Structural basis of Rho-dependent transcription termination.

Rho is a ring-shaped hexameric ATP-dependent molecular motor. Together with the transcription elongation factor NusG, Rho mediates factor-dependent transcription termination and transcription-translation-coupling quality control in Escherichia coli1-4. Here we report the preparation of complexes that are functional in factor-dependent transcription termination from Rho, NusG, RNA polymerase (RNAP), and synthetic nucleic acid scaffolds, and we report cryogenic electron microscopy structures of the complexes. The structures show that functional factor-dependent pre-termination complexes contain a closed-ring Rho hexamer; have RNA threaded through the central channel of Rho; have 60 nucleotides of RNA interacting sequence-specifically with the exterior of Rho and 6 nucleotides of RNA interacting sequence-specifically with the central channel of Rho; have Rho oriented relative to RNAP such that ATP-dependent translocation by Rho exerts mechanical force on RNAP; and have NusG bridging Rho and RNAP. The results explain five decades of research on Rho and provide a foundation for understanding Rho's function.

Visualized Tracking and Multidimensional Assessing of Mitochondria-Associated Pyroptosis in Cancer Cells by a Small-Molecule Fluorescent Probe.

Pyroptosis is closely related to the development and treatment of various cancers; thus, comprehensive studies of the correlations between pyroptosis and its inductive or inhibitive factors can provide new ideas for the intervention and diagnosis of tumors. The dysfunction of mitochondria may induce pyroptosis in cancer cells, which can be reflected by the fluctuations of the microenvironmental parameters in mitochondria as well as the changes of mitochondrial DNA level and morphology, etc. To precisely track and assess the mitochondria-associated pyroptosis process, simultaneous visualization of changes in multiphysiological parameters in mitochondria is highly desirable. In this work, we reported a nonreaction-based, multifunctional small-molecule fluorescent probe Mito-DK with the capability of crosstalk-free response to polarity and mtDNA as well as mitochondrial morphology. Accurate assessment of mitochondria-associated pyroptosis induced by palmitic acid/H2O2 was achieved through monitoring changes in mitochondrial multiple parameters with the help of Mito-DK. In particular, the pyroptosis-inducing ability of an antibiotic doxorubicin and the pyroptosis-inhibiting capacity of an anticancer agent puerarin were evaluated by Mito-DK. These results provide new perspectives for visualizing mitochondria-associated pyroptosis and offer new approaches for screening pyroptosis-related anticancer agents.

Post-annealing effect of low temperature atomic layer deposited Al2O3on the top gate IGZO TFT.

Electronical properties of top gate amorphous InGaZnO4thin film transistors (TFTs) could be controlled by post-annealing treatment, which has a great impact on the Al2O3insulator. To investigate the effect of post-annealing on Al2O3, Al/Al2O3/p-Si MOS capacitoras with Al2O3films treated under various post-deposition annealing (PDA) temperature were employed to analysis the change of electrical properties, surface morphology, and chemical components by electrical voltage scanning, atomic force microscope (AFM), and x-ray photoelectron spectroscopy (XPS) technologies. After PDA treatment, the top gate TFTs had a mobility about 7 cm2V-1s-1and the minimum subthreshold swing (SS) about 0.11 V/dec, and the threshold voltage (Vth) shifted from positive direction to negative direction as the post-annealing temperature increased. Electrical properties of MOS capacitors revealed the existence of positive fixed charges and the variation of trap state density with increasing PDA temperature, and further explained the change of negative bias stress (NBS) stability in TFT. AFM results clarified the increased leakage current, degraded SS, and NBS stability in MOS capacitors and TFTs, respectively. XPS results not only illuminated the origin of fixed charges and the trap density variation with PDA temperatures of Al2O3films, but also showed the O and H diffusion from Al2O3into IGZO during post-annealing process, which led to the deviation ofVth, the change of current density, and the negativeVthshift after positive bias stress in TFTs.

Structural and functional characterization of a mycobacterial methylenetetrahydrofolate reductase utilizing NADH as the exclusive cofactor.

5,10-Methylenetetraydrofolate reductase (MTHFR) is a key enzyme in folate metabolism. MSMEG_6649, a non-canonical MTHFR from Mycobacterium smegmatis, was previously reported as a monomeric protein lacking the flavin coenzyme. However, the structural basis for its unique flavin-independent catalytic mechanism remains poorly understood. Here, we determined the crystal structures of apo MTHFR MSMEG_6649 and its complex with NADH from M. smegmatis. Structural analysis revealed that the groove formed by the loops 4 and 5 of non-canonical MSMEG_6649 interacting with FAD was significantly larger than that of canonical MTHFR. Meanwhile, the NADH-binding site in MSMEG_6649 is highly similar to the FAD binding site in canonical MTHFR, suggesting that NADH plays the same role (immediate hydride donor for methylenetetraydrofolate) as FAD in the catalytic reaction. Using biochemical analysis, molecular modeling, and site-directed mutagenesis, the critical residues participating in the binding of NADH and the substrate 5,10-methylenetetrahydrofolate as well as the product 5-methyltetrahydrofolate were identified and validated. Taken together, this work not only provides a good starting point for understanding the potential catalytic mechanism for MSMEG_6649, but also identifies an exploitable target for the development of anti-mycobacterial drugs.

Conjugating Coumarin with Tetraphenylethylene to Achieve Dual-State Emission for Reversible Mechanofluorochromism and Live Cell Imaging.

Dual-state emission luminogens (DSEgens) are receiving research interest in the construction of multifunctional materials due to their inherent advantage of high emission efficiency in both the molecularly dispersed solution state and the solid state. However, it remains challenging in synthesizing DSEgens via a delicate manipulation of the molecular structures. This work presents an example of bright DSEgen synthesis by tuning the molecular electronic structures and conformations. Three coumarin-tetraphenylethylene (TPE) molecules with a donor-acceptor electronic structure and highly twisting conformations have been synthesized. While compound resulting from direct conjugation of coumarin with a TPE unit shows aggregation-induced emission, compound with an N,N-diaminoethyl modification on the 7-position of coumarin and compound with a further phenyl linker between coumarin and TPE units feature strong dual-state emission. Benefiting from their strong solid emission and twisting conformations, these fluorophores display reversible mechanofluorochromism. Finally, applications for rewritable information storage in the solid state and live-cell imaging in the solution state were demonstrated.

Chlorphoxim induces neurotoxicity in zebrafish embryo through activation of oxidative stress.

It is known that chlorphoxim is a broad-spectrum and high-effective pesticide. With the wide use in agricultural practice, chlorphoxim residue is also frequently detected in water, but its potential toxicity to aquatic life is still unclear. In this study, zebrafish is used as a model to detect the toxicity of chlorphoxim. Our results showed that exposure of high concentration of chlorphoxim at 96 h post-fertilization (hpf) resulted in a high mortality and pericardium edema rate, a low hatchability rate and heart rate. The nervous system damage, swimming behavior alteration and acetylcholinesterase (AChE) inhibition were measured in zebrafish embryos after a 6 days post-fertilization (dpf) of chlorphoxim exposure. The expression of neural-related genes is abnormal in zebrafish embryos. Chlorphoxim exposure significantly increases oxidative stress in zebrafish embryos by inhibiting antioxidant enzyme (SOD and CAT) and activating reactive oxygen species (ROS). As expected, chlorphoxim exposure induces apoptosis by enhancing the expression of apoptotic genes (Bax, Bcl2, and p53). Astaxanthin (ATX), an effective antioxidant, was found to be able to rescue the neurotoxicity of chlorphoxim through relieving oxidative stress and apoptosis. Altogether, the results showed that chlorphoxim exposure led to severe neurotoxicity to zebrafish embryos, which was contributed to a more comprehensive understanding of the safety use of the organophosphorus pesticide.

Heteromerization of short-chain trans-prenyltransferase controls precursor allocation within a plastidial terpenoid network.

Terpenes are the largest and most diverse class of plant specialized metabolites. Sesterterpenes (C25), which are derived from the plastid methylerythritol phosphate pathway, were recently characterized in plants. In Arabidopsis thaliana, four genes encoding geranylfarnesyl diphosphate synthase (GFPPS) (AtGFPPS1 to 4) are responsible for the production of GFPP, which is the common precursor for sesterterpene biosynthesis. However, the interplay between sesterterpenes and other known terpenes remain elusive. Here, we first provide genetic evidence to demonstrate that GFPPSs are responsible for sesterterpene production in Arabidopsis. Blockage of the sesterterpene pathway at the GFPPS step increased the production of geranylgeranyl diphosphate (GGPP)-derived terpenes. Interestingly, co-expression of sesterTPSs in GFPPS-OE (overexpression) plants rescued the phenotypic changes of GFPPS-OE plants by restoring the endogenous GGPP. We further demonstrated that, in addition to precursor (DMAPP/IPP) competition by GFPPS and GGPP synthase (GGPPS) in plastids, GFPPS directly decreased the activity of GGPPS through protein-protein interaction, ultimately leading to GGPP deficiency in planta. Our study provides a new regulatory mechanism of the plastidial terpenoid network in plant cells.

A recently evolved BAHD acetyltransferase, responsible for bitter soyasaponin A production, is indispensable for soybean seed germination.

Soyasaponins are major small molecules that accumulate in soybean (Glycine max) seeds. Among them, type-A soyasaponins, fully acetylated at the terminal sugar of their C22 sugar chain, are responsible for the bitter taste of soybean-derived foods. However, the molecular basis for the acetylation of type-A soyasaponins remains unclear. Here, we identify and characterize GmSSAcT1, encoding a BADH-type soyasaponin acetyltransferase that catalyzes three or four consecutive acetylations on type-A soyasaponins in vitro and in planta. Phylogenetic analysis and biochemical assays suggest that GmSSAcT1 likely evolved from acyltransferases present in leguminous plants involved in isoflavonoid acylation. Loss-of-function mutants of GmSSAcT1 exhibited impaired seed germination, which attribute to the excessive accumulation of null-acetylated type-A soyasaponins. We conclude that GmSSAcT1 not only functions as a detoxification gene for high accumulation of type-A soyasaponins in soybean seeds but is also a promising target for breeding new soybean varieties with lower bitter soyasaponin content.

Synthesis of 4-methylvaleric acid, a precursor of pogostone, involves a 2-isobutylmalate synthase related to 2-isopropylmalate synthase of leucine biosynthesis.

We show here that the side chain of pogostone, one of the major components of patchouli oil obtained from Pogostemon cablin and possessing a variety of pharmacological activities, is derived from 4-methylvaleric acid. We also show that 4-methylvaleric acid is produced through the one-carbon α-ketoacid elongation pathway with the involvement of the key enzyme 2-isobutylmalate synthase (IBMS), a newly identified enzyme related to isopropylmalate synthase (IPMS) of leucine (Leu) biosynthesis. Site-directed mutagenesis identified Met132 in the N-terminal catalytic region as affecting the substrate specificity of PcIBMS1. Even though PcIBMS1 possesses the C-terminal domain that in IPMS serves to mediate Leu inhibition, it is insensitive to Leu. The observation of the evolution of IBMS from IPMS, as well as previously reported examples of IPMS-related genes involved in making glucosinolates in Brassicaceae, acylsugars in Solanaceae, and flavour compounds in apple, indicate that IPMS genes represent an important pool for the independent evolution of genes for specialised metabolism.

Secondary Structure in Nonpeptidic Supramolecular Block Copolymers.

Proteins contain a level of complexity-secondary and tertiary structures-that polymer chemists aim to imitate. The bottom-up synthesis of protein-mimicking polymers mastering sequence variability and dispersity remains challenging. Incorporating polymers with predefined secondary structures, such as helices and π-π stacking sheets, into block copolymers circumvents the issue of designing and predicting one facet of their 3D architecture. Block copolymers with well-defined secondary-structure elements formed by covalent chain extension or supramolecular self-assembly may be considered for localized tertiary structures.In this Account, we describe a strategy toward block copolymers composed of units bearing well-defined secondary structures mixed in a "plug-and-play" manner that approaches a modicum of the versatility seen in nature. Our early efforts focused on the concept of single-chain collapse to achieve folded secondary structures through either hydrogen bonding or quadrupole attractive forces. These cases, however, required high dilution. Therefore, we turned to the ring-opening metathesis polymerization (ROMP) of [2.2]paracyclophane-1,9-dienes (pCpd), which forms conjugated, fluorescent poly(p-phenylenevinylene)s (PPVs) evocative of ß-sheets. Helical building blocks arise from polymers such as poly(isocyanide)s (PICs) or poly(methacrylamide)s (PMAcs) containing bulky, chiral side groups while the coil motif can be represented by any flexible chain; we frequently chose poly(styrene) (PS) or poly(norbornene) (PNB). We installed moieties for supramolecular assembly at the chain ends of our "sheets" to combine them with complementary helical or coil-shaped polymeric building blocks.Assembling hierarchical materials tantamount to the complexity of proteins requires directional interactions with high specificity, covalent chain extension, or a combination of both chemistries. Our design is based on functionalized reversible addition-fragmentation chain-transfer (RAFT) agents that allowed for the introduction of recognition motifs at the terminus of building blocks and chain-terminating agents (CTAs) that enabled the macroinitiation of helical polymers from the chain end of ROMP-generated sheets and/or coils. To achieve triblock copolymers with a heterotelechelic helix, we relied on supramolecular assembly with helix and coil-shaped building blocks. Our most diverse structures to date comprised a middle block of PPV sheets, parallel or antiparallel, and supramolecularly or covalently linked, respectively, end-functionalized with molecular recognition units (MRUs) for orthogonal supramolecular assembly. We explored PPV sheets with multiple folds achieved by chain extension using alternating pCpd and phenyl-pentafluorophenyl ß-hairpin turns. Using single-molecule polarization spectroscopy, we showed that folding occurs preferentially in multistranded over double-stranded PPV sheets. Our strategy toward protein-mimicking and foldable polymers demonstrates an efficient route toward higher ordered, well-characterized materials by taking advantage of polymers that naturally manifest secondary structures. Our studies demonstrate the retention of distinct architectures after complex assembly, a paradigm that we believe may extend to other polymeric folding systems.

Exploring the ellipticity dependency on vector helical Ince-Gaussian beams and their focusing properties.

We present a numerical study of the intensity and polarization structure of vector helical Ince-Gaussian (VHIG) modes, which present a distinct subclass of vector Ince-Gaussian modes with defined parameter settings. The intensity profile of VHIG beams has an elliptic hollow structure, while the polarization distribution shows multiple single-charge polarization vortices arranged along a line. By selecting the mode order, phase factor and ellipticity of the VHIG beams, we can control the number of elliptic rings, the number of polarization vortices, and the topology of the vector singularity. Furthermore, we simulate the focusing properties of VHIG beams based on vector diffraction theory. Our results indicate that the ellipticity parameter of VHIG beams could be a valuable degree of freedom to generate attractive transverse profiles and longitudinal distributions under focusing, which may have implications for lithography, material processing, optical communication, and even optical trapping and manipulation.

Development of a Smart Clinical Bluetooth Thermometer Based on an Improved Low-Power Resistive Transducer Circuit.

Smart sensors have been used in many engineering monitoring and control applications. This work focuses on the development of a new type of clinical Bluetooth thermometer, based on an improved low-power resistive transducer circuit. Most existing resistive transducers use relatively complicated circuits with higher cost and power consumption. To tackle these problems, especially in real applications, an improved low-power resistive transducer circuit is proposed in this work and is used to develop smart Bluetooth thermometers. The parameters of the resistive transducer circuit are selected by quantitative analysis and optimization to improve the performance of the low-power resistive transducer circuit. The effectiveness of the proposed design technology was verified by tests. The temperature measurement error of the new smart Bluetooth thermometer is less than 0.1 °C, which can not only meet the clinical use requirements but also has lower cost and power consumption.

Functional Prediction of trans-Prenyltransferases Reveals the Distribution of GFPPSs in Species beyond the Brassicaceae Clade.

Terpenoids are the most diverse class of plant primary and specialized metabolites, and trans-prenyltransferases (trans-PTs) are the first branch point to synthesize precursors of various chain lengths for further metabolism. Whereas the catalytic mechanism of the enzyme is known, there is no reliable method for precisely predicting the functions of trans-PTs. With the exponentially increasing number of available trans-PTs genes in public databases, an in silico functional prediction method for this gene family is urgently needed. Here, we present PTS-Pre, a web tool developed on the basis of the "three floors" model, which shows an overall 86% prediction accuracy for 141 experimentally determined trans-PTs. The method was further validated by in vitro enzyme assays for randomly selected trans-PTs. In addition, using this method, we identified nine new GFPPSs from different plants which are beyond the previously reported Brassicaceae clade, suggesting these genes may have occurred via convergent evolution and are more likely lineage-specific. The high accuracy of our blind prediction validated by enzymatic assays suggests that PTS-Pre provides a convenient and reliable method for genome-wide functional prediction of trans-PTs enzymes and will surely benefit the elucidation and metabolic engineering of terpenoid biosynthetic pathways.

The spillover effect of fiscal environmental protection spending on residents' medical and healthcare expenditure: evidence from China.

The Chinese government has not only been increasing investments in environmental protection, improving the quality of the ecological environment, but has also been focusing on curbing the excessive growth of medical and healthcare expenses so as to ease the economic burden of China's residents. Both aspects are significant concerns worldwide and have received much research attention individually, but the relationship between government environmental protection expenditure and residents' medical and healthcare expenditure remains unclear. Based on panel data from 31 provinces in China from 2007 to 2019, this paper empirically reveals that fiscal environmental protection expenditure is significantly negatively correlated with per capita medical and healthcare expenditure of residents (including outpatient expenditure and inpatient expenditure). This study shows that increasing the fiscal environmental protection expenditure can help curb the rising level of residents' medical and healthcare expenditure. In addition, the results of heterogeneity analysis indicate that the above relationship is stronger in provinces with a relatively low level of economic development or low proportion of the population over 65 years old. Management implications are discussed.

How can government environmental enforcement and corporate environmental responsibility consensus reduce environmental emergencies?

Environmental emergencies have become a severe challenge to human society due to their great harmfulness, which seriously restrict the sustainable development of human society. Previous studies mainly focused on the pollutant sources and consequences of environmental emergencies, yet lacking highlight of the antecedents of environmental emergencies. Based on a panel data of 31 provinces in China, this paper establishes a mediating effect model to empirically investigate how government environmental enforcement and corporate environmental responsibility consensus (CCER) influence environmental emergencies. The results show that there exists a significant positive correlation between the intensity of government environmental enforcement and CCER, while CCER has negative influence on the frequency of environmental emergencies. In addition, CCER plays a full mediating role in the relationship between government environmental enforcement and environmental emergencies. In short, this research clarified the relationship between government environmental enforcement, CCER, and environmental emergencies, verified the intermediary role of CCER. This paper uncovers another "black box" of the mechanism of environmental emergencies, makes up for the limitations of previous studies from a single perspective, expands the scope of research on environmental emergencies, and proposes corresponding policy recommendations.

Phase gradient protection of stored spatially multimode perfect optical vortex beams in a diffused rubidium vapor.

We experimentally investigate the optical storage of perfect optical vortex (POV) and spatially multimode perfect optical vortex (MPOV) beams via electromagnetically induced transparency (EIT) in a hot vapor cell. In particular, we study the role that phase gradients and phase singularities play in reducing the blurring of the retrieved images due to atomic diffusion. Three kinds of manifestations are enumerated to demonstrate such effect. Firstly, the suppression of the ring width broadening is more prominent for POVs with larger orbital angular momentum (OAM). Secondly, the retrieved double-ring MPOV beams' profiles present regular dark singularity distributions that are related to their vortex charge difference. Thirdly, the storage fidelities of the triple-ring MPOVs are substantially improved by designing line phase singularities between multi-ring MPOVs with the same OAM number but π offset phases between adjacent rings. Our experimental demonstration of MPOV storage opens new opportunities for increasing data capacity in quantum memories by spatial multiplexing, as well as the generation and manipulation of complex optical vortex arrays.

Optical storage of Ince-Gaussian modes in warm atomic vapor.

We report on the optical storage of Ince-Gaussian modes in a warm rubidium vapor cell based on electromagnetically induced transparency protocol, and we also qualitatively analyze how atomic diffusion affects the retrieved beams after storage. Ince-Gaussian modes possess very complex and abundant spatial structures and form a complete infinite-dimensional Hilbert space. Successfully storing such modes could open up possibilities for fundamental high-dimensional optical communication experiments.

Mechanical properties of 2D blue phosphorus and temperature effect.

Blue phosphorus is an emerging 2D material that exhibits finite electronic band gap and may find promising applications in advanced semiconducting devices. Comparing to its allotrope, black phosphorus, mechanical properties of blue phosphorus have not been explored in detail. Here we report molecular dynamics simulations of mechanical responses of blue phosphorus under uniaxial tensile, biaxial tensile and shear loadings. It is found that blue phosphorus shows less anisotropic effect as compared to black phosphorus, the room temperature Young's modulus is about 122.3 GPa and 121.6 GPa along armchair and zigzag directions, respectively, shear modulus is about 27.1 GPa and 28.6 GPa, respectively, along armchair and zigzag directions. Temperature effect on mechanical responses is also systematically studied within a range of 5-400 K. It is found that temperature reduces both Young's modulus and fracture strain and fracture strength of blue phosphorus, owing to the interplay between thermal energy and strain energy applied to the models. Brittle fracture mode is found in blue phosphorus in all loading conditions, with varied crack nucleation and propagation modes. The role of strain rate on the mechanical properties is examined and found to systematically modify the ultimate stress and ultimate strain of BlueP. Structural details including bond length and bond angle variations to external strain are analyzed to gain deeper insights into the underlying mechanisms.

Frictional characteristics of graphene layers with embedded nanopores.

Graphite possessing extraordinary frictional properties has been widely used as solid lubricants. Interesting frictional characteristics have been observed for pristine graphene layers, for defective graphene, the frictional signal shows richer behaviors such as those found in topological defective graphene and graphene step edges. Recently discovered nanoporous graphene represents a new category of defect in graphene and its impact on graphene frictional properties has not yet been explored. In this work, we perform molecular dynamics simulations on the frictional responses of nanoporous graphene layers when slid using a silicon tip. We show that the buried nanopore raises maximum friction signal amplitude while preserving the stick-slip character, the size of the nanopore plays a key role in determining the maximum frictional force. Negative friction is observed when the silicon tip scanned towards the center of the nanopore, this phenomenon originates from the asymmetrical variation of the in-plane strain and the out-of-plane deformation when indented by the silicon tip. Moreover, the layer dependent frictional character is examined for the buried graphene nanopores, showing that increasing graphene layers weakens the effect of nanopore on the frictional signal.

Intramolecular Folding of Coil-Helix Block Copolymers Induced by Quadrupole Interactions.

True tertiary architectures with defined local secondary structures are rare in synthetic systems. Adapting well-developed synthetic building blocks and controlling their folding through diverse interactions can be a general approach toward this goal. In this contribution, the synthesis of 3D hierarchical assemblies with distinct secondary domains formed through the intramolecular folding of a block copolymer containing a coil-like poly(styrene) (PS) block with a helical poly(isocyanide) block induced by phenyl-pentafluorophenyl quadrupole interactions is reported. The PS block is prepared via atom-transfer radical polymerization and end functionalized with a nickel complex that serves as a macroinitiator for the polymerization of chiral isocyanides bearing pentafluorophenyl pendants. The folding behavior of the coil-helix block copolymers is investigated by dynamic light scattering, NMR spectroscopy, wide-angle X-ray scattering, and differential scanning calorimetry.