Biology subjects

Rinne, S.

Publications and source records attributed to Rinne, S..

3 recordsLinked to original sources

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↗

bioRxiv2022

Differential Effects of Mutations of Popeye Domain Containing Proteins on Heteromeric Interaction and Membrane Trafficking

BackgroundThe Popeye domain containing (POPDC) genes encode sarcolemma-localised cAMP effector proteins. Mutations in BVES (POPDC1) and POPDC2 have been associated with limb-girdle muscular dystrophy and cardiac arrhythmia. Muscle biopsies of affected patients display impaired membrane trafficking of both POPDC isoforms. MethodsBiopsy material of patients carrying mutations in BVES were immunostained with POPDC antibodies. The interaction of POPDC proteins was investigated by co-precipitation, proximity ligation, bioluminescence resonance energy transfer and bimolecular fluorescence complementation. Site-directed mutagenesis was utilised to map the domains involved in protein interaction. FindingsPatients carrying a novel homozygous variant, BVES (c.547G>T, p.V183F) displayed only a skeletal muscle pathology and a mild impairment of membrane trafficking of both POPDC isoforms. This is in contrast to variants such as BVES p.Q153X or POPDC2 p.W188X, which were associated with a greater impairment of membrane trafficking. Co-transfection analysis in HEK293 cells revealed that POPDC proteins interact with each other through a helix-helix interface located at the C-terminus of the Popeye domain. Site-directed mutagenesis of an array of ultra-conserved hydrophobic residues demonstrated that some of them are required for membrane trafficking of the POPDC1-POPDC2 complex. InterpretationMutations in POPDC proteins that cause an impairment in membrane localisation affect POPDC complex formation while mutations which leave the protein interaction intact likely affect some other essential function of POPDC proteins. FundingThis study was funded by an EPSRC/British Heart Foundation co-funded Imperial Institute of Chemical Biology (ICB) Centre for Doctoral Training (CDT) PhD studentship (EP/S023518/1), a project grant of the British Heart Foundation (PG19/13/34247) and the Deutsche Forschungsgemeinschaft (DE1482/9-1). Research in ContextO_ST_ABSEvidence before this studyC_ST_ABSSeveral biallelic missense and nonsense variants in BVES (POPDC1) have been described and are associated with heart and skeletal muscle disease. Skeletal muscle biopsies of homozygous carriers of these variants display a loss of sarcolemmal localisation of POPDC1 and POPDC2. Added value of this studyWe demonstrate that POPDC1 and POPDC2 form a heteromeric complex and that complex formation is required for plasma membrane trafficking of POPDC proteins. Transfection of different disease variants in HEK293 cells replicates their defective membrane targeting observed in biopsy material. Structural modelling and site-directed mutagenesis identifies an interface of strongly conserved hydrophobic residues in POPDC proteins, which likely mediate the interaction of POPDC proteins. Implications of all the available evidenceThese data provide novel insight into the membrane targeting requirements of POPDC proteins. We recommend testing the membrane targeting properties of any novel variant in POPDC isoforms using a newly developed co-transfection assay in HEK293 cells to characterise its pathogenicity. Our novel insight into the requirement of heterodimerization for proper membrane targeting may also offer novel opportunities to treat patients carrying mutations in POPDC proteins.

genetics↗

bioRxiv2019

A unique lower X-gate in TASK channels traps inhibitors within the vestibule

TASK channels are unusual members of the two-pore domain potassium (K2P) channel family, with unique and unexplained physiological and pharmacological characteristics. TASKs are found in neurons1,2, cardiomyocytes3-5 and vascular smooth muscle cells6 where they are involved in regulation of heart rate7, pulmonary artery tone6,8, sleep/wake cycles9 and responses to volatile anaesthetics9-12. K2P channels regulate the resting membrane potential, providing background K+ currents controlled by numerous physiological stimuli13,14. Unlike other K2P channels, TASK channels have the capacity to bind inhibitors with high affinity, exceptional selectivity and very slow compound washout rates. These characteristics make the TASK channels some of the the most easily druggable potassium channels, and indeed TASK-1 inhibitors are currently in clinical trials for obstructive sleep apnea (OSA) and atrial fibrillation (Afib)15 (The DOCTOS and SANDMAN Trials). Generally, potassium channels have an intramembrane vestibule with a selectivity filter above and a gate with four parallel helices below. However, K2P channels studied to date all lack a lower gate. Here we present the structure of TASK-1, revealing a unique lower gate created by interaction of the two crossed C-terminal M4 transmembrane helices at the vestibule entrance, which we designate as an \"X-gate\". This structure is formed by six residues (V243LRFMT248) that are essential for responses to volatile anaesthetics11, neuro-transmitters16 and G-protein coupled receptors16. Interestingly, mutations within the X-gate and surrounding regions drastically affect both open probability and activation by anaesthetics. Structures of TASK-1 with two novel, high-affinity blockers, shows both inhibitors bound below the selectivity filter, trapped in the vestibule by the X-gate, thus explaining their exceptionally low wash-out rates. Thus, the presence of the X-gate in TASK channels explains many aspects of their unusual physiological and pharmacological behaviour, which is invaluable for future development and optimization of TASK modulators for treatment of heart, lung and sleep disorders.

molecular biology↗