NMR structure and functional characteristics of the hydrophilic N terminus of the potassium channel β-subunit Kvβ1.1

Abstract

Rapid N-type inactivation of voltage-dependent potassium (Kv) channels controls membrane excitability and signal propagation in central neurons and is mediated by protein domains (inactivation gates) occluding the open channel pore from the cytoplasmic side. Inactivation domains (ID) are donated either by the pore-forming α-subunit or certain auxiliary β-subunits. Upon coexpression, Kvβ1.1 was found to endow non-inactivating members of the Kv1α family with fast inactivation via its unique N terminus. Here we investigated structure and functional properties of the Kvβ1.1 N terminus (amino acids 1-62, βN-(1-62)) using NMR spectroscopy and patch clamp recordings. βN-(1-62) showed all hallmarks of N-type inactivation: it inactivated non-inactivating Kv1.1 channels when applied to the cytoplasmic side as a synthetic peptide, and its interaction with the α-subunit was competed with tetraethylammonium and displayed an affinity in the lower micromolar range. In aequous and physiological salt solution, βN-(1-62) showed no well defined three-dimensional structure, it rather existed in a fast equilibrium of multiple weakly structured states. These structural and functional properties of βN-(1-62) closely resemble those of the 'unstructured' ID from Shaker B, but differ markedly from those of the compactly folded ID of the Kv3.4 α-subunit.