The scorpion toxin and the potassium channel

Abstract

The structure of a complex containing a toxin bound to a potassium ion channel has been solved for the first time, revealing how scorpions have designed toxins that can recognize and target the filter that controls the movement of potassium ions through these channels.

Keywords: None; ion channel; scorpion toxin; toxin; voltage-dependent K+ channel.

Figure 1.

The crystal structure (A) of the voltage-dependent potassium ion channel studied by Banerjee et al. as viewed from outside the cell: the pore that allows the potassium ions (K⁺) to enter and leave the cell is defined by four protein subunits (shown in yellow) and is at right angles to the plane of the page. The pore domain, which is about 40 Å wide and 45 Å deep, also contains four sites within its lumen that K⁺ ions can bind to. This ion channel opens and closes in response to changes in the voltage of the lipid membrane around the cell: these changes are detected by voltage sensors (blue). Some toxins inhibit opening of the pore by binding to these voltage sensors, but charybdotoxin (not shown) targets the pore itself. (B) Cartoon representation of charybdotoxin (CTX) binding to the external end of a BK channel and plugging the pore (inspired by Figure 10 of MacKinnon and Miller, 1988). The outermost K⁺ ion binding site is in equilibrium with internal K⁺ ions, and when this site is occupied it repels the bound toxin.