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The precise control of an ion channel gate by environmental stimuli is crucial for the fulfilment of its biological role. The gate in Slo1 K + channels is regulated by two separate stimuli, intracellular Ca 2+ concentration and membrane voltage. Slo1 is thus central to understanding the relationship between intracellular Ca 2+ and membrane excitability. Here we present the Slo1 structure from Aplysia californica in the absence of Ca 2+ and compare it with the Ca 2+ -bound channel. We show that Ca 2+ binding at two unique binding sites per subunit stabilizes an expanded conformation of the Ca 2+ sensor gating ring. These conformational changes are propagated from the gating ring to the pore through covalent linkers and through protein interfaces formed between the gating ring and the voltage sensors. The gating ring and the voltage sensors are directly connected through these interfaces, which allow membrane voltage to regulate gating of the pore by influencing the Ca 2+ sensors. Two complementary studies present the full-length high-resolution structure of a Slo1 channel in the presence or absence of Ca 2+ ions, in which an unconventional allosteric voltage-sensing mechanism regulates the Ca 2+ sensor in addition to the voltage sensor’s direct action on the pore. Slo1 potassium channel structure and activity Dual activation by voltage and calcium ions makes Slo1/BK channels essential to processes that couple membrane electrical excitability and cellular calcium signalling, such as muscle contraction or neuronal communication. In two complementary studies, Roderick MacKinnon and colleagues present full-length structures for a Slo1 channel, either in the presence or the absence of Ca 2+ ions, suggesting an unconventional allosteric mechanism, whereby the voltage sensor regulates the Ca 2+ sensor instead of the channel's pore directly. These findings explain a large body of biochemical, genetic and physiological data, from both basic and clinical research.

The Ca 2+ -activated K + channel, Slo1, has an unusually large conductance and contains a voltage sensor and multiple chemical sensors. Dual activation by membrane voltage and Ca 2+ renders Slo1 central to processes that couple electrical signalling to Ca 2+ -mediated events such as muscle contraction and neuronal excitability. Here we present the cryo-electron microscopy structure of a full-length Slo1 channel from Aplysia californica in the presence of Ca 2+ and Mg 2+ at a resolution of 3.5 Å. The channel adopts an open conformation. Its voltage-sensor domain adopts a non-domain-swapped attachment to the pore and contacts the cytoplasmic Ca 2+ -binding domain from a neighbouring subunit. Unique structural features of the Slo1 voltage sensor suggest that it undergoes different conformational changes than other known voltage sensors. The structure reveals the molecular details of three distinct divalent cation-binding sites identified through electrophysiological studies of mutant Slo1 channels. Two complementary studies present the full-length high-resolution structure of a Slo1 channel in the presence or absence of Ca 2+ ions, in which an unconventional allosteric voltage-sensing mechanism regulates the Ca 2+ sensor in addition to the voltage sensor’s direct action on the pore. Slo1 potassium channel structure and activity Dual activation by voltage and calcium ions makes Slo1/BK channels essential to processes that couple membrane electrical excitability and cellular calcium signalling, such as muscle contraction or neuronal communication. In two complementary studies, Roderick MacKinnon and colleagues present full-length structures for a Slo1 channel, either in the presence or the absence of Ca 2+ ions, suggesting an unconventional allosteric mechanism, whereby the voltage sensor regulates the Ca 2+ sensor instead of the channel's pore directly. These findings explain a large body of biochemical, genetic and physiological data, from both basic and clinical research.

Mitochondria provide chemical energy for endoergonic reactions in the form of ATP, and their activity must meet cellular energy requirements, but the mechanisms that link organelle performance to ATP levels are poorly understood. Here we confirm the existence of a protein complex localized in mitochondria that mediates ATP-dependent potassium currents (that is, mitoK ATP ). We show that—similar to their plasma membrane counterparts—mitoK ATP channels are composed of pore-forming and ATP-binding subunits, which we term MITOK and MITOSUR, respectively. In vitro reconstitution of MITOK together with MITOSUR recapitulates the main properties of mitoK ATP . Overexpression of MITOK triggers marked organelle swelling, whereas the genetic ablation of this subunit causes instability in the mitochondrial membrane potential, widening of the intracristal space and decreased oxidative phosphorylation. In a mouse model, the loss of MITOK suppresses the cardioprotection that is elicited by pharmacological preconditioning induced by diazoxide. Our results indicate that mitoK ATP channels respond to the cellular energetic status by regulating organelle volume and function, and thereby have a key role in mitochondrial physiology and potential effects on several pathological processes. The pore-forming and ATP-binding subunits of a mitochondrial protein complex that mediates ATP-dependent potassium currents are identified and characterized, revealing the role of this channel in mitochondrial physiology and pathologies.

Channelrhodopsins are used widely for optical control of neurons, in which they generate photoinduced proton, sodium or chloride influx. Potassium (K+) is central to neuron electrophysiology, yet no natural K+-selective light-gated channel has been identified. Here, we report kalium channelrhodopsins (KCRs) from Hyphochytrium catenoides. Previously known gated potassium channels are mainly ligand- or voltage-gated and share a conserved K+-selectivity filter. KCRs differ in that they are light-gated and have independently evolved an alternative K+ selectivity mechanism. The KCRs are potent, highly selective of K+ over Na+, and open in less than 1 ms following photoactivation. The permeability ratio PK/PNa of 23 makes H. catenoides KCR1 (HcKCR1) a powerful hyperpolarizing tool to suppress excitable cell firing upon illumination, demonstrated here in mouse cortical neurons. HcKCR1 enables optogenetic control of K+ gradients, which is promising for the study and potential treatment of potassium channelopathies such as epilepsy, Parkinson’s disease and long-QT syndrome and other cardiac arrhythmias.The authors report a functional class of channelrhodopsins that are highly selective for K+ over Na+. These light-gated channels, named ‘kalium channelrhodopsins’, enable robust inhibition of mouse cortical neurons with millisecond precision.

The human voltage-gated potassium channel KCNQ2/KCNQ3 carries the neuronal M-current, which helps to stabilize the membrane potential. KCNQ2 can be activated by analgesics and antiepileptic drugs but their activation mechanisms remain unclear. Here we report cryo-electron microscopy (cryo-EM) structures of human KCNQ2-CaM in complex with three activators, namely the antiepileptic drug cannabidiol (CBD), the lipid phosphatidylinositol 4,5-bisphosphate (PIP 2 ), and HN37 (pynegabine), an antiepileptic drug in the clinical trial, in an either closed or open conformation. The activator-bound structures, along with electrophysiology analyses, reveal the binding modes of two CBD, one PIP 2 , and two HN37 molecules in each KCNQ2 subunit, and elucidate their activation mechanisms on the KCNQ2 channel. These structures may guide the development of antiepileptic drugs and analgesics that target KCNQ2. The potassium channel KCNQ2 can be activated by analgesics and antiepileptic drugs via an unclear mechanism. Here authors report structures of KCNQ2-CaM in complex with cannabidiol, PIP2, and HN37 and elucidate the mechanisms of activation.

The Kv1.3 potassium channel is expressed abundantly on activated T cells and mediates the cellular immune response. This role has made the channel a target for therapeutic immunomodulation to block its activity and suppress T cell activation. Here, we report structures of human Kv1.3 alone, with a nanobody inhibitor, and with an antibody-toxin fusion blocker. Rather than block the channel directly, four copies of the nanobody bind the tetramer’s voltage sensing domains and the pore domain to induce an inactive pore conformation. In contrast, the antibody-toxin fusion docks its toxin domain at the extracellular mouth of the channel to insert a critical lysine into the pore. The lysine stabilizes an active conformation of the pore yet blocks ion permeation. This study visualizes Kv1.3 pore dynamics, defines two distinct mechanisms to suppress Kv1.3 channel activity with exogenous inhibitors, and provides a framework to aid development of emerging T cell immunotherapies. The Kv1.3 potassium channel is expressed abundantly on activated T cells and mediates the cellular immune responses. Here, the authors report structures of the Kv1.3 potassium channel with and without immunoglobulin modulators, shedding light on the mechanisms of Kv1.3 gating and modulation.

The voltage-gated potassium channel AKT1 is responsible for primary K + uptake in Arabidopsis roots. AKT1 is functionally activated through phosphorylation and negatively regulated by a potassium channel α-subunit AtKC1. However, the molecular basis for the modulation mechanism remains unclear. Here we report the structures of AKT1, phosphorylated-AKT1, a constitutively-active variant, and AKT1-AtKC1 complex. AKT1 is assembled in 2-fold symmetry at the cytoplasmic domain. Such organization appears to sterically hinder the reorientation of C-linkers during ion permeation. Phosphorylated-AKT1 adopts an alternate 4-fold symmetric conformation at cytoplasmic domain, which indicates conformational changes associated with symmetry switch during channel activation. To corroborate this finding, we perform structure-guided mutagenesis to disrupt the dimeric interface and identify a constitutively-active variant Asp379Ala mediates K + permeation independently of phosphorylation. This variant predominantly adopts a 4-fold symmetric conformation. Furthermore, the AKT1-AtKC1 complex assembles in 2-fold symmetry. Together, our work reveals structural insight into the regulatory mechanism for AKT1. Arabidopsis thaliana potassium channel AKT1 is responsible for primary K + uptake from soil, which is functionally activated through phosphorylation and negatively regulated by an α-subunit AtKC1. Here, the authors report the structures of AKT1 at different states, revealing a 2- fold to 4-fold symmetry switch at cytoplasmic domain associated with AKT1 activity regulation.

Key Points Cortical spreading depression (CSD) is a slowly propagating wave of rapid, near-complete depolarization of brain cells that lasts for about 1 minute and silences brain electrical activity for several minutes; it can be induced in normally metabolizing tissue by depolarizing stimuli that increase extracellular K + concentration ([K + ] e ) above a critical value. Longer-lasting spreading depolarizations arise in metabolically compromised brain tissue. CSD initiation depends on the activation of ion channels located in dendrites of pyramidal cells and on the generation of a net self-sustaining inward current that initiates a positive-feedback cycle leading to a regenerative increase in [K + ] e and regenerative depolarization. NMDA receptors (NMDARs) and voltage-gated Ca 2+ channel (in particular Cav2.1)-dependent release of glutamate have a key role in the positive-feedback cycle that ignites CSD; depending on the method of induction, [Ca 2+ ] e -independent glutamate release may contribute. CSD propagation is probably mediated by interstitial diffusion of K + released during the depolarization (accompanied by [K + ] e -dependent glutamate release), initiating the positive-feedback cycle that ignites CSD in contiguous grey matter. The mechanisms initiating CSD and spreading depolarizations are different. Besides NMDARs, other ion channels and processes (probably including persistent voltage-gated Na + channels and mitochondrial depolarization) seem to be crucial for the initiation of spreading depolarizations. Propagating depolarizing events in brain have been linked to neurovascular disorders such as migraine and stroke. In migraine, CSD has been linked to migraine aura, trigeminal activation and headache as well as the actions of preventative drugs. It has been increasingly recognized that spreading depolarizations compromise energy metabolism and blood flow, contributing to poor tissue outcome when they erupt in the injured brain. Hence, there is an increasing demand for treatment strategies that selectively block initiation, propagation or enhance recovery to mitigate the impact of chaos and commotion that surrounds CSD and spreading depolarizations. Cortical spreading depressions and spreading depolarizations are associated with migraines and stroke, respectively. In this Review, Pietrobon and Moskowitz discuss recent data that provide insight into the mechanisms underlying the initiation and propagation of cortical spreading depressions and spreading depolarizations, and highlight the therapeutic potential of pharmacological targeting of these mechanisms. Punctuated episodes of spreading depolarizations erupt in the brain, encumbering tissue structure and function, and raising fascinating unanswered questions concerning their initiation and propagation. Linked to migraine aura and headache, cortical spreading depression contributes to the morbidity in the world's migraine with aura population. Even more ominously, erupting spreading depolarizations accelerate tissue damage during brain injury. The once-held view that spreading depolarizations may not exist in the human brain has changed, largely because of the discovery of migraine genes that confer cortical spreading depression susceptibility, the application of sophisticated imaging tools and efforts to interrogate their impact in the acutely injured human brain.

Potassium channels are presumed to have two allosterically coupled gates, the activation gate and the selectivity filter gate, that control channel opening, closing, and inactivation. However, the molecular mechanism of how these gates regulate K +  ion flow through the channel remains poorly understood. An activation process, occurring at the selectivity filter, has been recently proposed for several potassium channels. Here, we use X-ray crystallography and extensive molecular dynamics simulations, to study ion permeation through a potassium channel MthK, for various opening levels of both gates. We find that the channel conductance is controlled at the selectivity filter, whose conformation depends on the activation gate. The crosstalk between the gates is mediated through a collective motion of channel helices, involving hydrophobic contacts between an isoleucine and a conserved threonine in the selectivity filter. We propose a gating model of selectivity filter-activated potassium channels, including pharmacologically relevant two-pore domain (K2P) and big potassium (BK) channels. Potassium channels such as MthK are presumed to have two allosterically coupled gates, the activation gate and the selectivity filter gate, that control gating transitions. Here authors use X-ray crystallography and molecular dynamics simulations on MthK and observe crosstalk between the gates.

Tandem pore domain (K2P) potassium channels modulate resting membrane potentials and shape cellular excitability. For the mechanosensitive subfamily of K2Ps, the composition of phospholipids within the bilayer strongly influences channel activity. To examine the molecular details of K2P lipid modulation, we solved cryo-EM structures of the TREK1 K2P channel bound to either the anionic lipid phosphatidic acid (PA) or the zwitterionic lipid phosphatidylethanolamine (PE). At the extracellular face of TREK1, a PA lipid inserts its hydrocarbon tail into a pocket behind the selectivity filter, causing a structural rearrangement that recapitulates mutations and pharmacology known to activate TREK1. At the cytoplasmic face, PA and PE lipids compete to modulate the conformation of the TREK1 TM4 gating helix. Our findings demonstrate two distinct pathways by which anionic lipids enhance TREK1 activity and provide a framework for a model that integrates lipid gating with the effects of other mechanosensitive K2P modulators. Tandem pore (K2P) potassium channels set the cellular resting membrane potential in tissues throughout the body. Here, authors show how the composition of phospholipid within the bilayer may directly alter gating in this family of ion channels.