary forces are at work. Within the large family of bacterial zinc-containing metalloendopeptidases, smaller family units are observed, such as thermolysin-like, elastase-like, and Serratia protease-like metalloproteases from various bacterial species. While this review was in the process of construction, a new function for zinc-containing metalloproteases was discovered: the neurotoxins of Clostridium tetani and Clostridium botulinum type B have been shown to be zinc metalloproteases with specificity for synaptobrevin, an integral membrane protein of small synaptic vesicles which is involved in neurotransmission. Additional understanding of the mode of action of proteases which contribute to pathogenicity could lead to the development of inhibitors, such as chelators, surrogate substrates, or antibodies, which could prevent or interrupt the disease process. Further studies of this broad family of metalloproteases will provide important additional insights into the pathogenesis and structure-function relationships of enzymes and will lead to the development of products, including "designer proteins," which might be industrially and/or therapeutically useful.

LasR of Pseudomonas aeruginosa is a transcriptional activator of the alkaline protease gene (apr) and an enhancer of exotoxin A expression

The lasR gene of Pseudomonas aeruginosa is required for transcription of the genes for elastase (lasB) and LasA protease (lasA), two proteases associated with virulence. We report here that the alkaline protease gene (apr) also requires the lasR gene for transcription. Alkaline protease mRNA was absent in the lasR mutant PAO-R1 and present when an intact lasR gene was supplied in trans as determined by Northern (RNA) analysis. The lasR gene also enhances exotoxin A production. Exotoxin A activity in supernatants of PAO-R1 were 30% less than in supernatants of the parental strain, PAO-SR. Multiple copies of lasR in trans in PAO-R1 in increased toxin A activity to twice the parental levels. Analysis of PAO-R1 containing the toxA promoter fused to beta-galactosidase suggests that LasR acts at the toxA promoter or at upstream toxA mRNA sequences. beta-Galactosidase activity was approximately 40% lower in PAO-R1 than in the parental strain, PAO-SR. Furthermore, the effect of LasR on the toxA promoter is not due to the stimulation of transcription of regA, a transcriptional activator of toxA. No difference in chloramphenicol acetyltransferase (CAT) activity was noted between PAO-SR and PAO-R1 containing transcriptional regA promoter-CAT gene fusions. These results broaden the regulatory dominion of lasR and suggest that the lasR gene plays a global role in P. aeruginosa pathogenesis.

Site-directed mutagenesis of Glu-141 and His-223 in Pseudomonas aeruginosa elastase: catalytic activity, processing, and protective activity of the elastase against Pseudomonas infection

Both Pseudomonas aeruginosa elastase and Bacillus thermoproteolyticus thermolysin are zinc metalloproteases. On the basis of the high homology of the P. aeruginosa elastase with the Bacillus thermolysin, we hypothesized that Glu-141 and His-223 are the key residues for catalytic activity of the Pseudomonas elastase. To test this possibility, we replaced Glu-141 with Asp, Gln, and Gly and His-223 with Gly, Glu, and Leu by site-directed mutagenesis. These substitutions dramatically diminished the proteolytic activities of the mutant elastases when they were expressed in Escherichia coli cells. Although these mutant elastase precursors (proelastases) were produced, no appreciable processing was observed with these mutants. The possibility that autocatalysis is involved in both the processing and activation of elastase is discussed. Furthermore, by immunizing mice with vaccines made from these mutant elastase, we were able to obtain good protection against an intraperitoneal P. aeruginosa challenge.

Cloning, nucleotide sequence and characterization of the gene encoding the Erwinia chrysanthemi B374 PrtA metalloprotease: a third metalloprotease secreted via a C-terminal secretion signal

Erwinia chrysanthemi, a phytopathogenic enterobacterium, secretes three proteases (PrtA, PrtB and PrtC) into the extracellular medium. The gene encoding the 50 kDa protease, prtA, was subcloned from a recombinant cosmid carrying a fragment of the E. chrysanthemi B374 chromosome. prtA was shown to be located immediately 3' to the structural genes for the other two extracellular proteases. The amino acid sequence of PrtA, as predicted from the prtA nucleotide sequence, showed a high level of homology with a family of metalloproteases that are all secreted via a signal peptide-independent pathway, including PrtB and PrtC of E. chrysanthemi B374, PrtC of E. chrysanthemi EC16, PrtSM of Serratia marcescens and AprA of Pseudomonas aeruginosa. PrtA secretion requires the E. chrysanthemi protease secretion factors PrtD, PrtE and PrtF. The secretion signal of PrtA is near to the carboxy-terminal end of the protein, as was previously shown to be the case for PrtB and PrtSM and for Escherichia coli alpha-hemolysin. The C-termini of these four proteins do not show extensive primary sequence homology, but PrtA, PrtB and PrtSM each have a potential amphipathic alpha-helix located close to the C-terminus.

Sequence of a cluster of genes controlling synthesis and secretion of alkaline protease in Pseudomonas aeruginosa: relationships to other secretory pathways

A genetic locus implicated in the synthesis and secretion of alkaline protease (APR) in Pseudomonas aeruginosa has been previously described [Guzzo et al., J. Bacteriol. 172 (1990) 942-948]. The nucleotide sequence of the DNA fragment encoding these functions was determined and revealed the existence of five open reading frames: aprA, the structural gene encoding APR; aprI, which encodes a protease inhibitor; and aprD, aprE, aprF whose products are involved in protease secretion. The AprD, AprE and AprF proteins share significant homology with proteins implicated in secretion of Erwinia chrysanthemi proteases and Escherichia coli alpha-haemolysin. These results provide further evidence for the existence of a specialized secretory system widespread among Gram- bacteria.

A fourth metalloprotease gene in Erwinia chrysanthemi

Erwinia chrysanthemi, a Gram-negative phytopathogenic bacterium, was previously shown to secrete 3 related extracellular metalloproteases, A, B and C via a specific signal-peptide-independent pathway. A new gene (prtG) encoding a fourth, 52-kDa metalloprotease was identified on the same recombinant cosmid (pEW1) that carries the genes for the previously described proteases (prtA, prtB and prtC), for the specific secretion factors (prtD, prtE and prtF) and for a protease inhibitor (inh) cloned from E. chrysanthemi B374. The predicted sequence of PrtG was similar to those of PrtA, PrtB and PrtC, its secretion required PrtD, PrtE and PrtF; its secretion signal was located at the C terminus but its proteolytic activity was distinct from that of the 3 other proteases. Results presented here suggest that prtG could be the first gene of an operon that includes inh, prtD, prtE and prtF.

Monoclonal antibodies against Pseudomonas aeruginosa elastase: a neutralizing antibody which recognizes a conformational epitope related to an active site of elastase

We have established seven murine hybridoma cell lines which produce monoclonal antibodies (mAbs) against Pseudomonas aeruginosa elastase. The seven mAbs recognized at least six different epitopes on the elastase molecule. All mAbs inhibited both enzymatic activities of elastase and protease, in which elastin fluorescein and hide powder azure were used as substrates, respectively. One of them, mAb E-4D3, strongly neutralized enzymatic activities of peptidase in which furylacryloyl-glycyl-leucinamide was used as a substrate, as well as of elastase and protease. In contrast, the other six mAbs did not neutralize peptidase activity at all. The Ki value for furylacryloyl-glycl-leucinamide of E-4D3, as well as its Fab fragment, was comparable to those for metalloprotease inhibitors such as phosphoramidon and Zincov inhibitor. The binding of mAb E-4D3 was inhibited by phosphoramidon and Zincov inhibitor, but not by metal chelators such as EDTA and o-phenanthroline. A line of evidence suggests that mAb E-4D3 directly interacts with active site and highly neutralizes enzymatic activity of P. aeruginosa elastase. Data of Western blotting and ELISA suggest that mAb E-4D3 is likely to recognize an elastase molecule in a conformation-dependent manner as an epitope. In contrast, the neutralizing activity of the other mAbs against elastase and protease seems to be caused by a low accessibility of an enzyme to insoluble and high-molecular-mass substrates through the binding and steric hindrance of the mAbs to an enzyme.

Structural gene and complete amino acid sequence of Vibrio alginolyticus collagenase

The DNA encoding the collagenase of Vibrio alginolyticus was cloned, and its complete nucleotide sequence was determined. When the cloned gene was ligated to pUC18, the Escherichia coli expression vector, bacteria carrying the gene exhibited both collagenase antigen and collagenase activity. The open reading frame from the ATG initiation codon was 2442 bp in length for the collagenase structural gene. The amino acid sequence, deduced from the nucleotide sequence, revealed that the mature collagenase consists of 739 amino acids with an Mr of 81875. The amino acid sequences of 20 polypeptide fragments were completely identical with the deduced amino acid sequences of the collagenase gene. The amino acid composition predicted from the DNA sequence was similar to the chemically determined composition of purified collagenase reported previously. The analyses of both the DNA and amino acid sequences of the collagenase gene were rigorously performed, but we could not detect any significant sequence similarity to other collagenases.

Alternative sigma factors and the regulation of flagellar gene expression

Synthesis of bacterial flagella and the accompanying array of chemotaxis receptors and transducers represents a major commitment of energy and resources for a growing bacterial cell and is subject to numerous levels of regulation. Genes for flagellar and chemotaxis proteins are expressed in a complex transcriptional cascade. This regulatory hierarchy acts to ensure that the highly expressed filament structural protein, flagellin, is synthesized only after a prerequisite set of structural proteins has been expressed and properly assembled. Recent evidence suggests that many bacteria utilize an alternative sigma (sigma) subunit, similar in specificity to the Bacillus subtilis sigma 28 protein, to direct transcription of flagellin, chemotaxis and motility genes. In Caulobacter crescentus and Campylobacter spp., both a sigma 54-like factor and a sigma 28-like factor participate in the transcription of flagellar and chemotaxis genes. Conversely, a sigma 28-like factor controls non-motility functions in at least one non-flagellated organism.

Pseudomonas aeruginosa LasB mutant constructed by insertional mutagenesis reveals elastolytic activity due to alkaline proteinase and the LasA fragment

The extracellularly secreted endopeptidase elastase (LasB) is regarded as an important virulence factor of Pseudomonas aeruginosa. It has also been implicated in the processing of LasA which enhances elastolytic activity of LasB. In order to investigate the role of LasB in virulence and LasA processing, a LasB-negative mutant, PAO1E, was constructed by insertional mutagenesis of the LasB structural gene, lasB, in P. aeruginosa PAO. An internal 636 bp lasB fragment of the plasmid pRB1803 was ligated into a derivative of the mobilization vector pSUP201-1. The resulting plasmid, pBRMOB-LasB, was transformed into Escherichia coli and transferred by filter matings to the LasB-positive P. aeruginosa strain, PAO1. Plasmid integration in the lasB site of the chromosome was confirmed by Southern blot analysis. Radioimmunoassay and immunoblotting of PAO1E supernatant fluids yielded no detectable LasB (less than 1 ng ml-1 LasB). The absence of LasB in PAO1E was further proven by the inability of its culture supernatant fluid to cleave transferrin or rabbit immunoglobulin G (IgG) after a 72 h incubation. The residual proteolytic activity of PAO1E culture supernatant fluid was attributed to alkaline proteinase (Apr), since it was totally inhibited by specific antibodies against Apr. Residual elastolytic activity in culture supernatant fluid of PAO1E was due to the LasA fragment and to the combined action of the LasA fragment with Apr on elastin. The sizes of purified LasA from PAO1 and PAO1E were identical (22 kDa). These results show that, besides LasB and the LasA fragment, Apr may also act on elastin in the presence of the LasA fragment and that the proteolytic processing of LasA in P. aeruginosa is independent of LasB.