Structures of the R-type human Cav2.3 channel reveal conformational crosstalk of the intracellular segments

Structural biology of voltage-gated calcium channels

Voltage-gated calcium (Cav) channels mediate Ca2+ influx in response to membrane depolarization, playing critical roles in diverse physiological processes. Dysfunction or aberrant regulation of Cav channels can lead to life-threatening consequences. Cav-targeting drugs have been clinically used to treat cardiovascular and neuronal disorders for several decades. This review aims to provide an account of recent developments in the structural dissection of Cav channels. High-resolution structures have significantly advanced our understanding of the working and disease mechanisms of Cav channels, shed light on the molecular basis for their modulation, and elucidated the modes of actions (MOAs) of representative drugs and toxins. The progress in structural studies of Cav channels lays the foundation for future drug discovery efforts targeting Cav channelopathies.

Structural biology and molecular pharmacology of voltage-gated ion channels

Voltage-gated ion channels (VGICs), including those for Na+, Ca2+ and K+, selectively permeate ions across the cell membrane in response to changes in membrane potential, thus participating in physiological processes involving electrical signalling, such as neurotransmission, muscle contraction and hormone secretion. Aberrant function or dysregulation of VGICs is associated with a diversity of neurological, psychiatric, cardiovascular and muscular disorders, and approximately 10% of FDA-approved drugs directly target VGICs. Understanding the structure-function relationship of VGICs is crucial for our comprehension of their working mechanisms and role in diseases. In this Review, we discuss how advances in single-particle cryo-electron microscopy have afforded unprecedented structural insights into VGICs, especially on their interactions with clinical and investigational drugs. We present a comprehensive overview of the recent advances in the structural biology of VGICs, with a focus on how prototypical drugs and toxins modulate VGIC activities. We explore how these structures elucidate the molecular basis for drug actions, reveal novel pharmacological sites, and provide critical clues to future drug discovery.

A Rich Conformational Palette Underlies Human CaV2.1-Channel Availability

Depolarization-evoked opening of CaV2.1 (P/Q-type) Ca2+-channels triggers neurotransmitter release, while voltage-dependent inactivation (VDI) limits channel availability to open, contributing to synaptic plasticity. The mechanism of CaV2.1 response to voltage is unclear. Using voltage-clamp fluorometry and kinetic modeling, we optically tracked and physically characterized the structural dynamics of the four CaV2.1 voltage-sensor domains (VSDs). VSD-I seems to directly drive opening and convert between two modes of function, associated with VDI. VSD-II is apparently voltage-insensitive. VSD-III and VSD-IV sense more negative voltages and undergo voltage-dependent conversion uncorrelated with VDI. Auxiliary β -subunits regulate VSD-I-to-pore coupling and VSD conversion kinetics. CaV2.1 VSDs are differentially sensitive to voltage changes brief and long-lived. Specifically the voltage-dependent conformational changes of VSD-I are linked to synaptic release and plasticity.

Voltage-dependent G-protein regulation of CaV2.2 (N-type) channels

How G proteins inhibit N-type, voltage-gated, calcium-selective channels (CaV2.2) during presynaptic inhibition is a decades-old question. G proteins Gβγ bind to intracellular CaV2.2 regions, but the inhibition is voltage dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that Gβγ acts by selectively inhibiting a subset of the four different CaV2.2 voltage-sensor domains (VSDs I to IV). During regular "willing" gating, VSD-I and -IV activations resemble pore opening, VSD III activation is hyperpolarized, and VSD II appears unresponsive to depolarization. In the presence of Gβγ, CaV2.2 gating is "reluctant": pore opening and VSD I activation are strongly and proportionally inhibited, VSD IV is modestly inhibited, while VSD III is not. We propose that Gβγ inhibition of VSDs I and IV underlies reluctant CaV2.2 gating and subsequent presynaptic inhibition.

Native MS-guided lipidomics to define endogenous lipid microenvironments of eukaryotic receptors and transporters

The mammalian membrane is composed of various eukaryotic lipids interacting with extensively post-translationally modified proteins. Probing interactions between these mammalian membrane proteins and their diverse and heterogeneous lipid cohort remains challenging. Recently, native mass spectrometry (MS) combined with bottom-up 'omics' approaches has provided valuable information to relate structural and functional lipids to membrane protein assemblies in eukaryotic membranes. Here we provide a step-by-step protocol to identify and provide relative quantification for endogenous lipids bound to mammalian membrane proteins and their complexes. Using native MS to guide our lipidomics strategies, we describe the necessary sample preparation steps, followed by native MS data acquisition, tailored lipidomics and data interpretation. We also highlight considerations for the integration of different levels of information from native MS and lipidomics and how to deal with the various challenges that arise during the experiments. This protocol begins with the preparation of membrane proteins from mammalian cells and tissues for native MS. The results enable not only direct assessment of copurified endogenous lipids but also determination of the apparent affinities of specific lipids. Detailed sample preparation for lipidomics analysis is also covered, along with comprehensive settings for liquid chromatography-MS analysis. This protocol is suitable for the identification and quantification of endogenous lipids, including fatty acids, sterols, glycerolipids, phospholipids and glycolipids and can be used to interrogate proteins from recombinant sources to native membranes.

MODY Only Monogenic? A Narrative Review of the Novel Rare and Low-Penetrant Variants

Maturity-onset diabetes of the young (MODY) represents the most frequent form of monogenic diabetes mellitus (DM), currently classified in 14 distinct subtypes according to single gene mutations involved in the differentiation and function of pancreatic β-cells. A significant proportion of MODY has unknown etiology, suggesting that the genetic landscape is still to be explored. Recently, novel potentially MODY-causal genes, involved in the differentiation and function of β-cells, have been identified, such as RFX6, NKX2.2, NKX6.1, WFS1, PCBD1, MTOR, TBC1D4, CACNA1E, MNX1, AKT2, NEUROG3, EIF2AK3, GLIS3, HADH, and PTF1A. Genetic and clinical features of MODY variants remain highly heterogeneous, with no direct genotype-phenotype correlation, especially in the low-penetrant subtypes. This is a narrative review of the literature aimed at describing the current state-of-the-art of the novel likely MODY-associated variants. For a deeper understanding of MODY complexity, we also report some related controversies concerning the etiological role of some of the well-known pathological genes and MODY inheritance pattern, as well as the rare association of MODY with autoimmune diabetes. Due to the limited data available, the assessment of MODY-related genes pathogenicity remains challenging, especially in the setting of rare and low-penetrant subtypes. In consideration of the crucial importance of an accurate diagnosis, prognosis and management of MODY, more studies are warranted to further investigate its genetic landscape and the genotype-phenotype correlation, as well as the pathogenetic contribution of the nongenetic modifiers in this cohort of patients.

Electrical and G-protein Regulation of CaV2.2 (N-type) Channels

How G-proteins inhibit N-type, voltage-gated, calcium-selective channels (Ca V 2.2) during presynaptic inhibition is a decades-old question. G-proteins Gβγ bind to intracellular Ca V 2.2 regions, but the inhibition is voltage-dependent. Using the hybrid electrophysiological and optical approach voltage-clamp fluorometry, we show that Gβγ acts by selectively inhibiting a subset of the four different Ca V 2.2 voltage-sensor domains (VSDs I-IV). During regular "willing" gating, VSDs I and IV activation resemble pore opening, VSD III activation is hyperpolarized, and VSD II appears unresponsive to depolarization. In the presence of Gβγ, Ca V 2.2 gating is "reluctant": pore opening and VSD-I activation are strongly and proportionally inhibited, VSD IV is modestly inhibited while VSD III is not. We propose that Gβγ inhibition of VSD-I and -IV underlies reluctant Ca V 2.2 gating and subsequent presynaptic inhibition.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Structural basis for human Cav3.2 inhibition by selective antagonists

The Cav3.2 subtype of T-type calcium channels has been targeted for developing analgesics and anti-epileptics for its role in pain and epilepsy. Here we present the cryo-EM structures of Cav3.2 alone and in complex with four T-type calcium channel selective antagonists with overall resolutions ranging from 2.8 Å to 3.2 Å. The four compounds display two binding poses. ACT-709478 and TTA-A2 both place their cyclopropylphenyl-containing ends in the central cavity to directly obstruct ion flow, meanwhile extending their polar tails into the IV-I fenestration. TTA-P2 and ML218 project their 3,5-dichlorobenzamide groups into the II-III fenestration and place their hydrophobic tails in the cavity to impede ion permeation. The fenestration-penetrating mode immediately affords an explanation for the state-dependent activities of these antagonists. Structure-guided mutational analysis identifies several key residues that determine the T-type preference of these drugs. The structures also suggest the role of an endogenous lipid in stabilizing drug binding in the central cavity.

Structural basis for human Cav1.2 inhibition by multiple drugs and the neurotoxin calciseptine

Cav1.2 channels play crucial roles in various neuronal and physiological processes. Here, we present cryo-EM structures of human Cav1.2, both in its apo form and in complex with several drugs, as well as the peptide neurotoxin calciseptine. Most structures, apo or bound to calciseptine, amlodipine, or a combination of amiodarone and sofosbuvir, exhibit a consistent inactivated conformation with a sealed gate, three up voltage-sensing domains (VSDs), and a down VSDII. Calciseptine sits on the shoulder of the pore domain, away from the permeation path. In contrast, when pinaverium bromide, an antispasmodic drug, is inserted into a cavity reminiscent of the IFM-binding site in Nav channels, a series of structural changes occur, including upward movement of VSDII coupled with dilation of the selectivity filter and its surrounding segments in repeat III. Meanwhile, S4-5III merges with S5III to become a single helix, resulting in a widened but still non-conductive intracellular gate.

The Dysfunction of Ca2+ Channels in Hereditary and Chronic Human Heart Diseases and Experimental Animal Models

Chronic heart diseases, such as coronary heart disease, heart failure, secondary arterial hypertension, and dilated and hypertrophic cardiomyopathies, are widespread and have a fairly high incidence of mortality and disability. Most of these diseases are characterized by cardiac arrhythmias, conduction, and contractility disorders. Additionally, interruption of the electrical activity of the heart, the appearance of extensive ectopic foci, and heart failure are all symptoms of a number of severe hereditary diseases. The molecular mechanisms leading to the development of heart diseases are associated with impaired permeability and excitability of cell membranes and are mainly caused by the dysfunction of cardiac Ca2+ channels. Over the past 50 years, more than 100 varieties of ion channels have been found in the cardiovascular cells. The relationship between the activity of these channels and cardiac pathology, as well as the general cellular biological function, has been intensively studied on several cell types and experimental animal models in vivo and in situ. In this review, I discuss the origin of genetic Ca2+ channelopathies of L- and T-type voltage-gated calcium channels in humans and the role of the non-genetic dysfunctions of Ca2+ channels of various types: L-, R-, and T-type voltage-gated calcium channels, RyR2, including Ca2+ permeable nonselective cation hyperpolarization-activated cyclic nucleotide-gated (HCN), and transient receptor potential (TRP) channels, in the development of cardiac pathology in humans, as well as various aspects of promising experimental studies of the dysfunctions of these channels performed on animal models or in vitro.

Benzo[a]pyrene represses synaptic vesicle exocytosis by inhibiting P/Q-type calcium channels in hippocampal neurons

Humans are exposed to the common carcinogen benzo[a]pyrene (BaP) by ingesting contaminated foods and water or inhaling polluted air. Given the enriched lipids and reduced antioxidative properties in the brain and the accumulation of BaP in the brain due to its high lipophilicity, the brain is susceptible to BaP-induced toxicity. Exposure to BaP leads to impairments in learning and memory, increased anxiety behavior, and neuronal death. It induces protein dysfunctions in neuronal compartments that play essential roles in neuronal activity or physiology. However, the neurotoxicity of BaP on presynaptic terminals, which is crucial to neurotransmission by releasing synaptic vesicles that contain neurotransmitters, has not yet been investigated. In the present study, we investigated the toxicity of BaP at presynaptic terminals in living hippocampal neurons. These neurons were sourced from transgenic mice pups (postnatal 1-day, a total of 12 pups, equal numbers for each sex) that endogenously express synaptic vesicle-fused pHluorin, which is a green fluorescent protein that enables monitoring of synaptic vesicle dynamics. We observed that BaP suppressed synaptic vesicle exocytosis by inhibiting presynaptic Ca2+ entry via P/Q-type Ca2+ channels. Together with molecular docking simulation, we speculate that BaP and metabolites may bind to the P/Q Ca2+ channels. These results suggest the toxic mechanism of BaP exposure-induced abnormal behavior that provides a basis to evaluate the risk assessment of BaP-induced neurotoxicity.

Cryo-EM structure of human voltage-gated sodium channel Nav1.6

Voltage-gated sodium channel Na_v1.6 plays a crucial role in neuronal firing in the central nervous system (CNS). Aberrant function of Na_v1.6 may lead to epilepsy and other neurological disorders. Specific inhibitors of Na_v1.6 thus have therapeutic potentials. Here we present the cryo-EM structure of human Na_v1.6 in the presence of auxiliary subunits β1 and fibroblast growth factor homologous factor 2B (FHF2B) at an overall resolution of 3.1 Å. The overall structure represents an inactivated state with closed pore domain (PD) and all "up" voltage-sensing domains. A conserved carbohydrate-aromatic interaction involving Trp302 and Asn326, together with the β1 subunit, stabilizes the extracellular loop in repeat I. Apart from regular lipids that are resolved in the EM map, an unprecedented Y-shaped density that belongs to an unidentified molecule binds to the PD, revealing a potential site for developing Na_v1.6-specific blockers. Structural mapping of disease-related Na_v1.6 mutations provides insights into their pathogenic mechanism.