Placing steroid hormones within the human ABCC3 transporter reveals a compatible amphiphilic substrate-binding pocket.

The human ABC transporter ABCC3 (also known as MRP3) transports a wide spectrum of substrates, including endogenous metabolites and exogenous drugs. Accordingly, it participates in multiple physiological processes and is involved in diverse human diseases such as intrahepatic cholestasis of pregnancy, which is caused by the intracellular accumulation of bile acids and estrogens. Here, we report three cryogenic electron microscopy structures of ABCC3: in the apo-form and in complexed forms bound to either the conjugated sex hormones ß-estradiol 17-(ß-D-glucuronide) and dehydroepiandrosterone sulfate. For both hormones, the steroid nuclei that superimpose against each other occupy the hydrophobic center of the transport cavity, whereas the two conjugation groups are separated and fixed by the hydrophilic patches in two transmembrane domains. Structural analysis combined with site-directed mutagenesis and ATPase activity assays revealed that ABCC3 possesses an amphiphilic substrate-binding pocket able to hold either conjugated hormone in an asymmetric pattern. These data build on consensus features of the substrate-binding pocket of MRPs and provide a structural platform for the rational design of inhibitors.

Allosteric regulation of nitrate transporter NRT via the signaling protein PII.

Coordinated carbon and nitrogen metabolism is crucial for bacteria living in the fluctuating environments. Intracellular carbon and nitrogen homeostasis is maintained by a sophisticated network, in which the widespread signaling protein PII acts as a major regulatory hub. In cyanobacteria, PII was proposed to regulate the nitrate uptake by an ABC (ATP-binding cassette)-type nitrate transporter NrtABCD, in which the nucleotide-binding domain of NrtC is fused with a C-terminal regulatory domain (CRD). Here, we solved three cryoelectron microscopy structures of NrtBCD, bound to nitrate, ATP, and PII, respectively. Structural and biochemical analyses enable us to identify the key residues that form a hydrophobic and a hydrophilic cavity along the substrate translocation channel. The core structure of PII, but not the canonical T-loop, binds to NrtC and stabilizes the CRD, making it visible in the complex structure, narrows the substrate translocation channel in NrtB, and ultimately locks NrtBCD at an inhibited inward-facing conformation. Based on these results and previous reports, we propose a putative transport cycle driven by NrtABCD, which is allosterically inhibited by PII in response to the cellular level of 2-oxoglutarate. Our findings provide a distinct regulatory mechanism of ABC transporter via asymmetrically binding to a signaling protein.

Structural insights into the activation of autoinhibited human lipid flippase ATP8B1 upon substrate binding.

SignificanceATP8B1 is a P4 ATPase that maintains membrane asymmetry by transporting phospholipids across the cell membrane. Disturbance of lipid asymmetry will lead to the imbalance of the cell membrane and eventually, cell death. Thus, defects in ATP8B1 are usually associated with severe human diseases, such as intrahepatic cholestasis. The present structures of ATP8B1 complexed with its auxiliary noncatalytic partners CDC50A and CDC50B reveal an autoinhibited state of ATP8B1 that could be released upon substrate binding. Moreover, release of this autoinhibition could be facilitated by the bile acids, which are key factors that alter the membrane asymmetry of hepatocytes. This enabled us to figure out a feedback loop of bile acids and lipids across the cell membrane.

Bilayer LDPC Codes Combined with Perturbed Decoding for MLC NAND Flash Memory.

This paper presents a coding scheme based on bilayer low-density parity-check (LDPC) codes for multi-level cell (MLC) NAND flash memory. The main feature of the proposed scheme is that it exploits the asymmetric properties of an MLC flash channel and stores the extra parity-check bits in the lower page, which are activated only after the decoding failure of the upper page. To further improve the performance of the error correction, a perturbation process based on the genetic algorithm (GA) is incorporated into the decoding process of the proposed coding scheme, which can convert uncorrectable read sequences into error-correctable regions of the corresponding decoding space by introducing GA-trained noises. The perturbation decoding process is particularly efficient at low program-and-erase (P/E) cycle regions. The simulation results suggest that the proposed bilayer LDPC coding scheme can extend the lifetime of MLC NAND flash memory up to 10,000 P/E cycles. The proposed scheme can achieve a better balance between performance and complexity than traditional single LDPC coding schemes. All of these findings indicate that the proposed coding scheme is suitable for practical purposes in MLC NAND flash memory.

An Ultralow-concentration and Moisture-resistant Electrolyte of Lithium Difluoro(oxalato)borate in Carbonate Solvents for Stable Cycling in Practical Lithium-ion Batteries.

The electrolyte concentration not only impacts the battery performance but also affects the battery cost and manufacturing. Currently, most studies focus on high-concentration (>3 M) or localized high-concentration electrolytes (~1 M); however, the expensive lithium salt imposes a major concern. Most recently, ultralow concentration electrolytes (<0.3 M) have emerged as intriguing alternatives for battery applications, which feature low cost, low viscosity, and extreme-temperature operation. However, at such an early development stage, many works are urgently needed to further understand the electrolyte properties. Herein, we introduce an ultralow concentration electrolyte of 2 wt % (0.16 M) lithium difluoro(oxalato)borate (LiDFOB) in standard carbonate solvents. This electrolyte exhibits a record-low salt/solvent mass ratio reported to date, thus pointing to a superior low cost. Furthermore, this electrolyte is highly compatible with commercial Li-ion materials, forming stable and inorganic-rich interphases on the lithium cobalt oxide (LiCoO2) cathode and graphite anode. Consequently, the LiCoO2-graphite full cell demonstrates excellent cycling performance. Besides, this electrolyte is moisture-resistant and effectively suppresses the generation of hydrogen fluoride, which will markedly facilitate the battery assembly and recycling process under ambient conditions.

Tandem Synergistic Effect of Cu-In Dual Sites Confined on the Edge of Monolayer CuInP2 S6 toward Selective Photoreduction of CO2 into Multi-Carbon Solar Fuels.

One-unit-cell, single-crystal, hexagonal CuInP2 S6 atomically thin sheets of≈0.81 nm in thickness was successfully synthesized for photocatalytic reduction of CO2 . Exciting ethene (C2 H4 ) as the main product was dominantly generated with the yield-based selectivity reaching ≈56.4 %, and the electron-based selectivity as high as ≈74.6 %. The tandem synergistic effect of charge-enriched Cu-In dual sites confined on the lateral edge of the CuInP2 S6 monolayer (ML) is mainly responsible for efficient conversion and high selectivity of the C2 H4 product as the basal surface site of the ML, exposing S atoms, can not derive the CO2 photoreduction due to the high energy barrier for the proton-coupled electron transfer of CO2 into *COOH. The marginal In site of the ML preeminently targets CO2 conversion to *CO under light illumination, and the *CO then migrates to the neighbor Cu sites for the subsequent C-C coupling reaction into C2 H4 with thermodynamic and kinetic feasibility. Moreover, ultrathin structure of the ML also allows to shorten the transfer distance of charge carriers from the interior onto the surface, thus inhibiting electron-hole recombination and enabling more electrons to survive and accumulate on the exposed active sites for CO2 reduction.

Efficient continuous wave and passively Q switched Er:GdScO3 laser using Fe:ZnSe at 2.8 µm.

We report on diode-pumped continuous wave and passively Q switched Er:GdScO3 crystal lasers at around 2.8 µm. A continuous wave output power of 579 mW was obtained with a slope efficiency of 16.6%. Using Fe:ZnSe as a saturable absorber, a passively Q switched laser operation was realized. A maximum output power of 32 mW was generated with the shortest pulse duration of 286 ns at a repetition rate of 157.3 kHz, leading to a pulse energy of 204 nJ and a pulse peak power of 0.7 W.

[Effects of repetitive transcranial magnetic stimulation on neuronal excitability and ion channels in hindlimb unloading mice].

Weightlessness in the space environment affects astronauts' learning memory and cognitive function. Repetitive transcranial magnetic stimulation has been shown to be effective in improving cognitive dysfunction. In this study, we investigated the effects of repetitive transcranial magnetic stimulation on neural excitability and ion channels in simulated weightlessness mice from a neurophysiological perspective. Young C57 mice were divided into control, hindlimb unloading and magnetic stimulation groups. The mice in the hindlimb unloading and magnetic stimulation groups were treated with hindlimb unloading for 14 days to establish a simulated weightlessness model, while the mice in the magnetic stimulation group were subjected to 14 days of repetitive transcranial magnetic stimulation. Using isolated brain slice patch clamp experiments, the relevant indexes of action potential and the kinetic property changes of voltage-gated sodium and potassium channels were detected to analyze the excitability of neurons and their ion channel mechanisms. The results showed that the behavioral cognitive ability and neuronal excitability of the mice decreased significantly with hindlimb unloading. Repetitive transcranial magnetic stimulation could significantly improve the cognitive impairment and neuroelectrophysiological indexes of the hindlimb unloading mice. Repetitive transcranial magnetic stimulation may change the activation, inactivation and reactivation process of sodium and potassium ion channels by promoting sodium ion outflow and inhibiting potassium ion, and affect the dynamic characteristics of ion channels, so as to enhance the excitability of single neurons and improve the cognitive damage and spatial memory ability of hindlimb unloading mice.

Plastic structures for diverse substrates: A revisit of human ABC transporters.

ATP-binding cassette (ABC) superfamily is one of the largest groups of primary active transporters that could be found in all kingdoms of life from bacteria to humans. In humans, ABC transporters can selectively transport a wide spectrum of substrates across membranes, thus playing a pivotal role in multiple physiological processes. In addition, due to the ability of exporting clinic therapeutics, some ABC transporters were originally termed multidrug resistance proteins. Increasing investigations of human ABC transporters in recent years have provided abundant information for elucidating their structural features, based on the structures at distinct states in a transport cycle. This review focuses on the recent progress in human ABC structural analyses, substrate binding specificities, and translocation mechanisms. We dedicate to summarize the common features of human ABC transporters in different subfamilies, and to discuss the possibility to apply the fast-developing techniques, such as cryogenic electron microscopy, and artificial intelligence-assisted structure prediction, for future studies.

Herbivore-induced tomato plant volatiles lead to the reduction of insecticides susceptibility in Spodoptera litura.

Herbivore-induced plant volatiles (HIPVs) have been associated with plant-plant-herbivorous-natural enemies communication and an enhanced response to the subsequent attack. Spodoptera litura is a serious cosmopolitan pest that has developed a high level of resistance to many insecticides. However, the underlying molecular and biochemical mechanism by which HIPV priming reduces S. litura larval sensitivity to insecticides remains largely unknown. This study was conducted to explore the potential of volatile from undamaged, or artificially damaged, or S. litura-damaged tomato plants on the susceptibility of S. litura to the insecticides beta-cypermethrin indoxacarb and chlorpyrifos. We found that larvae exposed to volatile from S. litura-damaged or artificially damaged tomato plants were significantly less susceptible to the three insecticides than those exposed to volatile from undamaged tomato plants. Elevated activities of detoxifying enzymes [cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and esterases (ESTs)], were expressed in S. litura larvae exposed to volatile from S. litura-damaged tomato plants than those exposed to volatile from undamaged tomato plants. Similarly, seven detoxification-related genes [GSTs (SlGSTe1, SlGSTo1, and SlGSTe3) and P450s (CYP6B48, CYP9A40, CYP321A7, and CYP321B1)] in the midgut and fat body of larvae were up-regulated under exposure to volatile from S. litura-damaged tomato plants. Increased volatile organic compounds emissions were detected in the headspace of tomato plants damaged by S. litura compared to the undamaged plants. Collectively, these findings suggest that HIPVs can considerably reduce caterpillar susceptibility to insecticides, possibly through induction-enhanced detoxification mechanisms, and provide valuable information for implementing an effective integrated pest management strategy.

[Effects of transcranial magneto-acoustic electrical stimulation on calcium signals in prefrontal nerve clusters].

Transcranial magneto-acoustic electrical stimulation (TMAES) is a novel method of brain nerve regulation and research, which uses induction current generated by the coupling of ultrasound and magnetic field to regulate neural electrical activity in different brain regions. As the second special envoy of nerve signal, calcium plays a key role in nerve signal transmission. In order to investigate the effect of TMAES on prefrontal cortex electrical activity, 15 mice were divided into control group, ultrasound stimulation (TUS) group and TMAES group. The TMAES group received 2.6 W/cm 2 and 0.3 T of magnetic induction intensity, the TUS group received only ultrasound stimulation, and the control group received no ultrasound and magnetic field for one week. The calcium ion concentration in the prefrontal cortex of mice was recorded in real time by optical fiber photometric detection technology. The new object recognition experiment was conducted to compare the behavioral differences and the time-frequency distribution of calcium signal in each group. The results showed that the mean value of calcium transient signal in the TMAES group was (4.84 ± 0.11)% within 10 s after the stimulation, which was higher than that in the TUS group (4.40 ± 0.10)% and the control group (4.22 ± 0.08)%, and the waveform of calcium transient signal was slower, suggesting that calcium metabolism was faster. The main energy band of the TMAES group was 0-20 Hz, that of the TUS group was 0-12 Hz and that of the control group was 0-8 Hz. The cognitive index was 0.71 in the TMAES group, 0.63 in the TUS group, and 0.58 in the control group, indicating that both ultrasonic and magneto-acoustic stimulation could improve the cognitive ability of mice, but the effect of the TMAES group was better than that of the TUS group. These results suggest that TMAES can change the calcium homeostasis of prefrontal cortex nerve clusters, regulate the discharge activity of prefrontal nerve clusters, and promote cognitive function. The results of this study provide data support and reference for further exploration of the deep neural mechanism of TMAES.

Functional analysis of CYP6AE68, a cytochrome P450 gene associated with indoxacarb resistance in Spodoptera litura (Lepidoptera: Noctuidae).

Spodoptera litura (Fabricius) is a widely distributed, highly polyphagous pest that can cause severe damage to a variety of economically important crops. Various populations have developed resistance to different classes of insecticides. In this study, we report on two indoxacarb-resistant S. litura populations, namely Ind-R (resistance ratio = 18.37-fold) derived from an indoxacarb-susceptible (Ind-S) population and a population caught from a field (resistance ratio = 46.72-fold). A synergist experiment showed that piperonyl butoxide (PBO) combined with indoxacarb produced higher synergistic effects (synergist ratio = 5.29) in the Ind-R population as compared to Ind-S (synergist ratio = 3.08). Elevated enzyme activity of cytochrome P450 monooxygenases (P450s) was observed for Ind-R (2.15-fold) and the Field-caught population (4.03-fold) as compared to Ind-S, while only minor differences were noticed in the activities of esterases and glutathione S-transferases. Furthermore, expression levels of P450 genes of S. litura were determined by quantitative reverse transcription PCR to explore differences among the three populations. The results showed that the mRNA levels of CYP6AE68, a novel P450 gene belonging to the CYP6 family, were constitutively overexpressed in Ind-R (32.79-fold) and in the Field-caught population (68.11-fold). CYP6AE68 expression in S. litura was further analyzed for different developmental stages and in different tissues. Finally, we report that RNA interference-mediated silencing of CYP6AE68 increased the mortality of fourth-instar larvae exposed to indoxacarb at the LC50 dose level (increase by 33.89%, 29.44% and 22.78% for Ind-S, Ind-R and the Field-caught population, respectively). In conclusion, the findings of this study indicate that expression levels of CYP6AE68 in S. litura larvae are associated with indoxacarb resistance and that CYP6AE68 may play a significant role in detoxification of indoxacarb.

Structural and functional insights into the Asp1/2/3 complex mediated secretion of pneumococcal serine-rich repeat protein PsrP.

The accessory sec system consisting of seven conserved components is commonly distributed among pathogenic Gram-positive bacteria for the secretion of serine-rich-repeat proteins (SRRPs). Asp1/2/3 protein complex in the system is responsible for both the O-acetylation of GlcNAc and delivering SRRPs to SecA2. However, the molecular mechanism of how Asp1/2/3 transport SRRPs remains unknown. Here, we report the complex structure of Asp1/2/3 from Streptococcus pneumoniae at 2.9 Å. Further functional assays indicated that Asp1/2/3 can stimulate the ATPase activity of SecA2. In addition, the deletion of asp1/2/3 gene resulted in the accumulation of a secreted version of PsrP with an altered glycoform in protoplast fraction of the mutant cell, which suggested the modification/transport coupling of the substrate. Altogether, these findings not only provide structural basis for further investigations on the transport process of SRRPs, but also uncover the indispensable role of Asp1/2/3 in the accessory sec system.

Erratum: Three-Dimensional Dynamics of a Magnetic Hopfion Driven by Spin Transfer Torque [Phys. Rev. Lett. 124, 127204 (2020)].

This corrects the article DOI: 10.1103/PhysRevLett.124.127204.

Three-Dimensional Dynamics of a Magnetic Hopfion Driven by Spin Transfer Torque.

Magnetic hopfion is a three-dimensional (3D) topological soliton with novel spin structure that would enable exotic dynamics. Here, we study the current-driven 3D dynamics of a magnetic hopfion with a unit Hopf index in a frustrated magnet. Attributed to the spin Berry phase and symmetry of the hopfion, the phase space entangles multiple collective coordinates, thus the hopfion exhibits rich dynamics including longitudinal motion along the current direction, transverse motion perpendicular to the current direction, rotational motion, and dilation. Furthermore, the characteristics of hopfion dynamics is determined by the ratio between the nonadiabatic spin transfer torque parameter and the damping parameter. Such peculiar 3D dynamics of magnetic hopfion could shed light on understanding the universal physics of hopfions in different systems and boost the prosperous development of 3D spintronics.

A Unified Capacitive-Coupled Memristive Model for the Nonpinched Current-Voltage Hysteresis Loop.

The concept of the memristor, a resistor with memory, was proposed by Chua in 1971 as the fourth basic element of electric circuitry. Despite a significant amount of effort devoted to the understanding of memristor theory, our understanding of the nonpinched current-voltage (I-V) hysteresis loop in memristors remains incomplete. Here we propose a physical model of a memristor, with a capacitor connected in parallel, which explains how the nonpinched I-V hysteresis behavior originates from the capacitive-coupled memristive effect. Our model replicates eight types of characteristic nonlinear I-V behavior, which explains all observed nonpinched I-V curves seen in experiments. Furthermore, a reversible transition from a nonpinched I-V hysteresis loop to an ideal pinched I-V hysteresis loop is found, which explains the experimental data obtained in C15H11O6-based devices when subjected to an external stimulus (e.g., voltage, moisture, or temperature). Our results provide the vital physics models and materials insights for elucidating the origins of nonpinched I-V hysteresis loops ascribed to capacitive-coupled memristive behavior.

Structural insights into the catalysis and substrate specificity of cyanobacterial aspartate racemase McyF.

L-amino acids represent the most common amino acid form, most notably as protein residues, whereas D-amino acids, despite their rare occurrence, play significant roles in many biological processes. Amino acid racemases are enzymes that catalyze the interconversion of L- and/or D-amino acids. McyF is a pyridoxal 5'-phosphate (PLP) independent amino acid racemase that produces the substrate D-aspartate for the biosynthesis of microcystin in the cyanobacterium Microcystis aeruginosa PCC7806. Here we report the crystal structures of McyF in complex with citrate, L-Asp and D-Asp at 2.35, 2.63 and 2.80 Å, respectively. Structural analyses indicate that McyF and homologs possess highly conserved residues involved in substrate binding and catalysis. In addition, residues Cys87 and Cys195 were clearly assigned to the key catalytic residues of "two bases" that deprotonate D-Asp and L-Asp in a reaction independent of PLP. Further site-directed mutagenesis combined with enzymatic assays revealed that Glu197 also participates in the catalytic reaction. In addition, activity assays proved that McyF could also catalyze the interconversion of L-MeAsp between D-MeAsp, the precursor of another microcystin isoform. These findings provide structural insights into the catalytic mechanism of aspartate racemase and microcystin biosynthesis.

A Comparison of 1- and 3.2-MHz Low-Intensity Pulsed Ultrasound on Osteogenesis on Porous Titanium Alloy Scaffolds: An In Vitro and In Vivo Study.

OBJECTIVES: Low-intensity pulsed ultrasound (LIPUS) combined with porous scaffolds can be used as a new therapy to treat bone defect repair. The aim of this study was to evaluate the effects of 1 and 3.2 MHz LIPUS on osteogenesis on porous Ti64 alloy scaffolds for both in vitro and in vivo studies. METHODS: Scaffolds were randomly divided into the high-frequency ultrasound group, low-frequency ultrasound group, and control group. Mouse pre-osteoblast cells were cultured with porous Ti-6Al-4V scaffolds in vitro to evaluate cell proliferation and differentiation. In addition, scaffolds were implanted into rabbit mandibular defects in vivo. The effects of LIPUS on bone regeneration were evaluated by observing the micro-computed tomography (micro-CT), toluidine blue staining, and von Kossa staining. RESULTS: The results revealed no significant difference in the cell counting kit-8 values between the ultrasound groups and control groups (P > .05). Compared with the control group, ultrasound promoted alkaline phosphatase activity and osteocalcin levels of the cells on the scaffolds (P < .05), but there was no significant difference between the two frequencies. In addition, histomorphologic analyses revealed that the volume and amount of new bone formation increased and that bone maturity improved in the ultrasound groups compared with the control group, but no significant difference was noted between the two frequencies. CONCLUSIONS: Under the present experimental conditions, LIPUS promoted osteoblast differentiation and promoted bone maturity on porous Ti64 scaffolds. No significant differences were noted between the two frequencies.

A Consecutive C-H Functionalization Triggered by Oxidation of Active sp3 C-H Bonds: Construction of 3,4-Dihydroquinoline-3-one Derivatives.

We report a consecutive C-H functionalization that constructs 3,4-dihydroquinoline-3-one derivatives in high yields. This reaction is triggered by oxidation of active sp3 C-H bonds of glycines and N-benzylanilines. In this radical mediated transformation, four sp3 C-H bonds are functionalized efficiently, together with construction of one heterocyclic ring with a quaternary carbon center.

Biomechanical design optimization and experimental verification of Bezier curve based two-sectional cervical pillow with variable-density cellular structure.

The fundamental function of an optimal cervical pillow is to provide sufficient support to maintain normal spinal alignment and minimize biological stress on the contact surface throughout sleep. The recent advancements in cervical pillows have mainly focused on the subjective and objective evaluations of support comfort, as well as the relationship between pillow height and cervical vertebrae posture. However, only a few studies have addressed shape design guidelines and mechanical performances of the pillows themselves. In this study, a two-sectional contour cervical pillow comprising an arc and a Bezier curve is designed to support the head and neck. The design of the arc-shaped neck section incorporates the Cobb's angle and Borden value from healthy individuals to reflect the consistency of normal cervical anatomical features. The Bezier curve-based head section takes the head length and neck depth into account as significant individual differences. Static analysis and lattice optimization are performed in ANSYS Workbench to develop a variable-density cellular structure, aimed at improving air permeability and reducing the risk of pressure ulcers associated with the cervical pillow. The rapid prototyping technique fused deposition modeling (FDM) and thermoplastic material polylactic acid (PLA) are employed for fabricating different cellular structures. The results demonstrate that the neck section experiences less stress and greater deformation in comparison to the head section, indicating good comfort and support provided by the designed cervical pillow. Additionally, the compressive, bending, and cushion properties of the 3D-printed cervical pillow with variable-density cellular structure are experimentally validated, further confirming its effectiveness.