Structural Basis of Binding and Inhibition of Novel Tarantula Toxins in Mammalian Voltage-Dependent Potassium Channels

Abstract

Voltage-dependent potassium channel Kv2.1 is widely expressed in mammalian neurons and was suggested responsible for mediating the delayed rectifier (I(K)) currents. Further investigation of the central role of this channel requires the development of specific pharmacology, for instance, the utilization of spider venom toxins. Most of these toxins belong to the same structural family with a short peptide reticulated by disulfide bridges and share a similar mode of action. Hanatoxin 1 (HaTx1) from a Chilean tarantula was one of the earliest discussed tools regarding this and has been intensively applied to characterize the channel blocking not through the pore domain. Recently, more related novel toxins from African tarantulas such as heteroscordratoxins (HmTx) and stromatoxin 1 (ScTx1) were isolated and shown to act as gating modifiers such as HaTx on Kv2.1 channels with electrophysiological recordings. However, further interaction details are unavailable due to the lack of high-resolution structures of voltage-sensing domains in such mammalian Kv channels. Therefore, in the present study, we explored structural observation via molecular docking simulation between toxins and Kv2.1 channels based upon the solution structures of HaTx1 and a theoretical basis of an individual S3(C) helical channel fragment in combination with homology modeling for other novel toxins. Our results provide precise chemical details for the interactions between these tarantula toxins and channel, reasonably correlating the previously reported pharmacological properties to the three-dimensional structural interpretation. In addition, it is suggested that certain subtle structural variations on the interaction surface of toxins may discriminate between the related toxins with different affinities for Kv channels. Evolutionary links between spider peptide toxins and a "voltage sensor paddles" mechanism most recently found in the crystal structure of an archaebacterial K(+) channel, KvAP, are also delineated in this paper.

Leptin Modulates the Intrinsic Excitability of AgRP/NPY Neurons in the Arcuate Nucleus of the Hypothalamus

“…Kv channels exert a profound influence on neuronal firing (Spanswick et al, 1997(Spanswick et al, , 2000Cerda and Trimmer, 2010; and the AP waveform, both of which we observed here. To determine whether Kv channels contribute significantly to the basal firing rate in ARH NPY neurons, we used the Kv channel blocker 4-AP to block K ϩ flux through Kv channels.…”

“…Therefore, inhibition of Kv2.1 would be predicted to increase the spontaneous firing rate. Although specific blockers of Kv2.1 do not currently exist, there are several spider toxins that have a higher affinity for Kv2-and Kv4-containing channels, with little effect on other K ϩ channels (Escoubas et al, 2002;Shiau et al, 2003). Stromatoxin-1 (ScTx-1) is a high-affinity (nM) inhibitor of Kv2.1, Kv2.2, and Kv4.2 (Escoubas et al, 2002), but our results here suggest that Kv2.2 and Kv4.2 contribute only minimally to the voltage-dependent K ϩ current in NPY neurons (Figs.…”

“…AgRP/NPY neurons are activated by peripheral signals associated with hunger (e.g., ghrelin; Cowley et al, 2003;Takahashi and Cone, 2005;Yang et al, 2011;Liu et al, 2012), whereas peripheral satiety signals (e.g., leptin) inhibit their activity (Takahashi and Cone, 2005). The leptin-dependent inhibition of AgRP/NPY neurons is poorly understood, although it may be attributable in part to modulation of K ϩ channels such as K ATP and BK channels (Spanswick et al, 1997(Spanswick et al, , 2000. van den Top et al (2004) described a K ϩ conductance in ARH NPY neurons sensitive to the voltage-gated K ϩ (Kv) channel blocker 4-aminopyridine (4-AP), suggesting a critical role for Kv channels in regulating the intrinsic activity of ARH NPY neurons (van den Top et al, 2004).…”

A vital role for voltage-dependent potassium channels in dopamine transporter-mediated 6-hydroxydopamine neurotoxicity

“…3C). We also observed nearly complete neuroprotection by the Kv2.1-selective blocker stromatoxin (ScTX, 100 nM; Shiau et al, 2003;Grishin et al, 2005; Fig. 3C), but not by the K-ATP channel antagonist glibenclamide (1 μM; not shown).…”

Ghrelin Uses Gαi2 and Activates Voltage-Dependent K+ Channels to Attenuate Glucose-Induced Ca2+ Signaling and Insulin Release in Islet β-Cells

“…4D), suggesting that the enhancement of Kv channel conductance is linked to insulinostatic ability of ghrelin. Furthermore, ScTx (0.1 mol/l), an inhibitor of the Kv2.1 channel (27), potentiated glucose (8.3 mmol/l)-induced insulin release, and in the presence of ScTx ghrelin, it failed to attenuate glucose-induced insulin release (Fig. 4D).…”