New Insights into the Type II Toxins from the Sea Anemone Heteractis crispa

Toxins modulating Na(V) channels are the most abundant and studied peptide components of sea anemone venom. Three type-II toxins, δ-SHTX-Hcr1f (= RpII), RTX-III, and RTX-VI, were isolated from the sea anemone Heteractis crispa. RTX-VI has been found to be an unusual analog of RTX-III. The electrophysiological effects of Heteractis toxins on nine Na(V) subtypes were investigated for the first time. Heteractis toxins mainly affect the inactivation of the mammalian Na(V) channels expressed in the central nervous system (Na(V)1.1–Na(V)1.3, Na(V)1.6) as well as insect and arachnid channels (BgNa(V)1, VdNa(V)1). The absence of Arg13 in the RTX-VI structure does not prevent toxin binding with the channel but it has changed its pharmacological profile and potency. According to computer modeling data, the δ-SHTX-Hcr1f binds within the extracellular region of the rNa(V)1.2 voltage-sensing domain IV and pore-forming domain I through a network of strong interactions, and an additional fixation of the toxin at the channel binding site is carried out through the phospholipid environment. Our data suggest that Heteractis toxins could be used as molecular tools for Na(V) channel studies or insecticides rather than as pharmacological agents.