Structural Basis for Differences in Dynamics Induced by Leu Versus Ile Residues in the CD Loop of Kir Channels

The effect of the conserved Leu/Ile site in the CD loop on the gating dynamics of Kir channels and corresponding micro-structural mechanism remains unclear. Molecular dynamics simulations were performed to investigate the structural mechanism of chicken Kir2.2. Compared to WT, the I223L mutant channel bound to PIP₂ more strongly, was activated more rapidly, and maintained the activation state more stably after PIP₂ dissociation. Cellular electrophysiology assays of mouse Kir2.1 and human Kir2.2 indicated that, consistent with simulations, the Leu residue increased the channel responses to PIP₂ through increased binding affinity and faster activation kinetics, and the deactivation kinetics decreased upon PIP₂ inhibition. The Ile residue induced the opposite responses. This difference was attributed to the distinct hydrophobic side chain symmetries of Leu and Ile; switching between these residues caused the interaction network to redistribute and offered effective conformation transduction in the Leu systems, which had more rigid and independent subunits.