1. Functional analysis of ctenophore Shaker K + channels: N-type inactivation in the animal roots.
- Author
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Simonson BT, Jegla M, Ryan JF, and Jegla T
- Subjects
- Animals, Amino Acid Sequence, Phylogeny, Oocytes metabolism, Ctenophora metabolism, Ctenophora genetics, Shaker Superfamily of Potassium Channels metabolism, Shaker Superfamily of Potassium Channels genetics, Shaker Superfamily of Potassium Channels chemistry, Ion Channel Gating
- Abstract
Here we explore the evolutionary origins of fast N-type ball-and-chain inactivation in Shaker (Kv1) K
+ channels by functionally characterizing Shaker channels from the ctenophore (comb jelly) Mnemiopsis leidyi. Ctenophores are the sister lineage to other animals and Mnemiopsis has >40 Shaker-like K+ channels, but they have not been functionally characterized. We identified three Mnemiopsis channels (MlShak3-5) with N-type inactivation ball-like sequences at their N termini and functionally expressed them in Xenopus oocytes. Two of the channels, MlShak4 and MlShak5, showed rapid inactivation similar to cnidarian and bilaterian Shakers with rapid N-type inactivation, whereas MlShak3 inactivated ∼100-fold more slowly. Fast inactivation in MlShak4 and MlShak5 required the putative N-terminal inactivation ball sequences. Furthermore, the rate of fast inactivation in these channels depended on the number of inactivation balls/channel, but the rate of recovery from inactivation did not. These findings closely match the mechanism of N-type inactivation first described for Drosophila Shaker in which 1) inactivation balls on the N termini of each subunit can independently block the pore, and 2) only one inactivation ball occupies the pore binding site at a time. These findings suggest classical N-type activation evolved in Shaker channels at the very base of the animal phylogeny in a common ancestor of ctenophores, cnidarians, and bilaterians and that fast-inactivating Shakers are therefore a fundamental type of animal K+ channel. Interestingly, we find evidence from functional co-expression experiments and molecular dynamics that MlShak4 and MlShak5 do not co-assemble, suggesting that Mnemiopsis has at least two functionally independent N-type Shaker channels., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Biophysical Society. Published by Elsevier Inc. All rights reserved.)- Published
- 2024
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