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  • 1
    Electronic Resource
    Electronic Resource
    Biochemistry of Bacterial Cell Envelopes (1974)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biochemistry 43 (1974), S. 89-121 
    Details
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.bi.43.070174.000513
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  • 2
    Electronic Resource
    Electronic Resource
    Leaf rosette closure in the alpine rock species Saxifraga paniculata Mill.: significance for survival of drought and heat under high irradiation (1999)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The significance of leaf rosette closure for survival of drought and heat under high irradiation on alpine rock sites was investigated in the cushion forming rosette plant, Saxifraga paniculata Mill. With decreasing water content the leaves fold over the rosette centre reducing reversibly the evaporative leaf surface area by 80%. Internal water redistribution driven by an osmotic gradient from older to younger leaves occurs. The oldest leaves dry out to promote the survival of the individual. Leaf temperatures above 45 °C (which match heat tolerance limits 45–57 °C; LT50) co-occurred with low substrate water potentials (less than – 0·5 MPa) on 11·3% of summer days. Shading by leaves can be crucial to surviving high temperatures as it keeps the rosette centre up to 10 °C colder. Mutual shading prevented sustained drought-induced photoinhibition in upper leaf surfaces at relative water contents below 60%. In exposed lower leaf surfaces restoration of photosystem II took several days. Leaf temperatures above 40 °C (21·3% of summer days) induced photoinhibition in situ. Periods with sufficient water supply can be fully utilized as rehydration is fast (〈 12 h) and exposes the upper leaf surfaces that showed only minor photoinhibition. By reversible leaf rosette closure environmental extremes that otherwise could exceed tolerance are efficiently avoided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1999.00508.x
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  • 3
    Electronic Resource
    Electronic Resource
    Sequence of the fhuE outer-membrane receptor gene of Escherichia coli K12 and properties of mutants (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The fhuE gene of Escherichia coli codes for an outer-membrane receptor protein required for the uptake of iron(III) via coprogen, ferrioxamine B and rhodotorulic acid. The amino acid sequence, deduced from the nucleotide sequence, consisted of 729 residues. The mature form, composed of 693 residues, has a calculated molecular weight of 77453, which agrees with the molecular weight of 76000 determined by poly-acrylamide gel electrophoresis. The FhuE protein contains four regions of homology with other TonB-dependent receptors. A valine to proline exchange in the ‘TonB box’ absolished transport activity. Phenotypic revertants with substitutions of arginine, glutamine, or leucine at the valine position exhibited Increasing iron-coprogen transport rates. Point mutations resulting in the replacement of glycine (127) in the second homology region with either alanine, aspartate, valine, asparagine or histidine exhibited decreased transport rates (listed in descending order). A truncated FhuE protein lacking 24 amino acids at the C-terminal end was exported to the periplasm but failed to be inserted into the outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb00609.x
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  • 4
    Electronic Resource
    Electronic Resource
    Evolutionary relationship of uptake systems for biopolymers in Escherichia coli: cross-complementation between the TonB-ExbB-ExbD and the TolA-TolQ-TolR proteins (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: Escherichia coli possesses two energy-coupled import systems through which substances of low concentration and of a size too large to permit diffusion through the porins are translocated across the outer membrane. Group B colicins, ferric siderophores and vitamin B12 are taken up via the TonB-ExbB-ExbD, group A colicins via the TolA-TolQ-TolR system. Cross-complementation between the two systems was demonstrated in that tolQ tolR mutants transformed with plasmids carrying exbB exbD became sensitive to group A colicins, and exbB exbD mutants transformed with plasmid-encoded tolQ tolR became sensitive to group B colicins. TolQ-TolR interacted through TonB, and ExbB-ExbD interacted through TolA with the outer membrane receptors and colicins. Activity of ExbB ExbD via TolA was higher in cells laciting TonB, and activity of TolQ TolR via TonB was increased when TolA was missing. The very distinct TolA and TonB proteins mediate exclusive interaction with group A and group B receptors, respectively. ExbB-TolR and ExbD-TolQ mixtures showed little if any complementation of exbB exbD and tolQ tolR mutants indicating coevolution of ExbB with ExbD and TolQ with ToIR. Sequence homology and mutual functional substitution of ExbB-ExbD and TolQ-TolR suggest the evolution of the two import systems from a single import system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01570.x
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  • 5
    Electronic Resource
    Electronic Resource
    Activity domains of the TonB protein (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: Escherichia coli and related Gram-negative bacteria contain an energy-coupied transport system through the outer membrane which consists of the proteins TonB, ExbB, ExbD anchored in the cytoplasmic membrane and receptors in the outer membrane. Differences in the activities of the Escherichia coli and the Serratia marcescens TonB proteins were used to identify TonB functional domains. In E. coli TonB segments were replaced by equivalent fragments of S. marcescens TonB and the activities of the resulting chimaeric proteins were determined. In addition, E. coli TonB was truncated at the C-terminal end, and point mutants were generated using bisulphite. From the results obtained we draw the following conclusions: an important site of interaction between TonB and ExbB is located in the M-terminal region of TonB within or close to the cytoplasmic membrane since an N-terminal 44-residue fragment of TonB was stabilized by ExbB and interfered with wild-type TonB activity. In addition, the activity of a TonB derivative in which histidine residue 20 was replaced by arginine was strongly reduced, and a double mutant containing arginine-7 to histidine and alanine-22 to threonine substitutions displayed an impaired uptake of ferrichrome. Furthermore, the domain around residue 160 is involved in TonB activity. S. marcescens TonB segments of this region in E. coli TonB conferred S. marcescens TonB activities, and E. coli TonB pöint mutants displayed strongly impaired activities for the uptake of colicin B and M and ferric siderophores. Plasmid-encoded tonB mutants of this region showed negative complementation of chromosomal wild-type tonB, and certain tonB mutants suppressed colicin B TonB-box mutants. Uptake of colicins required different domains in TonB, for colicin B and M around residue 160 and for colicin la, a domain closer to the C-terminal end. Tandem duplication of the E. coli (EP)X(KP) region by insertion of the S. marcescens (EP)×(KP) region (38 residues) and replacement of lysine residue 91 by glutamate did not alter TonB activity so that no evidence was obtained for this region to be implicated in receptor binding. The aberrant electrophoretic mobility of TonB was caused by the praline-rich sequence since its removal resulted in a normal mobility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01584.x
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  • 6
    Electronic Resource
    Electronic Resource
    Import-defective colicin B derivatives mutated in the TonB box (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 4 (1990), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The pore-forming colicin B is taken up into Escherichia coli by a receptor and TonB-dependent process. The receptor and colicin B both contain a similar amino acid sequence, close to the N-terminal end, termed the TonB box. Point mutations were introduced into the TonB-box region of the colicin B structural gene cba resulting in colicin B derivatives which were partially or totally Inactive against E. coli cells. All derivatives still bound to the receptor. An inactive derivative killed cells when translocated across the outer membrane by osmotic shock treatment, and formed pores in planar lipid bilayer membranes identical to the wild-type colicin. Some of the mutations were partially suppressed by mutations in the tonB structural gene. It was concluded that the TonB-box mutations define a region that is involved in the uptake of colicin B across the outer membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1990.tb02063.x
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  • 7
    Electronic Resource
    Electronic Resource
    Integration of the Serratia marcescens haemolysin into human erythrocyte membranes (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The haemolytic activity of Serratia marcescens is determined by two proteins, ShIA and ShIB. ShIA integrates into the erythrocyte membrane and causes osmotic lysis through channel formation. The conformation of ShIA and its interaction with erythrocyte membranes were studied by determining the cleavage of ShIA by added trypsin. Our results suggest that the conformation of inactive ShIA (from an ShIB− strain) differs from the active ShIA, and that in a hydrophobic environment (detergent or membrane) active ShIA assumes a conformation distinct from that in buffer. Only active haemolysin adsorbed to erythrocytes. ShIA was firmly integrated into the erythrocyte membrane since it was only released under conditions which also dissolved the integral erythrocyte membrane proteins. Moreover, ShIA integrated into ‘ghosts’ remained there and was not haemolytic when incubated with erythrocytes. From the trypsin cleavage pattern obtained with haemolysin and C-terminally truncated, but still active, haemolysin derivatives integrated into erythrocytes, and sealed and unsealed erythrocyte ‘ghosts’, we conclude that ShiA is preferentially cleaved by trypsin at a few sites but only from the inside of the erythrocyte. Haemolysin in the erythrocyte membrane forms a water-filled channel and is resistant to trypsin and other proteases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00190.x
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  • 8
    Electronic Resource
    Electronic Resource
    The tonB gene of Serratia marcescens: sequence, activity and partial complementation of Escherichia coli tonB mutants (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The TonB protein plays a key role in the energy-coupled transport of iron siderophores, of vitamin B12, and of colicins of the B-group across the outer membrane of Escherichia coli. In order to obtain more data about which of its particular amino acid sequences are necessary for TonB function, we have cloned and sequenced the tonB gene of Serratia marcescens. The nucleotide sequence predicts an amino acid sequence of 247 residues (Mr 27389), which is unusually proline-rich and contains the tandem sequences (Glu-Pro)5 and (Lys-Pro)5. In contrast to the TonB proteins of E. coli and Salmonella typhimurium, translation of the S. marcescens TonB protein starts at the first methionine residue of the open reading frame, which is the only amino acid removed during TonB maturation and export. Only the N-terminal sequence is hydrophobic, suggesting its involvement in anchoring the TonB protein to the cytoplasmic membrane. The S. marcescens tonB gene complemented an E. coli tonB mutant with regard to uptake of iron siderophores, and sensitivity to phages T1 and φ 80, and to colicins B and M. However, an E. coli tonB mutant transformed with the S. marcescens tonB gene remained resistant to colicins la and Ib, to colicin B derivatives carrying the amino acid replacements Val/Ala and Val/Gly at position 20 in the TonB box, and they exhibited a tenfold lower activity with colicin D. In addition, the S. marcescens TonB protein did not restore T1 sensitivity of an E. coli exbB tolQ double mutant, as has been found for the overexpressed E. coli TonB protein, indicating a lower activity of the S. marcescens TonB protein. Although the S. marcescens TonB protein was less prone to proteolytic degradation, it was stabilized in E. coli by the ExbBD proteins. In E. coli, TonB activity of S. marcescens depended either on the ExbBD or the TolQR activities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb01986.x
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  • 9
    Electronic Resource
    Electronic Resource
    Binding of the immunity protein inactivates colicin M (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 5 (1991), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Colicin M (Cma) displays a unique mode of action in that it inhibits peptidoglycan and lipopolysaccharide biosynthesis through interference with bactoprenyl phosphate recycling. Protection of Cma-producing cells by the immunity protein (Cmi) was studied. The amount of Cmi determined the degree of inhibition of in vitro peptidoglycan synthesis by Cma. In cells, immunity breakdown could be achieved by overexpression of the Cma uptake system. Full immunity was restored after raising the cmi gene copy number. In sphaeroplasts, Cmi was degraded by trypsin, but this could be prevented by the addition of Cma. The N-terminal end includes the only hydrophobic amino acid sequence of Cmi, suggesting a function in anchoring of Cmi in the cytoplasmic membrane. It is proposed that Cmi does not act catalytically but binds Cma at the periplasmic face of the cytoplasmic membrane, thereby resulting in Cma inactivation. Two other possible modes of colicin M immunity, interference of Cmi with the uptake of Cma, and interaction of Cmi with the target of Cma, were ruled out by the data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1991.tb01883.x
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  • 10
    Electronic Resource
    Electronic Resource
    Assembly of colicin genes from a few DNA fragments. Nucleotide sequence of colicin D (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The nucleotide sequence of a 2.4 kb Dral-EcoRV fragment of pColD-CA23 DNA was determined. The segment of DNA contained the colicin D structural gene (cda) and the colicin D immunity gene (cdi). From the nucleotide sequence it was deduced that colicin D had a molecular weight of 74683D and that the immunity protein had a molecular weight of 10057D. The amino-terminal portion of colicin D was found to be 96% homologous with the same region of colicin B. Both colicins share the same cell-surface receptor, FepA, and require the TonB protein for uptake. A putative TonB box pentapeptide sequence was identified in the amino terminus of the colicin D protein sequence. Since colicin D inhibits protein synthesis, it was unexpected that no homology was found between the carboxy-terminal part of this colicin and that of the protein synthesis inhibiting colicin E3 and cloacin DF13. This could indicate that colicin D does not function in the same manner as the latter two bacteriocins. The observed homology with colicin B supports the domain structure concept of colicin organization. The structural organization of the colicin operon is discussed. The extensive amino-terminal homology between colicins D and B, and the strong carboxy-terminal homology between colicins B, A, and N suggest an evolutionary assembly of colicin genes from a few DNA fragments which encode the functional domains responsible for colicin activity and uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1989.tb00238.x
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