Two novel sodium channel inhibitors from Heriaeus melloteei spider venom differentially interacting with mammalian channel's isoforms.
Two new polypeptide toxins named Hm-1 and Hm-2 were isolated from the venom of the crab spider Heriaeus melloteei. These toxins consist of 37 and 40 amino acid residues, respectively, contain three intramolecular disulfide bonds, and presumably adopt the inhibitor cystine knot motif. Hm-1 is C-terminally amidated and shows a low degree of homology to spider toxins agelenin and micro-agatoxin-II, whereas Hm-2 has no relevantly related peptide sequences. Hm-1 and Hm-2 were found to act on mammalian voltage-gated Na(+) channels. Both toxins caused a strong decrease of Na(+) current peak amplitude, with IC(50) values of 336.4 and 154.8 nM, respectively, on Na(V)1.4. Hm-1 and Hm-2 did not shift the voltage-dependence of activation, nor did they change the kinetics of fast inactivation of the Na(+) currents. Interestingly, both toxins negatively shifted the steady-state inactivation process, which might have important functional consequences in vivo. However, this hyperpolarizing shift cannot by itself explain the observed inhibition of the Na(+) current, indicating that the two presented toxins could provide important structural information about the interaction of polypeptide inhibitors with voltage-gated Na(+) channels.
Billen
Bert
B
Laboratory of Toxicology, University of Leuven, Campus Gasthuisberg, O&N 2, P.O. Box 922, Herestraat 49, 3000 Leuven, Belgium.
Vassilevski
Alexander
A
Nikolsky
Anton
A
Tytgat
Jan
J
Grishin
Eugene
E
D000595:Amino Acid Sequence; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry* / Q000633:toxicity; D010063:Ovum / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms; D020539:Sequence Analysis, Protein; D026941:Sodium Channel Blockers / Q000737:chemistry* / Q000633:toxicity; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013111:Spider Venoms / Q000737:chemistry*; D013112:Spiders / Q000502:physiology*; D014982:Xenopus laevis
D009498:Neurotoxins; D020033:Protein Isoforms; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013111:Spider Venoms