Syntaxin 1A binds to the cytoplasmic C terminus of Kv2.1 to regulate channel gating and trafficking.
Voltage-gated K(+) (Kv) 2.1 is the dominant Kv channel that controls membrane repolarization in rat islet beta-cells and downstream insulin exocytosis. We recently showed that exocytotic SNARE protein SNAP-25 directly binds and modulates rat islet beta-cell Kv 2.1 channel protein at the cytoplasmic N terminus. We now show that SNARE protein syntaxin 1A (Syn-1A) binds and modulates rat islet beta-cell Kv2.1 at its cytoplasmic C terminus (Kv2.1C). In HEK293 cells overexpressing Kv2.1, we observed identical effects of channel inhibition by dialyzed GST-Syn-1A, which could be blocked by Kv2.1C domain proteins (C1: amino acids 412-633, C2: amino acids 634-853), but not the Kv2.1 cytoplasmic N terminus (amino acids 1-182). This was confirmed by direct binding of GST-Syn-1A to the Kv2.1C1 and C2 domains proteins. These findings are in contrast to our recent report showing that Syn-1A binds and modulates the cytoplasmic N terminus of neuronal Kv1.1 and not by its C terminus. Co-expression of Syn-1A in Kv2.1-expressing HEK293 cells inhibited Kv2.1 surfacing, which caused a reduction of Kv2.1 current density. In addition, Syn-1A caused a slowing of Kv2.1 current activation and reduction in the slope factor of steady-state inactivation, but had no affect on inactivation kinetics or voltage dependence of activation. Taken together, SNAP-25 and Syn-1A mediate secretion not only through its participation in the exocytotic SNARE complex, but also by regulating membrane potential and calcium entry through their interaction with Kv and Ca(2+) channels. In contrast to Ca(2+) channels, where these SNARE proteins act on a common synprint site, the SNARE proteins act not only on distinct sites within a Kv channel, but also on distinct sites between different Kv channel families.
Leung
Yuk M
YM
Department of Medicine, University of Toronto, Toronto M5S 1A8, Canada.
Kang
Youhou
Y
Gao
Xiaodong
X
Xia
Fuzhen
F
Xie
Huanli
H
Sheu
Laura
L
Tsuk
Sharon
S
Lotan
Ilana
I
Tsushima
Robert G
RG
Gaisano
Herbert Y
HY
D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D002478:Cells, Cultured; D051668:Delayed Rectifier Potassium Channels; D006801:Humans; D015640:Ion Channel Gating; D017136:Ion Transport; D007515:Islets of Langerhans / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D051669:Shab Potassium Channels; D015398:Signal Transduction; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1
D000954:Antigens, Surface; D051668:Delayed Rectifier Potassium Channels; C496988:KCNB1 protein, human; C496991:Kcnb1 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C494208:SNAP25 protein, human; C494212:STX1A protein, human; D051669:Shab Potassium Channels; C494210:Snap25 protein, rat; C494213:Stx1a protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1