Control of K+ channel gating by protein phosphorylation: structural switches of the inactivation gate

Fast N-type inactivation of voltage-dependent potassium (K-v) channels cont rols membrane excitability and signal propagation in central neurons and oc curs by a 'ball-and-chain'-type mechanism, In this mechanism an N-terminal protein domain (inactivation gate) occludes the pore from the cytoplasmic s ide. In K(v)3.4 channels, inactivation is not fixed but is dynamically regu lated by protein phosphorylation, Phosphorylation of several identified ser ine residues on the inactivation gate leads to reduction or removal of fast inactivation. Here, we investigate the structure-function basis of this ph ospho-regulation with nuclear magnetic resonance (NMR) spectroscopy and pat ch-clamp recordings using synthetic inactivation domains (ID), The dephosph orylated ID exhibited compact structure and displayed high-affinity binding to its receptor. Phosphorylation of serine residues in the N- or C-termina l half of the ID resulted in a loss of overall structural stability. Howeve r, depending on the residue(s) phosphorylated, distinct structural elements remained stable, These structural changes correlate with the distinct chan ges in binding and unbinding kinetics underlying the reduced inactivation p otency of phosphorylated IDs.