Structure of the shaker Kv channel in low K and mechanism of slow C-type inactivation.

Abstract

Voltage-activated potassium (Kv) channels open upon membrane depolarization and proceed to spontaneously inactivate. Inactivation controls neuronal firing and serves as a form of short-term memory and is implicated in various human neurological disorders. Inactivation can proceed through two distinct mechanisms: a fast ball-and-chain mechanism that blocks the inner pore, and a slower C-type mechanism that disables the ion selectivity filter. In our previous study, we determined the structures of the Shaker Kv channel and the C-type inactivated W434F mutant in 150 mM KCl condition. The Shaker Kv channel exhibits an open internal pore and the selectivity filter within the external pore in a conducting state. By contrast, the W434F mutant exhibits a 4 Å dilation of the external half of the ion selectivity filter and the repositioning of neighboring residues known to be critical for C-type inactivation. To further confirm whether the conformational change in W434F mutant is representative of C-type inactivation in the wild-type Shaker Kv channel, we solved the structure of Shaker in 4 mM KCl, a condition known to favor inactivation. The structure of Shaker in low KCl is higher resolution than structures solved in high KCl, yet otherwise is remarkably similar to the structure of the W434F. We conclude that slow C-type inactivation in the Shaker Kv channels results in localized conformational change that disrupts potassium ion binding sites by dilating the external end of the filter.