Conopeptide Vt3.1 Preferentially Inhibits BK Potassium Channels Containing β4 Subunits via Electrostatic Interactions*

Background: BK channel function is differentially modulated by tissue-specific (1-4) subunits. Results: Conopeptide Vt3.1 preferentially inhibits neuronal BK channels containing the 4 subunit. Conclusion: Electrostatic interactions between Vt3.1 and the extracellular loop of 4 decrease voltage-dependent activation of the channel. Significance: Vt3.1 is an excellent tool for studying the structure, function, and roles in neurophysiology of BK channels. BK channel subunits (1-4) modulate the function of channels formed by slo1 subunits to produce tissue-specific phenotypes. The molecular mechanism of how the homologous subunits differentially alter BK channel functions and the role of different BK channel functions in various physiologic processes remain unclear. By studying channels expressed in Xenopus laevis oocytes, we show a novel disulfide-cross-linked dimer conopeptide, Vt3.1 that preferentially inhibits BK channels containing the 4 subunit, which is most abundantly expressed in brain and important for neuronal functions. Vt3.1 inhibits the currents by a maximum of 71%, shifts the G-V relation by 45 mV approximately half-saturation concentrations, and alters both open and closed time of single channel activities, indicating that the toxin alters voltage dependence of the channel. Vt3.1 contains basic residues and inhibits voltage-dependent activation by electrostatic interactions with acidic residues in the extracellular loops of the slo1 and 4 subunits. These results suggest a large interaction surface between the slo1 subunit of BK channels and the 4 subunit, providing structural insight into the molecular interactions between slo1 and 4 subunits. The results also suggest that Vt3.1 is an excellent tool for studying subunit modulation of BK channels and for understanding the physiological roles of BK channels in neurophysiology.