National Center for
2MYH: Omega-Tbo-IT1: selective inhibitor of insect calcium channels isolated from Tibellus oblongus spider venom
Sci Rep (2015) 5 p.17232
Novel disulfide-containing polypeptide toxin was discovered in the venom of the Tibellus oblongus spider. We report on isolation, spatial structure determination and electrophysiological characterization of this 41-residue toxin, called omega-Tbo-IT1. It has an insect-toxic effect with LD50 19 mug/g in experiments on house fly Musca domestica larvae and with LD50 20 mug/g on juvenile Gromphadorhina portentosa cockroaches. Electrophysiological experiments revealed a reversible inhibition of evoked excitatory postsynaptic currents in blow fly Calliphora vicina neuromuscular junctions, while parameters of spontaneous ones were not affected. The inhibition was concentration dependent, with IC50 value 40 +/- 10 nM and Hill coefficient 3.4 +/- 0.3. The toxin did not affect frog neuromuscular junctions or glutamatergic and GABAergic transmission in rat brains. Ca(2+) currents in Calliphora vicina muscle were not inhibited, whereas in Periplaneta americana cockroach neurons at least one type of voltage gated Ca(2+) current was inhibited by omega-Tbo-IT1. Thus, the toxin apparently acts as an inhibitor of presynaptic insect Ca(2+) channels. Spatial structure analysis of the recombinant omega-Tbo-IT1 by NMR spectroscopy in aqueous solution revealed that the toxin comprises the conventional ICK fold containing an extended beta-hairpin loop and short beta-hairpin loop which are capable of making "scissors-like mutual motions".