Biomedical subjects

J Tommassen

Publications and source records attributed to J Tommassen.

At least 127 records · Page 7Linked to original sources

PubMed1991

Outer membrane protein PhoE as a carrier for the exposure of foreign antigenic determinants at the bacterial cell surface.

PhoE protein is an abundant outer membrane protein of the Escherichia coli K-12 outer membrane. This protein can be used as an exposure system to produce foregin antigenic determinants and for their transport to the bacterial cell surface. The system is very flexible, since insertions varying in length and nature could be made in different cell surface-exposed regions of PhoE, without interfering with the assembly process of the mutant proteins into the outer membrane. Two antigenic determinants of the structural VP1 protein of foot-and-mouth disease virus were inserted in different combinations in four cell surface-exposed regions of PhoE. The epitopes were exposed at the bacterial cell surface and they keep their antigenic and immunogenic properties in this PhoE-associated conformation. Immunization of guinea pigs with one hybrid protein, containing a combination of the two epitopes inserted in the fourth exposed region, resulted in complete protection against challenge with the virus. A T-cell epitope of the 65 kDa heat shock protein of Mycobacterium tuberculosis was inserted in the fourth exposed region of PhoE and in vitro proliferation of two T-cell specific clones was demonstrated. Thus, the PhoE exposure system has been shown to be suitable for presentation of both B-cell and T-cell determinants to the immune system. Furthermore, good expression of the hybrid protein in attenuated Salmonella strains, which can be used as live oral vaccines, was shown.

Amino Acid Sequence↗

PubMed1991

The ferric-pseudobactin receptor PupA of Pseudomonas putida WCS358: homology to TonB-dependent Escherichia coli receptors and specificity of the protein.

The initial step in the uptake of iron via ferric pseudobactin by the plant-growth-promoting Pseudomonas putida strain WCS358 is binding to a specific outer-membrane protein. The nucleotide sequence of the pupA structural gene, which codes for a ferric pseudobactin receptor, was determined. It contains a single open reading frame which potentially encodes a polypeptide of 819 amino acids, including a putative N-terminal signal sequence of 47 amino acids. Significant homology, concentrated in four boxes, was found with the TonB-dependent receptor proteins of Escherichia coli. The pupA mutant MH100 showed a residual efficiency of 30% in the uptake of 55Fe3+ complexed to pseudobactin 358, whereas the iron uptake of four other pseudobactins was not reduced at all. Cells of strain WCS374 supplemented with the pupA gene of strain WCS358 could transport ferric pseudobactin 358 but showed no affinity for three other pseudobactins. It is concluded that PupA is a specific receptor for ferric pseudobactin 358, and that strain WCS358 produces at least one other receptor for other pseudobactins.

Amino Acid Sequence↗

PubMed1991

Molecular characterization of an Enterobacter cloacae outer membrane protein (OmpX).

A chromosomal gene of Enterobacter cloacae encoding an outer membrane protein (OmpX) has been cloned. Overproduction of the OmpX protein decreased the quantity of porins in the outer membrane of the parental strain and of Escherichia coli HB101. The ompX gene was located by insertions of the gamma delta sequence into the recombinant plasmid. The polarity of the gene was determined by in vitro transcription and translation of the gamma delta-containing plasmids. The nucleotide sequence of the ompX gene was elucidated by using both inverted terminal repeats of the gamma delta sequence as starting points for M13 dideoxy sequencing. The gene was found to encode a precursor of the OmpX protein consisting of 172 amino acid residues with a molecular mass of 18.6 kDa. The protein contains an N-terminal signal sequence of 23 amino acid residues. The exact cleavage point was established by sequencing the N-terminal part of the mature protein. The OmpX protein has several characteristics in common with outer membrane proteins of gram-negative bacteria. The protein is rather hydrophilic and is devoid of long hydrophobic stretches. On the basis of these results, we present a model for the OmpX protein folding in an outer membrane.

Amino Acid Sequence↗

PubMed1990

Tryptophan fluorescence study on the interaction of the signal peptide of the Escherichia coli outer membrane protein PhoE with model membranes.

The interaction of the signal peptide of the Escherichia coli outer membrane protein PhoE with different phospholipid vesicles was investigated by fluorescence techniques, using a synthetic mutant signal peptide in which valine at position -8 in the hydrophobic sequence was replaced by tryptophan. First it was established that this mutation in the signal sequence of prePhoE does not affect in vivo and in vitro translocation efficiency and that the biophysical properties of the synthetic mutant signal peptide are similar to those of the wild-type signal peptide. Next, fluorescence experiments were performed which showed an increase in quantum yield and a blue shift of the emission wavelength maximum upon interaction of the signal peptide with lipid vesicles, indicating that the tryptophan moiety enters a more hydrophobic environment. These changes in intrinsic fluorescence were found to be more pronounced in the presence of phosphatidylglycerol (PG) or cardiolipin (CL) than with phosphatidylcholine (PC). In addition, quenching experiments demonstrated a shielding of the tryptophan fluorescence from quenching by the aqueous quenchers iodide and acrylamide upon interaction of the signal peptide with lipid vesicles, a shielding in the case of acrylamide that was more pronounced in the presence of negatively charged lipids. Finally it was found that acyl chain brominated lipids incorporated into phospholipid bilayers were able to quench the tryptophan fluorescence of the signal peptide, with the quenching efficiency in CL vesicles being much higher than in PC vesicles. The results clearly demonstrate that the PhoE signal peptide interacts strongly with different lipid vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1990

Outer-membrane PhoE protein of Escherichia coli K-12 as an exposure vector: possibilities and limitations.

The phosphate-limitation-inducible outer-membrane protein (PhoE) of Escherichia coli K-12 can be used in an expression system as a carrier for foreign antigenic determinants, facilitating their transport to the bacterial cell surface. The system is very flexible, since insertions varying in length and nature can be made in different cell-surface-exposed regions of PhoE protein, without interfering with the assembly process into the outer membrane. Multiple insertions of an antigenic determinant can be made in the second and eighth exposed regions, resulting in a total insert length of up to 30 and 50 amino acid (aa) residues. Insertions can be made in two exposed regions, simultaneously. However, some limitations were encountered, e.g., insertion of eight or more hydrophobic aa residues affected both the translocation process across the inner membrane and the assembly process into the outer membrane. Also, the insertion of sequences containing many charged residues resulted in accumulation of precursor protein in the cytoplasm.

Bacterial Outer Membrane Proteins↗

PubMed1990

Assembly of an in vitro synthesized Escherichia coli outer membrane porin into its stable trimeric configuration.

The folding of in vitro synthesized outer membrane protein PhoE of Escherichia coli was studied in immunoprecipitation experiments with monoclonal antibodies which recognize cell surface-exposed conformational epitopes. The signal sequence appears to interfere with the formation of these conformational epitopes, since a mutant PhoE protein which lacks the majority of the signal peptide could be precipitated four times better than the wild type precursor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitated PhoE protein revealed that part of the immunoprecipitated PhoE was present as a heat-modifiable form of the protein which migrated faster in the gels than the completely denatured protein. This form of the protein probably represents a folded monomer which might be an intermediate in the assembly of the protein. Outer membrane vesicles were required to induce the formation of small amounts of heat-stable trimers, the functional form of the protein in vivo.

Amino Acid Sequence↗

PubMed1990

Efficient recognition by rat T cell clones of an epitope of mycobacterial hsp 65 inserted in Escherichia coli outer membrane protein PhoE.

PhoE is a pore-forming protein, abundantly expressed in the Escherichia coli outer membrane. Previous investigations have shown the possibility of inserting antigenic determinants in cell surface-exposed regions of PhoE by recombinant DNA techniques without disturbing the biogenesis and the functioning of the protein. This method proved to be successful for foot-and-mouth disease virus B cell determinants. We have now shown for the first time that PhoE can also be used as a carrier molecule for T cell epitopes. A well-characterized T cell epitope (180-188) of the 65-kDa heat-shock protein (hsp 65) of Mycobacterium tuberculosis was expressed in PhoE and tested for recognition by specific T cell clones. Specific and efficient T cell proliferation was found after stimulation with this protein construct in vitro. Interestingly, paraformaldehyde fixation of antigen-presenting cells did not abrogate T cell recognition. Thus, in contrast to hsp 65 itself, recognition of epitope 180-188 in the context of PhoE appeared to be independent of antigen-processing events. At the level of polyclonal T cell responses the epitope in the context of PhoE is recognized more efficiently than 180-188 as synthetic peptide or in the context of the hsp 65 molecule itself. These findings indicate that PhoE may serve as attractive vaccine carrier not only for B, but also for T cell epitopes. Furthermore, the possibility for expression of PhoE constructs in attenuated Salmonella typhimurium strains offers the exciting prospect of new types of live oral vaccines expressing selected combinations of B and T cell epitopes.

Amino Acid Sequence↗

PubMed1990

Protein secretion in gram-negative bacteria: transport across the outer membrane involves common mechanisms in different bacteria.

The xcp genes are required for protein secretion by Pseudomonas aeruginosa. They are involved in the second step of the process, i.e. the translocation across the outer membrane, after the exoproteins have reached the periplasm in a signal peptide dependent fashion. The nucleotide sequence of a 2.5 kb DNA fragment containing xcp genes showed at least two complete open reading frames, potentially encoding proteins with molecular weights of 41 and 19 kd. Products with these apparent molecular weights were identified after expression of the DNA fragment in vitro and in vivo. Subcloning and complementation experiments showed that both proteins are required for secretion. The two products are located in the inner membrane and share highly significant homologies with the PulL and PulM proteins which are required for the specific secretion of pullulanase in Klebsiella pneumoniae. These homologies reveal the existence of a common mechanism for protein secretion in Pseudomonas aeruginosa and Klebsiella pneumoniae.

Amino Acid Sequence↗

PubMed1990

Outer membrane PhoE protein of Escherichia coli as a carrier for foreign antigenic determinants: immunogenicity of epitopes of foot-and-mouth disease virus.

Outer membrane protein PhoE of Escherichia coli was used for the expression of antigenic determinants of foot-and-mouth disease virus. Five hybrid PhoE proteins were constructed containing different combinations of two antigenic determinants of VP1 protein of the virus. The hybrid proteins were expressed in two E. coli strains and the proteins were correctly assembled into the outer membrane. The inserted epitopes were exposed at the surface of the cell and were antigenic in this PhoE-associated conformation. Immunization experiments, performed with partially purified protein, resulted in all cases in a significant anti-peptide antibody titre. In one case in which the hybrid protein with the largest insert was used, a neutralizing antibody response was detected.

Amino Acid Sequence↗

PubMed1990

Protection of guinea-pigs against foot-and-mouth disease virus by immunization with a PhoE-FMDV hybrid protein.

A hybrid protein was constructed containing two antigenic determinants of the structural protein VP1 of foot-and-mouth disease virus, inserted in a cell surface-exposed region of Escherichia coli outer membrane protein PhoE. Immunization of guinea-pigs with partially purified protein resulted in high levels of neutralizing antibodies and complete protection against challenge with the virus.

Amino Acid Sequence↗

PubMed1990

Isolation of Neisseria meningitidis mutants deficient in class 1 (porA) and class 3 (porB) outer membrane proteins.

The class 1 major outer membrane protein of Neisseria meningitidis is a serious candidate for a meningococcal vaccine. To facilitate studies on the function of this protein, mutants were isolated that lacked this protein or the structurally related class 3 protein. These mutants were obtained by using the antibody-dependent bactericidal action of the complement system. The class 1 protein-deficient strain grew normally in vitro, whereas growth of the class 3 protein-deficient strain was slightly retarded. The class 3 protein-deficient strain displayed increased resistance to the antibiotics tetracycline and cefsulodin, which is consistent with the proposed role of the protein as a pore-forming protein. The class 1 protein was purified to homogeneity from the class 3 protein-deficient strain. Lipid bilayer experiments revealed that this protein also formed pores. The class 1 protein pores were cation selective.

Bacterial Outer Membrane Proteins↗

PubMed1990

Monoclonal antibodies against the 70-kilodalton iron-regulated protein of Neisseria meningitidis are bactericidal and strain specific.

When grown under iron limitation, Neisseria meningitidis expresses a number of outer membrane proteins (OMPs), one of which is a 70-kilodalton (kDa) major OMP. After immunization of mice with outer membrane preparations of iron-depleted cells of strain H44/76 (B:15:P1.7,16), hybridoma cell lines producing monoclonal antibodies against the 70-kDa OMP were obtained. Some of these monoclonal antibodies demonstrated strong bactericidal activity against the homologous strain H44/76 in the presence of human complement, suggesting potential application of the 70-kDa OMP as a vaccine component. However, none of the 10 selected monoclonal antibodies was able to recognize the corresponding protein from five heterologous strains of various serosubtyping characteristics. A polyclonal anti-70-kDa OMP serum also did not react with the other strains. This result shows that immunodominant surface-exposed epitopes of the meningococcal 70-kDa iron-limitation-inducible OMP are strain specific.

Animals↗

PubMed1989

Role of the cell surface-exposed regions of outer membrane protein PhoE of Escherichia coli K12 in the biogenesis of the protein.

To investigate the role of the cell surface-exposed regions of outer membrane protein PhoE of Escherichia coli K12 in the biogenesis of the protein, deletions were generated in two presumed cell surface-exposed regions of the protein. Intact cells expressing these mutant proteins were recognized by PhoE-specific monoclonal antibodies, which recognize conformational epitopes on the cell surface-exposed parts of the protein and/or were sensitive to a PhoE-specific phage. This shows that the polypeptides were normally incorporated into the outer membrane. When the deletions extended four amino acid residues into the seventh presumed membrane-spanning segment, the polypeptides accumulated in the periplasm. In conclusion, exposed regions of PhoE protein apparently do not play an essential role in outer membrane localization, which is consistent with the observation that these regions are hypervariable when PhoE is compared to the related proteins OmpF and OmpC. In contrast, the membrane-spanning segments are essential for the assembly process.

Amino Acid Sequence↗

PubMed1989

Membrane biogenesis in Escherichia coli: effects of a secA mutation.

In Escherichia coli K-12, temperature-sensitive mutations in the secA gene have been shown to interfere with protein export. Here we show that the effect of a secA mutation is strongly pleiotropic on membrane biogenesis. Freeze-fracture experiments as well as cryosections of the cells revealed the appearance of intracytoplasmic membranes upon induction of the SecA phenotype. The permeability barrier of the outer membrane to detergents was lost. Two alterations in the outer membrane may be responsible for this effect, namely the reduced amounts of outer membrane proteins, or the reduction of the length of the core oligosaccharide of the lipopolysaccharide, which was observed in phage-sensitivity experiments and by SDS-polyacrylamide gel electrophoresis. Phospholipid analysis of the secA mutant, grown under restrictive conditions, revealed a lower content of the negatively charged phospholipid cardiolipin and of 18:1 fatty acid compared to those of the parental strain grown under identical conditions. These results are in line with the hypothesis that protein export and lipid metabolism are coupled.

Bacterial Outer Membrane Proteins↗

PubMed1989

One single lysine residue is responsible for the special interaction between polyphosphate and the outer membrane porin PhoE of Escherichia coli.

Site-directed mutagenesis was performed with the phosphate starvation-inducible outer membrane porin PhoE of Escherichia coli K-12 to study the molecular basis of its anion selectivity. Lysines 18, 29, 64, and 125 were replaced by glutamic acids, and the properties of the mutant porins were investigated in in vivo and in vitro experiments. Lipid bilayer experiments showed that all these mutations had no influence on the pore structure because PhoE and the mutants had the same single channel conductance in KCl solution. Selectivity measurements revealed that the mutations changed the ionic selectivity of PhoE, but the change was dependent on the location of the lysine. Replacement of Lys18 and Lys29 by glutamic acid had a relatively small influence. The effect of the Lys64 substitution was somewhat larger, and the effect of the replacement of Lys125 resulted in the most drastic change in selectivity and in the loss of the interaction of PhoE with polyphosphate, whereas the replacement of the other lysines had no effect on the polyphosphate interaction behavior. The results are consistent with the assumption that the charge spot in PhoE consists of only 1 lysine per monomer, located in position 125 of the primary sequence and probably close to the pore interior.

Bacterial Outer Membrane Proteins↗

PubMed1989

Molecular basis of porin selectivity: membrane experiments with OmpC-PhoE and OmpF-PhoE hybrid proteins of Escherichia coli K-12.

Lipid bilayer experiments were performed with one OmpF-PhoE and several OmpC-PhoE hybrid porins of Escherichia coli K-12. All hybrid pores had approximately the same pore-forming activity, which indicated that the structure of the pores remained essentially unchanged by the genetic manipulation. This result was supported by single-channel experiments because all pores had similar single-channel conductances in potassium chloride. Measurements with other salts indicated a drastic change in the ionic selectivity when the fusion site in the ompC-phoE hybrid genes passed along the sequence of the porins from the N-terminal to the C-terminal end. Selectivity measurements using zero-current membrane potentials showed that the selectivity suddenly changed from anion to cation selectivity when a relatively short portion from the N-terminal end of PhoE was replaced by the corresponding part of OmpC. The replacement of increasing portions led to an increase in the cation selectivity until that of OmpC was reached. The change in the anion to cation selectivity is correlated with exchange of lysine-18 and serine-28 by aspartic acids. The anion selectivity of the phosphate starvation-inducible PhoE porin is closely related to the presence of several lysines spread along the primary sequence of the polypeptide chain.

Amino Acid Sequence↗

PubMed1989

The role of the positively charged N-terminus of the signal sequence of E. coli outer membrane protein PhoE in export.

Signal sequences of prokaryotic exported proteins have a dipolar character due to positively charged amino-acid residues at the N-terminus and to a preferentially negatively charged region around the cleavage site. The role of the two lysine residues at the N-terminus of the signal sequence of outer membrane protein PhoE of E. coli-K12 was investigated. Replacement of both of these residues by aspartic acid slightly affected the kinetics of protein translocation in vivo. This export defect, which was observed only when PhoE was overproduced, could not be suppressed by the prlA4 mutation, which has been shown to restore export defects caused by alterations in the hydrophobic core of the signal sequences of various exported proteins. In an in vitro translocation assay, the export defect was more pronounced. Replacement of both lysines by uncharged residues did not disturb the kinetics of protein export in vivo. In the in vitro assay, an extraordinarily efficient processing was detected upon incubation of this precursor with inverted cytoplasmic membrane vesicles. However, this efficient processing was not accompanied by more efficient translocation of the protein. We conclude that the positively charged residues at the N-terminus of the signal sequence are not essential for protein export, but contribute to the efficiency of the process.

Bacterial Outer Membrane Proteins↗

PubMed1989

The role of the carboxy-terminal membrane-spanning fragment in the biogenesis of Escherichia coli K12 outer membrane protein PhoE.

PhoE protein of Escherichia coli K12 is an outer membrane protein which is supposed to span the membrane sixteen times. By creating a deletion which removes the last membrane-spanning fragment and studying the localization of the truncated PhoE, we show that this fragment is indispensable for trimerization and outer membrane localization. In addition, circumstantial evidence for the proposed topology model of the protein was obtained. An insertion mutation in a region supposed to be cell surface-exposed, interferes with the binding of a monoclonal antibody which recognizes a cell surface-exposed epitope of the protein.

Bacterial Outer Membrane Proteins↗