title: Neurotoxic phospholipases directly affect synaptic vesicle function.
abstract: Snake neurotoxic phospholipases (SPAN) exclusively affect pre-synaptic nerve terminals where they lead to a block of neurotransmission by not fully understood mechanisms. Here, we report that the SPANs, taipoxin and paradoxin, in nanomolar concentrations directly dissociate the synaptophysin/synaptobrevin (Syp/Syb) complex on isolated synaptic vesicles in the presence of synaptosomal cytosol. The phospholipase activity of SPANs depends on Ca(2+) but the dissociation of the Syp/Syb complex does not require Ca(2+). Ca(2+) (100 μM free) alone also dissociates the Syp/Syb complex in the presence of cytosol. Treatment with SPANs disturbs the lipid raft association of synaptophysin and synaptobrevin comparable to cholesterol depletion by β-methyl-cyclodextrin while Ca(2+) alone has no effect. SPANs but not Ca(2+) directly inhibit vesicular uptake of serotonin and glutamate. It is concluded that SPANs directly affect vesicular properties independent from their Ca(2+) -dependent phospholipase activity. SPANs and Ca(2+) dissociate the Syp/Syb complex as a prerequisite for exocytosis. SPANs also prevent the filling of synaptic vesicles thereby adding to the inhibition of neurotransmission.
authors.affiliation: AG Funktionelle Zellbiologie, Institut für Integrative Neuroanatomie, Charité Centrum 2 für Grundlagenmedizin, Berlin, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Treppmann
authors.forename: Irene
authors.initials: I
authors.lastname: Brunk
authors.forename: Terence
authors.initials: T
authors.lastname: Afube
authors.forename: Karin
authors.initials: K
authors.lastname: Richter
authors.forename: Gudrun
authors.initials: G
authors.lastname: Ahnert-Hilger
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003432:Cross-Linking Reagents; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004546:Elapid Venoms / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D047468:Immunoprecipitation; D021962:Membrane Microdomains / Q000187:drug effects; D009498:Neurotoxins / Q000633:toxicity*; D010740:Phospholipases / Q000633:toxicity*; D050683:R-SNARE Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism; D012910:Snake Venoms / Q000201:enzymology* / Q000633:toxicity*; D013347:Subcellular Fractions / Q000378:metabolism; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000187:drug effects*; D016708:Synaptophysin / Q000378:metabolism; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D003432:Cross-Linking Reagents; D004546:Elapid Venoms; D009498:Neurotoxins; D050683:R-SNARE Proteins; D012910:Snake Venoms; D016708:Synaptophysin; D047392:beta-Cyclodextrins; D012701:Serotonin; D018698:Glutamic Acid; D010740:Phospholipases; D002118:Calcium