Sequence and transcriptional start site of the Pseudomonas aeruginosa outer membrane porin protein F gene

Cell-free expression of the outer membrane protein OprF of Pseudomonas aeruginosa for vaccine purposes

Production of recombinant proteoliposomes containing OprF from P. aeruginosa promotes the active open conformation of the porin exposing native epitopes. These OprF proteoliposomes were used as vaccines to protect mice against a P. aeruginosa acute pulmonary infection model.

Pseudomonas aeruginosa is the second-leading cause of nosocomial infections and pneumonia in hospitals. Because of its extraordinary capacity for developing resistance to antibiotics, treating infections by Pseudomonas is becoming a challenge, lengthening hospital stays, and increasing medical costs and mortality. The outer membrane protein OprF is a well-conserved and immunogenic porin playing an important role in quorum sensing and in biofilm formation. Here, we used a bacterial cell-free expression system to reconstitute OprF under its native forms in liposomes and we demonstrated that the resulting OprF proteoliposomes can be used as a fully functional recombinant vaccine against P. aeruginosa. Remarkably, we showed that our system promotes the folding of OprF into its active open oligomerized state as well as the formation of mega-pores. Our approach thus represents an easy and efficient way for producing bacterial membrane antigens exposing native epitopes for vaccine purposes.

Recombinant N-terminal outer membrane porin (OprF) of Pseudomonas aeruginosa is a promising vaccine candidate against both P. aeruginosa and some strains of Acinetobacter baumannii

Pseudomonas aeruginosa is an evolving pathogen which can cause serious infections especially to immunocompromised patients. Its high resistance profile to antibiotics results in difficulty, and sometimes impossibility, in treating afflicted patients. Developing an effective vaccine against P. aeruginosa is an important approach to tackle this problem. A similar problematic situation exists for Acinetobacter baumannii. Several vaccine candidates have been investigated up till now but still there is no approved vaccine in the market. One important antigen of P. aeruginosa is the outer membrane protein F (OprF) which functions as a porin with relevant important roles in virulence. Previous studies focused mainly on the C-terminal peptidoglycan binding domain of OprF as a vaccine candidate. In the current study, we have investigated the N-terminal porin domain of OprF as a potential vaccine candidate against P. aeruginosa. Histidine-tagged recombinant N-terminal OprF (amino acid range 25-200; OprF25-200) was overexpressed in Escherichia coli and purified using metal affinity chromatography. Swiss albino mice were immunized with OprF25-200 adjuvanted with Bacillus Calmette-Guérin (BCG) and alum and the immune response was evaluated. Immunized mice developed antigen-specific IgG1 and IgG2a and were protected against challenge by both P. aeruginosa and a clinical isolate of A. baumannii expressing OprF. Serum from OprF25-200-immunized mice showed cross-reactivity with both pathogens using western blotting and whole cell enzyme-linked immunosorbent assay (ELISA). To our knowledge, this is the first report to demonstrate that the N-terminal domain of OprF is sufficiently immunogenic to protect against the two pathogens.

Pushing beyond the Envelope: the Potential Roles of OprF in Pseudomonas aeruginosa Biofilm Formation and Pathogenicity

The ability of Pseudomonas aeruginosa to form biofilms, which are communities of cells encased in a self-produced extracellular matrix, protects the cells from antibiotics and the host immune response. While some biofilm matrix components, such as exopolysaccharides and extracellular DNA, are relatively well characterized, the extracellular matrix proteins remain understudied. Multiple proteomic analyses of the P. aeruginosa soluble biofilm matrix and outer membrane vesicles, which are a component of the matrix, have identified OprF as an abundant matrix protein. To date, the few reports on the effects of oprF mutations on biofilm formation are conflicting, and little is known about the potential role of OprF in the biofilm matrix. The majority of OprF studies focus on the protein as a cell-associated porin. As a component of the outer membrane, OprF assumes dual conformations and is involved in solute transport, as well as cell envelope integrity. Here, we review the current literature on OprF in P. aeruginosa, discussing how the structure and function of the cell-associated and matrix-associated protein may affect biofilm formation and pathogenesis in order to inform future research on this understudied matrix protein.

Structure, function and regulation of Pseudomonas aeruginosa porins

Pseudomonas aeruginosa is a Gram-negative bacterium belonging to the γ-proteobacteria. Like other members of the Pseudomonas genus, it is known for its metabolic versatility and its ability to colonize a wide range of ecological niches, such as rhizosphere, water environments and animal hosts, including humans where it can cause severe infections. Another particularity of P. aeruginosa is its high intrinsic resistance to antiseptics and antibiotics, which is partly due to its low outer membrane permeability. In contrast to Enterobacteria, pseudomonads do not possess general diffusion porins in their outer membrane, but rather express specific channel proteins for the uptake of different nutrients. The major outer membrane 'porin', OprF, has been extensively investigated, and displays structural, adhesion and signaling functions while its role in the diffusion of nutrients is still under discussion. Other porins include OprB and OprB2 for the diffusion of glucose, the two small outer membrane proteins OprG and OprH, and the two porins involved in phosphate/pyrophosphate uptake, OprP and OprO. The remaining nineteen porins belong to the so-called OprD (Occ) family, which is further split into two subfamilies termed OccD (8 members) and OccK (11 members). In the past years, a large amount of information concerning the structure, function and regulation of these porins has been published, justifying why an updated review is timely.

Rapid Amplification of cDNA Ends for RNA Transcript Sequencing in Staphylococcus

Rapid amplification of cDNA ends (RACE) is a technique that was developed to swiftly and efficiently amplify full-length RNA molecules in which the terminal ends have not been characterized. Current usage of this procedure has been more focused on sequencing and characterizing RNA 5' and 3' untranslated regions. Herein is described an adapted RACE protocol to amplify bacterial RNA transcripts.

Bioinformatics of prokaryotic RNAs

The genome of most prokaryotes gives rise to surprisingly complex transcriptomes, comprising not only protein-coding mRNAs, often organized as operons, but also harbors dozens or even hundreds of highly structured small regulatory RNAs and unexpectedly large levels of anti-sense transcripts. Comprehensive surveys of prokaryotic transcriptomes and the need to characterize also their non-coding components is heavily dependent on computational methods and workflows, many of which have been developed or at least adapted specifically for the use with bacterial and archaeal data. This review provides an overview on the state-of-the-art of RNA bioinformatics focusing on applications to prokaryotes.

Transcription of the oprF gene of Pseudomonas aeruginosa is dependent mainly on the SigX sigma factor and is sucrose induced

The OprF porin is the major outer membrane protein of Pseudomonas aeruginosa. OprF is involved in several crucial functions, including cell structure, outer membrane permeability, environmental sensing, and virulence. The oprF gene is preceded by the sigX gene, which encodes the poorly studied extracytoplasmic function (ECF) sigma factor SigX. Three oprF promoters were previously identified. Two intertwined promoters dependent on σ(70) and SigX are located in the sigX-oprF intergenic region, whereas a promoter dependent on the ECF AlgU lies within the sigX gene. An additional promoter was found in the cmpX-sigX intergenic region. In this study, we dissected the contribution of each promoter region and of each sigma factor to oprF transcription using transcriptional fusions. In Luria-Bertani (LB) medium, the oprF-proximal region (sigX-oprF intergenic region) accounted for about 80% of the oprF transcription, whereas the AlgU-dependent promoter had marginal activity. Using the sigX mutant PAOSX, we observed that the SigX-dependent promoter was largely predominant over the σ(70)-dependent promoter. oprF transcription was increased in response to low NaCl or high sucrose concentrations, and this induced transcription was strongly impaired in the absence of SigX. The lack of OprF itself increased oprF transcription. Since these conditions led to cell wall alterations, oprF transcription could be activated by signals triggered by perturbation of the cell envelope.

Pseudomonas aeruginosa in chronic obstructive pulmonary disease

RATIONALE

Pseudomonas aeruginosa is isolated from adults with chronic obstructive pulmonary disease (COPD) in cross-sectional studies. However, patterns of carriage and the role of P. aeruginosa in COPD are unknown.

OBJECTIVES

To elucidate carriage patterns, phenotypes of strains, clinical manifestations, and the antibody response to P. aeruginosa in COPD.

METHODS

A prospective study of adults with COPD was conducted. Isolates of P. aeruginosa were subjected to genotypic and phenotypic analysis. Sputum samples were studied for P. aeruginosa DNA, and immune responses were assayed.

MEASUREMENTS AND MAIN RESULTS

We analyzed longitudinal clinical data, sputum cultures, pulsed-field gel electrophoresis of bacterial DNA, polymerase chain reaction of sputum, and immunoblot assays of serum. Fifty-seven episodes of acquisition of strains of P. aeruginosa were observed in 39 of 126 patients over 10 years. Acquisition of a new strain was associated with exacerbation. Thirty-one episodes of carriage were followed by clearance of the strain; 16 were of short (<1 mo) duration. Thirteen strains demonstrated persistence, and 13 strains were of indeterminate duration. Six strains were mucoid and were more likely to persist than nonmucoid strains (P = 0.005). Antibody responses developed in 53.8% of persistent carriage and in only 9.7% of short-term carriage episodes (P = 0.003). Antibiotics did not account for clearance.

CONCLUSIONS

Two distinct patterns of carriage by P. aeruginosa were observed: (1) short-term colonization followed by clearance and (2) long-term persistence. Mucoid strains showed persistence. Acquisition of P. aeruginosa is associated with the occurrence of an exacerbation. Serum antibody responses do not mediate clearance of P. aeruginosa.

Cloning, expression, and characterization of a lipolytic enzyme gene (lip8) from Pseudomonas aeruginosa LST-03

A lipolytic enzyme gene (lip8) was cloned from organic solvent-tolerant Pseudomonas aeruginosa LST-03 and sequenced. In the sequenced nucleotides, an open reading frame consisting of 1,173 nucleotides and encoding 391 amino acids was found. Lip8 is considered to belong to the family VIII of lipolytic enzymes whose serine in the consensus sequence of -Ser-Xaa-Xaa-Lys- acts as catalytic nucleophile. The gene was expressed in Escherichia coli and purified by a combination of ammonium sulfate fractionation and hydrophobic interaction and ion-exchange chromatographies to homogeneity on SDS-PAGE analysis. The optimum temperature and heat stability of Lip8 were not as high as those of Lip3 and LST-03 lipase, two other lipolytic enzymes from the same strain. Addition of glycerol to a solution containing Lip8 stabilized this enzyme. By measuring the activities against various triacylglycerols and fatty acid methyl esters having carbon chains of different lengths, Lip8 was categorized as an esterase which has higher activities against fatty acid methyl esters with short-chain fatty acids.

Recombinant OprF-OprI as a vaccine against Pseudomonas aeruginosa infections

A vaccine against Pseudomonas aeruginosa based on recombinant outer membranes has been developed. After intramuscularly injecting into patients with severe burns, antibodies against P. aeruginosa were induced. Vaccination was well tolerated. Intranasal application of the vaccine into volunteers, induced specific s-IgA antibodies. We conclude that the newly developed vaccine may be suitable for protection of the main risk groups of P. aeruginosa infections. In particular, for the protection of burn patients and patients with cystic fibrosis.

Cloning, expression and characterization of a lipase gene (lip3) from Pseudomonas aeruginosa LST-03

A lipase gene (lip3) was cloned from the Pseudomonas aeruginosa strain LST-03 (which tolerates organic solvents) and expressed in Escherichia coli. The cloned sequence includes an ORF consisting of 945 nucleotides, encoding a protein of 315 amino acids (Lip3 lipase, 34.8 kDa). The predicted Lip3 lipase belongs to the class of serine hydrolases; the catalytic triad consists of the residues Ser-137, Asp-258, and His-286. The gene cloned in the present study does not encode the LST-03 lipase, a previously isolated solvent-stable lipase secreted by P. aeruginosa LST-03, because the N-terminal amino acid sequence of the Lip3 lipase differs from that of the LST-03 lipase. Although the effects of pH on the activity and stability of the Lip3 lipase, and the temperature optimum of the enzyme, were similar to those of the LST-03 lipase, the relative activity of the Lip3 lipase at lower temperatures (0-35 degrees C) was higher than that of the LST-03 lipase. In the absence of organic solvents, the half-life of the Lip3 lipase was similar to that of the LST-03 lipase. However, in the presence of most of the organic solvents tested in this study (the exceptions were ethylene glycol and glycerol), the stability of the Lip3 lipase was lower than that of the LST-03 lipase.

Clinical study to assess the immunogenicity and safety of a recombinant Pseudomonas aeruginosa OprF-OprI vaccine in burn patients

In a recent clinical trial we evaluated the safety and immunogenicity of a recombinant OprF-OprI vaccine consisting of the mature outer membrane protein I (OprI) and amino acids 190-342 of OprF of Pseudomonas aeruginosa in burn patients and compared the elicited antibodies with antibodies against tetanus as response to a simultaneous immunization given on the day of admission. Safety and immunogenicity of the vaccine had been tested before in healthy human volunteers as published in 1999. In this first clinical trial we immunized eight burn patients suffering from second or third degree burns involving between 35% and 55% of the body surface three times with 100 microg of the OprF-OprI vaccine. The vaccine was found to be very well tolerated. The patients did not show any serious side effects - and in particular no activation of the mediator cascade was observed. None of the subjects showed systemic P. aeruginosa infections during or after the treatment of their burns. The serological tests (ELISA) for detection of antibodies against P. aeruginosa and tetanus toxoid showed seroconversion for seven patients after inoculation. The data indicate that OprF-OprI can be a useful vaccine in the therapeutic management of burn injuries.

Mucosal vaccination with a recombinant OprF-I vaccine of Pseudomonas aeruginosa in healthy volunteers: comparison of a systemic vs. a mucosal booster schedule

We compared the immunogenicity of two vaccination schedules with either a systemic or a mucosal booster, both following a mucosal primary vaccination with a recombinant outer membrane fusion protein of Pseudomonas aeruginosa (OprF-I) in 12 healthy volunteers. The systemic booster induced higher levels of OprF-I-specific serum antibodies of IgG isotype, with a mean+/-S.E.M. of 32.6+/-7.8x10(7) enzyme-linked immunosorbent assay (ELISA) units (EU) as compared to the nasal booster with 14.6+/-2.1x10(7) EU (P=0.05). Specific serum IgA antibodies and antibodies in saliva did not differ between the two vaccination groups. We conclude that a combined mucosal/systemic vaccination with the OprF-I vaccine may offer an enhanced systemic immunogenicity. Further studies on the long-term immunogenicity and induction of antibodies on the respiratory airway surface are warranted.

Whole-genome analysis of transporters in the plant pathogen Xylella fastidiosa

The transport systems of the first completely sequenced genome of a plant parasite, Xylella fastidiosa, were analyzed. In all, 209 proteins were classified here as constitutive members of transport families; thus, we have identified 69 new transporters in addition to the 140 previously annotated. The analysis lead to several hints on potential ways of controlling the disease it causes on citrus trees. An ADP:ATP translocator, previously found in intracellular parasites only, was found in X. fastidiosa. A P-type ATPase is missing-among the 24 completely sequenced eubacteria to date, only three (including X. fastidiosa) do not have a P-type ATPase, and they are all parasites transmitted by insect vectors. An incomplete phosphotransferase system (PTS) was found, without the permease subunits-we conjecture either that they are among the hypothetical proteins or that the PTS plays a solely metabolic regulatory role. We propose that the Ttg2 ABC system might be an import system eventually involved in glutamate import rather than a toluene exporter, as previously annotated. X. fastidiosa exhibits fewer proteins with > or =4 alpha-helical transmembrane spanners than any other completely sequenced prokaryote to date. X. fastidiosa has only 2.7% of all open reading frames identifiable as major transporters, which puts it as the eubacterium having the lowest percentage of open reading frames involved in transport, closer to two archaea, Methanococcus jannaschii (2.4%) and Methanobacterium thermoautotrophicum (2.4%).

Global genomic analysis of AlgU (sigma(E))-dependent promoters (sigmulon) in Pseudomonas aeruginosa and implications for inflammatory processes in cystic fibrosis

The conversion of Pseudomonas aeruginosa to the mucoid phenotype coincides with the establishment of chronic respiratory infections in cystic fibrosis (CF). A major pathway of conversion to mucoidy in clinical strains of P. aeruginosa is dependent upon activation of the alternative sigma factor AlgU (P. aeruginosa sigma(E)). Here we initiated studies of AlgU-dependent global expression patterns in P. aeruginosa in order to assess whether additional genes, other than those involved in the production of the mucoid exopolysaccharide alginate, are turned on during conversion to mucoidy. Using genomic information and the consensus AlgU promoter sequence, we identified 35 potential AlgU (sigma(E)) promoter sites on the P. aeruginosa chromosome. Each candidate promoter was individually tested by reverse transcription and mRNA 5'-end mapping using RNA isolated from algU(+) and algU::Tc(r) mutant cells. A total of 10 new AlgU-dependent promoters were identified, and the corresponding mRNA start sites were mapped. Two of the 10 newly identified AlgU promoters were upstream of predicted lipoprotein genes. Since bacterial lipoproteins have been implicated as inducers of inflammatory pathways, we tested whether lipopeptides corresponding to the products of the newly identified AlgU-dependent lipoprotein genes, lptA and lptB, had proinflammatory activity. In human peripheral blood monocyte-derived macrophages the peptides caused production of interleukin-8, a proinflammatory chemokine typically present at excessively high levels in the CF lung. Our studies show how genomic information can be used to uncover on a global scale the genes controlled by a given sigma factor (collectively termed here sigmulon) using conventional molecular tools. In addition, our data suggest the existence of a previously unknown connection between conversion to mucoidy and expression of lipoproteins with potential proinflammatory activity. This link may be of significance for infections and inflammatory processes in CF.

Media containing aromatic compounds induce peculiar proteins in Acinetobacter radioresistens, as revealed by proteome analysis

An Acinetobacter radioresistens strain able to grow on phenol or benzoate as sole carbon and energy source through the beta-ketoadipate pathway was isolated in our laboratories. In previous research, we found a different expression of catechol-1,2-dioxygenase isoenzymes (C-1,2-O) depending on the growth substrate (phenol or benzoate). In the present study, we used proteome techniques to extend our investigation to other enzymes involved in the aromatic degradation pathway. Since the first nontoxic metabolite in this route is cis,cis-muconic acid, we focused our attention on the enzymes leading to this compound, chiefly phenol hydroxylase (PH), benzoate dioxygenase (BD), cis-1,2-dihydroxycyclohexa-3,5-diene-1-carboxylate dehydrogenase (D) and C-1,2-O. In particular, the A. radioresistens proteome was monitored under different growth substrate conditions, using acetate, benzoate, or phenol as sole carbon source. We compared the protein maps by software image analysis and detected marked differences, suggesting the inducibility of most enzymes. This research also sought to evaluate the conditions allowing the best expression of enzymes to be used in immobilized systems suitable for bioremediation. The experimental data indicate that benzoate is the best carbon source to gain the highest amount of C-1,2-O and D, while phenol is the best growth substrate to obtain PH.

Safety and immunogenicity of an intranasal Pseudomonas aeruginosa hybrid outer membrane protein F-I vaccine in human volunteers

A hybrid protein [Met-Ala-(His)(6) OprF(190-342)-OprI(21-83)] consisting of the mature outer membrane protein I (OprI) and amino acids 190-342 of OprF of Pseudomonas aeruginosa was expressed in Escherichia coli and purified by Ni(2+) chelate-affinity chromatography. After several studies in healthy volunteers, as well as in patients, had proven the tolerability and immunogenicity of the the OprF-OprI vaccine, after intra-muscular application, we developed an emulgel for intranasal immunization. For this purpose we combined a highly concentrated OprF-I with sodium dodecylsulfate as vehicle and the gel matrix natriumlauryl sulfate. After safety and pyrogenicity evaluations in animals, eight healthy adult human volunteers received the OprF-I gel intranasally three times at 2-week intervals. The vaccination was well tolerated and no side effects were observed. An antibody induction (IgG and IgA) could be detected in the sera. These data support continued clinical investigation of the protection against infections in cystic fibrosis patients and patients prone to P. aeruginosa infections.

Purification, characterization and sequence analysis of Omp50,a new porin isolated from Campylobacter jejuni

A novel pore-forming protein identified in Campylobacter was purified by ion-exchange chromatography and named Omp50 according to both its molecular mass and its outer membrane localization. We observed a pore-forming ability of Omp50 after re-incorporation into artificial membranes. The protein induced cation-selective channels with major conductance values of 50-60 pS in 1 M NaCl. N-terminal sequencing allowed us to identify the predicted coding sequence Cj1170c from the Campylobacter jejuni genome database as the corresponding gene in the NCTC 11168 genome sequence. The gene, designated omp50, consists of a 1425 bp open reading frame encoding a deduced 453-amino acid protein with a calculated pI of 5.81 and a molecular mass of 51169.2 Da. The protein possessed a 20-amino acid leader sequence. No significant similarity was found between Omp50 and porin protein sequences already determined. Moreover, the protein showed only weak sequence identity with the major outer-membrane protein (MOMP) of Campylobacter, correlating with the absence of antigenic cross-reactivity between these two proteins. Omp50 is expressed in C. jejuni and Campylobacter lari but not in Campylobacter coli. The gene, however, was detected in all three species by PCR. According to its conformation and functional properties, the protein would belong to the family of outer-membrane monomeric porins.

Proteome analysis of the effect of mucoid conversion on global protein expression in Pseudomonas aeruginosa strain PAO1 shows induction of the disulfide bond isomerase, dsbA

Pseudomonas aeruginosa strains that cause chronic pulmonary infections in cystic fibrosis patients typically undergo mucoid conversion. The mucoid phenotype indicates alginate overproduction and is often due to defects in MucA, an antisigma factor that controls the activity of sigma-22 (AlgT [also called AlgU]), which is required for the activation of genes for alginate biosynthesis. In this study we hypothesized that mucoid conversion may be part of a larger response that activates genes other than those for alginate synthesis. To address this, a two-dimensional (2-D) gel analysis was employed to compare total proteins in strain PAO1 to those of its mucA22 derivative, PDO300, in order to identify protein levels enhanced by mucoid conversion. Six proteins that were clearly more abundant in the mucoid strain were observed. The amino termini of such proteins were determined and used to identify the gene products in the genomic database. Proteins involved in alginate biosynthesis were expected among these, and two (AlgA and AlgD) were identified. This result verified that the 2-D gel approach could identify gene products under sigma-22 control and upregulated by mucA mutation. Two other protein spots were also clearly upregulated in the mucA22 background, and these were identified as porin F (an outer membrane protein) and a homologue of DsbA (a disulfide bond isomerase). Single-copy gene fusions were constructed to test whether these proteins were enhanced in the mucoid strain due to increased transcription. The oprF-lacZ fusion showed little difference in levels of expression in the two strains. However, the dsbA-lacZ fusion showed two- to threefold higher expression in PDO300 than in PAO1, suggesting that its promoter was upregulated by the deregulation of sigma-22 activity. A dsbA-null mutant was constructed in PAO1 and shown to have defects predicted for a cell with reduced disulfide bond isomerase activity, namely, reduction in periplasmic alkaline phosphatase activity, increased sensitivity to dithiothreitol, reduced type IV pilin-mediated twitching motility, and reduced accumulation of extracellular proteases, including elastase. Although efficient secretion of elastase in the dsbA mutant was still demonstrable, the elastase produced appeared to be unstable, possibly as a result of mispaired disulfide bonds. Disruption of dsbA in the mucoid PDO300 background did not affect alginate production. Thus, even though dsbA is coregulated with mucoid conversion, it was not required for alginate production. This suggests that mucA mutation, which deregulates sigma-22, results in a global response that includes other factors in addition to increasing the production of alginate.

Complementing genomics with proteomics: the membrane subproteome of Pseudomonas aeruginosa PAO1

With the completion of many genome projects, a shift is now occurring from the acquisition of gene sequence to understanding the role and context of gene products within the genome. The opportunistic pathogen Pseudomonas aeruginosa is one organism for which a genome sequence is now available, including the annotation of open reading frames (ORFs). However, approximately one third of the ORFs are as yet undefined in function. Proteomics can complement genomics, by characterising gene products and their response to a variety of biological and environmental influences. In this study we have established the first two-dimensional gel electrophoresis reference map of proteins from the membrane fraction of P. aeruginosa strain PA01. A total of 189 proteins have been identified and correlated with 104 genes from the P. aeruginosa genome. Annotated membrane proteins could be grouped into three distinct categories: (i) those with functions previously characterised in P. aeruginosa (38%); (ii) those with significant sequence similarity to proteins with assigned function or hypothetical proteins in other organisms (46%); and (iii) those with unknown function (16%). Transmembrane prediction algorithms showed that each identified protein sequence contained at least one membrane-spanning region. Furthermore, the current methodology used to isolate the membrane fraction was shown to be highly specific since no contaminating cytosolic proteins were characterised. Preliminary analysis showed that at least 15 gel spots may be glycosylated in vivo, including three proteins that have not previously been functionally characterised. The reference map of membrane proteins from this organism is now the basis for determining surface molecules associated with antibiotic resistance and efflux, cell-cell signalling and pathogen-host interactions in a variety of P. aeruginosa strains.

Immunogenic efficacy of differently produced recombinant vaccines candidates against Pseudomonas aeruginosa infections

Three different variants of the recombinant hybrid outer membrane protein OprF (aa 190-342)-OprI (aa 21-83) could be obtained in high yield after expression in Escherichia coli. The hybrid protein was modified N terminally, either with a minimal histidine tag or with a homologous sequence of OprF. Both recombinant proteins were purified by nickel chelate affinity chromatography under native and denaturing conditions, and this produced three suitable candidates for a vaccination trial, protein His-F-I, which was purified in its native as well as in its refolded form; and the native purified N terminally extended protein, ex-F-I. In mice, significantly higher antibody titers and survival rates after challenge with Pseudomonas aeruginosa were observed following immunization with protein His-F-I, purified under native conditions.

Ion channel formation by N-terminal domain: a common feature of OprFs of Pseudomonas and OmpA of Escherichia coli

The proteolytic fragments of OprFs of Pseudomonas aeruginosa and Pseudomonas fluorescens were identified, respectively, as the first 175 and 177 amino acids from the N-terminal domain. They induced ion channels after reincorporation into planar lipid bilayers (85 and 75 pS, respectively, in 1 M NaCl). A similar conductance value (72 pS) was found for the eight beta-strand OmpA N-terminal domain (OmpA171) of Escherichia coli. We conclude that the N-terminal domain of OprFs is sufficient to induce ion channels and the comparison with OmpA171, provides strong evidence of the existence of an eight-stranded beta-barrel in the N-terminal domain of OprFs.

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.

Dual regulation of mucoidy in Pseudomonas aeruginosa and sigma factor antagonism

The conversion to mucoid, exopolysaccharide alginate-overproducing phenotype in Pseudomonas aeruginosa during chronic respiratory infections in cystic fibrosis patients occurs via mutations that activate the alternative sigma factor AlgU (sigmaE). In this study, we demonstrate that conversion to mucoidy can be caused via a second, algU-independent pathway, in which alginate production and transcription of the critical algD promoter depend on another alternative sigma factor, RpoN (sigma54). The algD promoters dependent on sigma54 and sigmaE showed a complete overlap resulting in identical mRNA 5' ends. The two pathways were not independent, as sigma54 also repressed sigmaE-dependent transcription of algD both in vitro and in vivo. The negative regulatory effect of sigma54 on sigmaE-dependent algD expression was based on sigma54 binding to the algD promoter and its interference with sigmaE-dependent transcription. This phenomenon, referred to here as sigma factor antagonism, reflects the unique properties of sigma54, which lacks an intrinsic ability to form open transcription initiation complexes. We propose that this peculiar feature of sigma54 has evolved in part to allow its recruitment as a repressor of certain promoter subsets. The repression of algD by sigma54 also depends on environmental conditions, supporting the notion that sigma factor antagonism plays a physiological role in controlling alginate production in P. aeruginosa during adaptation to different ecological sites (e.g. biofilm development, stress and other growth conditions) and unique environments in the chronically infected host.

Influence of a putative ECF sigma factor on expression of the major outer membrane protein, OprF, in Pseudomonas aeruginosa and Pseudomonas fluorescens

The gene encoding OprF, a major outer membrane protein in Pseudomonas species (formerly known as type 1 pseudomonads), was thought to be constitutively transcribed from a single sigma 70 promoter immediately upstream of the gene. We now report the identification of a novel putative ECF (extracytoplasmic function) sigma factor gene, sigX, located immediately upstream of oprF in both Pseudomonas aeruginosa PAO1 and Pseudomonas fluorescens OE 28.3 and show that disruption of this gene significantly reduces OprF expression. In P. aeruginosa, Northern analysis demonstrated that this reduction was a result of an effect on transcription of monocistronic oprF combined with a polar effect due to termination of a transcript containing sigX and oprF. Comparison of sigX-disrupted and wild-type cell transcripts by primer extension indicated that monocistronic transcription of oprF occurs from two overlapping promoters, one that is SigX-dependent and resembles ECF sigma factor promoters in its minus-35 region and another promoter that is independent of SigX and is analogous to the sigma 70-type promoter previously reported. Complementation of the P. aeruginosa sigX-disrupted mutant with plasmid-encoded OprF did not resolve the phenotypes associated with this mutant, which included a markedly reduced logarithmic-phase growth rate in rich medium (compared to that in minimal medium), further reduction of the growth rate in a low-osmolarity environment, secretion of an unidentified pigment, and increased sensitivity to the antibiotic imipenem. This indicates that SigX is involved in the regulation of other genes in P. aeruginosa. Disruption of the sigX gene in P. fluorescens also had an effect on the logarithmic-phase growth rate in rich medium. A conserved sigX gene was also identified in a Pseudomonas syringae isolate and six P. aeruginosa clinical isolates. Collectively, these data indicate that an ECF sigma factor plays a role in the regulation and expression of OprF and also affects other genes.

The rice inoculant strain Alcaligenes faecalis A15 is a nitrogen-fixing Pseudomonas stutzeri

The taxonomic position of the nitrogen-fixing rice isolate A15, previously classified as Alcaligenes faecalis, was reinvestigated. On the basis of its small subunit ribosomal RNA (16S rRNA) sequence this strain identifies as Pseudomonas stutzeri. Phenotyping and fatty acid profiling confirm this result. DNA:DNA hybridisations, using the optical renaturation rate method, between strain A15 and Pseudomonas stutzeri LMG 11199T revealed a mean DNA-binding of 77%. The identification was further corroborated by comparative sequence analysis of the oprF gene, which encodes the major outer membrane protein of rRNA homology group I pseudomonads. Furthermore we determined the nifH sequence of this strain and of two putative diazotrophic Pseudomonas spp. and made a comparative analysis with sequences of other diazotrophs. These Pseudomonas NifH sequences cluster with NifH sequences isolated from the rice rhizosphere by PCR and of proteobacteria from the beta and gamma subclasses.

A recombinant hybrid outer membrane protein for vaccination against Pseudomonas aeruginosa

Among the numerous targets which can be used for the development of vaccines against Pseudomonas aeruginosa we focused on the outer membrane proteins OprF and OprI. The C-terminal part of OprF from aa 190 to aa 350 was investigated for its conservation and its localization of B-cell epitopes. A hybrid protein which combines the protective epitopes of OprF and OprI was expressed in E. coli and was proven to be highly protective against an intraperitoneal challenge with P. aeruginosa by active immunization of immunocompromised mice as well as by passive immunization of SCID mice with specific antisera. A purification procedure of the N-terminal His-tagged hybrid antigen was established using immobilized-metal-affinity chromatography. To evaluate its safety and immunogenicity the recombinant protein was purified for the immunization of human volunteers. The OprF/OprI hybrid protein is considered to be a candidate for a vaccine against P. aeruginosa.

Safety and immunogenicity of a Pseudomonas aeruginosa hybrid outer membrane protein F-I vaccine in human volunteers

A hybrid protein [Met-Ala-(His)6OprF190-342-OprI21-83] consisting of the mature outer membrane protein I (OprI) and amino acids 190 to 342 of OprF of Pseudomonas aeruginosa was expressed in Escherichia coli and purified by Ni2+ chelate-affinity chromatography. After safety and pyrogenicity evaluations in animals, four groups of eight adult human volunteers were vaccinated intramuscularly three times at 4-week intervals and revaccinated 6 months later with either 500, 100, 50, or 20 microg of OprF-OprI adsorbed onto A1(OH)3. All vaccinations were well tolerated. After the first vaccination, a significant rise of antibody titers against P. aeruginosa OprF and OprI was measured in volunteers receiving the 100- or the 500-microg dose. After the second vaccination, significant antibody titers were measured for all groups. Elevated antibody titers against OprF and OprI could still be measured 6 months after the third vaccination. The capacity of the elicited antibodies to promote complement binding and opsonization could be demonstrated by a C1q-binding assay and by the in vitro opsonophagocytic uptake of P. aeruginosa bacteria. These data support the continued development of an OprF-OprI vaccine for use in humans.

Pseudomonas aeruginosa fur overlaps with a gene encoding a novel outer membrane lipoprotein, OmlA

A novel outer membrane lipoprotein in Pseudomonas aeruginosa is encoded by the omlA gene, which was identified immediately upstream of the fur (ferric uptake regulator) gene. The omlA and fur genes were divergently transcribed and had overlapping promoter regions. The proximal fur P2 promoter and the omlA promoter shared a 5-bp DNA motif for their -10 promoter elements. The distal fur P1 promoter was located within the omlA coding sequence, and the omlA and fur T1 mRNAs overlapped by 154 nucleotides. Optimal expression of both fur and omlA required roughly 200 bp of DNA upstream of the promoter regions, suggesting the presence of cis-acting transcriptional activation elements located within the omlA and fur genes, respectively. The levels of Fur and OmlA proteins had no influence on omlA or fur expression, excluding any trans-acting cross-regulation between fur and omlA. Expression of omlA was constitutive regardless of growth phase, oxygen tension, iron concentration, pH, and temperature. OmlA contained a signal sequence typical of bacterial lipoproteins, with a cysteine as a putative cleavage and lipid attachment site. Inhibition of signal peptidase II by globomycin resulted in failure to process OmlA, thus giving strong evidence that OmlA is a lipoprotein. Cell fractionation followed by Western blot analysis indicated that all OmlA protein is localized in the outer membrane. Mature OmlA was an acidic (pI = 4. 5) protein of 17.3 kDa and had close to 40% amino acid sequence identity to SmpA (small protein A) of Escherichia coli, Vibrio cholerae, and Haemophilus influenzae, a protein of unknown function. All P. aeruginosa strains tested as well as Pseudomonas fluorescens were found to produce OmlA. A mutant strain with impaired production of OmlA but no change in the expression of the overlapping fur gene was constructed. The omlA mutant was hypersusceptible to anionic detergents such as sodium dodecyl sulfate and deoxycholate, and it showed increased susceptibility to various antibiotics, including nalidixic acid, rifampin, novobiocin, and chloramphenicol. A structural role of OmlA in maintaining the cell envelope integrity is proposed.

Molecular characterization of the Serratia marcescens OmpF porin, and analysis of S. marcescens OmpF and OmpC osmoregulation

Serratia marcescens is a nosocomial pathogen with a high incidence of beta-lactam resistance. Reduced amounts of outer-membrane porins have been correlated with increased resistance to beta-lactams but only one porin, OmpC, has been characterized at the molecular level. In this study we present the molecular characterization of a second porin, OmpF, and an analysis of the expression of S. marcescens porins in response to various environmental changes. Two porins were isolated from the outer membrane using urea-SDS-PAGE and the relative amounts were shown to be influenced by the osmolarity of the medium and the presence of salicylate. From a S. marcescens genomic DNA library an 8 kb EcoRI fragment was isolated that hybridized with an oligonucleotide encoding the published N-terminal amino acid sequence of the S. marcescens 41 kDa porin. A 41 kDa protein was detected in the outer membrane of Escherichia coli NM522 carrying the cloned S. marcescens DNA. The cloned gene was sequenced and shown to code for a protein that shared 60-70% identity with other known OmpF and OmpC sequences. The upstream DNA sequence of the S. marcescens gene was similar to the corresponding E. coli ompF sequence; however, a regulatory element important in repression of E. coli ompF at high osmolarity was absent. The cloned S. marcescens OmpF in E. coli increased in expression in conditions of high osmolarity. The potential involvement of micF in the observed osmoregulation of S. marcescens porins is discussed.

An outer-membrane porin inducible by short-chain amides and urea in the methylotrophic bacterium Methylophilus methylotrophus

The fmdA and fmdB genes encoding formamidase and a putative regulatory protein, respectively, from the methylotrophic bacterium Methylophilus methylotrophus were recloned with additional flanking DNA (pSW1). fmdC, encoding a weakly hydrophilic protein containing an N-terminal signal sequence, was identified upstream of fmdAB. The derived amino acid sequence of mature FmdC (M(r) 39204) showed that it was rich in beta-sheet and aromatic amino acids, and exhibited significant similarities to several outer-membrane porins from other bacteria. Cell fractionation studies showed that the protein was located in the outer membrane. Mature FmdC was purified and shown to consist of a single type of subunit (M(r) 40,000) with the predicted N-terminal amino acid sequence (GATISF-). SDS-PAGE and Western blotting of cells grown in continuous culture under various conditions showed that mature FmdC was induced by formamide, acetamide and urea, repressed by excess ammonia, and over-expressed during prolonged growth under formamide limitation. It is concluded that mature FmdC is a porin involved in the transport of short-chain amides and urea through the outer membrane of M. methylotrophus under conditions where these nitrogen sources are present at very low concentration.

Molecular and immunological characterization of OprL, the 18 kDa outer-membrane peptidoglycan-associated lipoprotein (PAL) of Pseudomonas aeruginosa

Immunological screening of a Pseudomonas aeruginosa cosmid library led to the identification of clones producing an 18 kDa outer-membrane protein. This protein reacted in Western blots with a polyclonal antiserum against outer-membrane proteins of P. aeruginosa and with a monoclonal antibody (MA1-6) specific for OprL, the peptidoglycan-associated outer-membrane lipoprotein (PAL). Sequencing of pOML7, a subclone expressing oprL, revealed an ORF of 504 bp encoding a polypeptide with a typical lipoprotein signal recognition sequence. Another ORF was found upstream of oprL, with homology to the TolB protein of Escherichia coli and Haemophilus influenzae. Downstream of oprL, a second ORF, of 321 bp, was found (orf2), encoding a protein with a signal peptide and with no homology with proteins of known biological function. After the stop codon of orf2, a rho-independent terminator sequence was detected which is part of the P. aeruginosa PAO1 insertion element IS222. OprL showed homologies with all known PALs from Gram-negative bacteria, especially in the C-terminal part. mAb MA1-6 reacted with P. aeruginosa cells in immunofluorescence, and with E. coli cells expressing oprL, which had an abnormal, elongated morphology, an indication that production of the protein perturbed the division process.

A phosphate-starvation-inducible outer-membrane protein of Pseudomonas fluorescens Ag1 as an immunological phosphate-starvation marker

A phosphate-starvation-inducible outer-membrane protein of Pseudomonas fluorescens Ag1, expressed at phosphate concentrations below 0.08-0.13 mM, was purified and characterized. The purification method involved separation of outer-membrane proteins by SDS-PAGE and extraction of the protein from nitrocellulose or PVDF membranes after electrotransfer of proteins to the membranes. The N-terminal amino acid sequence of the purified protein, called Psi1, did not show homology to any known proteins, and in contrast to the phosphate-specific porin OprP of P. aeruginosa its mobility in SDS-PAGE was not affected by solubilization temperature. An antiserum against Psi1 recognized a protein of M, 55,000 in four other P. fluorescens strains among 24 tested strains representing Pseudomonas rRNA homology group I, showing antigenic heterogeneity within this group. A method for immunofluorescence microscopy involving cell permeabilization was adapted to visualize cell-specific expression of Psi1 in P. fluorescens exposed to limiting amounts of phosphate. This approach should be useful for further exploration of Psi1 as a marker to study the availability of phosphate to P. fluorescens in natural environments.

Secondary structure of the outer membrane proteins OmpA of Escherichia coli and OprF of Pseudomonas aeruginosa

When purified without the use of ionic detergents, both OmpA and OprF proteins contained nearly 20% alpha-helical structures, which disappeared completely upon the addition of sodium dodecyl sulfate. This result suggests that the proteins fold in a similar manner, with an N-terminal, membrane-spanning beta-barrel domain and a C-terminal, globular, periplasmic domain.

Secondary structure of the outer membrane proteins OmpA of Escherichia coli and OprF of Pseudomonas aeruginosa

When purified without the use of ionic detergents, both OmpA and OprF proteins contained nearly 20% alpha-helical structures, which disappeared completely upon the addition of sodium dodecyl sulfate. This result suggests that the proteins fold in a similar manner, with an N-terminal, membrane-spanning beta-barrel domain and a C-terminal, globular, periplasmic domain.

Structural and phylogenetic analysis of the MotA and MotB families of bacterial flagellar motor proteins

MotA and MotB are two well-characterized proteins in Escherichia coli which are believed to function as the proton channel and the anchor, respectively, of the motor component of the bacterial flagellum. We have identified and analysed all currently sequenced members of the MotA and MotB families. Members of these families include (1) these E. coli proteins, (2) their pmf-interacting motor homologues in other bacteria, (3) two ORFs which map downstream of the gene encoding the catabolite repression-mediating CepA protein in Bacillus species and (4) unidentified open reading frames. With one exception (the MotB protein of Rhodobactec sphaeroides), members of the MotB family exhibit a C-terminal domain that is homologous to peptidoglycan-interaction domains of numerous sequenced lipoproteins and outer membrane proteins. Multiple alignments, average hydropathy and similarity plots, and phylogenetic trees have allowed (1) identification of regions of relative conservation, (2) definition of signature sequences for these protein families and (3) determination of relative phylogenetic distances relating all members of each family. The phylogenies of these proteins do not follow those of the organisms from which they were isolated, suggesting the presence of divergent isoforms in many bacteria. Phylogenetic analyses of the peptidoglycan-interaction domains of MotB proteins indicated that, except for MotB of R. sphaeroides, these domains became associated with the MotB proteins early during evolutionary history, before members of the MotB family or members of the outer membrane protein family diverged from each other.

The Pseudomonas putida peptidoglycan-associated outer membrane lipoprotein is involved in maintenance of the integrity of the cell cell envelope

Pseudomonas putida 14G-3, a derivative of the natural soil inhabitant P. putida KT2440, exhibited a chromosomal insertion of a mini-Tn5/'phoA transposon that resulted in reduced ability to colonize soil. In vitro characterization of P. putida 14G-3 revealed that it exhibited an altered cell morphology and envelope, as revealed by electron microscopy. The derived strain was sensitive to sodium dodecyl sulfate, deoxycholate, and EDTA, produced clumps when it reached high cell densities in the late logarithmic growth phase, and did not grow on low-osmolarity medium. The P. putida DNA surrounding the mini-Tn5/'phoA insertion was cloned and used as a probe to rescue the wild-type gene, which was sequenced. Comparison of the deduced peptide sequence with sequences in the Swiss-Prot database allowed the knocked-out gene to be identified as that encoding the peptidoglycan-associated lipoprotein (Pal or OprL) of P. putida. The protein was identified in coupled transcription and translation assays in vitro.

Aeromonas salmonicida possesses two genes encoding homologs of the major outer membrane protein, OmpA

Two homologs of the outer membrane protein OmpA were identified in Aeromonas salmonicida by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and amino-terminal sequence analyses. An A. salmonicida genomic DNA library was constructed by using lambda GEM-11 and recombinant phage carrying both genes ompAI and ompAII) selected by immunoscreening. A 5.0-kb BamHI fragment containing the two genes in tandem was subcloned in pBluescript and used for further subcloning and sequencing of the genes. The encoded proteins (Mr = 33,564 and 32,536 for mature OmpAI and OmpAII, respectively) had only 64% identity with each other and otherwise had the highest level of homology to OmpA proteins from the members of the family Enterobacteriaceae. Based on the Escherichia coli OmpA model, an eight-stranded amphipathic beta-barrel model for the membrane assembly of the N-terminal half of OmpAI and OmpAII was predicted. Most variation between the two proteins was localized to the predicted surface loops and periplasmic turns, while the transmembrane strands and C-terminals domains were highly conserved. Expression of ompAI and ompAII separately in E. coli indicated that both genes could be independently transcribed from their own promoters and that both gene products were assembled into the E. coli outer membrane. A survey of different Aeromonas spp. by PCR revealed that possession of two tandem ompA genes was widespread among this genus. This is the first report of any bacterial species possessing two genes for homologs of this major outer membrane protein.

Outer membrane proteins of Pseudomonas aeruginosa as vaccine candidates

We tested the ability of the recombinant outer membrane proteins of Pseudomonas aeruginosa to serve as a protective vaccine against this Gram-negative pathogen in the presence of two main pathophysiological events leading to P. aeruginosa sepsis: (i) systemic infection during immunosuppression; and (ii) bacterial translocation. A hybrid vaccine was cloned which combined the protective epitopes of outer membrane protein F (OprF) and outer membrane protein I (OprI). This vaccine proved to be highly protective against an intraperitoneal challenge with P. aeruginosa in immunosuppressed mice. Oral immunization of mice with recombinant OprI expressing Salmonella dublin, induced s-IgA antibodies in the gut mucosa against OprI. These provided protection against translocation of P. aeruginosa in an immunosuppressed mouse model. To test whether OprI is effective in man, recombinant OprI was purified and used for the immunization of human volunteers. Immunization was tolerated well, and no side effects were observed. Antibody titers against OprI were measured in 90% of the volunteers after immunization.

Mapping of a surface-exposed, conformational epitope of the P6 protein of Haemophilus influenzae

P6 is an outer membrane protein of Haemophilus influenzae that is antigenically conserved and considered a candidate component of future H. influenzae vaccines. P6 contains a surface-exposed epitope recognized by monoclonal antibody (MAb) 3B9. This epitope has been shown to be distinct from that recognized by the P6-specific MAbs 7F3 and 4G4 in a competitive inhibition enzyme-linked immunosorbent assay (ELISA). MAb 3B9 did not bind to synthetic P6-specific sequential and overlapping hexameric peptides. Five peptides made to correspond to P6 sequences with high probabilities of surface exposure did not inhibit binding of MAb 3B9 to P6. An antiserum to one of the peptides, designated SP66, inhibited binding of MAb 3B9 to P6. A rabbit antiserum to P6 bound to sequential hexameric peptides, Gly-87AsnThrAspGluArgGlyThr-94, which were in the SP66 region of P6. This antiserum inhibited the binding of P6 to MAb 3B9 in a competitive inhibition ELISA. P6 mutations with His and Ala substitutions at residues Thr-88 and Asn-89 still bound MAb 3B9. MAb 3B9 reacted with Escherichia coli OmpA and Salmonella typhimurium OmpA. Sequence comparisons of P6 with these proteins indicated that the residue in the SP66 region responsible for binding is either Gly-87, Asp-90, or Gly-93. Mercaptoethanol reduction abolished MAb 3B9 binding to E. coli OmpA and S. typhimurium OmpA. In these proteins, immediately downstream of the second cysteine, there is an ArgArg dipeptide which is identical to and aligns with Arg-147Arg-148 in P6. This dipeptide has a high probability of surface exposure in P6. Mutagenesis of the Arg-147Arg-148 to an AlaAla dipeptide in P6 abolished binding of MAb 3B9, demonstrating that it was either a portion of the epitope or important in the protein folding necessary for expression of this epitope. This study demonstrates that MAb 3B9 recognizes a conserved conformational determinant on the surface of H. influenzae that is composed of two discontinuous regions of P6.

Escherichia coli invasion of brain microvascular endothelial cells in vitro and in vivo: molecular cloning and characterization of invasion gene ibe10

Most cases of neonatal Escherichia coli meningitis develop as a result of hematogenous spread, but it is not clear how circulating E. coli crosses the blood-brain barrier. In an attempt to identify E. coli structures contributing to invasion into the central nervous system (CNS), TnphoA mutagenesis was performed with an invasive CSF isolate of E. coli K1 strain RS218 (O18:K1:H7), and TnphoA mutants were examined for their noninvasive capability in brain microvascular endothelial cells (BMEC). The noninvasive mutants exhibited the invasive ability of < 1% of the parent strain. One of the noninvasive mutants (10A-23) with a single TnphoA insertion and no changes in phenotypic characteristics was found to be significantly less invasive into the CNS in the newborn rat model of hematogenous E. coli meningitis. The TnphoA inserts with flanking sequences were cloned and sequenced. A novel open reading frame (8.2 kDa) was identified. Open reading frame analysis indicated that the 8.2-kDa protein (Ibe10) contained multiple transmembrane domains. ibe10 was cloned into an expression vector, pQE30, and the purified Ibe10 was shown to inhibit invasion of BMEC by strain RS218. These findings indicate that ibe10 is one of the E. coli genes involved in the invasion of BMEC in vitro and in vivo.

Purification and characterization of the Pseudomonas aeruginosa NfxB protein, the negative regulator of the nfxB gene

The protein NfxB, involved in conferring resistance to quinolones in Pseudomonas aeruginosa, has a helix-turn-helix motif which is similar to that of other DNA-binding proteins. It appears to affect the membrane-associated energy-driven efflux of some antibiotics (H. Nikaido, Science 264:382-388, 1994). We constructed a plasmid that overproduced NfxB in Escherichia coli and purified the protein. Two species of NfxB (23 and 21 kDa), which are probably translated from different initiation codons, were isolated. Both proteins are also expressed in vivo in P. aeruginosa, with the 23-kDa NfxB being the major species. NfxB specifically binds upstream of the nfxB coding region as demonstrated by gel retardation and DNase I footprinting. Expression of the phi (nfxB'-lacZ+) (Hyb) gene was repressed in the presence of the nfxB gene product provided by a second compatible plasmid in E. coli. In the P. aeruginosa wild-type strain (PAO2142), NfxB was undetectable by immunoblotting; however, it was detected in the nfxB missense mutant (PK1013E). These results suggested that NfxB negatively autoregulates the expression of nfxB itself. Since the 54-kDa outer membrane protein (OprJ) (N. Masuda, E. Sakagawa, and S. Ohya, Antimicrob. Agents Chemother. 39:645-649, 1995) was overproduced in nfxB mutants, NfxB may also regulate the expression of membrane proteins that are involved in the drug efflux machinery of P. aeruginosa.

Conformational analysis of the Campylobacter jejuni porin

The major outer membrane protein (MOMP) of Campylobacter jejuni was purified to homogeneity by selective solubilization and fast protein liquid chromatography. The amino acid composition of the MOMP indicates the presence of cysteine residues. The amino-terminal sequence, determined over 31 residues, shows no significant homology with any other porin from gram-negative bacteria except in a discrete region. Immunocross-reactivity between Escherichia coli OmpC and the MOMP was analyzed, and a common antigenic site between these two porins was identified with an anti-peptide antibody. From circular dichroism and immunological investigations, the existence of a stable folded monomer, containing a high level of beta-sheet secondary structure, is evident. Conformational analyses show the presence of a native trimeric state generated by association of the three folded monomers; the stability of this trimer is reduced compared with that of E. coli porins. This study clearly reveals that the C. jejuni MOMP is related to the family of trimeric bacterial porins.

Porin activity and sequence analysis of a 31-kilodalton Treponema pallidum subsp. pallidum rare outer membrane protein (Tromp1)

We have recently reported the isolation and purification of the Treponema pallidum outer membrane and the identification of its rare protein constituents, including a 31-kDa protein markedly enriched in the outer membrane preparation (D.R. Blanco, K. Reimann, J. Skare, C.I. Champion, D. Foley, M. M. Exner, R. E. W. Hancock, J. N. Miller, and M. A. Lovett, J. Bacteriol. 176:6088-6099, 1994). In this study, we report the cloning, sequencing, and expression of the structural gene which encodes the 31-kDa outer membrane protein, designated Tromp1. The deduced amino acid sequence from the tromp1 gene sequence encodes a 318-amino-acid polypeptide with a putative 40-amino-acid signal peptide. Processing of Tromp1 results in a mature protein with a predicted molecular mass of 30,415 Da and a calculated pI of 6.6. Secondary-structure predictions identified repeated stretches of amphipathic beta-sheets typical of outer membrane protein membrane-spanning sequences. A topological model of Tromp1 containing 14 transmembrane segments is proposed. Specific antiserum against a recombinant Tromp1 fusion protein was generated and was used to identify native Tromp1 in cellular fractionation. Upon Triton X-114 extraction and phase separation of T. pallidum, the 31-kDa Tromp1 protein was detected in the detergent-phase fraction but not in the protoplasmic cylinder or aqueousphase fractions, consistent with a hydrophobic outer membrane protein. Anti-Tromp1 antiserum was also used to identify native Tromp1 purified from whole T. pallidum by Triton X-100 solubilization followed by nondenaturing isoelectric focusing. Reconstitution of purified Tromp1 into planar lipid bilayers showed porin activity based on the measured single channel conductanes of 0.15 and 0.7 nS in 1 M KCl. These findings demonstrate that Tromp1 is a transmembrane outer membrane porin protein of T. pallidum.

Pseudomonas aeruginosa outer membrane protein OprF as an expression vector for foreign epitopes: the effects of positioning and length on the antigenicity of the epitope

OprF, the major outer membrane (OM) protein of Pseudomonas aeruginosa, has been proposed to be comprised of a series of beta-strands separated by periplasmic or surface-exposed loop regions. In this study, a simple malarial epitope was used to demonstrate that OprF can be used as an expression vector to present foreign peptide sequences, namely, the 4-amino-acid (aa) repeating epitope (Asn-Ala-Asn-Pro = NANP) of the circumsporozoite protein of the human malarial parasite Plasmodium falciparum. Eight permissive sites, that allowed the expression and surface exposure of the malarial epitope, were identified throughout OprF. Using a monoclonal antibody (mAb) specific for the malarial epitope, we investigated the effects of positioning and length of the epitope on its antigenicity in the OprF expression vector system. It was demonstrated that the malarial epitope inserted at aa26 was significantly more reactive with the epitope-specific mAb (i.e., more antigenic) when assayed in the context of whole cells whereas those at aa213 and aa290 were more antigenic when assayed in the OM. The malarial epitope inserted at aa188 and aa196 was moderately antigenic, while this epitope inserted at aa215 and aa310 showed low antigenicity with the same mAb in both whole cell and OM assays. For two insertion sites, aa26 and aa213, we demonstrated that the insertion of multiple copies of the epitope enhanced reactivity with the malarial epitope-specific mAb. These data are discussed with respect to the local OprF sequences into which the epitope was inserted.

Protection of immunocompromised mice against lethal infection with Pseudomonas aeruginosa by active or passive immunization with recombinant P. aeruginosa outer membrane protein F and outer membrane protein I fusion proteins

Recombinant outer membrane proteins (Oprs) of Pseudomonas aeruginosa were expressed in Escherichia coli as glutathione S-transferase (GST)-linked fusion proteins. GST-linked Oprs F and I (GST-OprF190-350 [GST linked to OprF spanning amino acids 190 to 350] and GST-OprI21-83, respectively) and recombinant hybrid Oprs (GST-OprF190-342-OprI21-83 and GST-OprI21-83-OprF190-350) were isolated and tested for their efficacy as vaccines in immunodeficient mice. GST-OprF-OprI protected the mice against a 975-fold 50% lethal dose of P. aeruginosa. Expression of GST-unfused OprF-OprI failed in E. coli, although this hybrid protein has been expressed without a fusion part in Saccharomyces cerevisiae and used for immunizing rabbits. The immune rabbit sera protected severe combined deficient (SCID) mice against a 1,000-fold 50% lethal dose of P. aeruginosa. Evidence is provided to show that the most C-terminal part of OprF (i.e., amino acids 332 to 350) carries an important protective epitope. Opr-based hybrid proteins may have implications for a clinical vaccine against P. aeruginosa.

Development of multiple-antibiotic-resistant (Mar) mutants of Pseudomonas aeruginosa after serial exposure to fluoroquinolones

Laboratory-derived fluoroquinolone-resistant mutants were created by serially passaging wild-type Pseudomonas aeruginosa on fluoroquinolone-containing agar to obtain high-level fluoroquinolone resistance (e.g., ciprofloxacin MIC of 1,024 micrograms/ml). With increases of 4- to 32-fold in MICs of fluoroquinolones, these organisms demonstrated (relative to wild-type) normal morphology, resistance to fluoroquinolones only, no change in fluoroquinolone uptake, and no change in lipopolysaccharide profiles or outer membrane protein profiles. Complementation with wild-type Escherichia coli gyrA restored fluoroquinolone susceptibility, suggesting that these were gyrA mutants. After 4- to 32-fold increases in fluoroquinolone MICs (with continued passage on fluoroquinolone-containing agar) isolates demonstrated altered morphology, a multiple-antibiotic-resistant (Mar) phenotype (including cross-resistance to beta-lactams, chloramphenicol, and tetracycline), reduced fluoroquinolone uptake and altered outer membrane proteins (reductions in the 25- and 38-kDa bands as well as several bands in the 43- to 66-kDa region). Complementation with wild-type E. coli gyrA partially reduced the level of fluoroquinolone resistance by approximately 8- to 32-fold, suggesting that these mutants displayed both gyrA and non-gyrA mutations.