N-Type Inactivation Variances in Honeybee and Asian Giant Hornet Kv Channels.

Abstract

Background: With the emergence of the Asian giant hornet as a threat to honeybee survival, knowledge of potential ion channel targets expressed in the nervous system can propel the development of new insecticides that are safe for pollinators. We therefore examined the biophysical properties of the Shaker-like voltage-gated potassium (Kv) channel of Apis mellifera (AmKv1; Western honeybee) and Vespa mandarinia (VmKv1; Asian giant hornet) and compared these data with isoforms that differ in N-terminal amino acid sequence.

Methods: We expressed AmKv1 and VmKv1 in Xenopus laevis oocytes and determined their gating characteristics using electrophysiological measurements. Resulting features were compared with those gleaned from N-terminal isoforms.

Results: AmKv1 generates large potassium currents, but lacks an extended N-terminal region and therefore rapid N-type inactivation, as originally described in Shaker channels. Of its seven isoforms, two have a long N-tail and subsequently display inactivation. Notably, the isoform with the lengthiest N-terminal region only partially inactivates. VmKv1 potassium currents display N-type inactivation, as expected with an extended N-tail. One isoform shows an enhanced inactivation rate, whereas currents from another isoform with a substantially different N-terminal sequence could not be measured.

Conclusion: AmKv1 and VmKv1 are functional Kv channels with strikingly different gating properties. Due to the presence of an extended N-terminal region, VmKv1 inactivates rapidly, whereas AmKv1 does not possess these residues and N-type inactivation is absent. Remarkably, virtually all isoforms of AmKv1 lack fast inactivation, whereas all studied VmKv1 isoforms inactivate, thereby suggesting a functional divergence that may be exploited for insecticide design.