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 ÎM 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. © 2011 The Authors.