The N-Terminal Domain of a K+Channel β Subunit Increases the Rate of C-Type Inactivation from the Cytoplasmic Side of the Channel

• Published in: Proceedings of the National Academy of Sciences - PNAS 1996-12, Vol.93 (26), p.15119-15123
• Main Authors: Morales, Michael J., Wee, Jonny O., Wang, Shimin, Strauss, Harold C., Rasmusson, Randall L.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Animals; Base Sequence; Biological Sciences; Biophysics; Cell Membrane - physiology; Cytoplasm - physiology; Female; Ferrets; Genetic mutation; Kinetics; Kv1.1 Potassium Channel; Kv1.2 Potassium Channel; Macromolecular Substances; Models, Structural; Molecular Sequence Data; Mutagenesis, Site-Directed; Neurons; Nucleotides; Oligodeoxyribonucleotides; Oligonucleotides; Oocytes; Oocytes - physiology; Point Mutation; Polymerase Chain Reaction; Potassium Channels - biosynthesis; Potassium Channels - chemistry; Potassium Channels - physiology; Potassium Channels, Voltage-Gated; Protein Structure, Secondary; Recombinant Fusion Proteins - biosynthesis; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - metabolism; RNA; Xenopus
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.26.15119

Voltage-gated K+channels are complexes of membrane-bound, ion-conducting α and cytoplasmic ancillary (β ) subunits. The primary physiologic effect of coexpression of α and β subunits is to increase the intrinsic rate of inactivation of the α subunit. For one β subunit, Kvβ 1.1, inactivation is enhanced through an N-type mechanism. A second β subunit, Kvβ 1.2, has been shown to increase inactivation, but through a distinct mechanism. Here we show that the degree of enhancement of Kvβ 1.2 inactivation is dependent on the amino acid composition in the pore mouth of the α subunit and the concentration of extracellular K+. Experimental conditions that promote C-type inactivation also enhance the stimulation of inactivation by Kvβ 1.2, showing that this β subunit directly stimulates C-type inactivation. Chimeric constructs containing just the nonconserved N-terminal region of Kvβ 1.2 fused with an α subunit behave in a similar fashion to coexpressed Kvβ 1.2 and α subunit. This shows that it is the N-terminal domain of Kvβ 1.2 that mediates the increase in C-type inactivation from the cytoplasmic side of the pore. We propose a model whereby the N terminus of Kvβ 1.2 acts as a weakly binding ``ball'' domain that associates with the intracellular vestibule of the α subunit to effect a conformational change leading to enhancement of C-type inactivation.