Topology of the pore-region of a K+ channel revealed by the NMR-derived structures of scorpion toxins

Abstract

The architecture of the pore-region of a voltage-gated K+ channel, Kv1.3, was probed using four high affinity scorpion toxins as molecular calipers. We established the structural relatedness of these toxins by solving the structures of kaliotoxin and margatoxin and comparing them with the published structure of charybdotoxin; a homology model of noxiustoxin was then developed. Complementary mutagenesis of Kv1.3 and these toxins, combined with electrostatic compliance and thermodynamic mutant cycle analyses, allowed us to identify multiple toxin-channel interactions. Our analyses reveal the existence of a shallow vestibule at the external entrance to the pore. This vestibule is approximately 28-32 A wide at its outer margin, approximately 28-34 A wide at its base, and approximately 4-8 A deep. The pore is 9-14 A wide at its external entrance and tapers to a width of 4-5 A at a depth of approximately 5-7 A from the vestibule. This structural information should directly aid in developing topological models of the pores of related ion channels and facilitate therapeutic drug design.

Mitochondrial potassium channel Kv1.3 mediates Bax-induced apoptosis in lymphocytes

“…However, we expected this behavior because the orientation of the channel in mitochondria is the same as in the plasma membrane as suggested by the sensitivity of the mitochondrial channel to MgTx (13). Previous studies indicated that the binding of the highly specific Kv1.3 inhibitor toxin (e.g., MgTx), which docks in the outer-facing vestibule of Kv1.3, is pH dependent, and that protonation of Histidine 404 of Kv1.3 weakens the pore-toxin interaction (18). Accordingly, the IC 50 of GST-Bax increased from 4 to 12 nM when the bath solution pH was lowered to pH 6.7 and to a value Ͼ Ͼ 50 nM at pH 6.0, indicating a toxin-like interaction between Bax and the external vestibule of Kv1.3 (Fig.…”

Cobatoxins 1 and 2 from Centruroides noxius Hoffmann constitute a subfamily of potassium‐channel‐blocking scorpion toxins

“…Residue 449 changes from Thr (Shaker) to Tyr (K V 1.1), which might cause a steric-hindrance effect involving Ile23, as was observed for [Ile29]charybdotoxin/[Phe449]Shaker [124]. In contrast, from the study of the toxin blockade of K V 1.3 [44] a favourable interaction between residue 449 and Arg18 can be assumed. Concerning the block- analyses will be necessary to dissect single effects of the residue channels and residues Thr8 and Thr9 [42].…”

“…Fig. 9 A shows the position of the residues forming pressed in oocytes) showed the following K d values : charybdo-charybdotoxin [42,44] in agitoxin 2 and cobatoxin 1. Cobatoxin 1 displays a bulky residue in position 4 (Val), which is more voluminous than the equivalent residue in charybdotoxin (Thr).…”

“…Another two residues were proposed to be spatially close to the Phe425 resi-of these channels. Neurons of the central nervous system were shown to widely express subunits of voltage-dependent K ϩ due in other channel subunits, namely Trp14 and Lys31 [44]. Agitoxin 2 presents Thr9, Gly10, Ile15 and Arg31 in the posi-channels of the Shaker-type K V 1, which might assemble to homotetramers or, more likely, heterotetramers [125].…”

Developmental Biology of Neoplastic Growth

“…For example, DTX-I, MCD-peptide, kaliotoxin and ShK peptide, isolated from snake, bee, scorpion and sea anemone venoms respectively, were of primary importance in characterizing the function of Kv1.1 channels in epilepsy and the contribution of Kv1.3 channels in inflammatory processes (Beeton et al 2001(Beeton et al , 2003Mourre et al 1997). Due to their high specificity and affinity for K + channels, these toxins have facilitated the purification of K + channels, determination of their subunit stoichiometry and sub-cellular localization and tissue distribution (Aiyar et al 1995;Legros et al 2000;MacKinnon 1991;Mourre et al 1986; Rehm and Lazdunski 1988).…”