Biology subjects

Riel, E. B.

Publications and source records attributed to Riel, E. B..

4 recordsLinked to original sources

bioRxiv2026

Genetically engineered rapamycin responsive K2P channels

Establishment of electrical potentials across biological membranes is a universal feature of all cells. Tandem pore domain (K2P) potassium ion channels play pivotal roles in maintaining cellular membrane potentials, shaping physiological responses across a diverse range of cell types. With only a limited repertoire of high-aAinity and subtype-selective K2P modulators available for experimental or therapeutic use, we devised a strategy to genetically engineer K2P channels that are potently activated by rapamycin or non-immunomodulatory rapamycin analogs. Insertion of the FRB domain of mTOR into a short flexible cytoplasmic loop between the second and third transmembrane (TM) domains of the TREK1 K2P channel yielded fusion channels that are activated by nanomolar concentrations of rapamycin. Rapamycin-induced potentiation requires recruitment of an FKBP binding partner, from either the endogenous pool of FKBP within the cell or through fusion of FKBP to the C-terminus of TREK1. Formation of an FRB/rapamycin/FKBP ternary complex within the core of the TREK1 channel leads to an increase in TREK1 single-channel open probability and unitary current, mimicking positive modulatory eAects of conventional TREK1 activating cues. Cryo-EM structures demonstrate that rapamycin-induced ternary complex formation rigidifies the position of the FRB and stabilizes the TM2/TM3 loop in an active channel conformation. We demonstrate that FRB fusion can be employed to successfully activate several K2P channel isoforms, providing chemogenetically targetable tools for direct manipulation of cellular membrane potential.

bioengineering↗

bioRxiv2026

Down- to up-state transition is the default pathway in TREK K2P channel activation and does not involve a lipid occluded pore

Two crystallographic states of mechanosensitive TREK/TRAAK K2P channels - a low-activity down-state and a high-activity up-state - have been proposed to underlie gating, but the origin of the low activity remains debated. Competing models suggest either lipid-mediated pore block or selectivity filter (SF) inactivation. Using systematic mutagenesis of M2/M4 helices, we identified 16 highly active mutants and assessed their activation mechanisms via free-energy calculations, molecular dynamics simulations, and a state-dependent pharmacological probe. The computational approaches reliably predicted mutation-induced shifts in the down-up equilibrium. We further show that intracellular acidification and regulatory lipids primarily stabilize the up-state, consistent with stretch, temperature, and dephosphorylation. These findings support the down-up transition as the principal physiological activation pathway and suggest that mechanosensitivity arises from the larger membrane footprint of the up-state. Our data argue against a physiological role of a lipid-blocked pore and instead support gating via conformational control of the SF in TREK/TRAAK channels.

physiology↗

bioRxiv2023

Ion occupancy of the selectivity filter controls opening of a cytoplasmic gate in the K2P channel TALK-2

Two-pore domain K+ (K2P) channel activity was previously thought to be controlled primarily via a selectivity filter (SF) gate. However, recent crystal structures of TASK-1 and TASK-2 revealed a lower gate at the cytoplasmic pore entrance. Here, we report functional evidence of such a lower gate in the K2P channel K2P17.1 (TALK-2, TASK-4). We identified compounds (drugs and lipids) and mutations that opened the lower gate allowing the fast modification of pore cysteine residues. Surprisingly, stimuli that exclusively target the SF gate (i.e., pHe., Rb+ permeation, membrane depolarization) also opened the cytoplasmic gate suggesting that the SF can induce global structural changes in TALK-2. Reciprocally, opening of the lower gate reduced the electrical work required to force ions into the SF to induce its opening as apparent in large shifts of the conductance-voltage (G-V) curves. These shifts, thereby, represent the mechanical work done by the SF to induce a global structural re-arrangement that opened the lower gate. In conclusion, it appears that the SF is so rigidly locked into the TALK-2 protein structure that changes in ion occupancy can pry open a distant lower gate. Vice versa, we show that opening of the lower gate concurrently forces the SF gate to open. This concept might extent to other K+ channels that contain two gates (e.g., voltage-gated K+ channels) for which such a positive gate coupling has been suggested, but so far not directly demonstrated. SynopsisO_LITALK-2 channels, like most K2P channels, possess a functional gate in the selectivity filter (SF; the upper gate) that is opened by rising extracellular pH and voltage-dependent ion binding (voltage gating). C_LIO_LIA second (lower) permeation gate in TALK-2 at the cytoplasmic end of TM4 is identified using cysteine modification, scanning mutagenesis and structural modelling. This gate can be opened by anionic lipids (LC-CoA) as well as pharmacological ligands (e.g., 2-APB). C_LIO_LIThe modification reactivity of a cysteine introduced between the two gates reveal that stimuli targeting the SF gate also open the lower gate. Furthermore, stimuli that open the lower gate reduce the voltage (i.e., electrical work or mechanical load) required to open the SF gate. These findings demonstrate a tight positive coupling between the two gates. C_LIO_LIThe concept of strong positive gate coupling might extend to other K+ channels with two gates (e.g., voltage-gated K+ channels) for which positive gate coupling has been suggested but so far not directly demonstrated. C_LI

biophysics↗

bioRxiv2021

The versatile regulation of K2P channels by polyanionic lipids of the phosphoinositide (PIP2) and fatty acid metabolism (LC-CoA)

Work of the past three decades provided tremendous insight into the regulation of K+ channels - in particular Kir channels - by polyanionic lipids of the phosphoinositide (e.g. PIP2) and fatty acid metabolism (e.g. oleoyl-CoA). However, comparatively little is known regarding the phosphoinositide regulation in the K2P channel family and the effects of long-chain fatty acid CoA esters (LC-CoA, e.g. oleoyl-CoA) are so far unexplored. By screening most mammalian K2P channels (12 in total), we report strong effects of polyanionic lipids (activation and inhibition) for all tested K2P channels. In most cases the effects of PIP2 and oleoyl-CoA were similar causing either activation or inhibition depending on the respective subgroup. Activation was observed for members of the TREK, TALK and THIK subfamily with the strongest activation by PIP2 seen for TRAAK (~110-fold) and by oleoyl-CoA for TALK-2 (~90-fold). In contrast, inhibition was observed for members of the TASK and TRESK subfamilies up to ~85 %. In TASK-2 channels our results indicated an activatory as well as an inhibitory PIP2 site with different affinities. Finally, we provided evidence that PIP2 inhibition in TASK-1 and TASK-3 channels is mediated by closure of the recently identified lower X-gate as critical mutations within the gate (i.e. L244A, R245A) prevent PIP2 induced inhibition. Our results disclosed K2P channels as a family of ion channels highly sensitive to polyanionic lipids (PIP2 and LC-CoA), extended our knowledge on the mechanisms of lipid regulation and implicate the metabolisms of these lipids as possible effector pathways to regulate K2P channel activity.

biophysics↗