Insect-Active Toxins with Promiscuous Pharmacology from the African Theraphosid Spider Monocentropus balfouri.

Many chemical insecticides are becoming less efficacious due to rising resistance in pest species, which has created much interest in the development of new, eco-friendly bioinsecticides. Since insects are the primary prey of most spiders, their venoms are a rich source of insect-active peptides that can be used as leads for new bioinsecticides or as tools to study molecular receptors that are insecticidal targets. In the present study, we isolated two insecticidal peptides, µ/ω-TRTX-Mb1a and -Mb1b, from venom of the African tarantula Recombinant µ/ω-TRTX-Mb1a and -Mb1b paralyzed both (Australian sheep blowfly) and (housefly), but neither peptide affected larvae of (cotton bollworms). Both peptides inhibited currents mediated by voltage-gated sodium (Na) and calcium channels in (American cockroach) dorsal unpaired median neurons, and they also inhibited the cloned (German cockroach) Na channel (BgNa1). An additional effect seen only with Mb1a on BgNa1 was a delay in fast inactivation. Comparison of the Na channel sequences of the tested insect species revealed that variations in the S1-S2 loops in the voltage sensor domains might underlie the differences in activity between different phyla.