Assignment of voltage-gated potassium channel blocking activity to κ-KTx1.3, a non-toxic homologue of κ-hefutoxin-1, from Heterometrus spinifer venom
Author(s)
Nirthanan, S
Pil, J
Abdel-Mottaleb, Y
Sugahara, Y
Gopalakrishnakone, P
Joseph, JS
Sato, K
Tytgat, J
Griffith University Author(s)
Year published
2005
Metadata
Show full item recordAbstract
A new family of weak K+ channel toxins (designated κ-KTx) with a novel "bi-helical" scaffold has recently been characterized from Heterometrus fulvipes (Scorpionidae) venom. Based on the presence of the minimum functional dyad (Y5 and K19), κ-hefutoxin-1 (κ-KTx1.1) was investigated and found to block Kv 1.2 (IC50 ~40 μM and Kv 1.3 (IC50 ~150 μM channels. In the present study, κ-KTx1.3, that shares ~60% identity with κ-hefutoxin 1, has been isolated from Heterometrus spinifer venom. Interestingly, despite the presence of the functional dyad (Y5 and K19), κ-KTx1.3 failed to reproduce the K+ channel blocking activity of ...
View more >A new family of weak K+ channel toxins (designated κ-KTx) with a novel "bi-helical" scaffold has recently been characterized from Heterometrus fulvipes (Scorpionidae) venom. Based on the presence of the minimum functional dyad (Y5 and K19), κ-hefutoxin-1 (κ-KTx1.1) was investigated and found to block Kv 1.2 (IC50 ~40 μM and Kv 1.3 (IC50 ~150 μM channels. In the present study, κ-KTx1.3, that shares ~60% identity with κ-hefutoxin 1, has been isolated from Heterometrus spinifer venom. Interestingly, despite the presence of the functional dyad (Y5 and K19), κ-KTx1.3 failed to reproduce the K+ channel blocking activity of κ-hefutoxin-1. Since the dyad lysine in κ-KTx1.3 was flanked by another lysine (K20), it was hypothesized that this additional positive charge could hinder the critical electrostatic interactions known to occur between the dyad lysine and the Kv 1 channel selectivity filter. Hence, mutants of κ-KTx1.3, substituting K20 with a neutral (K20A) or a negatively (K20E) or another positively (K20R) charged amino acid were synthesized. κ-KTx1.3 K20E, in congruence with κ-hefutoxin 1 with respect to subtype selectivity and affinity, produced blockade of Kv 1.2 (IC50 = 36.8 ᠴ 4.9 μM and Kv 1.3 (IC50 = 53.7 ᠶ.6.7 μM but not Kv 1.1 channels. κ-KTx1.3 K20A produced blockade of both Kv 1.2 (IC50 = 36.9 ᠴ.4.9 μM and Kv 1.3 (IC50 = 115.7 ᠷ.7.3 μM and in addition, acquired affinity for Kv 1.1 channels (IC50 = 110.7 ᠷ.7.7 μM . κ-KTx1.3 K20R failed to produce any blockade on the channel subtypes tested. These data suggest that the presence of an additional charged residue in a position adjacent to the dyad lysine impedes the functional block of Kv 1 channels produced by κ-KTx1.3.
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View more >A new family of weak K+ channel toxins (designated κ-KTx) with a novel "bi-helical" scaffold has recently been characterized from Heterometrus fulvipes (Scorpionidae) venom. Based on the presence of the minimum functional dyad (Y5 and K19), κ-hefutoxin-1 (κ-KTx1.1) was investigated and found to block Kv 1.2 (IC50 ~40 μM and Kv 1.3 (IC50 ~150 μM channels. In the present study, κ-KTx1.3, that shares ~60% identity with κ-hefutoxin 1, has been isolated from Heterometrus spinifer venom. Interestingly, despite the presence of the functional dyad (Y5 and K19), κ-KTx1.3 failed to reproduce the K+ channel blocking activity of κ-hefutoxin-1. Since the dyad lysine in κ-KTx1.3 was flanked by another lysine (K20), it was hypothesized that this additional positive charge could hinder the critical electrostatic interactions known to occur between the dyad lysine and the Kv 1 channel selectivity filter. Hence, mutants of κ-KTx1.3, substituting K20 with a neutral (K20A) or a negatively (K20E) or another positively (K20R) charged amino acid were synthesized. κ-KTx1.3 K20E, in congruence with κ-hefutoxin 1 with respect to subtype selectivity and affinity, produced blockade of Kv 1.2 (IC50 = 36.8 ᠴ 4.9 μM and Kv 1.3 (IC50 = 53.7 ᠶ.6.7 μM but not Kv 1.1 channels. κ-KTx1.3 K20A produced blockade of both Kv 1.2 (IC50 = 36.9 ᠴ.4.9 μM and Kv 1.3 (IC50 = 115.7 ᠷ.7.3 μM and in addition, acquired affinity for Kv 1.1 channels (IC50 = 110.7 ᠷ.7.7 μM . κ-KTx1.3 K20R failed to produce any blockade on the channel subtypes tested. These data suggest that the presence of an additional charged residue in a position adjacent to the dyad lysine impedes the functional block of Kv 1 channels produced by κ-KTx1.3.
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Journal Title
Biochemical Pharmacology
Volume
69
Issue
4
Publisher URI
Subject
Biochemistry and cell biology
Receptors and membrane biology
Pharmacology and pharmaceutical sciences
Basic pharmacology