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ProTx-I  

T-type Ca²⁺-Channel Blocker with Na⁺/K⁺-Channel Blocking Activity

ProTx-I was isolated from the venom of the tarantula Thrixopelma pruriens and its primary structure was determined to consist of 35 amino acid residues with three intrachain disulfide bonds[Biochemistry 41, 14734 (2002)]. This peptide shows sequence similarity to hanatoxin1 and belongs to a member of the “inhibitor cystine knot” peptide family.

ProTx-I :

    Glu-Cys-Arg-Tyr-Trp-Leu-Gly-Gly-Cys-Ser-
    Ala-Gly-Gln-Thr-Cys-Cys-Lys-His-Leu-Val-
    Cys-Ser-Arg-Arg-His-Gly-Trp-Cys-Val-Trp-
    Asp-Gly-Thr-Phe-Ser

Like other venomous toxins, ProTx-I exerts inhibitory activities for each ion channels; i) T-type Ca²⁺ channel [Ca_v3.1 (α_1G), IC₅₀ = 53 nM], ii) Na⁺ channel [Na_v1.2, Na_v1.5, Na_v1.7 (IC₅₀ = 51 nM), and Na_v1.8 (IC₅₀ = 27 nM)], and iii) K⁺ channel [K_v2.1 (IC₅₀ = 411 nM) and K_v1.3 (40% blocking at 730 nM)].

ProTx-I thus elicits multiple channel blocking activities with certain selectivity since K⁺ channel inhibitory activity is relatively weak. ProTx-I is one of the first high-affinity ligands to be identified that possess tetrodotoxin-resistant Na⁺ and T-type Ca²⁺ channel blocking activity. This peptide should prove useful for elucidating the gating mechanism of voltage-dependent ion channels.

Related Peptide

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