Selectivity filter instability dominates the low intrinsic activity of the TWIK-1 K2P K+ channel

• Published in: The Journal of biological chemistry Vol. 295; no. 2; pp. 610 - 618
• Main Authors: Nematian-Ardestani, Ehsan, Abd-Wahab, Firdaus, Chatelain, Franck C., Sun, Han, Schewe, Marcus, Baukrowitz, Thomas, Tucker, Stephen J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 10.01.2020; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Biochemistry, Molecular Biology; Biophysics; Cations, Monovalent - metabolism; Cell Behavior; Cellular Biology; gating; Genomics; HEK293 Cells; Humans; Immunology; ion channel; Ion Channel Gating; Life Sciences; Medication; membrane biophysics; membrane protein; Molecular biology; Molecular Biophysics; Molecular Dynamics Simulation; Neurobiology; Neurons and Cognition; Pharmaceutical sciences; Pharmacology; Potassium - metabolism; potassium channel; Potassium Channels, Tandem Pore Domain - chemistry; Potassium Channels, Tandem Pore Domain - metabolism; Protein Conformation; Protein Conformation, alpha-Helical; Rubidium - metabolism; Subcellular Processes; Xenopus; gating; potassium channel; membrane protein; membrane biophysics; ion channel; Filter Gate; TWIK-1; KCNK1; Potassium Channel
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA119.010612

Two-pore domain K+ (K2P) channels have many important physiological functions. However, the functional properties of the TWIK-1 (K2P1.1/KCNK1) K2P channel remain poorly characterized because heterologous expression of this ion channel yields only very low levels of functional activity. Several underlying reasons have been proposed, including TWIK-1 retention in intracellular organelles, inhibition by posttranslational sumoylation, a hydrophobic barrier within the pore, and a low open probability of the selectivity filter (SF) gate. By evaluating these potential mechanisms, we found that the latter dominates the low intrinsic functional activity of TWIK-1. Investigating this further, we observed that the low activity of the SF gate appears to arise from the inefficiency of K+ in stabilizing an active (i.e. conductive) SF conformation. In contrast, other permeant ion species, such as Rb+, NH4+, and Cs+, strongly promoted a pH-dependent activated conformation. Furthermore, many K2P channels are activated by membrane depolarization via an SF-mediated gating mechanism, but we found here that only very strong nonphysiological depolarization produces voltage-dependent activation of heterologously expressed TWIK-1. Remarkably, we also observed that TWIK-1 Rb+ currents are potently inhibited by intracellular K+ (IC50 = 2.8 mm). We conclude that TWIK-1 displays unique SF gating properties among the family of K2P channels. In particular, the apparent instability of the conductive conformation of the TWIK-1 SF in the presence of K+ appears to dominate the low levels of intrinsic functional activity observed when the channel is expressed at the cell surface.