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First published online October 17, 2008
Journal of Experimental Biology 211, 3442-3453 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.022608
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Non-linear intramolecular interactions and voltage sensitivity of a KV1 family potassium channel from Polyorchis penicillatus (Eschscholtz 1829)

Tara L. Klassen1, Megan L. O'Mara2, Megan Redstone2, Andrew N. Spencer1,3 and Warren J. Gallin1,*

1 Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
2 Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
3 Malaspina University College, 900 Fifth Street, Nanaimo, British Columbia, Canada V9R 5S5

* Author for correspondence (e-mail: wgallin{at}ualberta.ca)

Accepted 2 September 2008

Voltage sensitivity of voltage-gated potassium channels (VKCs) is a primary factor in shaping action potentials in excitable cells. Variation in the amino acid sequence of the channel proteins is responsible for differences in the voltage range over which the channel opens. Thus, understanding how changes in voltage sensitivity are effected by changes in channel protein sequence illuminates the functional evolution of excitability. The KV1-family channel jShak1, from the jellyfish Polyorchis penicillatus, differs from most other KV1 channels in ways that are useful for studying the problem of how voltage sensitivity is related to channel sequence. We assessed the contributions of changes in sequence of the S4, voltage sensing, helix and changes in one asparagine residue in the S2 helix, to the relative stability of the open and closed states of the channel. Mutation of the neutral S2 residue (Asn227) to glutamate stabilized the open conformation of the channel. Different modifications of charge and length in S4 favoured either the closed conformation or the open conformation. The interactions between pairs of mutations revealed that some of the S4 mutations alter the conformation of the voltage-sensing domain such that the S4 helix is constrained to be closer to the S2 helix than in the wild-type conformation. These results, taken in conjunction with three-dimensional models of the channel, identify intra-molecular interactions that control the balance between open and closed states. These interactions are likely to be relevant to understanding the functional characteristics of members of this channel family from other organisms.

Key words: site-directed mutagenesis, ion channel gating, electrophysiology


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