Biology subjects

Sorum, B.

Publications and source records attributed to Sorum, B..

4 recordsLinked to original sources

bioRxiv2024

Cannabinoid inhibition of mechanosensitive K+ channels

Cannabidiol (CBD) is a prominent non-psychoactive small molecule produced by cannabis plants used clinically as an antiepileptic. Here, we show CBD and other cannabinoids are potent inhibitors of mechanosensitive two-pore domain K+ (K2P) channels, including TRAAK and TREK-1 that contribute to spike propagation in myelinated axons. Five TRAAK mutations that cause epilepsy or the neurodevelopmental syndrome FHEIG (facial dysmorphism, hypertrichosis, epilepsy, intellectual/developmental delay, and gingival overgrowth) retain sensitivity to cannabinoid inhibition. A cryo-EM structure reveals CBD binds in the intracellular cavity of TREK-1 to sterically block ion conduction. These results show that cannabinoids and endogenous lipids compete for a common binding site to inhibit channel activity, identify mechanosensitive K2Ps as potential physiological targets of CBD, and suggest cannabinoids could counter gain-of-function in TRAAK channelopathies. SummaryWe discover cannabinoids inhibit mechanosensitive K+ channels including mutants that cause disease and reveal the mechanism for channel block.

neuroscience↗

bioRxiv2023

Pressure and ultrasound activate mechanosensitive TRAAK K+ channels through increased membrane tension

TRAAK is a mechanosensitive two-pore domain K+ (K2P) channel found in nodes of Ranvier within myelinated axons. It displays low leak activity at rest and is activated up to one hundred-fold by increased membrane tension. Structural and functional studies have led to physical models for channel gating and mechanosensitivity, but no quantitative analysis of channel activation by tension has been reported. Here, we use simultaneous patch-clamp recording and fluorescent imaging to determine the tension response characteristics of TRAAK. TRAAK shows high sensitivity and a broad response to tension spanning nearly the entire physiologically relevant tension range. This graded response profile distinguishes TRAAK from similarly low-threshold mechanosensitive channels Piezo1 and MscS, which activate in a step-like fashion over a narrow tension range. We further use patch imaging to show that ultrasonic activation of TRAAK and MscS is due to increased membrane tension. Together, these results provide mechanistic insight into TRAAK tension gating, a framework for exploring the role of mechanosensitive K+ channels at nodes of Ranvier, and biophysical context for developing ultrasound as a mechanical stimulation technique for neuromodulation.

biophysics↗

bioRxiv2020

Ultrasound activates mechanosensitive TRAAK K+ channels directly through the lipid membrane

Ultrasound modulates the electrical activity of excitable cells and offers advantages over other neuromodulatory techniques; for example, it can be non-invasively transmitted through skull and focused to deep brain regions. However, the fundamental cellular, molecular, and mechanistic bases of ultrasonic neuromodulation are largely unknown. Here, we demonstrate ultrasound activation of the mechanosensitive K+ channel TRAAK with sub-millisecond kinetics to an extent comparable to canonical mechanical activation. Single channel recordings reveal a common basis for ultrasonic and mechanical activation with stimulus-graded destabilization of long-duration closures and promotion of full conductance openings. Ultrasonic energy is transduced to TRAAK directly through the membrane in the absence of other cellular components, likely increasing membrane tension to promote channel opening. We further demonstrate ultrasonic modulation of neuronally expressed TRAAK. These results suggest mechanosensitive channels underlie physiological responses to ultrasound and provides a framework for developing channel-based sonogentic actuators for acoustic neuromodulation of genetically targeted cells.

neuroscience↗

bioRxiv2020

Cryo-EM structure of the SARS-CoV-2 3a ion channel in lipid nanodiscs

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes the coronavirus disease 2019 (COVID-19). SARS-CoV-2 encodes three putative ion channels: E, 8a, and 3a1,2. 3a is expressed in SARS patient tissue and anti-3a antibodies are observed in patient plasma3-6. 3a has been implicated in viral release7, inhibition of autophagy8, inflammasome activation9, and cell death10,11 and its deletion reduces viral titer and morbidity in mice1, raising the possibility that 3a could be an effective vaccine or therapeutic target3,12. Here, we present the first cryo-EM structures of SARS-CoV-2 3a to 2.1 [A] resolution and demonstrate 3a forms an ion channel in reconstituted liposomes. The structures in lipid nanodiscs reveal 3a dimers and tetramers adopt a novel fold with a large polar cavity that spans halfway across the membrane and is accessible to the cytosol and the surrounding bilayer through separate water- and lipid-filled openings. Electrophysiology and fluorescent ion imaging experiments show 3a forms Ca2+-permeable non-selective cation channels. We identify point mutations that alter ion permeability and discover polycationic inhibitors of 3a channel activity. We find 3a-like proteins in multiple Alphacoronavirus and Betacoronavirus lineages that infect bats and humans. These data show 3a forms a functional ion channel that may promote COVID-19 pathogenesis and suggest targeting 3a could broadly treat coronavirus diseases.

biophysics↗