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  • 1
    Electronic Resource
    Electronic Resource
    Topology of the PhoR protein of Escherichia coli and functional analysis of internal deletion mutants (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 PhoR protein of Escherichia coli K-12 belongs to a family of structurally related sensor-kinases that regulate responses to environmental stimuli. These proteins are often located in the inner membrane with two membrane-spanning segments that are separated by a periplasmic domain, which is supposed to sense the environmental stimuli. However, the hydrophobicity plot of PhoR suggests a somewhat different topology in which a large periplasmic domain is lacking and an extended cytoplasmic domain is present besides the kinase domain. In protease-accessibility experiments and by using phoR-phoA gene fusions, the topology of PhoR was investigated and the absence of a large periplasmic domain was confirmed. Furthermore, the function of the extended cytoptasmic domain was studied by creating internal deletions. The mutations in this domain resulted in a constitutive expression of the pho regulon, indicating that the mutant PhoR proteins are locked in their kinase function. We propose that this extended cytoplasmic domain functions by sensing an internal signal that represses the kinase function of the PhoR protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01571.x
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  • 2
    Electronic Resource
    Electronic Resource
    Topology of PhoE porin: the ‘eyelet’ region (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 7 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A model for the topology of the PhoE porin has been proposed according to which the polypeptide traverses the outer membrane sixteen times mostly as amphipathic β-sheets, thereby exposing eight loops at the cell surface. Until now, no evidence has been obtained for the surface exposure of the third loop. Recently, the structure of porin of Rhodobacter capsulatus has been determined. The proposed model of PhoE is very similar to the structure of the R capsulatus porin, which has an ‘eyelet’ region, extending into the interior of the pore. The proposed third external loop of PhoE might form a similar ‘eyelet’ region. To determine the location of the predicted third external loop of PhoE, multiple copies of an oligonucleotide linker encoding an antigenic determinant of VP1 protein of foot-and-mouth disease virus (FMDV) were inserted. All hybrid proteins were properly inserted in the outer membrane. The monoclonal antibody MA11, directed against the linear FMDV epitope, was able to bind only to intact cells expressing a hybrid PhoE protein with at least three copies of the FMDV epitope present. Antibiotic sensitivity tests and single-channel conductance measurements revealed that the insertions influenced the channel size. These results are consistent with a location of the third loop of PhoE within the pore channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01104.x
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  • 3
    Electronic Resource
    Electronic Resource
    SecB-binding does not maintain the translocation-competent state of prePhoE (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The rote of SecB protein in the export of the precursor of outer membrane protein PhoE and mutant forms of this precursor was studied in vitro. When synthesized in the absence of SecB, translocation-competent prePhoE was observed post-translationally, but addition of SecB was required for efficient translocation into inner membrane vesicles. The translocation competency of in vitro synthesized prePhoE diminished with a similar half-life during incubations in the presence or absence of SecB. The loss of translocation competency of prePhoE, synthesized in the presence of SecB, was not due to dissociation of prePhoE–SecB complexes as could be demonstrated in co-immunoprecipitation experiments with anti-SecB serum. Apparently, SecB does not maintain the translocation-competent conformation of prePhoE, but is mainly required for efficient targeting of this precursor to the export apparatus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1992.tb01506.x
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  • 4
    Electronic Resource
    Electronic Resource
    Protein secretion in Pseudomonas aeruginosa: characterization of seven xcp genes and processing of secretory apparatus components by prepilin peptidase (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 6 (1992), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1992.tb01452.x
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  • 5
    Electronic Resource
    Electronic Resource
    ΔμH+ dependency of in vitro protein translocation into Escherichia coli inner-membrane vesicles varies with the signal-sequence core-region composition (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 19 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Signal sequences frequently contain α-helix-destabilizing amino acids in the hydrophobic core. Nuclear magnetic resonance studies on the conformation of signal sequences in membrane mimetic environments revealed that these residues cause a break in the α-helix. In the precursor of the Escherichia coli outer membrane protein PhoE (pre-PhoE), a glycine residue at position -10 (Gly−10) is thought to be responsible for the break in the α-helix. We investigated the role of this glycine residue in the translocation process by employing site-directed mutagenesis. SDS-PAGE analysis showed drastic variations in the electrophoretic mobilities of the mutant precursor proteins, suggesting an important role of the glycine residue in determining the conformation of the signal sequence. In vivo, no drastic differences in the translocation kinetics were observed as compared with wild-type PhoE, except when a charged residue (Arg) was substituted for Gly−10. However, the in vitro translocation of all mutant proteins into inverted inner-membrane vesicles was affected. Two classes of precursors could be distinguished. Translocation of one class of mutant proteins (Ala, Cys and Leu for Gly−10) was almost independent of the presence of a ΔμH+, whereas translocation of the other class of precursors (wild type or Ser) was strongly decreased in the absence of the ΔμH+. Apparently, the ΔμH+ dependency of in vitro protein translocation varies with the signal-sequence core-region composition. Furthermore, a proline residue at position -10 resulted in a signal sequence that did not prevent the folding of the precursor in an in vitro trimerization assay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1996.tb02466.x
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  • 6
    Electronic Resource
    Electronic Resource
    The secretion apparatus of Pseudomonas aeruginosa: identification of a fifth pseudopilin, XcpX (GspK family) (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 27 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The xcp gene products in Pseudomonas aeruginosa are required for the secretion of proteins across the outer membrane. Four of the Xcp proteins, XcpT, U, V and W, present sequence homology to the subunits of type IV pili at their N-termini, and they were therefore designated pseudopilins. In this study, we characterized the xcpX gene product, a bitopic cytoplasmic membrane protein. Remarkably, amino acid sequence comparisons also suggested that the XcpX protein resembles the pilins and pseudopilins at the N-terminus. We show that XcpX could be processed by the prepilin peptidase, PilD/XcpA, and that the highly conserved glycine residue preceding the hydrophobic segment could not be mutated without loss of the XcpX function. We, therefore, classified XcpX (GspK) as the fifth pseudopilin of the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00653.x
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  • 7
    Electronic Resource
    Electronic Resource
    The outer membrane component, YscC, of the Yop secretion machinery of Yersinia enterocolitica forms a ring-shaped multimeric complex (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 26 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The YscC protein of Yersinia enterocolitica is essential for the secretion of anti-host factors, called Yops, into the extracellular environment. It belongs to a family of outer membrane proteins, collectively designated secretins, that participate in a variety of transport processes. YscC has been shown to exist as a stable oligomeric complex in the outer membrane. The production of the YscC complex is regulated by temperature and is reduced in strains carrying mutations in the yscN-U operon or in the virG gene. The VirG lipoprotein was shown to be required for efficient targeting of the complex to the outer membrane. Electron microscopy revealed that purified YscC complexes form ring-shaped structures of ≈20 nm with an apparent central pore. Because of the architecture of the multimer, YscC appears to represent a novel type of channel-forming proteins in the bacterial outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.6141981.x
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  • 8
    Electronic Resource
    Electronic Resource
    Role of the lipB gene product in the folding of the secreted lipase of Pseudomonas glumae (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The LipB protein of Pseudomonas glumae is essential for the production of active extracellular lipase encoded by the lipA gene. When lipase is overproduced in P. glumae in the absence of a functional lipB gene, the enzyme accumulates intracellularly in an inactive conformation. Heterologous expression of the lipase in Pseudomonas aeruginosa, Bacillus subtilis and Escherichia coli indicated that LipB is not directly involved in the trans location of the lipase across the inner or outer membrane. However, the presence of LipB was essential for obtaining active lipase and had a profound influence on the stability of the protein to proteolytic degradation. Inactive iipase, produced in the absence of LipB could be activated in vitro by unfolding and refolding, which demonstrates that LipB activity is not responsible for an essential covalent modification of the enzyme. We propose that LipB is a lipase-specific foldase. Furthermore, proper folding of the lipase in the periplasm appears to be essential for Xcp-mediated translocation across the outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01719.x
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  • 9
    Electronic Resource
    Electronic Resource
    An accessory gene, lipB, required for the production of active Pseudomonas glumae lipase (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Pseudomonas glumae PG1 is able to secrete lipase into the extracellular medium. The lipase is produced as a precursor protein, with an N-terminal signal sequence. A second open reading frame (ORF) was found immediately downstream of the lipase structural gene, lip A, a situation found for the lipases of some other Pseudomonas species. Inactivation of this ORF resulted in a lipase-negative phenotype, indicating its importance in the production of active extracellular lipase. The ORF, lipB, potentially encodes a protein of 353-amtno-acid residues, having a hydrophobic N-terminal (amino acids 1 to 90) and a hydrophilic C-terminal part. As a first step in determining the role of LipB, its subcellular location was determined. The protein was found to fractionate with the inner membranes. The expression of fusions of lipB fragments with phoA revealed an Nin–Cout topology for the LipB protein, which was confirmed by protease accessibility studies on EDTA-permeabilized cells and on inverted inner membrane vesicles. These and other results indicate that most of the LipB polypeptide is located in the periplasm and anchored to the inner membrane by an an N-terminal transmembrane helix, located between amino acids 19 and 40.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01718.x
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of an Escherichia coli rotA mutant, affected in periplasmic peptidyl-prolyl cis/trans isomerase (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Science Ltd
    Molecular microbiology 18 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The rotA gene of Escherichia coli encodes a peptidyl-prolyl cis/trans isomerase (PPlase), which is supposed to catalyse protein folding in the periplasm. To investigate the importance of the enzyme, the rotA gene was cloned and a chromosomal deletion mutant was created. The rotA mutant was normally viable. No residual PPlase activity could be detected in the periplasmic fraction of the mutant. Comparison of the patterns of periplasmic and outer membrane proteins by SDS-PAGE revealed no differences in protein composition between the rotA mutant and its parental strain. Similarly, the kinetics of periplasmic protein folding and outer membrane protein assembly appeared unaffected by the rotA mutation. Our results show that the periplasmic PPlase of E. coli is not essential and that the protein does not play an important role in protein folding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_18020313.x
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