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  • 1
    Digitale Medien
    Digitale Medien
    Membrane topology of penicillin-binding protein 3 of Escherichia coli (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The β-lactamase fusion vector, pJBS633, has been used to analyse the organization of penicillin-binding protein 3 (PBP3) in the cytoplasmic membrane of Escherichia coli. The fusion junctions in 84 in-frame fusions of the coding region of mature TEM β-lactamase to random positions within the PBP3 gene were determined. Fusions of β-lactamase to 61 different positions in PBP3 were obtained. Fusions to positions within the first 31 residues of PBP3 resulted in enzymatically active fusion proteins which could not protect single cells of E. coli from killing by ampicillin, indicating that the β-lactamase moieties of these fusion proteins were not translocated to the peri-plasm. However, all fusions that contained: ≥36 residues of PBP3 provided single ceils of E coli with substantial levels of resistance to ampicillin, indicating that the β-lactamase moieties of these fusion proteins were translocated to the periplasm. PBP3 therefore appeared to have a simple membrane topology with residues 36 to the carboxy-terminus exposed on the periplasmic side of the cytoplasmic membrane. This topology was confirmed by showing that PBP3 was protected from proteolytic digestion at the cytoplasmic side of the inner membrane but was completely digested by proteolytic attack from the periplasmic side. PBP3 was only inserted in the cytoplasmic membrane at its amino terminus since replacement of its putative lipoprotein signal peptide with a normal signal peptide resulted in a water-soluble, periplasmic form of the enzyme. The periplasmic form of PBP3 retained its penicillin-binding activity and appeared to be truly water-soluble since it fractionated, in the absence of detergents, with the expected molecular weight on Sephadex G-100 and was not retarded by hydrophobic interaction chromatography on Phenyl-Superose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00278.x
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  • 2
    Digitale Medien
    Digitale Medien
    Horizontal transfer of multiple penicillin-binding protein genes, and capsular biosynthetic genes, in natural populations of Streptococcus pneumoniae (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Multiply antibiotic-resistant serotype 23F isolates of Streptococcus pneumoniae are prevalent in Spain and have also been recovered recently in the United Kingdom and the United States. Analysis of populations of these isolates by multilocus enzyme electrophoresis, and restriction endonuclease cleavage electrophoretic profiling of penicillin-binding protein (PBP) genes, has demonstrated that these isolates are a single clone (Muñoz et al., 1991). Here we report studies of non-serotype 23F penicillin-resistant pneumococci isolated in Spain and the United Kingdom. One of the isolates expressed serotype 19 capsule but was otherwise indistinguishable from the serotype 23F clone on the basis of multilocus enzyme electrophoresis, antibiotic resistance profiling, and restriction endonuclease patterns of genes encoding PBP1A, PBP2B and PBP2X, a result which suggests that horizontal transfer of capsular biosynthesis genes had occurred. These same techniques revealed that six other resistant isolates, all expressing serotype 9 polysaccharide capsule, represent a clone. Interestingly, the chromosomal lineage of this clone is not closely related to the 23F clone; however, the serotype 9 and 23F clones harbour apparently identical PBP1 A, -2B and -2X genes. To explain these data, we favour the interpretation that horizontal gene transfer in natural populations has distributed genes encoding altered forms of PBP1A, -2B and -2X to distinct evolutionary lineages of S. pneumoniae.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb02155.x
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  • 3
    Digitale Medien
    Digitale Medien
    Extensive re-modelling of the transpeptidase domain of penicillin-binding protein 2B of a penicillin-resistant South African isolate of Streptococcus pneumoniae (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Clinical isolates of Streptococcus pneumoniae that have greatly increased levels of resistance to penicillin (〉1000-fold) have been reported from South Africa during the last ten years. Penicillin resistance in these strains is entirely due to the development of penicillin-binding proteins (PBPs) with decreased affinity for penicillin. We have cloned and sequenced the coding region for the transpeptidase domain of penicillin-binding protein 2B from three penicillin-sensitive strains of S. pneumoniae and from a penicillin-resistant South African strain. The amino acid sequences of the transpeptidase domains of PBP2B of the three penicillin-sensitive strains were identical and there were only between one and four differences in the nucleotide sequences of their coding regions. The corresponding region of the PBP2B gene from the penicillin-resistant strain differed by 74 nucleotide substitutions which resulted in 17 alterations in the amino acid sequence of PBP2B. The most remarkable alteration that has occurred during the development of the‘penicillin-resistant’form of PBP2B is the substitution of seven consecutive residues in a region that is predicted to form a loop at the bottom of the penicillin-binding site.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00108.x
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  • 4
    Digitale Medien
    Digitale Medien
    Use of a β-lactamase fusion vector to investigate the organization of penicillin-binding protein 1B in the cytoplasmic membrane of Escherichia coli (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 1 (1987), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The coding region for the mature form of TEM β–lactamase was fused to random positions within the coding region of the penicillin–binding protein 1B (PBP 1B) gene and the nucleotide sequences across the fusion junctions of 100 in–frame fusions were determined. All fusion proteins that contained at least the NH2–terminal 94 residues of PBP 1B provided individual cells of E. coli with substantial levels of ampicillin resistance, suggesting that the β–lactamase moiety had been translocated to the periplasm. Fusion proteins that contained ≤ 63 residues of PBP 1B possessed β–lactamase activity, but could not protect single cells of E. coli from ampicillin, indicating that the 3–lactamase moiety of these fusion proteins remained in the cytoplasm. The β–lactamase fusion approach suggested a model for the organization of PBP 1B in which the protein is embedded in the cytoplasmic membrane by a single hydrophobic trans–membrane segment (residues 64–87), with a short NH2–terminal domain (residues 1–63), and the remainder of the polypeptide (residues 68–844) exposed on the periplasmic side of the cytoplasmic membrane. The proposed model for the organization of PBP 1B was supported by experiments which showed that the protein was completely digested by proteinase K added from the periplasmic side of the cytoplasmic membrane but was only slightly reduced in size by protease attack from the cytoplasmic side of the membrane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1987.tb00533.x
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  • 5
    Digitale Medien
    Digitale Medien
    Interspecies recombinational events during the evolution of altered PBP 2x genes in penicillin-resistant clinical isolates of Streptococcus pneumoniae (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Penicillin resistance in pneumococci is due to the appearance of high molecular-weight penicillin-binding proteins (PBPs) that have reduced affinity for the antibiotic. We have compared the PBX2x genes (pbpX) of one penicillin-susceptible and five penicillin-resistant clinical isolates of Streptococcus pneumoniae isolated from various parts of the world. All of the resistant isolates contained a low-affinity form of PBP 2x. The 2kb region of the two penicillin-susceptible isolates differed at only eight nucleotide sites (0.4%) and resulted in one single amino acid difference in PBP 2x. In contrast, the sequences of the PBP 2x genes from the resistant isolates differed overall from those of the susceptible isolates at between 7 and 18% of nucleotide sites and resulted in between 27 and 86 amino acid substitutions in PBP 2x. The altered PBP 2x genes consisted of regions that were similar to those of susceptible strains (〈3% diverged), alternating with regions that were very different (18–23% diverged). The presence of highly diverged regions within the PBP 2x genes of the resistant isolates contrasts with the uniformity of the sequences of the amylomaltase genes from the same isolates, and with the uniformity of the PBP 2x genes in the two susceptible isolates. It suggests that the altered PBP 2x genes have arisen by localized interspecies recombinational events involving the PBP 2x genes of closely related streptococci, as has been suggested to occur for altered PBP 2b genes (Dowson etal., 1989b). The PBP 2x genes from the resistant isolates could transform the susceptible strain R6 to increased levels of resistance to β-lactam antibiotics. Indicating that the altered forms of PBP 2x in the resistant isolates contribute to their resistance to penicillin.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb00821.x
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  • 6
    Digitale Medien
    Digitale Medien
    Penicillin-binding protein 2 genes of non-β-lactamase-producing, penicillin-resistant strains of Neisseria gonorrhoeae (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Oligonucleotides that correspond to regions of the penicillin-binding protein 2 gene (penA) that differ between penicillin-sensitive and penicillin-resistant strains have been used as probes to classify the penA genes in a collection of penicillin-resistant gonococci isolated in Britain. 44/47 of those gonococcal strains that had minimal inhibitory concentrations of ≥0.25 μg benzylpenicillin per ml contained extensively altered penA genes which appeared to be very similar (or identical) to one or other of the two classes of altered penA genes that have been described previously. Since these two classes of altered penA genes are related, it appears that the great majority of the altered penA genes of non-β-lactamase-producing penicillin-resistant gonococci have a clonal origin. The other three penicillin-resistant strains had altered penA genes that were different to those described previously. A crucial step in the development of the altered forms of PBP2 with decreased affinity for penicillin appears to have been the insertion of an extra codon within the transpeptidase domain of the penA gene. This insertion was found in the penA gene of all gonococci with minimal inhibitory concentrations of 〉0.016μg benzylpenicillin per ml but was not found in any strains with minimal inhibitory concentrations of ≤0.016μg per ml.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00101.x
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  • 7
    Digitale Medien
    Digitale Medien
    Insertion of an extra amino acid is the main cause of the low affinity of penicillin-binding protein 2 in penicillin-resistant strains of Neisseria gonorrhoeae (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Non-β-lactamase- producing, penicillin-resistant strains of Neisseria gonorrhoeae (CMRNG strains) produce altered forms of penicillin-binding protein 2 (PBP2) that have decreased affinity for penicillin. A feature of PBP2 from all CMRNG strains is the presence of an additional residue (Asp-345A) that is absent from PBP2 of penicillin-sensitive strains. The role of the additional aspartic acid residue in the decreased affinity of PBP2 is unclear as PBP2 of all previously examined CMRNG strains possess several other amino acid sequence alterations, in addition to the insertion of Asp-345A, compared to PBP2 of penicillin-sensitive strains. Site-directed mutagenesis has been used to insert the Asp-345A codon into the penA gene from a penicillin-sensitive gonococcus. The resulting penA gene expressed an altered form of PBP2 that had a decreased affinity for benzylpenicillin and was able to transform a pencillin-sensitive strain of N. gonorrhoeae to an increased level of resistance to benzylpenicillin. Insertion of amino acids other than aspartic acid did not produce forms of PBP2 that provided increased resistance to penicillin. Removal of the Asp-345A codon from the penA gene of a CMRNG strain reduced its ability to transform a penicillin-sensitive strain to an increased level of penicillin resistance. The reduction in the affinity of PBP2 in CMRNG strains is therefore largely, although not exclusively, due to the insertion of Asp-345A. Clinical isolates that produce altered forms of PBP2 that differ from that of penicillin-sensitive strains only in the insertion of Asp-345A have been identified.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb00664.x
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  • 8
    Digitale Medien
    Digitale Medien
    A simple method for maximizing the yields of membrane and exported proteins expressed in Escherichia coli (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The feasibility of using a β-lactamase fusion approach for maximizing the levels of periplasmic or membrane-bound proteins expressed in Escherichia coli was investigated. The coding region for mature TEM β-lactamase was fused after the signal peptide and amino-terminal portion of the coding region of a weakly expressed periplasmic protein, PBP3*. The resultant plasmid was mutagenized and transformants expressing increased levels of ampicillin resistance were selected. The PBP3*gene of the unmutagenized I β-lactamase fusion plasmid, and of two mutant derivatives encoding increased ampicillin resistance, were then reassembled and the latter constructs were found to express increased levels of PBP3*. The applications of a β-lactamase fusion approach in monitoring and optimizing levels of extracytoplasmic gene products expressed in E. coli are considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00167.x
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  • 9
    Digitale Medien
    Digitale Medien
    The plasmid of Salmonella typhimurium LT2 (1973)
    Springer
    Molecular genetics and genomics 121 (1973), S. 347-353 
    Details
    ISSN: 1617-4623
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Salmonella typhimurium LT2 and its mutants carry a large plasmid of molecular weight 60×106. Strains lacking autonomous plasmid DNA have been isolated. No plasmiddetermined functions have been identified, other than replication and a possible involvement in gene duplication. The plasmid neither co-transfers non-transmissible plasmids nor is itself co-transferred by F with which it does not exhibit superinfection immunity. Its replication, like that of F, is dependent on some host functions and on continuing protein synthesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00433233
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  • 10
    Digitale Medien
    Digitale Medien
    Physiological and genetical studies on a mutant of Salmonella typhimurium which is temperature-sensitive for DNA synthesis (1972)
    Springer
    Molecular genetics and genomics 114 (1972), S. 35-49 
    Details
    ISSN: 1617-4623
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The following evidence supports the view that a temperature-sensitive mutant of Salmonella typhimurium (11 G) is defective in DNA synthesis initiation: a) the increment in DNA synthesis at 38° is abolished by prior completion of rounds of replication at 25°. b) The extent of the increment at 38° is greatly increased by prior growth in the presence of a DNA synthesis inhibitor. c) Density gradient centrifugation demonstrates that the terminal region of the chromosomes is preferentially replicated at 38°. d) Preferential replication of the chromosome origins occurs at 25° after a period at 38°. The parental strain in the presence of a DNA synthesis inhibitor or the mutant at 38° (without inhibitor) show increased sensitivity to the detergent sodium deoxycholate, possibly due to a secondary effect of DNA synthesis inhibition on membrane composition. Strains of 11 G carrying episomes transfer the episomes very poorly at 38° suggesting a rôle for the chromosomal initiation apparatus in episome transfer. Continued cell division of 11 G with the production of DNA-less cells at 38° is not due to the presence of a rec mutation and no secondary mutation responsible for such division has been found. The lesion maps close to leu on the Salmonella chromosome.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00268745
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