Gating Modulation of KCNQ2/3 via N-C termini Interaction

Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Israel.M-channels are slowly activated, non-inactivating, voltage-dependent potassium channels. Heteromeric assembly of subunits, encoded by two members of the KCNQ gene family KCNQ2 and KCNQ3, recapitulate the functional properties of the M-current. KCNQ2 and KCNQ3 are co-expressed on the cell body and dendrites of hippocampal and cortical neurons. Importantly, KCNQ2 but not KNCQ3, is expressed on neuronal axons, where it might regulate action potential propagation or neurotransmitter release.Previously, we showed that Syntaxin 1A physically interacts with homomeric KCNQ2 in brain synaptosomes and in Xenopus oocytes. In oocytes, this interaction results in a reduction of the current's amplitude and reduction of the channel's activation rate. In vitro pull down revealed that Syntaxin 1A specifically binds the Helix A domain located in the C-terminus of both KCNQ2 and KCNQ3. However, binding of Syntaxin to Helix A does not mediate Syntaxin's effect on the channel. We propose that the N-trminus of KCNQ2 plays a major role in the syntaxin's modulation since substitution of the proximal N-terminus of KCNQ2 with that of KCNQ3 abolished this effect.Since the effect of syntaxin 1A is mediated through the N-terminus we assume that the N-C termini of the channel interact. To study this hypothesis we used florescence resonance energy transfer (FRET) experiments, single channel analysis and biochemical approaches using chimeric channels.Together, our results point toward an allosteric modulation of KCNQ2 gating by Syntaxin 1A, facilitated by N-C termini interaction.