A unique mechanism of inactivation gating of the Kv channel family member Kv7.1 and its modulation by PIP2 and calmodulin.

Inactivation of voltage-gated K (Kv) channels mostly occurs by fast N-type or/and slow C-type mechanisms. Here, we characterized a unique mechanism of inactivation gating comprising two inactivation states in a member of the Kv channel superfamily, Kv7.1. Removal of external Ca in wild-type Kv7.1 channels produced a large, voltage-dependent inactivation, which differed from N- or C-type mechanisms. Glu and Asp located, respectively, in the turret and pore entrance are involved in Ca coordination, allowing Asp to form H-bonding with the pore helix Trp, which stabilizes the selectivity filter and prevents inactivation. Phosphatidylinositol 4,5-bisphosphate (PIP2) and Ca-calmodulin prevented Kv7.1 inactivation triggered by Ca-free external solutions, where Ser at the S2-S3 linker relays the calmodulin signal from its inner boundary to the external pore to allow proper channel conduction. Thus, we revealed a unique mechanism of inactivation gating in Kv7.1, exquisitely controlled by external Ca and allosterically coupled by internal PIP2 and Ca-calmodulin.