THE STRUCTURE OF VERSUTOXIN (DELTA-ATRACOTOXIN-HV1) PROVIDES INSIGHTSINTO THE BINDING OF SITE 3 NEUROTOXINS TO THE VOLTAGE-GATED SODIUM-CHANNEL

Background: Versutoxin (delta-ACTX-Hv1) is the major component of the venom of the Australian Blue Mountains funnel web spider, Hadronyche v ersuta. delta-ACTX-Hv1 produces potentially fatal neurotoxic symptoms in primates by slowing the inactivation of voltage-gated sodium channe ls; delta-ACTX-Hv1 is therefore a useful tool for studying sodium chan nel function. We have determined the three-dimensional structure of de lta ACTX-Hv1 as the first step towards understanding the molecular bas is of its interaction with these channels. Results: The solution struc ture of delta-ACTX-Hv1, determined using NMR spectroscopy, comprises a core beta region containing a triple-stranded antiparallel beta sheet , a thumb-like extension protruding from the beta region and a C-termi nal 3(10) helix that is appended to the beta domain by virtue of a dis ulphide bond. The beta region contains a cystine knot motif similar to that seen in other neurotoxic polypeptides. The structure shows homol ogy with mu-agatoxin-l, a spider toxin that also modifies the inactiva tion kinetics of vertebrate voltage-gated sodium channels. More surpri singly, delta-ACTX-Hv1 shows both sequence and structural homology wit h gurmarin, a plant polypeptide. This similarity leads us to suggest t hat the sweet-taste suppression elicited by gurmarin may result from a n interaction with one of the downstream ion channels involved in swee t-taste transduction. Conclusions: delta-ACTX-Hv1 shows no structural homology with either sea anemone or alpha-scorpion toxins, both of whi ch also modify the inactivation kinetics of voltage-gated sodium chann els by interacting with channel recognition site 3. However, we have s hown that delta-ACTX-Hv1 contains charged residues that are topologica lly related to those implicated in the binding of sea anemone and alph a-scorpion toxins to mammalian voltage-gated sodium channels, suggesti ng similarities in their mode of interaction with these channels.