NMR structure and functional characteristics of the hydrophilic N terminusof the potassium channel beta-subunit Kv beta 1.1

Rapid N-type inactivation of voltage-dependent potassium (Kv) channels cont rols membrane excitability and signal propagation in central neurons and is mediated by protein domains (inactivation gates) occluding the open channe l pore from the cytoplasmic side, Inactivation domains (ID) are donated eit her by the pore-forming alpha-subunit or certain auxiliary beta-subunits. U pon coexpression, Kv beta 1.1 was found to endow non-inactivating members o f the Kv1 alpha family with fast inactivation via its unique N terminus, He re we investigated structure and functional properties of the Kv beta 1.1 N terminus (amino acids 1-62, beta N-(1-62)) using NMR spectroscopy and patc h clamp recordings, beta N-(1-62) showed all hallmarks of N-type inactivati on: it inactivated non-inactivating Kv1.1 channels when applied to the cyto plasmic side as a synthetic peptide, and its interaction with the cu-subuni t was competed with tetraethylammonium and displayed an affinity in the low er micromolar range. In aequous and physiological salt solution, beta N-(1- 62) showed no well defined three-dimensional structure, it rather existed i n a fast equilibrium of multiple weakly structured states. These structural and functional properties of beta N-(1-62) closely resemble those of the " unstructured" ID from Shaker B, but differ markedly from those of the compa ctly folded ID of the Kv3.4 alpha-subunit.