Referenced in: none

Automatically associated channels: Slo1

Title: Calcium ions open a selectivity filter gate during activation of the MthK potassium channel.

Authors: David J Posson, Radda Rusinova, Olaf S Andersen, Crina M Nimigean

Journal, date & volume: Nat Commun, 2015 , 6, 8342

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/26395539

Abstract
Ion channel opening and closing are fundamental to cellular signalling and homeostasis. Gates that control K(+) channel activity were found both at an intracellular pore constriction and within the selectivity filter near the extracellular side but the specific location of the gate that opens Ca(2+)-activated K(+) channels has remained elusive. Using the Methanobacterium thermoautotrophicum homologue (MthK) and a stopped-flow fluorometric assay for fast channel activation, we show that intracellular quaternary ammonium blockers bind to closed MthK channels. Since the blockers are known to bind inside a central channel cavity, past the intracellular entryway, the gate must be within the selectivity filter. Furthermore, the blockers access the closed channel slower than the open channel, suggesting that the intracellular entryway narrows upon pore closure, without preventing access of either the blockers or the smaller K(+). Thus, Ca(2+)-dependent gating in MthK occurs at the selectivity filter with coupled movement of the intracellular helices.