Structural mechanisms of the human cardiac sodium-calcium exchanger NCX1.

Na+/Ca2+ exchangers (NCX) transport Ca2+ in or out of cells in exchange for Na+. They are ubiquitously expressed and play an essential role in maintaining cytosolic Ca2+ homeostasis. Although extensively studied, little is known about the global structural arrangement of eukaryotic NCXs and the structural mechanisms underlying their regulation by various cellular cues including cytosolic Na+ and Ca2+. Here we present the cryo-EM structures of human cardiac NCX1 in both inactivated and activated states, elucidating key structural elements important for NCX ion exchange function and its modulation by cytosolic Ca2+ and Na+. We demonstrate that the interactions between the ion-transporting transmembrane (TM) domain and the cytosolic regulatory domain define the activity of NCX. In the inward-facing state with low cytosolic [Ca2+], a TM-associated four-stranded ß-hub mediates a tight packing between the TM and cytosolic domains, resulting in the formation of a stable inactivation assembly that blocks the TM movement required for ion exchange function. Ca2+ binding to the cytosolic second Ca2+-binding domain (CBD2) disrupts this inactivation assembly which releases its constraint on the TM domain, yielding an active exchanger. Thus, the current NCX1 structures provide an essential framework for the mechanistic understanding of the ion transport and cellular regulation of NCX family proteins.

Lysosomal LAMP proteins regulate lysosomal pH by direct inhibition of the TMEM175 channel.

Maintaining a highly acidic lysosomal pH is central to cellular physiology. Here, we use functional proteomics, single-particle cryo-EM, electrophysiology, and in vivo imaging to unravel a key biological function of human lysosome-associated membrane proteins (LAMP-1 and LAMP-2) in regulating lysosomal pH homeostasis. Despite being widely used as a lysosomal marker, the physiological functions of the LAMP proteins have long been overlooked. We show that LAMP-1 and LAMP-2 directly interact with and inhibit the activity of the lysosomal cation channel TMEM175, a key player in lysosomal pH homeostasis implicated in Parkinson's disease. This LAMP inhibition mitigates the proton conduction of TMEM175 and facilitates lysosomal acidification to a lower pH environment crucial for optimal hydrolase activity. Disrupting the LAMP-TMEM175 interaction alkalinizes the lysosomal pH and compromises the lysosomal hydrolytic function. In light of the ever-increasing importance of lysosomes to cellular physiology and diseases, our data have widespread implications for lysosomal biology.

Effectiveness of corticosteroids to treat coronavirus disease 2019 symptoms: A meta-analysis.

Objective: Currently, corticosteroids are widely used to treat coronavirus disease 2019 (COVID-19) symptoms. However, the therapeutic role of corticosteroids remains highly controversial. To that end, we aimed to assess the efficacy of corticosteroids in treating COVID-19 patients. Method: We searched PubMed, Embase, and Cochrane Library to select suitable studies. Our primary study endpoint was all-cause mortality. The secondary study endpoint was the length of hospital stay. Results: A total of 9 randomized controlled trials (RCTs) with 7907 patients were assessed. The pooled result indicated that corticosteroids treatment could significantly reduce all-cause mortality in patients with COVID-19 (RR = 0.88, 95% CI [0.82, 0.95], P = 0.002). When subgroup analyses were performed, we found that corticosteroids were associated with decreased all-cause mortality in severe COVID-19 patients (RR = 0.77, 95% CI [0.68, 0.88], P < 0.0001), however no obvious difference was observed in all-cause mortality of non-severe COVID-19 patients between the corticosteroid and control group (RR = 0.96, 95% CI [0.86, 1.06], P = 0.41), meanwhile, a low dose (RR = 0.89, 95% CI [0.82, 0.97], P = 0.007) of dexamethasone (RR = 0.9, 95% CI [0.83, 0.98], P = 0.01) with a long treatment course (RR = 0.89, 95% CI [0.82, 0.98], P = 0.02) was beneficial for all-cause mortality in COVID-19 patients. Additionally, we found that corticosteroids might be associated with a longer length of hospital stay in non-severe COVID-19 patients (MD = 3.83, 95% CI [1.11, 6.56], P = 0.006). Conclusion: Our results showed that corticosteroid therapy was related to a reduction in all-cause mortality in severe COVID-19 patients. However, in patients with non-severe COVID-19, the use of corticosteroids did not decrease all-cause mortality and may prolong the duration of hospital stay. In addition, we revealed that a low dose of dexamethasone with a long treatment course could reduce all-cause mortality in COVID-19 patients.

Objetivo: Actualmente, los glucocorticoides se utilizan ampliamente para tratar los síntomas de la enfermedad por coronavirus 2019 (COVID-19). Sin embargo, el papel terapéutico de los glucocorticoides sigue siendo muy controvertido, por ello, nos propusimos evaluar su eficacia en el tratamiento de los pacientes con COVID-19. Método: Se realizaron búsquedas en PubMed, Embase y Cochrane Library para seleccionar los estudios adecuados. El criterio de valoración principal del estudio fue la mortalidad por todas las causas. El criterio de valoración secundario del estudio fue la duración de la estancia en el hospital. Resultados: Se evaluó un total de 9 ensayos controlados aleatorizados con 7.907 pacientes. En general, el tratamiento con glucocorticoides redujo la mortalidad por todas las causas en los pacientes con COVID-19 (RR = 0,88, IC 95% [0,82; 0,95], p = 0,002). Al realizar análisis de subgrupos, se observó que los glucocorticoides se asociaban a una disminución de la mortalidad por todas las causas en los pacientes con COVID-19 grave (RR = 0,77, IC 95% [0,68; 0,88], p < 0,0001), sin embargo no se observaron diferencias evidentes en la mortalidad por todas las causas de los pacientes con COVID-19 no grave entre el grupo de glucocorticoides y el de control (RR = 0,96, IC 95% [0,86; 1,06], p = 0,41), mientras que una dosis baja (RR = 0,89, IC 95% [0,82; 0,97], p = 0,007) de dexametasona (RR = 0,9, IC 95% [0,83; 0,98], p = 0,01) con un curso de tratamiento largo (RR = 0,89, IC 95% [0,82; 0,98], p = 0,02) fue beneficiosa para la mortalidad por todas las causas en los pacientes con COVID-19. Además, encontramos que los glucocorticoides podrían estar asociados con una mayor duración de la estancia hospitalaria en los pacientes con COVID-19 no grave (DM = 3,83, IC 95% [1,11; 6,56], p = 0,006). Conclusión: Nuestros resultados mostraron que el tratamiento con glucocorticoides estaba relacionado con una reducción de la mortalidad por todas las causas en los pacientes con COVID-19 grave. Sin embargo, en los pacientes con COVID-19 no grave, el uso de glucocorticoides no disminuyó la mortalidad por todas las causas y puede prolongar la duración de la estancia hospitalaria. Además, descubrimos que una dosis baja de dexametasona con un curso de tratamiento largo podría reducir la mortalidad por todas las causas en los pacientes con COVID-19.

Effectiveness of corticosteroids to treat coronavirus disease 2019 symptoms: A meta-analysis.

OBJECTIVE: Currently, corticosteroids are widely used to treat coronavirus disease 2019 (COVID-19) symptoms. However, the therapeutic role of corticosteroids remains highly controversial. To that end, we aimed to assess the efficacy of corticosteroids in treating COVID-19 patients. METHOD: We searched PubMed, Embase, and Cochrane Library to select suitable studies. Our primary study endpoint was all-cause mortality. The secondary study endpoint was the length of hospital stay. RESULTS: A total of 9 randomized controlled trials (RCTs) with 7907 patients were assessed. The pooled result indicated that corticosteroids treatment could significantly reduce all-cause mortality in patients with COVID-19 (RR=0.88, 95% CI [0.82, 0.95], P=0.002). When subgroup analyses were performed, we found that corticosteroids were associated with decreased all-cause mortality in severe COVID-19 patients (RR=0.77, 95% CI [0.68, 0.88], P<0.0001), however no obvious difference was observed in all-cause mortality of non-severe COVID-19 patients between the corticosteroid and control group (RR=0.96, 95% CI [0.86, 1.06], P=0.41), meanwhile, a low dose (RR=0.89, 95% CI [0.82, 0.97], P=0.007) of dexamethasone (RR=0.9, 95% CI [0.83, 0.98], P=0.01) with a long treatment course (RR=0.89, 95% CI [0.82, 0.98], P=0.02) was beneficial for all-cause mortality in COVID-19 patients. Additionally, we found that corticosteroids might be associated with a longer length of hospital stay in non-severe COVID-19 patients (MD=3.83, 95% CI [1.11, 6.56], P=0.006). CONCLUSION: Our results showed that corticosteroid therapy was related to a reduction in all-cause mortality in severe COVID-19 patients. However, in patients with non-severe COVID-19, the use of corticosteroids did not decrease all-cause mortality and may prolong the duration of hospital stay. In addition, we revealed that a low dose of dexamethasone with a long treatment course could reduce all-cause mortality in COVID-19 patients.

Integrated Single Cell and Bulk RNA-Seq Analysis Revealed Immunomodulatory Effects of Ulinastatin in Sepsis: A Multicenter Cohort Study.

Sepsis is a leading cause of morbidity and mortality in the intensive care unit, which is caused by unregulated inflammatory response leading to organ injuries. Ulinastatin (UTI), an immunomodulatory agent, is widely used in clinical practice and is associated with improved outcomes in sepsis. But its underlying mechanisms are largely unknown. Our study integrated bulk and single cell RNA-seq data to systematically explore the potential mechanisms of the effects of UTI in sepsis. After adjusting for potential confounders in the negative binomial regression model, there were more genes being downregulated than being upregulated in the UTI group. These down-regulated genes were enriched in the neutrophil involved immunity such as neutrophil activation and degranulation, indicating the immunomodulatory effects of UTI is mediated via regulation of neutrophil activity. By deconvoluting the bulk RNA-seq samples to obtain fractions of cell types, the Myeloid-derived suppressor cells (MDSC) were significantly expanded in the UTI treated samples. Further cell-cell communication analysis revealed some signaling pathways such as ANEEXIN, GRN and RESISTIN that might be involved in the immunomodulatory effects of UTI. The study provides a comprehensive reference map of transcriptional states of sepsis treated with UTI, as well as a general framework for studying UTI-related mechanisms.

Structural mechanism of allosteric activation of TRPML1 by PI(3,5)P2 and rapamycin.

Transient receptor potential mucolipin 1 (TRPML1) is a Ca2+-permeable, nonselective cation channel ubiquitously expressed in the endolysosomes of mammalian cells and its loss-of-function mutations are the direct cause of type IV mucolipidosis (MLIV), an autosomal recessive lysosomal storage disease. TRPML1 is a ligand-gated channel that can be activated by phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2] as well as some synthetic small-molecule agonists. Recently, rapamycin has also been shown to directly bind and activate TRPML1. Interestingly, both PI(3,5)P2 and rapamycin have low efficacy in channel activation individually but together they work cooperatively and activate the channel with high potency. To reveal the structural basis underlying the synergistic activation of TRPML1 by PI(3,5)P2 and rapamycin, we determined the high-resolution cryoelectron microscopy (cryo-EM) structures of the mouse TRPML1 channel in various states, including apo closed, PI(3,5)P2-bound closed, and PI(3,5)P2/temsirolimus (a rapamycin analog)-bound open states. These structures, combined with electrophysiology, elucidate the molecular details of ligand binding and provide structural insight into how the TRPML1 channel integrates two distantly bound ligand stimuli and facilitates channel opening.

Structural mechanisms of assembly, permeation, gating, and pharmacology of native human rod CNG channel.

Mammalian cyclic nucleotide-gated (CNG) channels are nonselective cation channels activated by cGMP or cAMP and play essential roles in the signal transduction of the visual and olfactory sensory systems. CNGA1, the principal component of the CNG channel from rod photoreceptors, can by itself form a functional homotetrameric channel and has been used as the model system in the majority of rod CNG studies. However, the native rod CNG functions as a heterotetramer consisting of three A1 and one B1 subunits and exhibits different functional properties than the CNGA1 homomer. Here we present the functional analysis of human rod CNGA1/B1 heterotetramer and its cryo-EM structures in apo, cGMP-bound, cAMP-bound, and L-cis-Diltiazem-blocked states. These structures, with resolution ranging from 2.6 to 3.3 Å, elucidate the structural mechanisms underlying the 3:1 subunit stoichiometry, the asymmetrical gating upon cGMP activation, and the unique pharmacological property of the native rod CNG channel.

Voltage-gating and cytosolic Ca2+ activation mechanisms of Arabidopsis two-pore channel AtTPC1.

Arabidopsis thaliana two-pore channel AtTPC1 is a voltage-gated, Ca2+-modulated, nonselective cation channel that is localized in the vacuolar membrane and responsible for generating slow vacuolar (SV) current. Under depolarizing membrane potential, cytosolic Ca2+ activates AtTPC1 by binding at the EF-hand domain, whereas luminal Ca2+ inhibits the channel by stabilizing the voltage-sensing domain II (VSDII) in the resting state. Here, we present 2.8 to 3.3 Å cryoelectron microscopy (cryo-EM) structures of AtTPC1 in two conformations, one in closed conformation with unbound EF-hand domain and resting VSDII and the other in a partially open conformation with Ca2+-bound EF-hand domain and activated VSDII. Structural comparison between the two different conformations allows us to elucidate the structural mechanisms of voltage gating, cytosolic Ca2+ activation, and their coupling in AtTPC1. This study also provides structural insight into the general voltage-gating mechanism among voltage-gated ion channels.

TMEM120A is a coenzyme A-binding membrane protein with structural similarities to ELOVL fatty acid elongase.

TMEM120A, also named as TACAN, is a novel membrane protein highly conserved in vertebrates and was recently proposed to be a mechanosensitive channel involved in sensing mechanical pain. Here we present the single-particle cryogenic electron microscopy (cryo-EM) structure of human TMEM120A, which forms a tightly packed dimer with extensive interactions mediated by the N-terminal coiled coil domain (CCD), the C-terminal transmembrane domain (TMD), and the re-entrant loop between the two domains. The TMD of each TMEM120A subunit contains six transmembrane helices (TMs) and has no clear structural feature of a channel protein. Instead, the six TMs form an α-barrel with a deep pocket where a coenzyme A (CoA) molecule is bound. Intriguingly, some structural features of TMEM120A resemble those of elongase for very long-chain fatty acids (ELOVL) despite the low sequence homology between them, pointing to the possibility that TMEM120A may function as an enzyme for fatty acid metabolism, rather than a mechanosensitive channel.

Structural mechanisms of gating and selectivity of human rod CNGA1 channel.

Mammalian cyclic nucleotide-gated (CNG) channels play an essential role in the signal transduction of the visual and olfactory sensory systems. Here we reveal the structural mechanism of ligand gating in human rod CNGA1 channel by determining its cryo-EM structures in both the apo closed and cGMP-bound open states. Distinct from most other members of voltage-gated tetrameric cation channels, CNGA1 forms a central channel gate in the middle of the membrane, occluding the central cavity. Structural analyses of ion binding profiles in the selectivity filters of the wild-type channel and the E365Q filter mutant allow us to unambiguously define the two Ca2+ binding sites inside the selectivity filter, providing structural insights into Ca2+ blockage and permeation in CNG channels. The structure of the E365Q mutant also reveals two alternative side-chain conformations at Q365, providing a plausible explanation for the voltage-dependent gating of CNG channel acquired upon E365 mutation.

Increase of donor derived tumor occurrence by transfer of ex vivo expanded antigen specific regulatory T cells.

OBJECTIVES: Using regulatory T cells (Tregs) as a cellular therapy to control rejection is an attractive immunosuppressive strategy in transplantation, but immunosuppression mediated by Tregs need to be investigated before application. METHODS: In our experiment, mature Dendritic Cells (DCs) were generated through inducing bone marrow cells of C57BL/6 (H-2b) mice. CD4+CD25+Tregs were sorted by magnetic activated cell sorting (MACS) from BALB/C (H-2d) mice, and Tregs were expanded ex vivo with anti-CD3/CD28 microbeads and high concentration of recombinant murine (rm) IL-2 for 14 days, after that, expanded polyclonal Tregs were collected and cocultured with mature DCs (H-2b) in the presence of lower concentration of rmIL-2 for 7 days to get antigen-specific Tregs. Subsequently, BALB/C mice were randomly divided into three groups: BALB/c mice were inoculated with 5 × 105 B16-F10 (H-2b) cells via tail vein, the other were inoculated with 1 × 107 BALB/c expanded polyclonal Tregs and 5 × 105 B16-F10, the last with 1 × 107 antigen-specific BALB/c Tregs and 5 × 105 B16-F10 cells. After 14 days, mice were sacrificed and the black tumor nodules in lungs were counted. RESULTS: Adoptive transfer of ex vivo expanded polyclonal Tregs rendered BALB/c mice (recipient) susceptible to MHC-mismatched tumor (B16-F10 cells, H-2b). If ex vivo expanded polyclonal Tregs from BALB/c were cocultured with mature DCs from C57BL/6 after expansion, suppression of tumor immunity against B16-F10 cells was further. CONCLUSION: We suggested that ex vivo expanded antigen-specific Tregs could more dampen recipient tumor immunity compare with polyclonal Tregs, and the increased risk of donor derived tumor should be considered.

[Electroacupuncture protects septic rats from acute lung injury through the JAK1/STAT3 pathway].

OBJECTIVE: To explore the protective effect of electroacupuncture against acute lung injury (ALI) in septic rats and explore the mechanism. METHODS: Sixty male SD rats were randomly divided into cecal ligation and puncture (CLP)-induced sepsis group (n=45) and sham operation group (n=15; with laparotomy but without CLP). The rat models of sepsis were randomized into ALI group (n=15) without further treatment, ALI + SEA group (n=15) treated with electroacupuncture at the point far from the Zusanli acupoint for 30 min, and ALI + EA group (n=15) with electroacupuncture at Zusanli with identical frequency, intensity and duration of electrical stimulation. All the rats were sacrificed at 12 h after CLP for measurement of the weight and the wet/dry weight (W/D) ratio of the lungs. Pathological changes of the lung tissues were examined using HE staining, and the contents of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the homogenate of the lung tissues were detected using enzyme-linked immunosorbent assay (ELISA). TUNEL staining was used to detect the apoptotic cells, and the expressions of Bax, caspase-3 and the important proteins in the JAK1/STAT3 signaling pathway (JAK1 and STAT3) were detected with Western blotting. RESULTS: Compared with those in the sham operation group, the rats in ALI group showed obvious lung pathologies with significantly increased lung W/D ratio (P < 0.01), pulmonary expressions of TNF-α and IL-6 (P < 0.01), and obvious up-regulation of JAK1, STAT3, caspase-3, and Bax expressions (P < 0.01); similar changes were also observed in ALI+SEA group (P > 0.05). Compared with those in ALI+SEA group, the rats in ALI+EA group showed significantly milder lung pathologies, lowered lung W/D ratio (P < 0.01) and decreased pulmonary expressions of TNF-α, IL-6, JAK1, STAT3, caspase-3 and Bax (P < 0.01). CONCLUSIONS: Electroacupuncture can inhibit the release of inflammatory mediators and cell apoptosis via the JAK1/STAT3 pathway to reduce lung injuries in septic rats.

Cryo-EM structures of human ZnT8 in both outward- and inward-facing conformations.

ZnT8 is a Zn2+/H+ antiporter that belongs to SLC30 family and plays an essential role in regulating Zn2+ accumulation in the insulin secretory granules of pancreatic ß cells. However, the Zn2+/H+ exchange mechanism of ZnT8 remains unclear due to the lack of high-resolution structures. Here, we report the cryo-EM structures of human ZnT8 (HsZnT8) in both outward- and inward-facing conformations. HsZnT8 forms a dimeric structure with four Zn2+ binding sites within each subunit: a highly conserved primary site in transmembrane domain (TMD) housing the Zn2+ substrate; an interfacial site between TMD and C-terminal domain (CTD) that modulates the Zn2+ transport activity of HsZnT8; and two adjacent sites buried in the cytosolic domain and chelated by conserved residues from CTD and the His-Cys-His (HCH) motif from the N-terminal segment of the neighboring subunit. A comparison of the outward- and inward-facing structures reveals that the TMD of each HsZnT8 subunit undergoes a large structural rearrangement, allowing for alternating access to the primary Zn2+ site during the transport cycle. Collectively, our studies provide the structural insights into the Zn2+/H+ exchange mechanism of HsZnT8.

Ectopic expression of a rice plasma membrane intrinsic protein (OsPIP1;3) promotes plant growth and water uptake.

Plasma membrane intrinsic proteins (PIPs) are known to be major facilitators of the movement of a number of substrates across cell membranes. From a drought-resistant cultivar of Oryza sativa (rice), we isolated an OsPIP1;3 gene single-nucleotide polymorphism (SNP) that is mostly expressed in rice roots and is strongly responsive to drought stress. Immunocytochemistry showed that OsPIP1;3 majorly accumulated on the proximal end of the endodermis and the cell surface around the xylem. Expression of GFP-OsPIP1;3 alone in Xenopus oocytes or rice protoplasts showed OsPIP1;3 mislocalization in the endoplasmic reticulum (ER)-like neighborhood, whereas co-expression of OsPIP2;2 recruited OsPIP1;3 to the plasma membrane and led to a significant enhancement of water permeability in oocytes. Moreover, reconstitution of 10×His-OsPIP1;3 in liposomes demonstrated water channel activity, as revealed by stopped-flow light scattering. Intriguingly, by patch-clamp technique, we detected significant NO3- conductance of OsPIP1;3 in mammalian cells. To investigate the physiological functions of OsPIP1;3, we ectopically expressed the OsPIP1;3 gene in Nicotiana benthamiana (tobacco). The transgenic tobacco plants exhibited higher photosynthesis rates, root hydraulic conductivity (Lpr ) and water-use efficiency, resulting in a greater biomass and a higher resistance to water deficit than the wild-type did. Further experiments suggested that heterologous expression of OsPIP1;3 in cyanobacterium altered bacterial growth under different conditions of CO2 gas supply. Overall, besides shedding light on the multiple functions played by OsPIP1;3, this work provides insights into the translational value of plant AQPs.

Livelihood capitals on income inequality among rural households: evidence from China / Efeito das capitais de subsistência na desigualdade de renda entre as famílias rurais: evidências da China

ABSTRACT: We used the data of the China Labor-force Dynamics Survey 2014 to examine the effects of livelihood capitals which include natural, material, human, financial, and social capitals on total household income, per capita income, agricultural income, wage income, operational income, and property income inequality among rural households in China. Results showed that different kinds of livelihood capitals have different effects on different types of rural households' income. Specifically; (1) although, the area of cultivated land reduces agricultural income inequality, it increases per capita income inequality. (2) Forest land area enlarges per capita income inequality and total household income inequality. (3) Tractor variable reduces inequality in agricultural income and total household income. (4) While reducing the property income inequality, education variable enlarges the wage income inequality, the per capita income inequality and the total household income inequality. (5) Book variable reduces property income inequality. (6) Loan variable increases inequality in agricultural incomes. (7) Party variable reduces the agricultural income inequality. (8) Although, the internet variable increases agricultural income inequality, and property income inequality, it reduces wage income inequality, operational income inequality, per capita income, and total household income inequality.

RESUMO: Utilizamos os dados da Pesquisa de Dinâmica da Força de Trabalho da China de 2014 para examinar os efeitos dos capitais de subsistência, que incluem capitais natural, material, humano, financeiro e social sobre a renda total da família, renda per capita, renda agrícola, renda salarial, renda operacional e desigualdade de renda da propriedade entre as famílias rurais da China. Os resultados mostraram que diferentes tipos de capitais de subsistência têm efeitos diferentes sobre os diferentes tipos de renda das famílias rurais. Especificamente, (1) embora a área de terra cultivada reduza a desigualdade de renda agrícola, aumenta a desigualdade de renda per capita. (2) A área florestal aumenta a desigualdade de renda per capita e a desigualdade total de renda familiar. (3) A variável trator reduz a desigualdade na renda agrícola e na renda familiar total. (4) Embora reduza a desigualdade de renda da propriedade, a variável educação aumenta a desigualdade de renda salarial, a desigualdade de renda per capita e a desigualdade total de renda familiar. (5) A variável contábil reduz a desigualdade de renda da propriedade. (6) A variável empréstimo aumenta a desigualdade na renda agrícola. (7) A variável partidária reduz a desigualdade de renda agrícola. (8) Embora a variável internet aumente a desigualdade de renda agrícola e a desigualdade de renda da propriedade, reduz a desigualdade de renda salarial, a desigualdade de renda operacional, a renda per capita e a desigualdade total de renda familiar.

Publisher Correction: Ca2+-regulated Ca2+ channels with an RCK gating ring control plant symbiotic associations.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Ca2+-regulated Ca2+ channels with an RCK gating ring control plant symbiotic associations.

A family of plant nuclear ion channels, including DMI1 (Does not Make Infections 1) and its homologs CASTOR and POLLUX, are required for the establishment of legume-microbe symbioses by generating nuclear and perinuclear Ca2+ spiking. Here we show that CASTOR from Lotus japonicus is a highly selective Ca2+ channel whose activation requires cytosolic/nucleosolic Ca2+, contrary to the previous suggestion of it being a K+ channel. Structurally, the cytosolic/nucleosolic ligand-binding soluble region of CASTOR contains two tandem RCK (Regulator of Conductance for K+) domains, and four subunits assemble into the gating ring architecture, similar to that of large conductance, Ca2+-gated K+ (BK) channels despite the lack of sequence similarity. Multiple ion binding sites are clustered at two locations within each subunit, and three of them are identified to be Ca2+ sites. Our in vitro and in vivo assays also demonstrate the importance of these gating-ring Ca2+ binding sites to the physiological function of CASTOR as well as DMI1.

Structural Mechanism of EMRE-Dependent Gating of the Human Mitochondrial Calcium Uniporter.

Mitochondrial calcium uptake is crucial to the regulation of eukaryotic Ca2+ homeostasis and is mediated by the mitochondrial calcium uniporter (MCU). While MCU alone can transport Ca2+ in primitive eukaryotes, metazoans require an essential single membrane-spanning auxiliary component called EMRE to form functional channels; however, the molecular mechanism of EMRE regulation remains elusive. Here, we present the cryo-EM structure of the human MCU-EMRE complex, which defines the interactions between MCU and EMRE as well as pinpoints the juxtamembrane loop of MCU and extended linker of EMRE as the crucial elements in the EMRE-dependent gating mechanism among metazoan MCUs. The structure also features the dimerization of two MCU-EMRE complexes along an interface at the N-terminal domain (NTD) of human MCU that is a hotspot for post-translational modifications. Thus, the human MCU-EMRE complex, which constitutes the minimal channel components among metazoans, provides a framework for future mechanistic studies on MCU.

Structural and functional characterization of an otopetrin family proton channel.

The otopetrin (OTOP) proteins were recently characterized as proton channels. Here we present the cryo-EM structure of OTOP3 from Xenopus tropicalis (XtOTOP3) along with functional characterization of the channel. XtOTOP3 forms a homodimer with each subunit containing 12 transmembrane helices that can be divided into two structurally homologous halves; each half assembles as an α-helical barrel that could potentially serve as a proton conduction pore. Both pores open from the extracellular half before becoming occluded at a central constriction point consisting of three highly conserved residues - Gln232/585-Asp262/Asn623-Tyr322/666 (the constriction triads). Mutagenesis shows that the constriction triad from the second pore is less amenable to perturbation than that of the first pore, suggesting an unequal contribution between the two pores to proton transport. We also identified several key residues at the interface between the two pores that are functionally important, particularly Asp509, which confers intracellular pH-dependent desensitization to OTOP channels.

Structural mechanisms of phospholipid activation of the human TPC2 channel.

Mammalian two-pore channels (TPCs) regulate the physiological functions of the endolysosome. Here we present cryo-EM structures of human TPC2 (HsTPC2), a phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2)-activated, Na+ selective channel, in the ligand-bound and apo states. The apo structure captures the closed conformation, while the ligand-bound form features the channel in both open and closed conformations. Combined with functional analysis, these structures provide insights into the mechanism of PI(3,5)P2-regulated gating of TPC2, which is distinct from that of TPC1. Specifically, the endolysosome-specific PI(3,5)P2 binds at the first 6-TM and activates the channel - independently of the membrane potential - by inducing a structural change at the pore-lining inner helix (IS6), which forms a continuous helix in the open state but breaks into two segments at Gly317 in the closed state. Additionally, structural comparison to the voltage-dependent TPC1 structure allowed us to identify Ile551 as being responsible for the loss of voltage dependence in TPC2.