title: Tyrosine phosphorylation modulates the activity of clostridial neurotoxins.
abstract: Clostridial neurotoxins' metalloprotease domain selectively cleaves proteins implicated in the process of synaptic vesicle fusion with the plasma membrane and, accordingly, blocks neurotransmitter release into the synaptic cleft. Here we investigate the potential modulation of these neurotoxins by intracellular cascades triggered by environmental signals, which in turn may alter its activity on target substrates. We report that the nonreceptor tyrosine kinase Src phosphorylates botulinum neurotoxins A, B, and E and tetanus neurotoxin. Protein tyrosine phosphorylation of serotypes A and E dramatically increases both their catalytic activity and thermal stability, while dephosphorylation reverses the effect. This suggests that the biologically significant form of the neurotoxins inside neurons is phosphorylated. Indeed, in PC12 cells in which tyrosine kinases such as Src and PYK2 are highly abundant, stimulation by membrane depolarization in presence of extracellular calcium induces rapid and selective tyrosine phosphorylation of internalized light chain, the metalloprotease domain, of botulinum toxin A. These findings provide a conceptual framework to connect intracellular signaling pathways involving tyrosine kinases, G-proteins, phosphoinositides, and calcium with the action of botulinum neurotoxins in abrogating vesicle fusion and neurosecretion.
authors.affiliation: Department of Biology, University of California San Diego, La Jolla, California 92093-0366, USA.
authors.forename: A V
authors.initials: AV
authors.lastname: Ferrer-Montiel
authors.forename: J M
authors.initials: JM
authors.lastname: Canaves
authors.forename: B R
authors.initials: BR
authors.lastname: DasGupta
authors.forename: M C
authors.initials: MC
authors.lastname: Wilson
authors.forename: M
authors.initials: M
authors.lastname: Montal
mesh_terms: D000818:Animals; D001905:Botulinum Toxins / Q000378:metabolism* / Q000494:pharmacology*; D051418:Focal Adhesion Kinase 2; D066298:In Vitro Techniques; D007700:Kinetics; D008565:Membrane Proteins; D008666:Metalloendopeptidases / Q000378:metabolism; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism* / Q000494:pharmacology*; D016716:PC12 Cells; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D013379:Substrate Specificity; D009435:Synaptic Transmission / Q000187:drug effects; D013572:Synaptic Vesicles / Q000187:drug effects; D050825:Synaptosomal-Associated Protein 25; D014443:Tyrosine / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; C494209:Snap25 protein, mouse; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051418:Focal Adhesion Kinase 2; C496053:Ptk2b protein, mouse; C496054:Ptk2b protein, rat; D019061:src-Family Kinases; D008666:Metalloendopeptidases; D001905:Botulinum Toxins