In vivo and in vitro testing of native α-conotoxins from the injected venom of Conus purpurascens

α-Conotoxins inhibit nicotinic acetylcholine receptors (nAChRs) and are used as probes to study cholinergic pathways in vertebrates. Model organisms, such as Drosophila melanogaster, express nAChRs in their CNS that are suitable to investigate the neuropharmacology of α-conotoxins in vivo. Here we report the paired nanoinjection of native α-conotoxin PIA and two novel α-conotoxins, PIC and PIC[O7], from the injected venom of Conus purpurascens and electrophysiological recordings of their effects on the giant fiber system (GFS) of D. melanogaster and heterologously expressed nAChRs in Xenopus oocytes. α-PIA caused disruption of the function of giant fiber dorsal longitudinal muscle (GF-DLM) pathway by inhibiting the Dα7 nAChR a homolog to the vertebrate α7 nAChR, whereas PIC and PIC[O7] did not. PIC and PIC[O7] reversibly inhibited ACh-evoked currents mediated by vertebrate rodent (r)α1β1δγ, rα1β1δε and human (h)α3β2, but not hα7 nAChR subtypes expressed in Xenopus oocytes with the following selectivity: rα1β1δε > rα1β1δγ ≈ hα3β2 >> hα7. Our study emphasizes the importance of loop size and α-conotoxin sequence specificity for receptor binding. These studies can be used for the evaluation of the neuropharmacology of novel α-conotoxins that can be utilized as molecular probes for diseases such as, Alzheimer's, Parkinson's, and cancer. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Tubby domain superfamily protein is required for the formation of the 7S SNARE complex in Drosophila

Tubby domain superfamily protein (TUSP) is a distant member of the Tubby-like protein (TULP) family. Although other TULPs play important roles in sensation, metabolism, and development, the molecular functions of TUSP are completely unknown. Here, we explore the function of TUSP in the Drosophila nervous system where it is expressed in all neurons. Tusp mutant flies exhibit a temperature-sensitive paralysis. This paralysis can be rescued by tissue-specific expression of Tusp in the giant fibers and peripherally synapsing interneurons of the giant fiber system, a well-characterized neuronal circuit that mediates rapid escape behavior in flies. Consistent with this paralytic phenotype, we observed a profound reduction in the assembly of the ternary 7S SNARE complex that is required for neurotransmitter release despite seeing no changes in the expression of each individual SNARE complex component. Together, these data suggest TUSP is a novel regulator of SNARE assembly and, therefore, of neurotransmitter release.