title: Interaction of syntaxin 1A with the N-terminus of Kv4.2 modulates channel surface expression and gating.
abstract: Kv4.2 channels are responsible in the heart for the Ca2+-independent transient outward currents and are important in regulating myocardial excitability and Ca2+ homeostasis. We have identified previously the expression of syntaxin 1A (STX1A) on the cardiac ventricular myocyte plasma membranes, and its modulation of cardiac ATP-sensitive K+ channels. We speculated that STX1A interacts with other cardiac ion channels, thus we examined the interaction of STX1A with Kv4.2 channels. Co-immunoprecipitation and GST pulldown assays demonstrated a direct interaction of STX1A with the Kv4.2 N-terminus. We next investigated the functional alterations of Kv4.2 gating by STX1A in Xenopus oocytes. Coexpression of Kv4.2 with STX1A (1) resulted in a reduction of Kv4.2 current amplitude; (2) caused a depolarizing shift of the steady-state inactivation curve; (3) enhanced the rate of current decay; and (4) accelerated the rate of recovery from inactivation. Additional coexpression of botulinum neurotoxin C, which cleaves STX1A, reversed the effects of STX1A on Kv4.2. STX1A inhibited partially the gating changes by KChIP2, suggesting a competitive interaction of these proteins for an overlapping binding region on the N-terminus of Kv4.2. Indeed, the N-terminal truncation mutants of Kv4.2 (Kv4.2Delta2-40 and Kv4.2Delta7-11), which form part of the KChIP2 binding site, displayed reduced sensitivity to STX1A modulation. Our study suggests that STX1A directly modulates Kv4.2 current amplitude and gating through its interaction with an overlapping region of the KChIP binding motif domain on the Kv4.2 N-terminus.
authors.affiliation: Department of Medicine, University of Toronto, Toronto, Ontario, M5S 1A8 Canada.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamakawa
authors.forename: Shazahra
authors.initials: S
authors.lastname: Saith
authors.forename: Yanan
authors.initials: Y
authors.lastname: Li
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Gao
authors.forename: Herbert Y
authors.initials: HY
authors.lastname: Gaisano
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tsushima
mesh_terms: D000818:Animals; D001665:Binding Sites; D019274:Botulinum Toxins, Type A / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D016466:CHO Cells / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology*; D006224:Cricetinae; D003412:Cricetulus; D015870:Gene Expression / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D015640:Ion Channel Gating / Q000502:physiology*; D051605:Kv Channel-Interacting Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D032342:Muscle Cells / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D017384:Sequence Deletion; D051672:Shal Potassium Channels / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D050827:Syntaxin 1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D051605:Kv Channel-Interacting Proteins; D051672:Shal Potassium Channels; D050827:Syntaxin 1; D019274:Botulinum Toxins, Type A