Modulation of Kv2.1 channel gating and TEA sensitivity by distinct domains of SNAP-25

Distinct domains within the SNARE (soluble N -ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins, STX1A (syntaxin 1A) and SNAP-25 (synaptosome-associated protein-25 kDa), regulate hormone secretion by their actions on the cell9s exocytotic machinery, as well as voltage-gated Ca 2+ and K + channels. We examined the action of distinct domains within SNAP-25 on Kv2.1 (voltage gated K + 2.1) channel gating. Dialysis of N-terminal SNAP-25 domains, S197 (SNAP-25 1–197 ) and S180 (SNAP-25 1–180 ), but not S206 (full-length SNAP-25 1–206 ) increased the rate of Kv2.1 channel activation and slowed channel inactivation. Remarkably, these N-terminal SNAP-25 domains, acting on the Kv2.1 cytoplasmic N-terminus, potentiated the external TEA (tetraethylammonium)-mediated block of Kv2.1. To further examine whether these are effects of the channel pore domain, internal K + was replaced with Na + and external K + was decreased from 4 to 1 mM, which decreased the IC 50 of the TEA block from 6.8±0.9 mM to >100 mM. Under these conditions S180 completely restored TEA sensitivity (7.9±1.5 mM). SNAP-25 C-terminal domains, SNAP-25 198–206 and SNAP-25 181–197 , had no effect on Kv2.1 gating kinetics. We conclude that different domains within SNAP-25 can form distinct complexes with Kv2.1 to execute a fine allosteric regulation of channel gating and the architecture of the outer pore structure in order to modulate cell excitability.