Structural mechanism of voltage-gated sodium channel slow inactivation.

Voltage-gated sodium (NaV) channels mediate a plethora of electrical activities. NaV channels govern cellular excitability in response to depolarizing stimuli. Inactivation is an intrinsic property of NaV channels that regulates cellular excitability by controlling the channel availability. The fast inactivation, mediated by the Ile-Phe-Met (IFM) motif and the N-terminal helix (N-helix), has been well-characterized. However, the molecular mechanism underlying NaV channel slow inactivation remains elusive. Here, we demonstrate that the removal of the N-helix of NaVEh (NaVEhΔN) results in a slow-inactivated channel, and present cryo-EM structure of NaVEhΔN in a potential slow-inactivated state. The structure features a closed activation gate and a dilated selectivity filter (SF), indicating that the upper SF and the inner gate could serve as a gate for slow inactivation. In comparison to the NaVEh structure, NaVEhΔN undergoes marked conformational shifts on the intracellular side. Together, our results provide important mechanistic insights into NaV channel slow inactivation.

Termination of convulsion seizures by destabilizing and perturbing seizure memory engrams.

Epileptogenesis, arising from alterations in synaptic strength, shares mechanistic and phenotypic parallels with memory formation. However, direct evidence supporting the existence of seizure memory remains scarce. Leveraging a conditioned seizure memory (CSM) paradigm, we found that CSM enabled the environmental cue to trigger seizure repetitively, and activating cue-responding engram cells could generate CSM artificially. Moreover, cue exposure initiated an analogous process of memory reconsolidation driven by mammalian target of rapamycin-brain-derived neurotrophic factor signaling. Pharmacological targeting of the mammalian target of rapamycin pathway within a limited time window reduced seizures in animals and interictal epileptiform discharges in patients with refractory seizures. Our findings reveal a causal link between seizure memory engrams and seizures, which leads us to a deeper understanding of epileptogenesis and points to a promising direction for epilepsy treatment.

Structural basis for NaV1.7 inhibition by pore blockers.

Voltage-gated sodium channel NaV1.7 plays essential roles in pain and odor perception. NaV1.7 variants cause pain disorders. Accordingly, NaV1.7 has elicited extensive attention in developing new analgesics. Here we present cryo-EM structures of human NaV1.7/ß1/ß2 complexed with inhibitors XEN907, TC-N1752 and NaV1.7-IN2, explaining specific binding sites and modulation mechanism for the pore blockers. These inhibitors bind in the central cavity blocking ion permeation, but engage different parts of the cavity wall. XEN907 directly causes α- to π-helix transition of DIV-S6 helix, which tightens the fast inactivation gate. TC-N1752 induces π-helix transition of DII-S6 helix mediated by a conserved asparagine on DIII-S6, which closes the activation gate. NaV1.7-IN2 serves as a pore blocker without causing conformational change. Electrophysiological results demonstrate that XEN907 and TC-N1752 stabilize NaV1.7 in inactivated state and delay the recovery from inactivation. Our results provide structural framework for NaV1.7 modulation by pore blockers, and important implications for developing subtype-selective analgesics.

N-type fast inactivation of a eukaryotic voltage-gated sodium channel.

Voltage-gated sodium (NaV) channels initiate action potentials. Fast inactivation of NaV channels, mediated by an Ile-Phe-Met motif, is crucial for preventing hyperexcitability and regulating firing frequency. Here we present cryo-electron microscopy structure of NaVEh from the coccolithophore Emiliania huxleyi, which reveals an unexpected molecular gating mechanism for NaV channel fast inactivation independent of the Ile-Phe-Met motif. An N-terminal helix of NaVEh plugs into the open activation gate and blocks it. The binding pose of the helix is stabilized by multiple electrostatic interactions. Deletion of the helix or mutations blocking the electrostatic interactions completely abolished the fast inactivation. These strong interactions enable rapid inactivation, but also delay recovery from fast inactivation, which is ~160-fold slower than human NaV channels. Together, our results provide mechanistic insights into fast inactivation of NaVEh that fundamentally differs from the conventional local allosteric inhibition, revealing both surprising structural diversity and functional conservation of ion channel inactivation.

Deficiency of autism-related Scn2a gene in mice disrupts sleep patterns and circadian rhythms.

Autism spectrum disorder (ASD) affects ~2% of the population in the US, and monogenic forms of ASD often result in the most severe manifestation of the disorder. Recently, SCN2A has emerged as a leading gene associated with ASD, of which abnormal sleep pattern is a common comorbidity. SCN2A encodes the voltage-gated sodium channel NaV1.2. Predominantly expressed in the brain, NaV1.2 mediates the action potential firing of neurons. Clinical studies found that a large portion of children with SCN2A deficiency have sleep disorders, which severely impact the quality of life of affected individuals and their caregivers. The underlying mechanism of sleep disturbances related to NaV1.2 deficiency, however, is not known. Using a gene-trap Scn2a-deficient mouse model (Scn2atrap), we found that Scn2a deficiency results in increased wakefulness and reduced non-rapid-eye-movement (NREM) sleep. Brain region-specific Scn2a deficiency in the suprachiasmatic nucleus (SCN) containing region, which is involved in circadian rhythms, partially recapitulates the sleep disturbance phenotypes. At the cellular level, we found that Scn2a deficiency disrupted the firing pattern of spontaneously firing neurons in the SCN region. At the molecular level, RNA-sequencing analysis revealed differentially expressed genes in the circadian entrainment pathway including core clock genes Per1 and Per2. Performing a transcriptome-based compound discovery, we identified dexanabinol (HU-211), a putative glutamate receptor modulator, that can partially reverse the sleep disturbance in mice. Overall, our study reveals possible molecular and cellular mechanisms underlying Scn2a deficiency-related sleep disturbances, which may inform the development of potential pharmacogenetic interventions for the affected individuals.

The spatio-temporal characteristics of aerosol optical thickness as well as the relationship with PM2.5 in Xiamen city, China.

Long-term aerosol optical thickness (AOT) composited data (2002-2017) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua spacecraft was used to evaluate the temporal and spatial variability of aerosol in Xiamen city by using wavelet analysis, and the relationship between the surface mass concentrations of particulate matter with aerodynamic diameters less than 2.5 µm (PM2.5) and the AOT was analyzed by using linear regression. The results showed that AOT increased gradually from 2002 to 2011, and then decreased. AOT displayed a significant 9-month periodicity in AOT was inferred wavelet analysis. AOT also showed significant annual variability in response to changes in weather and aerosol pollution. We observed highest AOT values in April, with a monthly mean of 1.00 ± 0.18. Lowest values were observed in December, with a mean AOT of 0.52 ± 0.11. Multi-year monthly AOT fluctuations were lowest in January with a low variation coefficient (0.14), and the largest fluctuations appeared in July with a high variation coefficient (0.29). Higher AOT values (~ 1.1) were predominantly located in the southern urban areas of Xiamen and lower AOT values (~ 0.3) were mainly located in northern rural regions. The aerosol pollution was serious in April with the smallest spatial variation coefficient of 0.25, and the highest spatial variation coefficient appeared in July. Highest intraannual variability predominantly occurred in the high-value areas in the center of Xiamen. AOT values remained high in Xiamen Island throughout the year with a multi-year mean of 0.87. There was a moderate correlation between ground-based PM2.5 and MODIS AOT. Therefore, we confirm the suitability of MODIS AOT to accurately estimate PM2.5 concentration and evaluate the temporal and spatial characteristics of air quality in Xiamen.

A three-dimensional chiral crystal structure constructed from a chiral triazolate ligand showing an SrSi2 topology: poly[bis(µ3-3,5-diethyl-1,2,4-triazolato-κ(3)N(1):N(2):N(4))trisilver nitrate].

In the title metal-organic framework (MOF), {[Ag3(C6H10N3)2]NO3}n, the Ag(I) cation is coordinated by two N atoms from two different 3,5-diethyl-1,2,4-triazolate (detz) ligands in a linear configuration. Each Ag(I) cation is then connected to two adjacent Ag(I) cations via a µ3-N(1):N(2):N(4)-detrz ligand, resulting in a three-dimensional chiral silver-triazolate structure showing an SrSi2 (srs) net with 10(3) topology.