Scorpion Toxins Modify C-Type Inactivation in a Mutant Potassium Channel

Abstract

The amino acid at position 399 in the outer vestibule of hKv1.3 channels (in Shaker 449) critically determines the C-type inactivation time course. In the present study we generated an hKv1.3_H399N mutant channel with asparagines in the outer vestibule. This mutant channel showed faster inactivation and recovery time courses compared to the wild-type channel. We investigated the effect of MgTX and CTX on C-type inactivation of the mutant channel in NMDG+ (K+:4.5 mM) solutions using the whole-cell patch-clamp technique. Our results showed that the inactivation time course of the mutant channel increased around 10-fold in the presence of MgTX and 3-fold in CTX. In both cases the toxin affinity to the mutant channel is much lower compared to the wild-type channel. Other peptide toxins (NTX, AgTX2 and KTX) did not show any remarkable effects on C-type inactivation. We think that MgTX and CTX can bind to the outer vestibule of the mutant channel thereby impeding the structural changes in the outer mouth of the channel that are involved in the inactivation process. Rearrangement of the outer vestibule during C-type inactivation has been proposed earlier (Grissmer et al., 1989, Biophys J 55:203; Choi et al., 1991, PNAS 88:5092; Liu et al., 1996, Neuron 16:859).We conclude that C-type inactivation in voltage-gated potassium channels induce structural changes in the outer vestibule and therefore differs from the C-type inactivation in KcsA channels (Cuello et al., 2010, Nature 466:203), which shows little changes in the outer vestibule of the KcsA channel. This work was supported by a grant from the Deutsche Forschungsgemeinschaft (Gr-848/14-1).