The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
M. Quik - One of the best experts on this subject based on the ideXlab platform.
-
Growth Related Role for the Nicotinic α-Bungarotoxin Receptor
Effects of Nicotine on Biological Systems II, 1995Co-Authors: M. QuikAbstract:Accumulating evidence now suggests that neurotransmitters are not only involved in synaptic transmission but may also exert a trophic or developmental function in the nervous system. This includes acetylcholine which may mediate such a role through an interaction with nicotinic receptors. In neuronal tissue, a nicotinic receptor population which has been implicated in the modulation of neurite outgrowth is the nicotinic α-Bungarotoxin receptor. Interestingly, earlier work had shown that activation of nicotinic α-Bungarotoxin sites on muscle cells led to muscle cell degeneration. Furthermore, α-Bungarotoxin sites present on non-neuronal cells also appear to be involved in a trophic role as exposure of these cells to nicotine elicits an increase in cell number which is blocked by α-Bungarotoxin. These combined studies suggest a common role of the α-Bungarotoxin receptor in growth related activities.
-
α-Bungarotoxin blocks the nicotinic receptor mediated increase in cell number in a neuroendocrine cell line
Brain research, 1994Co-Authors: M. Quik, J. Chan, J. PatrickAbstract:Exposure of H69 small cell lung carcinoma cells to nicotinic agonists resulted in a significant increase (up to 100%) in cell number after 6 to 12 days. The effect of nicotine (10(-8) M to 10(-4) M) was both dose and time dependent as was that of another nicotinic agonist cytisine (10(-6) M to 10(-4) M). Interestingly, both the nicotine and cytisine induced increases in H69 cell number were blocked by alpha-Bungarotoxin, as well as d-tubocurarine a nicotinic blocker which appears to interact with most nicotinic receptors. These results suggest that the nicotine induced increase in cell number is mediated through an interaction at the nicotinic alpha-Bungarotoxin receptor. This idea is further supported by experiments which show (1) that H69 cells possess high affinity alpha-Bungarotoxin sites (Kd = 25 nM, Bmax = 10.4 fmol/10(6) cells) with the characteristics of a nicotinic alpha-Bungarotoxin receptor and (2) that the potencies of nicotinic receptor ligands in the alpha-Bungarotoxin binding assay were similar to those observed in the functional studies. Northern analysis showed that mRNA for alpha 7, a putative nicotinic alpha-Bungarotoxin binding subunit, and for alpha 5 were present in H69 cells. The present data provide further evidence that nicotine increases cell number in small cell lung carcinoma and are the first to show that this effect is mediated through an interaction at the nicotinic alpha-Bungarotoxin receptor population. These results suggest that the alpha-Bungarotoxin site may be involved in modulating proliferative responses in neuroendocrine derived SCLC cells.
-
Nicotine-induced intracellular calcium changes are not antagonized by α-Bungarotoxin in adrenal medullary cells
Brain research, 1994Co-Authors: R. Afar, J.-m. Trifaró, M. QuikAbstract:The snake toxin alpha-Bungarotoxin distinguishes between neuronal nicotinic receptor subtypes. In chick ciliary ganglion neurons, activation of alpha-Bungarotoxin-sensitive nicotinic receptors has been proposed to produce elevations in intracellular calcium levels. In the present study we show that prolonged treatment with alpha-Bungarotoxin did not affect the nicotine-evoked calcium response in suspended chromaffin cells. On the other hand, the classical nicotinic receptor blocker d-tubocurarine potently blocked nicotinic receptor mediated effects. The degree of inhibition of the nicotinic response observed with d-tubocurarine was not modified by prior treatment with alpha-Bungarotoxin. These results suggest that nicotinic alpha-Bungarotoxin receptors are not primarily involved in nicotine-mediated increases in intracellular calcium in bovine adrenal medullary cells.
-
A role for the nicotinic α-Bungarotoxin receptor in neurite outgrowth in PC12 cells
Neuroscience, 1993Co-Authors: J. Chan, M. QuikAbstract:Abstract The addition of nicotine decreased neuritic outgrowth in PC12 cells in culture. This effect occurs as early as one day after addition of nicotine to the culture medium in a concentration-dependent manner. The nicotine-induced decline in neunte outgrowth was prevented by d -tubocurarine (10 − M) indicating that the effect was mediated through a nicotinic receptor. α-Bungarotoxin (10 −8 M) was also able to inhibit the nicotine-induced decrease in process formation in a dose-dependent manner. The concentrations of α-Bungarotoxin required to affect process outgrowth correlated with those required to inhibit radiolabelled α-Bungarotoxin binding. α-Bungarotoxin had no effect on [ 3 H]noradrenaline release, a functional response mediated through the α-Bungarotoxin-insensitive neuronal nicotinic acetylcholine receptor, suggesting that α-Bungarotoxin specifically interacts with the neuronal α-Bungarotoxin receptor. The present results suggest a functional role for the neuronal nicotinic α-Bungarotoxin receptor in neurite outgrowth.
-
Thymopoietin, a thymic polypeptide, potently interacts at muscle and neuronal nicotinic alpha-Bungarotoxin receptors.
Molecular neurobiology, 1992Co-Authors: M. QuikAbstract:Current studies suggest that several distinct populations of nicotinic acetylcholine (ACh) receptors exist. One of these is the muscle-type nicotinic receptors with which neuromuscular nicotinic receptor ligands and the snake toxin alpha-Bungarotoxin interact. alpha-Bungarotoxin potently binds to these nicotinic receptors and blocks their function, two characteristics that have made the alpha-toxin a very useful probe for the characterization of these sites. In neuronal tissues, several populations of nicotinic receptors have been identified which, although they share a nicotinic pharmacology, have unique characteristics. The alpha-Bungarotoxin-insensitive neuronal nicotinic receptors, which may be involved in mediating neuronal excitability, bind nicotinic agonists with high affinity but do not interact with alpha-Bungarotoxin. Subtypes of these alpha-toxin-insensitive receptors appear to exist, as evidenced by findings that some are inhibited by neuronal Bungarotoxin whereas others are not. In addition to the alpha-Bungarotoxin-insensitive sites, alpha-Bungarotoxin-sensitive neuronal nicotinic receptors are also present in neuronal tissues. These latter receptors bind alpha-Bungarotoxin with high affinity and nicotinic agonists with an affinity in the microM range. The function of the nicotinic alpha-Bungarotoxin receptors are as yet uncertain. Thymopoietin, a polypeptide linked to immune function, appears to interact specifically with nicotinic receptor populations that bind alpha-Bungarotoxin. Thus, in muscle tissue where alpha-Bungarotoxin both binds to the receptor and blocks activity, thymopoietin also potently binds to the receptor and inhibits nicotinic receptors-mediated function. In neuronal tissues, thymopoietin interacts only with the nicotinic alpha-Bungarotoxin site and not the alpha-Bungarotoxin-insensitive neuronal nicotinic receptor population. These observations that thymopoietin potently and specifically interacts with nicotinic alpha-Bungarotoxin-sensitive receptors in neuronal and muscle tissue, together with findings that thymopoietin is an endogenously occurring agent, could suggest that this immune-related polypeptide represents a ligand for the alpha-Bungarotoxin receptors. The function of thymopoietin at the alpha-Bungarotoxin receptor is as yet uncertain; however, a potential trophic, as well as other roles are suggested.
John Harris - One of the best experts on this subject based on the ideXlab platform.
-
β Bungarotoxin induced depletion of synaptic vesicles at the mammalian neuromuscular junction
Neuropharmacology, 2004Co-Authors: S. Prasarnpun, J. Walsh, John HarrisAbstract:Abstract The neurotoxic phospholipase A 2 , β-Bungarotoxin, caused the failure of the mechanical response of the indirectly stimulated rat diaphragm. Exposure to β-Bungarotoxin had no effect on the response of the muscle to direct stimulation. Resting membrane potentials of muscle fibres exposed to the toxin were similar to control values, and the binding of FITC-labelled α-Bungarotoxin to nAChR at the neuromuscular junction was unchanged. Motor nerve terminal boutons at a third of cell junctions were destroyed by exposure to β-Bungarotoxin leaving only a synaptic gutter filled with Schwann cell processes and debris. At other junctions, some or all boutons survived exposure to the toxin. Synaptic vesicle density in surviving terminal boutons was reduced by 80% and synaptophysin immunoreactivity by >60% in preparations exposed to β-Bungarotoxin, but syntaxin and SNAP-25 immunoreactivity was largely unchanged. Terminal bouton area was also unchanged. The depletion of synaptic vesicles was completely prevented by prior exposure to botulinum toxin C and significantly reduced by prior exposure to conotoxin ω-MVIIC. The data suggest that synaptic vesicle depletion is caused primarily by a toxin-induced entry of Ca 2+ into motor nerve terminals via voltage gated Ca 2+ channels and an enhanced exocytosis via the formation of t- and v-SNARE complexes.
-
β-Bungarotoxin-induced depletion of synaptic vesicles at the mammalian neuromuscular junction
Neuropharmacology, 2004Co-Authors: S. Prasarnpun, J. Walsh, John HarrisAbstract:The neurotoxic phospholipase A(2), beta-Bungarotoxin, caused the failure of the mechanical response of the indirectly stimulated rat diaphragm. Exposure to beta-Bungarotoxin had no effect on the response of the muscle to direct stimulation. Resting membrane potentials of muscle fibres exposed to the toxin were similar to control values, and the binding of FITC-labelled alpha-Bungarotoxin to nAChR at the neuromuscular junction was unchanged. Motor nerve terminal boutons at a third of cell junctions were destroyed by exposure to beta-Bungarotoxin leaving only a synaptic gutter filled with Schwann cell processes and debris. At other junctions, some or all boutons survived exposure to the toxin. Synaptic vesicle density in surviving terminal boutons was reduced by 80% and synaptophysin immunoreactivity by >60% in preparations exposed to beta-Bungarotoxin, but syntaxin and SNAP-25 immunoreactivity was largely unchanged. Terminal bouton area was also unchanged. The depletion of synaptic vesicles was completely prevented by prior exposure to botulinum toxin C and significantly reduced by prior exposure to conotoxin omega-MVIIC. The data suggest that synaptic vesicle depletion is caused primarily by a toxin-induced entry of Ca(2+) into motor nerve terminals via voltage gated Ca(2+) channels and an enhanced exocytosis via the formation of t- and v-SNARE complexes.
John P. Horn - One of the best experts on this subject based on the ideXlab platform.
-
The sensitivity of nicotinic synapses in bullfrog sympathetic ganglia to α-Bungarotoxin and neuronal-Bungarotoxin
British journal of pharmacology, 1994Co-Authors: Weixing Shen, Phillip Jobling, John P. HornAbstract:1. The sensitivity of nicotinic synapses to alpha-Bungarotoxin (alpha-Bgt) and neuronal-Bungarotoxin (n-Bgt) was measured in the B and C cell systems of bullfrog paravertebral sympathetic ganglia 9 and 10 by recording extracellular compound postganglionic action potentials from the rami communicantes. 2. High concentrations (10 microM) of alpha-Bgt applied for up to 8 h had no effect upon synaptic transmission in either the B or C cell system. Ganglia pretreated with collagenase were also insensitive to alpha-Bgt. In control experiments on isolated sartorius muscle preparations, nerve-evoked twitches were fully blocked by 30-100 nM alpha-Bgt. 3. Nicotinic transmission in the B and C cell systems was reversibly blocked by 30-300 nM n-Bgt. Block appeared within 25-45 min of exposure to toxin and reversed fully with a half-time of 40-80 min. This was indistinguishable from washout times after block by 100 microM (+)-tubocurarine. 4. The results demonstrate close parallels between the Bungarotoxin sensitivity of neuronal nicotinic receptors mediating ganglionic transmission in functional subclasses of bullfrog sympathetic neurones and the Bungarotoxin sensitivity which has been reported for autonomic in avian and mammalian preparations.
Long-sen Chang - One of the best experts on this subject based on the ideXlab platform.
-
Characterization and Gene Organization of Taiwan Banded Krait (Bungarus multicinctus) γ-Bungarotoxin
Journal of Protein Chemistry, 2002Co-Authors: Long-sen Chang, Charling Chung, Chen-chung YangAbstract:γ-Bungarotoxin was isolated from Bungarus multicinctus (Taiwan banded krait) venom using a combination of chromatography on a SP-Sephadex C-25 column and a reverse-phase high-performance liquid chromatography column. Circular dichroism (CD) measurement revealed that its secondary structure was dominant with β-sheet structure as is that of snake venom α-neurotoxins and cardiotoxins. γ-Bungarotoxin exhibits activity on inhibiting the binding of [^3H]quinuclidinyl benzilate to the M2 muscarinic acetylcholine receptor subtype, and competes weakly with radioiodinated α-Bungarotoxin for binding to the Torpedo nicotinic acetylcholine receptor. Moreover, the toxin inhibits collagen-induced platelet aggregation, with an IC_50 of approximately 200 nM. The genomic DNA encoding the γ-Bungarotoxin precursor is amplified by polymerase chain reaction (PCR). The gene is organized with three exons separated by two introns, and shares virtually identical overall organization with those reported for α-neurotoxin and cardiotoxin genes, including similar intron insertions. The intron sequences of these genes share sequence identity up to 85%, but the exon sequences are highly variable. These observations suggest that γ-Bungarotoxin, α-neurotoxins, and cardiotoxins originate from a common ancestor, and the evolution of these genes shows a tendency to diversify the functions of snake venom proteins.
-
Characterization and Gene Organization of Taiwan Banded Krait (Bungarus multicinctus) γ-Bungarotoxin
Journal of protein chemistry, 2002Co-Authors: Long-sen Chang, Charling Chung, Chen-chung YangAbstract:gamma-Bungarotoxin was isolated from Bungarus multicinctus (Taiwan banded krait) venom using a combination of chromatography on a SP-Sephadex C-25 column and a reverse-phase high-performance liquid chromatography column. Circular dichroism (CD) measurement revealed that its secondary structure was dominant with beta-sheet structure as is that of snake venom alpha-neurotoxins and cardiotoxins. gamma-Bungarotoxin exhibits activity on inhibiting the binding of [3H]quinuclidinyl benzilate to the M2 muscarinic acetylcholine receptor subtype, and competes weakly with radioiodinated alpha-Bungarotoxin for binding to the Torpedo nicotinic acetylcholine receptor. Moreover, the toxin inhibits collagen-induced platelet aggregation, with an IC50 of approximately 200 nM. The genomic DNA encoding the gamma-Bungarotoxin precursor is amplified by polymerase chain reaction (PCR). The gene is organized with three exons separated by two introns, and shares virtually identical overall organization with those reported for alpha-neurotoxin and cardiotoxin genes, including similar intron insertions. The intron sequences of these genes share sequence identity up to 85%, but the exon sequences are highly variable. These observations suggest that gamma-Bungarotoxin, alpha-neurotoxins, and cardiotoxins originate from a common ancestor, and the evolution of these genes shows a tendency to diversify the functions of snake venom proteins.
-
cDNA Sequence Analysis and Expression of κ-Bungarotoxin from Taiwan Banded Krait☆☆☆
Biochemical and biophysical research communications, 1997Co-Authors: Long-sen Chang, Jordge Lin, Chun-chang Chang, Enjone HongAbstract:The cDNAs encoding kappa-Bungarotoxin was constructed from the cellular RNA isolated from the venom glands of Bungarus multicinctus by reverse transcription-polymerase chain reaction. A high degree of nucleotide sequence homology was observed between kappa-Bungarotoxin and other kappa-neurotoxins. The kappa-Bungarotoxin was subcloned into the expression vector pET32a(+) and transformed into BL21(DE3) E. coli strain. The recombinant toxin was expressed as a fusion protein. Recombinant kappa-Bungarotoxin was separated from the fused protein by cleavage with CNBr and purified by reversed phase high performance liquid chromatography. In addition to kappa-Bungarotoxin, the cDNA fragment encoding kappa3-Bungarotoxin was also found in the cDNA mixtures prepared from the cellular RNA of the venom glands of the same snake. This result suggests that the venom glands of Taiwanese B. multicinctus should secrete at least two kinds of kappa-neurotoxins.
-
Status of tryptophan residue in cobrotoxin and α-Bungarotoxin
Biochemistry and molecular biology international, 1993Co-Authors: Long-sen Chang, Kou-wha Kuo, Chun-chang ChangAbstract:Acrylamide quenching studies indicated that the exposure degree of the Trp residue in cobrotoxin was higher than that in alpha-Bungarotoxin. The Trp residue of cobrotoxin was in a positively charged environment as revealed by iodide quenching, while the Trp residue of alpha-Bungarotoxin was not accessible for iodide. Analysis of hydrophilicity profile and local concentration of positively charged residues of toxin molecule also indicated that Trp in cobrotoxin was in a highly hydrophilic and positively charged environment. Measurement of Trp fluorescence with increasing temperature showed that the stability of environment of Trp in alpha-Bungarotoxin was higher than in cobrotoxin. Result of competitive binding for nicotinic acetylcholine receptor (AchR) between cobrotoxin and alpha-Bungarotoxin revealed that the molecular interaction of the two toxins with AchR was not the same. These, together with the fact that the cationic groups of the two toxins are involved in the binding with AchR, suggest that the observed different environment surrounded Trp residue and different AchR binding mechanism might fulfill a different requirement of the invariant Trp in the lethality of cobrotoxin and alpha-Bungarotoxin.
Edward Hawrot - One of the best experts on this subject based on the ideXlab platform.
-
nmr structural analysis of α Bungarotoxin and its complex with the principal α neurotoxin binding sequence on the α7 subunit of a neuronal nicotinic acetylcholine receptor
Journal of Biological Chemistry, 2002Co-Authors: Leonard Moise, Vladimir J. Basus, Andrea Piserchio, Edward HawrotAbstract:Abstract We report a new, higher resolution NMR structure of α-Bungarotoxin that defines the structure-determining disulfide core and β-sheet regions. We further report the NMR structure of the stoichiometric complex formed between α-Bungarotoxin and a recombinantly expressed 19-mer peptide (178IPGKRTESFYECCKEPYPD196) derived from the α7 subunit of the chick neuronal nicotinic acetylcholine receptor. A comparison of these two structures reveals binding-induced stabilization of the flexible tip of finger II in α-Bungarotoxin. The conformational rearrangements in the toxin create an extensive binding surface involving both sides of the α7 19-mer hairpin-like structure. At the contact zone, Ala7, Ser9, and Ile11 in finger I and Arg36, Lys38, Val39, and Val40 in finger II of α-Bungarotoxin interface with Phe186, Tyr187, Glu188, and Tyr194 in the α7 19-mer underscoring the importance of receptor aromatic residues as critical neurotoxin-binding determinants. Superimposing the structure of the complex onto that of the acetylcholine-binding protein (1I9B), a soluble homologue of the extracellular domain of the α7 receptor, places α-Bungarotoxin at the peripheral surface of the inter-subunit interface occluding the agonist-binding site. The disulfide-rich core of α-Bungarotoxin is suggested to be tilted in the direction of the membrane surface with finger II extending into the proposed ligand-binding cavity.
-
Functional expression and site-directed mutagenesis of a synthetic gene for alpha-Bungarotoxin.
The Journal of biological chemistry, 1994Co-Authors: Julie A. Rosenthal, Sigmund Hsu, Dinesh Schneider, Lisa N. Gentile, Norma J. Messier, Charles A. Vaslet, Edward HawrotAbstract:In order to explore the structure-function relationships of the curare mimetic alpha-neurotoxins we have constructed and cloned a synthetic gene for Bungarus multicinctus alpha-Bungarotoxin which is expressed in Escherichia coli. The recombinant alpha-Bungarotoxin is expressed as a fusion protein with alpha-Bungarotoxin linked to the COOH-terminal end of the T7 Gene 9-encoded coat protein. After treatment of the fusion protein with Factor Xa protease, a recombinant alpha-Bungarotoxin is released that co-migrates with authentic alpha-Bungarotoxin upon reverse-phase high performance liquid chromatography and ion-exchange chromatography. Final yields of active recombinant alpha-Bungarotoxin were about 0.4 mg/liter of starting bacterial culture. The recombinant alpha-Bungarotoxin contains 10 additional residues linked to the NH2-terminal Ile of the alpha-Bungarotoxin sequence due apparently to the inaccessibility of the engineered cleavage site to Factor Xa. Nevertheless, the recombinant alpha-Bungarotoxin is capable of binding to the nicotinic acetylcholine receptor with an apparent affinity that is only decreased approximately 1.7-fold from that of authentic alpha-Bungarotoxin. Alanine substitution of a residue, Asp30, highly conserved among alpha-neurotoxins and previously suggested to play a key role in receptor recognition, resulted in a recombinant alpha-Bungarotoxin whose receptor binding activity is indistinguishable from authentic alpha-Bungarotoxin.
