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  • 1
    Electronic Resource
    Electronic Resource
    haemolysin of Escherichia coli: Comparison of pore-forming properties between chromosome and plasmid-encoded haemolysins (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 105 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Lipid bilayer experiments were performed with chromosome-encoded haemolysin of Escherichia coli. The addition of the toxin to the aqueous phase bathing lipid bilayer membranes of asolectin resulted in the formation of transient ion-permeable channels with two states at small transmembrane voltages. One is prestate (single-channel conductance 40 pS in 0.15 M KCl) of the open state, which had a single-channel conductance of 420 pS in 0.15 M KCl and a mean lifetime of 30 s. Membranes formed of pure lipids were rather inactive targets for this haemolysin. Experiments with different salts suggested that the haemolysin channel was highly cation-selective at neutral pH. The mobility sequence of the cations in the channel was similar if not identical to their mobility sequence in the aqueous phase. The single-channel data were consistent with a wide, water-filled channel with an estimated minimal diameter of about 1 nm. The pore-forming properties of chromosome-encoded haemolysin were compared with those of plasmid-encoded haemolysin. Both toxins share common features, oligomerize probably to form pores in lipid bilayer membranes. Both types of haemolysin channels have similar properties but different lifetimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05887.x
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  • 2
    Electronic Resource
    Electronic Resource
    Transcriptional regulation of prfA and PrfA-regulated virulence genes in Listeria monocytogenes (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 11 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The ActA protein, the lecithinase PlcB and listeriolysin are the major PrfA-dependant proteins synthesized when brain-heart infusion (BHI)-cultured Listeria monocytogenes is shifted to minimum essential medium (MEM) In the presence of the transcriptional inhibitor rifampicin. Enhanced synthesis of all three proteins under these conditions depends, however, on a short incubation (about 5 min) of the bacteria in MEM without rifampicin, suggesting that induction of these proteins in MEM requires de novo transcription. The enhanced synthesis of these three proteins is observed in the L. monocytogenes wild-type strains EGD and NCTC 7973, both of which belong to the serotype 1/2a. A significant induction of the bicistronic mRNA for ActA and PlcB is observed in both strains shortly after shifting the bacteria from BHI to MEM. This mRNA as well as the monocistronic listeriolysin (hly)-specific mRNA is highly stable in L. monocytogenes NCTC 7973 shifted to MEM. In contrast to the actA-plcB mRNA, no enhanced transcription in MEM is observed for the regulatory prfA gene or for the PrfA-controlled virulence genes hlyA and plcA in strain NCTC 7973. However, transcription of these genes is induced in strain EGD. Transcriptional induction of the mpl gene is observed in neither strain NCTC 7973 nor in strain EGD. The life-time of the prfA, plcA, and mpl transcripts is short. ActA was also found to be the most abundant newly synthesized surface protein when the two wild-type strains of L. monocytogenes replicated within the phagocytic cell line J774. ActA synthesis seemed to be induced in the cytoplasm since the non-haemolytic mutant M3 did not induce ActA when taken up by J774 cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00390.x
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  • 3
    Electronic Resource
    Electronic Resource
    Surface-associated, PrfA-regulated proteins of Listeria monocytogenes synthesized under stress conditions (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 8 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The expression of the five clustered genes of Listeria monocytogenes: plcA, hly, mpl, actA and plcB is under the control of the positive regulation factor PrfA. Listeriolysin, encoded by the hly gene, is the only prominent PrfA-controlled gene product observed when L. monocytogenes strain NCTC 7973 is cultured in a rich medium at 37°C to the logarithmic growth phase. Stress conditions such as heat-shock or stationary culture conditions lead to the induction of additional PrfA-dependent proteins (PdPs): ActA (92 kDa), a 38kDa protein of unknown function and a 34kDa protein which probably represents PlcA. Under nutrient-stress conditions PdPs are preferentially synthesized and in addition to the already known PdPs at least five new, not yet functionally identified PdPs are detected. All PdPs are either secreted or are localized at the cell surface. Differences in the amount as well as the sizes of the PdPs are observed in different L. monocytogenes strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01566.x
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  • 4
    Electronic Resource
    Electronic Resource
    The virulence regulator protein of Listeria ivanovii is highly homologous to PrfA from Listeria monocytogenes and both belong to the Crp-Fnr family of transcription regulators (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 13 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The two pathogenic Listeria species, L. ivanovii and L monocytogenes, can be differentiated biochemically and show different host ranges. Virulence of L. monocytogenes is dependent on the integrity of prfA which positively and coordinately regulates transcription of several virulence genes. Until now, a prfA homologue had not been identified in L. ivanovii. We have now cloned a chromosomal region from L. ivanovii comprising two genes with high homology to the picA and prfA genes from L. monocytogenes. Distal from prfA, an open reading frame highly homologous to a phosphorlbosyl pyrophosphate synthetase gene (prs) was newly identified, defining the border of the virulence gene cluster. Transcription of the gene for ivanolysin O and expression of other genes of the virulence gene cluster in L. ivanovii were dependent on PrfA. The pattern of PrfA-dependent proteins (PdPs) expressed in L ivanovii was similar, but not identical to that of L. monocytogenes. The PrfA proteins, as predicted from nucleotide sequences of both pathogenic Listeria species, are very similar and show significant homology to the Crp-Fnr family of global transcription regulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00409.x
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  • 5
    Electronic Resource
    Electronic Resource
    Oligomerization of Escherichia coli haemolysin (HlyA) is involved in pore formation (1993)
    Springer
    Molecular genetics and genomics 241 (1993), S. 89-96 
    Details
    ISSN: 1617-4623
    Keywords: Haemolysin ; Escherichia coli ; Oligomerization of HlyA ; Pore formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Coexpression of pairs of nonhaemolytic H1yA mutants in the recombination-deficient (recA) strain Escherichia coli HB101 resulted in a partial reconstitution of haemolytic activity, indicating that the mutation in one H1yA molecule can be complemented by the corresponding wild-type sequence in the other mutant HlyA molecule and vice versa. This suggests that two or more HlyA molecules aggregate prior to pore formation. Partial reconstitution of the haemolytic activity was obtained by the combined expression of a nonhaemolytic HlyA derivative containing a deletion of five repeat units in the repeat domain and several nonhaemolytic HlyA mutants affected in the pore-forming hydrophobic region. The simultaneous expression of two inactive mutant HlyA proteins affected in the region at which HlyA is covalently modified by HlyC and the repeat domain, respectively, resulted in a haemolytic phenotype on blood agar plates comparable to that of wild-type haemolysin. However, complementation was not possible between pairs of HlyA molecules containing site-directed mutations in the hydrophobic region and the modification region, respectively. In addition, no complementation was observed between HlyA mutants with specific mutations at different sites of the same functional domain, i.e. within the hydrophobic region, the modification region or the repeat domain. The aggregation of the HlyA molecules appears to take place after secretion, since no extracellular haemolytic activity was detected when a truncated but active HlyA lacking the C-terminal secretion sequence was expressed together with a non-haemolytic but transport-competent HlyA mutant containing a deletion in the repeat domain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280205
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  • 6
    Electronic Resource
    Electronic Resource
    Gene disruption by plasmid integration in Listeria monocytogenes: Insertional inactivation of the listeriolysin determinant IisA (1991)
    Springer
    Molecular genetics and genomics 228 (1991), S. 177-182 
    Details
    ISSN: 1617-4623
    Keywords: Insertional inactivation ; lisA ; Listeria protoplast transformation ; Listeriolysin ; Shuttle vector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A plasmid integration technique was developed for insertional inactivation of chromosomal Listeria monocytogenes genes. A Listeria-Escherichia coli shuttle vector (pLSV1) was constructed which carried the temperature-sensitive gram-positive replication origin from plasmid pTV32(Ts). An internal fragment of the listeriolysin gene (IisA) was cloned into pLSV1 to create pLSV2. In L. monocytogenes pLSV2 transformants, plasmid pLSV2 integrated into the L. monocytogenes chromosome at a frequency of 2 × 10−3 via lisA homology and these cells could be selected at 42° C using a plasmid-encoded erythromycin resistance. Plasmid integration resulted in disruption of the lisA gene, production of a truncated, immunologically cross-reactive listeriolysin protein and loss of the hemolytic phenotype. An improved Listeria protoplast transformation method is also described which facilitates genetic manipulation of Listeria species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00282463
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  • 7
    Electronic Resource
    Electronic Resource
    Topological and functional studies on HlyB of Escherichia coli (1992)
    Springer
    Molecular genetics and genomics 232 (1992), S. 40-48 
    Details
    ISSN: 1617-4623
    Keywords: E. coli haemolysin ; Secretion of haemolysin ; Topology and function of HlyB
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The topology of HlyB, a protein located in the inner membrane of Escherichia coli and involved in the secretion of α-haemolysin (HlyA), was determined by the generation of HlyB-PhoA and HlyB-LacZ fusion proteins. The data obtained by this biochemical method together with computer predictions suggest that HlyB is inserted in the cytoplasmic membrane by six stable hydrophobic, α-helical transmembrane segments. These segments extend from amino acid positions 158 to 432 of HlyB. The cytoplasmic loops between these transmembrane segments are relatively large and carry an excess of positively charged amino acids, while the periplasmic loops are rather small. In addition to these six transmembrane segments, two additional regions in the 78 N-terminal amino acids of HlyB appear to be also inserted in the cytoplasmic membrane. However, the association of these two segments with the cytoplasmic membrane seems to be less tight, since active PhoA and LacZ fusions were obtained by insertion into the same positions of these segments. A LacZ-HlyAs fusion protein carrying, at the C-terminus of LacZ, the 60-amino acid signal sequence of HlyA was not secreted in the presence of HlyB/HlyD. However, transport of this fusion protein into the cytoplasmic membrane appeared to be initiated, as suggested by the tight association of this protein with the inner membrane. A similar close association of LacZ-HlyAs with the inner membrane was also observed in the presence of HlyB alone but not in its absence. These data suggest that HlyB recognizes the HlyA signal sequence and initiates the transport of HlyA into the membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299135
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  • 8
    Electronic Resource
    Electronic Resource
    A topological model for the haemolysin translocator protein HlyD (1992)
    Springer
    Molecular genetics and genomics 234 (1992), S. 155-163 
    Details
    ISSN: 1617-4623
    Keywords: Escherichia coli haemolysin ; Secretion of haemolysin ; Topology and function of HlyD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A topological model for HlyD is proposed that is based on results obtained with gene fusions of lacZ and phoA to hlyD. Active H1yD-LacZ fusion proteins were only generated when lacZ was fused to hlyD. within the first 180 by (60 amino acids). H1yD-PhoA proteins exhibiting alkaline phosphatase (AP) activity were obtained when phoA was inserted into hlyD. between nucleotides 262 (behind amino acid position 87) and 1405 (behind amino acid position 468, only 10 amino acids away from the C-terminus of HlyD Active insertions of phoA into the middle region of hlyD. were not observed on in vivo transposition but such fusions exhibiting AP activity could be constructed by in vitro techniques. A fusion protein that carried the PhoA part close to the C-terminal end of HlyD proved to be the most stable HlyD-PhoA fusion protein. In contrast to the other, rather unstable, HlyD-PhoA+ fusions, no proteolytic degradation product of this HlyD-PhoA protein was observed and nearly all the alkaline phosphatase activity was membrane bound. Protease accessibility and cell fractionation experiments indicated that the alkaline phosphatase moiety of this fusion protein was located in the periplasm as for all other HlyD-PhoA+ proteins. These data and computer-assisted predictions suggest a topological model for HlyD with the N-terminal 60 amino acids located in the cytoplasm, a single transmembrane segment from amino acids 60 to 80 and a large periplasmic region extending from amino acid 80 to the C-terminus. Neither the HlyD fusion proteins obtained nor a mutant HlyD protein that had lost the last 10 amino acids from the C-terminus of HlyD exhibited translocator activity for HlyA or other reporter proteins carrying the HlyA signal sequence. The C-terminal 10 amino acids of HlyD showed significant similarity with the corresponding sequences of other HlyD-related proteins involved in protein secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00272357
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  • 9
    Electronic Resource
    Electronic Resource
    Processing by OmpT of fusion proteins carrying the HlyA transport signal during secretion by theEscherichia coli hemolysin transport system (1992)
    Springer
    Molecular genetics and genomics 233 (1992), S. 42-48 
    Details
    ISSN: 1617-4623
    Keywords: Secretion ; Recombinant DNA ; Hemolysin ; HlyB/H1yD complementation ; OmpT protease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A fusion gene (ces-hlyA s) was constructed by ligating the genetic information for the C-terminal 60 amino acids (hlyA s) ofEscherichia coli hemolysin (H1yA) to the ces gene for a cholesterol esterase/lipase (CE) from aPseudomonas species. Part (about 30 %) of the expressed fusion protein CE-H1yAs was secreted inE. coli carryinghlyB andhlyD genes. Following the insertion between the reporter gene andhlyA s of a linker sequence that contains the information for potential cleavage sites for the outer membrane protease OmpT, two different fusion proteins (PhoA-H1yAs and CE-HlyAs) were shown to be cleaved by OmpT between the two parts during H1yB/H1yD-mediated secretion. Processed PhoA and CE accumulated in the supernatant. The efficiency of cleavage by OmpT was considerably improved by increasedompT gene dose. It was further shown that OmpT preferentially recognizes potential cleavage sites within the linker sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587559
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  • 10
    Electronic Resource
    Electronic Resource
    Identification and characterization of two functional domains of the hemolysin translocator protein HlyD (1994)
    Springer
    Molecular genetics and genomics 245 (1994), S. 203-211 
    Details
    ISSN: 1617-4623
    Keywords: Escherichia coli hemolysin secretion system ; HlyD protein ; HlyD-related proteins ; HlyD functional domains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Secretion of Escherichia coli hemolysin is mediated by a sec-independent pathway which requires the products of at least three genes, hlyB, hlyD and tolC. Two regions of HlyD were studied. The first region (region A), consisting of the 33-amino acid, C-terminal part of the HlyD protein, is predicted to form a potential helix-loop-helix structure. This sequence is conserved among HlyD analogues of similar transport systems of other bacterial species. Using site-directed mutagenesis, we showed that the amino acids Leu475, Glu477 and Arg478 of this region are essential for HlyD function. The last amino acid of HlyD, Arg478, is possibly involved in the release of the HlyA protein, since cells bearing a hlyD gene mutant at this position produce similar amounts of HlyA to the wild-type strain, but most of the protein remains cell-associated. Competition experiments between wild-type and mutant HlyD proteins indicate that region A interacts directly with a component of the secretion apparatus. The second region of HIyD (region B), located between amino acids Leul27 and Leu170, is highly homologous to the otherwise unrelated outer membrane protein TolC. Deletion of this region abolishes secretion of hemolysin. This sequence of HlyD also seems to interact with a component of the hemolysin secretion machinery since a hybrid HIyD protein carrying the corresponding TolC sequence, although inactive in the transport of HlyA, is able to displace wild-type HlyD from the secretion apparatus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00283268
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