title: Functional stoichiometry underlying KChIP regulation of Kv4.2 functional expression.
abstract: K channel-interacting proteins (KChIPs) enhance functional expression of Kv4 channels by binding to an N-terminal regulatory region located in the first 40 amino acids of Kv4.2 that we call the functional expression regulating N-terminal (FERN) domain. Mutating two residues in the FERN domain to alanines, W8A and F11A, disrupts KChIP binding and regulation of Kv4.2 without eliminating the FERN domain's control of basal expression level or regulation by DPP6. When Kv4.2(W8A,F11A) is co-expressed with wild type Kv4.2 and KChIP3 subunits, a dominant negative effect is seen where the current expression is reduced to levels normally seen without KChIP addition. The dominant negative effect correlates with heteromultimeric channels remaining on intracellular membranes despite KChIP binding to non-mutant Kv4.2 subunits. In contrast, the deletion mutant Kv4.2(Δ1-40), eliminating both KChIP binding and the FERN domain, has no dominant negative effect even though the maximal conductance level is 5x lower than seen with KChIP3. The 5x increased expression seen with KChIP integration into the channel is fully apparent even when a reduced number of KChIP subunits are incorporated as long as all FERN domains are bound. Our results support the hypothesis that KChIPs enhances Kv4.2 functional expression by a 1 : 1 suppression of the N-terminal FERN domain and by producing additional positive regulatory effects on functional channel expression.
authors.affiliation: Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Kumud
authors.initials: K
authors.lastname: Kunjilwar
authors.forename: Yan
authors.initials: Y
authors.lastname: Qian
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Pfaffinger
mesh_terms: D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D006224:Cricetinae; D049452:Green Fluorescent Proteins / Q000235:genetics; D007425:Intracellular Membranes / Q000378:metabolism; D015640:Ion Channel Gating / Q000502:physiology; D051605:Kv Channel-Interacting Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D016296:Mutagenesis / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051672:Shal Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: C496749:KCNIP3 protein, human; D051605:Kv Channel-Interacting Proteins; D021122:Protein Subunits; D012097:Repressor Proteins; D051672:Shal Potassium Channels; D049452:Green Fluorescent Proteins
keywords: A-current; KChIP; Kv4; auxiliary subunit; dominant negative; potassium channel