title: The stoichiometry and biophysical properties of the Kv4 potassium channel complex with K+ channel-interacting protein (KChIP) subunits are variable, depending on the relative expression level.
abstract: Kv4 is a voltage-gated K(+) channel, which underlies somatodendritic subthreshold A-type current (ISA) and cardiac transient outward K(+) (Ito) current. Various ion channel properties of Kv4 are known to be modulated by its auxiliary subunits, such as K(+) channel-interacting protein (KChIP) or dipeptidyl peptidase-like protein. KChIP is a cytoplasmic protein and increases the current amplitude, decelerates the inactivation, and accelerates the recovery from inactivation of Kv4. Crystal structure analysis demonstrated that Kv4 and KChIP form an octameric complex with four Kv4 subunits and four KChIP subunits. However, it remains unknown whether the Kv4·KChIP complex can have a different stoichiometry other than 4:4. In this study, we expressed Kv4.2 and KChIP4 with various ratios in Xenopus oocytes and observed that the biophysical properties of Kv4.2 gradually changed with the increase in co-expressed KChIP4. The tandem repeat constructs of Kv4.2 and KChIP4 revealed that the 4:4 (Kv4.2/KChIP4) channel shows faster recovery than the 4:2 channel, suggesting that the biophysical properties of Kv4.2 change, depending on the number of bound KChIP4s. Subunit counting by single-molecule imaging revealed that the bound number of KChIP4 in each Kv4.2·KChIP4 complex was dependent on the expression level of KChIP4. Taken together, we conclude that the stoichiometry of Kv4·KChIP complex is variable, and the biophysical properties of Kv4 change depending on the number of bound KChIP subunits.
authors.affiliation: From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kitazawa
authors.affiliation: From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kubo
authors.affiliation: From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan knakajo@nips.ac.jp.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakajo
mesh_terms: D000818:Animals; D006801:Humans; D051605:Kv Channel-Interacting Proteins / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D051381:Rats; D051672:Shal Potassium Channels / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: C452817:Kcnip4 protein, rat; D051605:Kv Channel-Interacting Proteins; D046912:Multiprotein Complexes; D051672:Shal Potassium Channels
keywords: Electrophysiology; Fluorescence; Imaging; Ion Channel; K+ Channel-interacting Protein (KChIP); Potassium Channel; Protein Complex; Single Molecule Imaging; Stoichiometry