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  • 1
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Single channel conductance ; Ion selectivity ; pH dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The conductance of channels formed by diphtheria toxin (DT) in lipid bilayer membranes depends strongly on pH. We have previously shown that a 61 amino acid region of the protein, denoted TH8-9, is sufficient to form channels having the same pH-dependent conductance properties as those of whole toxin channels. One residue in this region, Aspartate 352, is responsible for all the dependence of single channel conductance on trans pH, whereas another, Glutamate 349, has no effect. Here, we report that of the seven remaining charged residues in the TH8-9 region, mutations altering the charge on H322, H323, H372, and R377 have minimal effects on single channel conductance; mutations of Glutamates 326, 327, or 362, however, significantly affect single channel conductance as well as its dependence on cis pH. Moreover, Glutamate 362 is titratable from both the cis and trans sides of the membrane, suggesting that this residue lies within the channel; it is more accessible, however, to cis than to trans protons. These results are consistent with the membrane-spanning topology previously proposed for the TH8-9 region, and suggest a geometric model for the DT channel.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Single channel conductance ; Ion selectivity ; pH dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Ion-conducting channels formed in lipid bilayers by diphtheria toxin are highly pH dependent. Among other properties, the channel's single channel conductance and selectivity depend on proton concentrations on either side of the membrane. We have previously shown that a 61 amino acid fragment of DT is sufficient to form a channel having the same pH-dependent single channel properties as that of the intact toxin. This region corresponds to an a-helical hairpin in the recently published crystal structure of DT in solution; the hairpin contains two α-helices, each long enough to span a membrane, connected by a loop of about nine residues. This paper reports on the single channel effects of mutations which alter the two negatively charged residues in this loop. Changing Glutamate 349 to neutral glutamine or to positive lysine has no effect on the DT channel's single channel conductance or selectivity. In contrast, mutations of Aspartate 352 to neutral asparagine (DT-D352N) or positive lysine (DT-D352K) cause progressive reductions in single channel conductance at pH 5.3 cis/7.2 trans (in 1 m KCl), consistent with this group interacting electrostatically with ions in the channel. The cation selectivity of these mutant channels is also reduced from that of wild-type channels, a direction consistent with residue 352 influencing permeant ions via electrostatic forces. When both sides of the membrane are at pH 4, the conductance difference between wild-type and DT-D352N channels is minimal, suggesting that Asp 352 (in the wild type) is neutral at this pH. Differences observed between wild-type and DT-D352N channels at pH 4.0 cis/7.2 trans (with a high concentration of permeant buffer in the cis compartment) imply that residue 352 is on or near the trans side of the membrane. Comparing the conductances of wild-type and DT-D352K channels at large (cis) positive voltages supports this conclusion. The trans location of position 352 severely constrains the number of possible membrane topologies for this region.
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  • 3
    ISSN: 1432-1424
    Keywords: Diphtheria toxin ; Site-directed mutagenesis ; Planar lipid bilayers ; Ion channels ; T-domain ; Channel-forming peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diphtheria Toxin (DT) is a 535 amino acid exotoxin, whose active form consists of two polypeptide chains linked by an interchain disulphide bond. DT's N-terminal A fragment kills cells by enzymatically inactivating their protein synthetic machinery; its C terminal B chain is required for the binding of toxin to sensitive cells and for the translocation of the A fragment into the cytosol. This B fragment, consisting of its N-terminal T domain (amino acids 191–386) and its C-terminal R domain (amino acids 387–535) is responsible for the ion-conducting channels formed by DT in lipid bilayers and cellular plasma membranes. To further delineate the channel-forming region of DT, we studied channels formed by deletion mutants of DT in lipid bilayer membranes under several pH conditions. Channels formed by mutants containing only the T domain (i.e., lacking the A fragment and/or the R domain), as well as those formed by mutants replacing the R domain with Interleukin-2 (Il–2), have single channel conductances and selectivities essentially identical to those of channels formed by wild-type DT. Furthermore, deleting the N-terminal 118 amino acids of the T domain also has minimal effect on the single channel conductance and selectivity of the mutant channels. Together, these data identify a 61 amino acid stretch of the T domain, corresponding to the region which includes α-helices TH8 and TH9 in the crystal structure of DT, as the channel-forming region of the toxin.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 105 (1992), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Diphtheria toxin (DT) forms transmembrane, voltage-dependent channels in a planar lipid bilayer. Channels with similar characteristics were obtained with CB1, a cyanogen bromide peptide of diphtheria toxin B fragment (DTB) (res 340–459). Tryptophan 398 is in interaction with the hydrophobic core of the lipid bilayer. Using the Eisenberg method in association with the Shiffer-Edmunson wheel representation, we have identified two amphipathic α-helices within CB1 (res 346–364 and 389–406) that could be involved in the interaction with lipids. Bearing this information in mind, we are providing a model for the structure of the CB1 channel.
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  • 5
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 21 (1990), S. 541-566 
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 1991-11-15
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
  • 8
    Publication Date: 2015-09-26
    Description: Mitchell et al. argue that divergence-time estimates for our avian phylogeny were too young because of an "inappropriate" maximum age constraint for the most recent common ancestor of modern birds and that, as a result, most modern bird orders diverged before the Cretaceous-Paleogene mass extinction event 66 million years ago instead of after. However, their interpretations of the fossil record and timetrees are incorrect.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cracraft, Joel -- Houde, Peter -- Ho, Simon Y W -- Mindell, David P -- Fjeldsa, Jon -- Lindow, Bent -- Edwards, Scott V -- Rahbek, Carsten -- Mirarab, Siavash -- Warnow, Tandy -- Gilbert, M Thomas P -- Zhang, Guojie -- Braun, Edward L -- Jarvis, Erich D -- Howard Hughes Medical Institute/ -- New York, N.Y. -- Science. 2015 Sep 25;349(6255):1460. doi: 10.1126/science.aab1578.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Ornithology, American Museum of Natural History, New York, NY 10024, USA. jlc@amnh.org ebraun68@ufl.edu jarvis@neuro.duke.edu. ; Department of Biology, New Mexico State University, Las Cruces, NM 88003, USA. ; School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia. ; Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158, USA. ; Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen O, Denmark. ; Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Oster Voldgade 5-7, 1350 Copenhagen, Denmark. ; Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA. ; Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen O, Denmark. Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot SL5 7PY, UK. ; Department of Computer Science, The University of Texas at Austin, Austin, TX 78712, USA. ; Department of Computer Science, The University of Texas at Austin, Austin, TX 78712, USA. Departments of Bioengineering and Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. ; Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Oster Voldgade 5-7, 1350 Copenhagen, Denmark. Trace and Environmental DNA Laboratory Department of Environment and Agriculture, Curtin University, Perth, Western Australia 6102, Australia. ; China National GeneBank, BGI-Shenzhen, Shenzhen 518083, China. Centre for Social Evolution, Department of Biology, Universitetsparken 15, University of Copenhagen, DK-2100 Copenhagen, Denmark. ; Department of Biology and Genetics Institute, University of Florida, Gainesville, FL 32611, USA. jlc@amnh.org ebraun68@ufl.edu jarvis@neuro.duke.edu. ; Department of Neurobiology, Duke University Medical Center, Durham, NC 27710, USA. Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA. jlc@amnh.org ebraun68@ufl.edu jarvis@neuro.duke.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26404820" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Birds/*genetics ; *Genome ; *Phylogeny
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 2019
    Description: Background: Tobacco use is the leading cause of preventable death in the world, with a higher burden in low- and middle-income countries. The aim of this study was to quantify the prevalence and predictors of smoking among Gambian men using nationally representative data. Methods: Data was collected in 2010 from a random, nationally representative sample of 4111 adults aged 25–64 years (78% response rate) using the World Health Organization (WHO) STEPwise cross-sectional survey methods. Our analyses focused on men with valid information on smoking status (n = 1766) because of the low prevalence of smoking among women (1%). Results: The prevalence of current smoking among men was 31.4% (95% CI: 27.2–35.9). The median age of starting smoking was 19 years; 25% started before the age of 18 years and 10% started aged 8–10 years. Rural residence, underweight, and hypertension were significantly associated with smoking. Conclusion: The study reveals a high prevalence of smoking among Gambian men. It is evident that cigarettes are obtained by minors in The Gambia, as a high proportion of current smokers started at a young age. Advice and support to quit smoking should be extended to all smokers regardless of their age and whether or not they have any underlying health conditions.
    Print ISSN: 1661-7827
    Electronic ISSN: 1660-4601
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Published by MDPI
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  • 10
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