The structure of versutoxin (delta-atracotoxin-Hv1) provides insights into 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 versuta. delta-ACTX-Hv1 produces potentially fatal neurotoxic symptoms in primates by slowing the inactivation of voltage-gated sodium channels; delta-ACTX-Hv1 is therefore a useful tool for studying sodium channel function. We have determined the three-dimensional structure of delta-ACTX-Hv1 as the first step towards understanding the molecular basis of its interaction with these channels.


RESULTS
The solution structure 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-terminal 310 helix that is appended to the beta domain by virtue of a disulphide bond. The beta region contains a cystine knot motif similar to that seen in other neurotoxic polypeptides. The structure shows homology with mu-agatoxin-I, a spider toxin that also modifies the inactivation kinetics of vertebrate voltage-gated sodium channels. More surprisingly, delta-ACTX-Hv1 shows both sequence and structural homology with gurmarin, a plant polypeptide. This similarity leads us to suggest that the sweet-taste suppression elicited by gurmarin may result from an interaction with one of the downstream ion channels involved in sweet-taste transduction.


CONCLUSIONS
delta-ACTX-Hv1 shows no structural homology with either sea anemone or alpha-scorpion toxins, both of which also modify the inactivation kinetics of voltage-gated sodium channels by interacting with channel recognition site 3. However, we have shown that delta-ACTX-Hv1 contains charged residues that are topologically related to those implicated in the binding of sea anemone and alpha-scorpion toxins to mammalian voltage-gated sodium channels, suggesting similarities in their mode of interaction with these channels.
Fletcher
J I
JI
Department of Biochemistry University of Sydney Sydney, NSW 2006, Australia.
Chapman
B E
BE
Mackay
J P
JP
Howden
M E
ME
King
G F
GF
D060848:Agatoxins; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004220:Disulfides / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008322:Mammals; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D015222:Sodium Channels / Q000378:metabolism*; D013111:Spider Venoms / Q000737:chemistry* / Q000378:metabolism*
D060848:Agatoxins; D004220:Disulfides; D009479:Neuropeptides; D009498:Neurotoxins; D010940:Plant Proteins; D015222:Sodium Channels; D013111:Spider Venoms; C055477:versutoxin; C098538:Mu-agatoxin-Aa1a; C075206:Gurmarin protein, Gymnema sylvestre