title: NMR analysis of KChIP4a reveals structural basis for control of surface expression of Kv4 channel complexes.
abstract: Potassium channel-interacting proteins (KChIPs) are EF-hand calcium-binding proteins of the recoverin/neuronal calcium sensor 1 family that co-assemble with the pore-forming Kv4 alpha-subunits and thus control surface trafficking of the voltage-gated potassium channels mediating the neuronal I(A) and cardiac I(to) currents. Different from the other KChIPs, KChIP4a largely reduces surface expression of the Kv4 channel complexes. Using solution NMR we show that the unique N terminus of KChIP4a forms a 6-turn alpha-helix that is connected to the highly conserved core of the KChIP protein via a solvent-exposed linker. As identified by chemical shift changes, N-terminal alpha-helix and core domain of KChIP4a interact with each other through the same hydrophobic surface pocket that is involved in intermolecular interaction between the N-terminal helix of Kv4alpha and KChIP in Kv4-KChIP complexes. Electrophysiological recordings and biochemical interaction assays of complexes formed by wild-type and mutant Kv4alpha and KChIP4a proteins suggest that competition of these two helical domains for the surface groove is responsible for the reduced trafficking of Kv4-KChIP4a complexes to the plasma membrane. Surface expression of Kv4 complexes may thus be controlled by an auto-inhibitory domain in the KChIP subunit.
authors.affiliation: Institute of Physiology II, University of Freiburg, D-79104 Freiburg, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Schwenk
authors.forename: Gerd
authors.initials: G
authors.lastname: Zolles
authors.forename: Nikolaos G
authors.initials: NG
authors.lastname: Kandias
authors.forename: Isabel
authors.initials: I
authors.lastname: Neubauer
authors.forename: Hubert
authors.initials: H
authors.lastname: Kalbacher
authors.forename: Manuel
authors.initials: M
authors.lastname: Covarrubias
authors.forename: Bernd
authors.initials: B
authors.lastname: Fakler
authors.forename: Detlef
authors.initials: D
authors.lastname: Bentrop
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation / Q000502:physiology; D057927:Hydrophobic and Hydrophilic Interactions; D051605:Kv Channel-Interacting Proteins / Q000096:biosynthesis / Q000737:chemistry*; D051379:Mice; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D051672:Shal Potassium Channels / Q000096:biosynthesis / Q000737:chemistry*
chemical_list: C455273:Kcnip4 protein, mouse; D051605:Kv Channel-Interacting Proteins; D051672:Shal Potassium Channels