title: ADP-ribosylation of cerebrocortical synaptosomal proteins by cholera, pertussis and botulinum toxins.
abstract: Certain microbial toxins ADP-ribosylate G proteins that may be related to those postulated to participate in secretion, whilst botulinum neurotoxins, produced by Clostridium botulinum, block Ca2(+)-dependent neurotransmitter release. Thus, botulinum, pertussis and cholera toxins were examined for ADP-ribosyl transferase activity using isolated nerve terminals. Although type D botulinum, cholera and pertussis toxins exhibited such enzymic activity, this was not detectable with types A or B botulinum neurotoxins or their individual chains, in any synaptosomal fraction. Botulinum type D and pertussis toxins ADP-ribosylated proteins with mol. wt approximately 24,000 and 42,000 respectively, whereas cholera toxin modified several proteins including a 51,000/47,000 mol. wt doublet. Pre-incubation of synaptosomes with type A, B or D toxins did not inhibit type D-induced labelling in the corresponding lysate. Similar pre-incubations with cholera or pertussis toxins reduced ADP-ribosylation of their substrates. Hence, under conditions in which these botulinum toxins were shown to block Ca2(+)-dependent transmitter release no ADP-ribosylated substrate was produced in the intact nerve terminals. Moreover, direct correlation was not found between the concentration dependencies of type D toxin for protein modification and inhibition of [3H]noradrenaline release from synaptosomes. These collective findings implicate C3, a non-neurotoxic contaminant of type D, in the enzymic action. The substrate for type D toxin was found in the cytosolic fraction and to a lesser extent in synaptic membranes, the reverse of the situation for pertussis toxin. A combination of the membranes and cytosol was required for maximal labelling of the 51,000/47,000 doublet by cholera toxin. Purified synaptic vesicles contained proteins labelled by type D and pertussis toxins but lacked major cholera toxin substrates. Future research will determine the possible involvement of these toxin-susceptible vesicular proteins in transmitter release.
authors.affiliation: Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, England, U.K.
authors.forename: A C
authors.initials: AC
authors.lastname: Ashton
authors.forename: K
authors.initials: K
authors.lastname: Edwards
authors.forename: J O
authors.initials: JO
authors.lastname: Dolly
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D001905:Botulinum Toxins / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D037342:Pertussis Toxin; D051381:Rats; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D037342:Pertussis Toxin; D001905:Botulinum Toxins; D009638:Norepinephrine