Stromatoxin 1 (ScTx1) has been isolated from the venom of the African tarantula Stromatopelma calceatum. Stromatoxin-1 is a 34 amino-acid long peptide that belongs to the structural family of inhibitor cystine knot peptides reticulated by three disulfide bridges. It has an amidated C-terminus and bears strong homology with hanatoxin 1 (83%). Stromatoxin-1 inhibits with high affinities Kv2.1 and Kv2.2, that encode delayed K⁺ channels (respectively, with IC₅₀ of 12 and 21 nM). The block is voltage-dependent and slowly reversible. Stromatoxin-1 is also a very sensitive inhibitor of Kv4.2, that encodes a transient K⁺ current (IC₅₀ of 1.2 nM). Here also, the block is voltage-dependent indicating that ScTx-1 acts as a gating modifier rather than a pore blocker. Reversibility is faster on Kv4.2 channels. In contrast, Stromatoxin-1 has no effect on Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6 or Kv3.4 channels. The toxin has also no effect on voltage-dependent Na⁺ and Ca²⁺ channels of cerebellar granule cells. Stromatoxin-1 was found to increase the spontaneous phasic contraction amplitude, muscle force and tone in isolated rat urinary bladder smooth muscle. It also enhances myogenic constriction in pressurized arterial segments.
Acts as a gating-modifier to inhibit voltage-gated potassium channels. It inhibits delayed Kv2.1/KCNB1 (IC50 is 12.7 nM), Kv2.1/Kv9.3 (IC50 is 7.2 nM) (KCNB1/KCNS3), Kv2.2/KCNB2 (IC50 is 21.4 nM), and transient Kv4.2/KCND2 (IC50 is 1.2 nM) channels. Miscellaneous: Negative results: does not have effect on Kv4.1/KCND1 and Kv4.3/KCND3. Intracerebroventricular injection into mice does not induce observable neurotoxicity symptoms.
ZJ26F0636580
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