Land-use simulation for synergistic pollution and carbon reduction: Scenario analysis and policy implications.

Simulations of sustainable land use and management are required to achieve targets to reduce pollution and carbon emissions. Limited research has been conducted on synergistic pollution and carbon reduction (SPCR) in land-use simulations. This study proposed a framework for land-use simulation focused on SPCR. The non-dominated sorting genetic algorithm (NSGA-Ⅱ) and the entropy weight-based technique for order of preference by similarity to an ideal solution (TOPSIS) were used to optimize the land-use structure according to minimum net carbon, nitrogen, and phosphorus emissions. The cellular automata (CA) Markov model was then utilized to simulate the land-use spatial pattern according to the optimal conditions. The proposed framework was applied to the Dongjiang River Basin, South China, and three other scenarios (natural development (ND), carbon minimization (CM), and pollution minimization (PM)) were designed to validate the effectiveness of pollution and carbon emissions reduction under the SPCR scenario. The land-use structure and the pollution and carbon emissions in the scenarios were compared. The results showed the following. (1) The proportions of cultivated land, woodland, grassland, water, and construction land In the SPCR scenario accounted for 14%, 72%, 4%, 3%, and 7% of the total area, respectively. The carbon, nitrogen, and phosphorus emissions were 42.4%, 6.6%, and 7.8% lower, respectively, in the SPCR scenario than in the ND scenario, demonstrating the advantages of simultaneous pollution and carbon reduction. (2) The kappa coefficient of the CA-Markov model was 0.8729, indicating high simulation accuracy. (3) The simulated land-use spatial patterns exhibited low spatial heterogeneity under the CM, PM, and SPCR scenarios. However, there were significant disparities between the ND and SPCR scenarios. The cultivated and construction land areas were significantly smaller in the SPCR scenario than in the ND scenario. In contrast, the woodland and grassland areas were larger, with most differences in the central and southwestern regions of the Dongjiang River Basin. The results of the current study can be used to formulate effective land use policies and strategies in the Dongjiang Basin and similar areas to achieve the Coupling coordination between pollution reduction and carbon reduction. Policy recommendations include increasing the proportion of woodland and grassland, implementing reasonable constraints on expanding cultivated and construction lands, and establishing farmland red lines to promote synergistic pollution and carbon reduction.

Spatiotemporal links between meteorological and agricultural droughts impacted by tropical cyclones in China.

Both droughts and tropical cyclones (TCs) are among the world's most widespread natural disasters. This paper is concentrated on the effects of TCs on the links between meteorological droughts (MDs) and agricultural droughts (ADs). Specifically, changes in characteristics of drought events and variations in propagation features of matched MD and AD event pairs are quantified by using the renowned three-dimensional connected components algorithm; both alleviation and exacerbation effects of TCs are evaluated; and the Spearman's correlation is employed to identify potential contributors to exacerbated droughts after TCs. The results show that TCs exhibit more pronounced and widespread alleviation effects on MD events compared to AD events. >98 % of small-scale drought events are terminated by TCs, leading to 65 % reduction in the total area of MD events smaller than 50,000 km2 and 32 % reduction in AD events of the same scale. In the meantime, TCs can reshape the spatiotemporal links between MDs and ADs by reducing the overall propagation rate from 77 % to 40 % and ameliorating the characteristics of drought event pairs with higher propagation efficiency, by >40 %. After TCs, over 55 % of drought exacerbations in TC-affected regions occur first in the vicinity of the residual large-scale AD events. This occurrence is partially associated with the reduction in moisture exports from these residual droughts downwind to the interior of TC-affected regions, a process potentially facilitated by the TC-induced temperature cooling. The in-depth evaluation of this paper presents useful information for better drought preparation and mitigation under TCs.

Imaging mRNA in vitro and in vivo with nanofirecracker probes via intramolecular hybridization chain reaction.

Hybridization chain reaction (HCR) based enzyme-free amplification techniques have recently been developed for the visualization of intracellular messenger RNA (mRNA). However, the slow kinetics and potential interference with the intricate biological environments hinder its application in the clinic and in vivo. Herein, we designed a nanofirecracker probe-based strategy using intramolecular hybridization chain reaction (IHCR) amplifier for rapid, efficient, sensitive, specific detection and imaging of survivin mRNA both in vitro and vivo. Two probes, HP1 and HP2, in IHCR were simultaneously incorporated into a DNA nanowire scaffolds to bring HP1 and HP2 to close proximity on the assembled nanowire scaffolds. Empowered by the DNA nanowire scaffolds and spatial confinement effect, the nanofirecracker probe-based IHCR sensing system exhibited improved biostability, accelerated reaction kinetics, and enhanced signal amplification. This new strategy has been successfully applied to imaging mRNA in both cultured cells and in mice. Importantly, this novel sensing method was capable of detecting survivin mRNA in clinical blood samples from subjects with colorectal cancer. Thus, this novel nanofirecracker probe-based IHCR strategy holds great potential in advancing both biomedical research and in molecular diagnostics.

Removal of Hexamethyldisiloxane via a Novel Hydrophobic (3-Aminopropyl)Trimethoxysilane-Modified Activated Porous Carbon.

Volatile methyl siloxanes (VMS) must be removed because the formation of silica in the combustion process seriously affects the resource utilization of biogas. Herein, a series of APTMS ((3-aminopropyl)trimethoxysilane)-modified activated porous carbon (APC) adsorbents (named APTMS@APC) were prepared for VMS efficient removal. The as-prepared adsorbents were characterized using SEM, FTIR, Raman, X-ray diffraction analyses, and N2 adsorption/desorption. The results showed that the surface modification with APTMS enhanced the hydrophobicity of APC with the water contact angle increasing from 74.3° (hydrophilic) to 127.1° (hydrophobic), and meanwhile improved its texture properties with the SBET increasing from 981 to 1274 m2 g-1. The maximum breakthrough adsorption capacity of APTMS@APC for hexamethyldisiloxane (L2, model pollutant) was 360.1 mg g-1. Effects of an inlet L2 concentration (31.04-83.82 mg L-1) and a bed temperature (0-50 °C) on the removal of L2 were investigated. Meanwhile, after five adsorption-desorption cycles, the APTMS@APC demonstrated a superior cycling performance. This indicated that the hydrophobic APTMS@APC has a great significance to remove VMS.

Hexamethyldisiloxane Removal from Biogas Using a Fe3O4-Urea-Modified Three-Dimensional Graphene Aerogel.

Volatile methyl siloxanes (VMS), which are considered to be the most troublesome impurities in current biogas-cleaning technologies, need to be removed. In this study, we fabricated a series of Fe3O4-urea-modified reduced graphene-oxide aerogels (Fe3O4-urea-rGOAs) by using industrial-grade graphene oxide as the raw material. A fixed-bed dynamic adsorption setup was built, and the adsorption properties of the Fe3O4-urea-rGOAs for hexamethyldisiloxane (L2, as a VMS model pollutant) were studied. The properties of the as-prepared samples were investigated by employing various characterization techniques (SEM, TEM, FTIR, XRD, Raman spectroscopy, and N2 adsorption/desorption techniques). The results showed that the Fe3O4-urea-rGOA-0.4 had a high specific surface area (188 m2 g-1), large porous texture (0.77 cm3 g-1), and the theoretical maximum adsorption capacity for L2 (146.5 mg g-1). The adsorption capacity considerably increased with a decrease in the bed temperature of the adsorbents, as well as with an increase in the inlet concentration of L2. More importantly, the spent Fe3O4-urea-rGOA adsorbent could be readily regenerated and showed an excellent adsorption performance. Thus, the proposed Fe3O4-urea-rGOAs are promising adsorbents for removing the VMS in biogas.

Structures of the holoenzyme TglHI required for 3-thiaglutamate biosynthesis.

Structural diverse natural products like ribosomally synthesized and posttranslationally modified peptides (RiPPs) display a wide range of biological activities. Currently, the mechanism of an uncommon reaction step during the biosynthesis of 3-thiaglutamate (3-thiaGlu) is poorly understood. The removal of the ß-carbon from the Cys in the TglA-Cys peptide catalyzed by the TglHI holoenzyme remains elusive. Here, we present three crystal structures of TglHI complexes with and without bound iron, which reveal that the catalytic pocket is formed by the interaction of TglH-TglI and that its activation is conformation dependent. Biochemical assays suggest a minimum of two iron ions in the active cluster, and we identify the position of a third iron site. Collectively, our study offers insights into the activation and catalysis mechanisms of the non-heme dioxygen-dependent holoenzyme TglHI. Additionally, it highlights the evolutionary and structural conservation in the DUF692 family of biosynthetic enzymes that produce diverse RiPPs.

Water resources allocation considering water supply and demand uncertainties using newsvendor model-based framework.

A novel newsvendor model-based framework for regional industrial water resources allocation that considers uncertainties in water supply and demand was proposed in this study. This framework generates optimal water allocation schemes while minimizing total costs. The total cost of water allocation consists of the allocated water cost, the opportunity loss for not meeting water demand, and the loss of the penalty for exceeding water demand. The uncertainties in water demand and supply are expressed by cumulative distribution functions. The optimal water allocation for each water use sector is determined by the water price, the unit loss of the penalty and opportunity loss, and the cumulative distribution functions. The model was then applied to monthly water allocation for domestic, industrial, and agricultural water use in two counties of Huizhou City, China, whose water supply mainly depends on Baipenzhu Reservoir. The water demand for each water use sector and the monthly reservoir inflow showed good fits with the uniform and P-III distributions, respectively. The water demand satisfied ratio for each water use sector was stable and increased for the optimal water allocation scheme from the newsvendor model-based framework, and the costs were lower compared with the actual water allocation scheme. The novel framework is characterized by less severe water shortages, lower costs, and greater similarity to actual water use compared with the traditional deterministic multi-objective analysis model, and demonstrates strong robustness in the advantages of lower released surplus water and higher water demand satisfied ratio. This novel framework yields the optimal water allocation for each water use sector by integrating the properties of the market (i.e., determining the opportunity loss for not meeting water demand) with the government (i.e., determining the water price and the loss of the penalty for exceeding water demand) under the strictest water resources management systems.

Gut microbiome interacts with pregnancy hormone metabolites in gestational diabetes mellitus.

Introduction: Change in the composition of intestinal microbiota is associated with metabolic disorders such as gestational diabetes mellitus (GDM). Methods: To understand how the microbiota impacts the development of gestational diabetes mellitus, we profiled the intestinal microbiome of 54 pregnant women, including 27 GDM subjects, by employing 16S rRNA gene sequencing. Additionally, we conducted targeted metabolomics assays to validate the identified pathways with overrepresented metabolites. Results: We evaluated the patterns of changing abundances of operational taxonomic units (OTU) between GDM and the healthy counterparts over three timepoints. Based on the significant OTUs, we inferred 132 significantly altered metabolic pathways in GDM. And identified two overrepresented metabolites of pregnancy hormone, butyrate and mevalonate, as potential intermediary metabolites of intestinal microbiota in GDM. Finally, we validated the impacts of the intestinal microbiota on GDM by demonstrating consistent changes of the serum levels of progesterone, estradiol, butyrate, and mevalonate in an independent cohort. Discussion: Our findings confirm that alterations in the microbiota play a role in the development of GDM by impacting the metabolism of pregnancy hormones. This provides a novel perspective on the pathogenesis of GDM and introduces potential biomarkers that can be used for early diagnosis and prevention of the disease.

Spatial confinement-based Figure-of-Eight nanoknots accelerated simultaneous detection and imaging of intracellular microRNAs.

Developing highly efficient and reliable methods for simultaneous imaging of microRNAs in living cells is often appealed to understanding their synergistic functions and guiding the diagnosis and treatment of human diseases, such as cancers. In this work, we rationally engineered a four-arm shaped nanoprobe that can be stimuli-responsively tied into a Figure-of-Eight nanoknot via spatial confinement-based dual-catalytic hairpin assembly (SPACIAL-CHA) reaction and applied for accelerated simultaneous detection and imaging of different miRNAs in living cells. The four-arm nanoprobe was facilely assembled from a cross-shaped DNA scaffold and two pairs of CHA hairpin probes (21HP-a and 21HP-b for miR-21, while 155HP-a and 155HP-b for miR-155) via the "one-pot" annealing method. The DNA scaffold structurally provided a well-known spatial-confinement effect to improve the localized concentration of CHA probes and shorten their physical distance, resulting in an enhanced intramolecular collision probability and accelerating the enzyme-free reaction. The miRNA-mediated strand displacement reactions can rapidly tie numerous four-arm nanoprobes into Figure-of-Eight nanoknots, yielding remarkably dual-channel fluorescence proportional to the different miRNA expression levels. Moreover, benefiting from the nuclease-resistant DNA structure based on the unique arched DNA protrusions makes the system ideal for operating in complicated intracellular environments. We have demonstrated that the four-arm-shaped nanoprobe is superior to the common catalytic hairpin assembly (COM-CHA) in stability, reaction speed, and amplification sensitivity in vitro and living cells. Final applications in cell imaging have also revealed the capacity of the proposed system for reliable identification of cancer cells (e.g., HeLa and MCF-7) from normal cells. The four-arm nanoprobe shows great potential in molecular biology and biomedical imaging with the above advantages.

A Study of the Mechanisms and Characteristics of Fluorescence Enhancement for the Detection of Formononetin and Ononin.

In this work, the origins for the spectral difference between two isoflavones, formononetin (F) and ononin (FG), are revealed via a comparison study of the fluorescence molecular structure. The fluorescence enhancement of FG in hot alkaline conditions is reported for the first time. For F, there is almost no fluorescence under acidic conditions, but when the pH is >4.8, its fluorescence begins to increase due to the deprotonation of 7-OH. Under a pH between 9.3 and 12.0, the anionic form of F produces a strong and stable fluorescence. The fluorescence quantum yield (Yf) of F is measured to be 0.042. FG shows only weak fluorescence in aqueous solutions under a wide range of pH until it is placed in hot alkaline solutions, which is attributed to the cleavage reaction of the γ-pyrone ring in FG. The Yf of FG is determined to be 0.020. Based on the fluorescence sensitization methods of F and FG, the quantitative analysis and detection of two substances can be realized. The limit of the detections for F and FG are 2.60 ng·mL-1 and 9.30 ng·mL-1, respectively. The linear detection ranges of F and FG are 11.7~1860 ng·mL-1 and 14.6~2920 ng·mL-1, respectively. Although the structural relationship between F and FG is glycoside and aglycone, under hot alkaline conditions, the final products after the cleavage and hydrolysis reactions are essentially different. The different fluorescence characteristics between F and FG pave a way for further identification and a quantitative analysis of the corresponding components in Chinese herbal medicine.

Branch-Shaped Trapping Device Regulates Accelerated Catalyzed Hairpin Assembly and Its Application for MicroRNA In Situ Imaging.

Enzyme-free DNA strand displacement process is often practical when detecting miRNAs expressed at low levels in living cells. However, the poor kinetics, tedious reaction period, and multicomponent system hamper its in vivo applications to a great extent. Herein, we design a branch-shaped trapping device (BTD)-based spatial confinement reactor and applied it for accelerated miRNA in situ imaging. The reactor consists of a pair of trapped probe-based catalyzed hairpin assembly (T-CHA) reactions attached around the BTD. The trapping device naturally offered CHA reactions a good spatial-confinement effect by integrating the metastable probes (MHPa and MHPb) of the traditional CHA with the four-branched arm of BTD, which greatly improved the localized concentration of probes and shortened their physical distance. The autonomous and progressive walk of miRNA on the four-arm nanoprobes via T-CHA can rapidly tie numerous four-arm nanoprobes into figure-of-eight nanoknots (FENs), yielding strong fluorescence that is proportional to the miRNA expression level. The unique nanoarchitecture of the FEN also benefits the restricted freedom of movement (FOM) in a confined cellular environment, which makes the system ideally suitable for in situ imaging of intracellular miRNAs. In vitro and in situ analyses also demonstrated that the T-CHA overall outperformed the dissociative probe-based CHA (D-CHA) in stability, reaction speed, and amplification sensitivity. The final application of the T-CHA-based four-arm nanoprobe for imagings of both cancer cells and normal cells shows the potential of the platform for accurately and timely revealing miRNA in biological systems.

Association Between High-sensitivity C-reactive Protein and Predicted Cardiovascular Risks in Schizophrenia.

Context: Cardiovascular disease (CVD) is one of the main causes of premature death in patients with schizophrenia. High-sensitivity C-reactive protein (hs-CRP) is closely related to various risk factors of CVD in the general population and is a sensitive marker of subclinical inflammation. Objectives: The study intended to evaluate the predictive value of hs-CRP for high cardiovascular risk in patients with schizophrenia. Design: The research team designed a cross-sectional retrospective study. Setting: The study took place at the Affiliated Brain Hospital of Guangzhou Medical University in Guangzhou, Guangdong Province, China. Participants: Participants were 387 patients with schizophrenia who had been admitted to the inpatient clinic at the hospital between January 1, 2018 and December 30, 2019. Outcome Measures: The research team: (1) measured participants' hs-CRP and calculated the 10-year general cardiovascular risk, with a risk of >20% being defined as a high risk; (2) compared participants' demographics and traditional cardiovascular risk factors, and the prevalence of high cardiovascular risk according to the hs-CRP quartile; (3) used the receiver operating characteristic (ROC) curves to determine the optimal cutoff value for hs-CRP to predict high cardiovascular risk; and (4) used multivariate logistic regression analysis to assess the association between hs-CRP and high cardiovascular risk. Results: Of the 387 participants, 23 had a high cardiovascular risk (5.9%). The prevalence of high cardiovascular risk in quartiles Q1, Q2, Q3, and Q4 groups was 0%, 2.0%, 12.5%, and 9.4%, respectively, with a P trend < .001. The ROC analysis showed that an hs-CRP cutoff value of 2.13mg/L was a fair discriminator for high cardiovascular risk, with a C statistic of 0.74. After adjusting confounding factors by multivariate logistic regression analysis, an hs-CRP of ≥2.13 mg/L was significantly associated with high cardiovascular risk (OR = 7.81, 95% CI: 1.73 - 35.39, P = .008). Conclusions: An hs-CRP of ≥2.13 mg/L can be an independent predictor of high cardiovascular risk in patients with schizophrenia. Detection of hs-CRP may be beneficial in identifying patients at high risk of cardiovascular events in this population. Further prospective studies are needed to determine the hs-CRP threshold for evaluating cardiovascular risk in schizophrenia.

In situ imaging miRNAs using multifunctional linear DNA nanostructure.

The microRNAs (miRNAs) play a critical role in many biological processes and are essential biomarkers for diagnosing disease. However, the sensitive and specific quantification of microRNAs (miRNAs) expression in living cells still faces a huge challenge. Our study designed a multifunctional linear DNA nanostructure (MLN) as a carrier of molecular beacons (MB-21) for detecting and intracellular imaging miRNA-21. The MLN-MB consists of three parts: aptamer, MLN, and MB-21. The aptamer (AS1411) could media MLN-MB enter live cells without additional transfection reagents. Once inside the cells, the intracellular miRNA-21 could hybridize the MB-21s, resulting in significantly enhanced fluorescence signals. The whole process was enzyme-free, autonomous, and continuous, which avoided the necessity of adding external fuel strands or enzymes. We demonstrated that the MLN-MB could be used to screen the miRNA-21 with a detection limit of 320 pM in a short time (10 min) and show high specificity toward miRNA-21 against other miRNAs. Moreover, the proposed MLN-MB could detect the miRNA-21 in complex matrixes stably. With its outstanding stability, dual recognition, and biocompatibility, MLN-MB is capable of delivering into living cells to identify specific cancer cells. Therefore, our sensing approach, with high sensitivity, specificity, and simplicity advantages, holds great potential for early cancer diagnosis.

The pathogenic mechanism of Mycobacterium tuberculosis: implication for new drug development.

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a tenacious pathogen that has latently infected one third of the world's population. However, conventional TB treatment regimens are no longer sufficient to tackle the growing threat of drug resistance, stimulating the development of innovative anti-tuberculosis agents, with special emphasis on new protein targets. The Mtb genome encodes ~4000 predicted proteins, among which many enzymes participate in various cellular metabolisms. For example, more than 200 proteins are involved in fatty acid biosynthesis, which assists in the construction of the cell envelope, and is closely related to the pathogenesis and resistance of mycobacteria. Here we review several essential enzymes responsible for fatty acid and nucleotide biosynthesis, cellular metabolism of lipids or amino acids, energy utilization, and metal uptake. These include InhA, MmpL3, MmaA4, PcaA, CmaA1, CmaA2, isocitrate lyases (ICLs), pantothenate synthase (PS), Lysine-ε amino transferase (LAT), LeuD, IdeR, KatG, Rv1098c, and PyrG. In addition, we summarize the role of the transcriptional regulator PhoP which may regulate the expression of more than 110 genes, and the essential biosynthesis enzyme glutamine synthetase (GlnA1). All these enzymes are either validated drug targets or promising target candidates, with drugs targeting ICLs and LAT expected to solve the problem of persistent TB infection. To better understand how anti-tuberculosis drugs act on these proteins, their structures and the structure-based drug/inhibitor designs are discussed. Overall, this investigation should provide guidance and support for current and future pharmaceutical development efforts against mycobacterial pathogenesis.

Efficient Removal of Siloxane from Biogas by Using ß-Cyclodextrin-Modified Reduced Graphene Oxide Aerogels.

In this study, ß-cyclodextrin-modified reduced graphene oxide aerogels (ß-CD-rGOAs) were synthesized via a one-step hydrothermal method and were used to remove hexamethyldisiloxane (L2) from biogas. The ß-CD-rGOAs were characterized by the Brunner-Emmet-Teller technique, using Fourier-transform infrared spectroscopy, Raman spectrometry, scanning electron microscopy (SEM), contact angle measurements, and X-ray diffraction. The results of the characterizations indicate that ß-CD was grafted onto the surface of rGOAs as a cross-linking modifier. The ß-CD-rGOA had a three-dimensional, cross-linked porous structure. The maximum breakthrough adsorption capacity of L2 on ß-CD-rGOA at 273 K was 111.8 mg g-1. A low inlet concentration and bed temperature facilitated the adsorption of L2. Moreover, the ß-CD-rGOA was regenerated by annealing at 80 °C, which renders this a promising material for removing L2 from biogas.

Highly sensitive detection and intracellular imaging of MicroRNAs based on target-triggered cascade catalytic hairpin assembly.

MicroRNAs (miRNAs) have been identified as important biomarkers with great significance for diagnosis and treatment of various diseases. However, their unique properties, such as small size, high sequence homology, and low abundance, make quantitative analysis of miRNAs extremely challenging. Herein, we reported a cascade catalytic hairpin assembly (CCHA) for sensitive and selective detection of miRNA with three kinds of hairpin probes (HP1, HP2, and HP3). In the presence of target miRNA, a series of toehold-mediated intermolecular DNA strand displacement and hybridization was activated among HP1, HP2, and HP3 to assembly numbers of DNA nanoobjects. During this period, the fluorescence response was greatly intensified to indicate the presence and expression level of interested target miRNA. We have demonstrated that the proposed method exhibits a high assay sensitivity to detect low concentration target and an excellent sequence specificity to distinguish even a single-nucleotide difference in vitro. Moreover, we also demonstrated that our design enables the intracellular imaging of miRNA in live cancer and normal cells. These results showing the promising potential of our CCHA for powerful biosensing, clinic diagnosis, or prognosis.

The Structure and Function of Biomaterial Endolysin EFm1 from E. faecalis Phage.

The endolysin EFm1 from the E. faecalis 002 (002) phage IME-EF1 efficiently lyses E. faecalis, a gram-positive bacterium that severely threatens human health. Here, the structure and lytic activity of EFm1 toward E. faecalis were further investigated. Lytic activity shows that EFm1 specifically lyses 002 and 22 other clinically isolated E. faecalis, but not E. faecalis 945. Therefore, EFm1 may be an alternative biomaterial to prevent and treat diseases caused by E. faecalis. A structural analysis showed that EFm1D166Q is a tetramer consisting of one full-length unit with additional C-terminal domains (CTDs), while EFm1166-237 aa is an octamer in an asymmetric unit. Several crucial domains and novel residues affecting the lytic activity of EFm1 were identified, including calcium-binding sites (D20, D22 and D31), a putative classic amidohydrolase catalytic triad (C29, H90 and D108), a tetramerization site (M168 and M227), putative ion channel sites (IGGK, 186-198 aa), and other residues (R208 and Y209). Furthermore, EFm1 exhibited no significant activity when expressed alone in vivo, and IME-EF1 lytic activity decreased when efm1 was knocked down. These findings provide valuable insights into the molecule mechanism of a potential functional biomaterial for the treatment of the disease caused by the opportunistic pathogen E. faecalis.

Fluorescence, Absorption, Chromatography and Structural Transformation of Chelerythrine and Ethoxychelerythrine in Protic Solvents: A Comparative Study.

Chelerythrine (CH) and ethoxychelerythrine (ECH) are chemical reference substances for quality control of Chinese herbal medicines, and ECH is the dihydrogen derivative of CH. In this study, their fluorescence and absorption spectra, as well as their structural changes in different protic solvents were compared. It was observed that their emission fluorescence spectra in methanol were almost the same (both emitted at 400 nm), which may be attributed to the nucleophilic and exchange reactions of CH and ECH with methanol molecules with the common product of 6-methoxy-5,6-dihydrochelerythrine (MCH). When diluted with water, MCH was converted into CH, which mainly existed in the form of positively charged CH+ under acidic and near-neutral conditions with the fluorescence emission at 550 nm. With the increase of pH value of the aqueous solution, CH+ converted to 6-hydroxy-5,6-dihydrochelerythrine (CHOH) with the fluorescence emission at 410 nm. The fluorescence quantum yields of MCH and CHOH were 0.13 and 0.15, respectively, and both the fluorescence intensities were much stronger than that of CH+. It is concluded that CH and ECH can substitute each other in the same protic solvent, which was further verified by high-performance liquid chromatography. This study will help in the investigation of structural changes of benzophenanthridine alkaloids and will provide the possibility for the mutual substitution of standard substances in relevant drug testing.

Structural insights into the catalytic and inhibitory mechanisms of the flavin transferase FmnB in Listeria monocytogenes.

Listeria monocytogenes, a food-borne Gram-positive pathogen, often causes diseases such as gastroenteritis, bacterial sepsis, and meningitis. Newly discovered extracellular electron transfer (EET) from L. monocytogenes plays critical roles in the generation of redox molecules as electron carriers in bacteria. A Mg2+-dependent protein flavin mononucleotide (FMN) transferase (FmnB; UniProt: LMRG_02181) in EET is responsible for the transfer of electrons from intracellular to extracellular by hydrolyzing cofactor flavin adenine dinucleotide (FAD) and transferring FMN. FmnB homologs have been investigated in Gram-negative bacteria but have been less well studied in Gram-positive bacteria. In particular, the catalytic and inhibitory mechanisms of FmnB homologs remain elusive. Here, we report a series of crystal structures of apo-FmnB and FmnB complexed with substrate FAD, three inhibitors AMP, ADP, and ATP, revealing the unusual catalytic triad center (Asp301-Ser257-His273) of FmnB. The three inhibitors indeed inhibited the activity of FmnB in varying degrees by occupying the binding site of the FAD substrate. The key residue Arg262 of FmnB was profoundly affected by ADP but not AMP or ATP. Overall, our studies not only provide insights into the promiscuous ligand recognition behavior of FmnB but also shed light on its catalytic and inhibitory mechanisms.

Crystal structure and catalytic mechanism of the MbnBC holoenzyme required for methanobactin biosynthesis.

Methanobactins (Mbns) are a family of copper-binding peptides involved in copper uptake by methanotrophs, and are potential therapeutic agents for treating diseases characterized by disordered copper accumulation. Mbns are produced via modification of MbnA precursor peptides at cysteine residues catalyzed by the core biosynthetic machinery containing MbnB, an iron-dependent enzyme, and MbnC. However, mechanistic details underlying the catalysis of the MbnBC holoenzyme remain unclear. Here, we present crystal structures of MbnABC complexes from two distinct species, revealing that the leader peptide of the substrate MbnA binds MbnC for recruitment of the MbnBC holoenzyme, while the core peptide of MbnA resides in the catalytic cavity created by the MbnB-MbnC interaction which harbors a unique tri-iron cluster. Ligation of the substrate sulfhydryl group to the tri-iron center achieves a dioxygen-dependent reaction for oxazolone-thioamide installation. Structural analysis of the MbnABC complexes together with functional investigation of MbnB variants identified a conserved catalytic aspartate residue as a general base required for MbnBC-mediated MbnA modification. Together, our study reveals the similar architecture and function of MbnBC complexes from different species, demonstrating an evolutionarily conserved catalytic mechanism of the MbnBC holoenzymes.