Discovery of a Fungal P450 with an Unusual Two-Step Mechanism for Constructing a Bicyclo[3.2.2]nonane Skeleton.

The successful biomimetic or chemoenzymatic synthesis of target natural products (NPs) and their derivatives relies on enzyme discovery. Herein, we discover a fungal P450 BTG5 that can catalyze the formation of a bicyclo[3.2.2]nonane structure through an unusual two-step mechanism of dimerization and cyclization in the biosynthesis of beticolin 1, whose bicyclo[3.2.2]nonane skeleton connects an anthraquinone moiety and a xanthone moiety. Further investigation reveals that BTG5-T318 not only determines the substrate selectivity but also alters the catalytic reactions, which allows the separation of the reaction to two individual steps, thereby understanding its catalytic mechanism. It reveals that the first heterodimerization undergoes the common oxidation process for P450s, while the second uncommon formal redox-neutral cyclization step is proved as a redox-mediated reaction, which has never been reported. Therefore, this work advances our understanding of P450-catalyzed reactions and paves the way for expansion of the diversity of this class of NPs through synthetic biology.

Structure-based interface engineering methodology in designing a thermostable amylose-forming transglucosylase.

Many drugs and prebiotics derive their activities from sugar substituents. Due to the prevalence and complexity of these biologically active compounds, enzymatic glycodiversification that facilitates easier access to these compounds can make profound contributions to the pharmaceutical, food, and feed industries. Amylosucrases (ASases) are attractive tools for glycodiversification because of their broad acceptor substrate specificity, but the lack of structural information and their poor thermostability limit their industrial applications. Herein, we reported the crystal structure of ASase from Calidithermus timidus, which displays a homotetrameric quaternary organization not previously observed for other ASases. We employed a workflow composed of five common strategies, including interface engineering, folding energy calculations, consensus sequence, hydrophobic effects enhancement, and B-factor analysis, to enhance the thermostability of C. timidus ASase. As a result, we obtained a quadruple-point mutant M31 ASase with a half-life at 65 °C increased from 22.91 h to 52.93 h, which could facilitate biosynthesis of glucans with a degree of polymerization of more than 20 using sucrose as a substrate at 50 °C. In conclusion, this study provides a structural basis for understanding the multifunctional biocatalyst ASase and presents a powerful methodology to effectively and systematically enhance protein thermostability.

Treatment of acetabular fracture involving anterior and posterior columns using a single pararectus approach: surgical experience and preliminary results.

PURPOSE: This study aims to evaluate the efficacy of single pararectus approach in patients confirmed with acetabular fracture involving anterior and posterior columns. METHODS: A total of 58 patients confirmed with acetabular fracture involving anterior and posterior columns and treated at our hospital between January 2015 and January 2020 were retrospectively analyzed. A single pararectus approach was applied for all patients. Routine X-rays were performed at follow-up of one, three, six, 12, and 18 months, and three-dimensional CT scans were added at six and 18 months. Fracture reduction quality was assessed using the Matta score system, and functional assessment used the Modified Merle D'Aubigné and Postel score system. Post-operative complications, including fat liquefaction and deep vein thrombosis, were recorded and analyzed. RESULTS: The median operation time was 186 min while the intra-operative blood loss was 421 mL. The rate of good-to-excellent reduction was 94.8%, and the rate of good-to-excellent hip function score reached 93.1%. Seven patients presented with post-operative complications, including three intra-operative small vascular injuries, two peritoneal small perforations, one fat liquefaction, and one deep vein thrombosis. CONCLUSION: Using a single pararectus approach is convenient and effective for treating acetabular fracture involving anterior and posterior columns, especially those involving the quadrilateral area. TRIAL REGISTRATION: ChiCTR, ChiCTR2100054604. Registered 21 December 2022. Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=144783 .

Discovery of the Biosynthetic Pathway of Beticolin 1 Reveals a Novel Non-Heme Iron-Dependent Oxygenase for Anthraquinone Ring Cleavage.

This study used light-mediated comparative transcriptomics to identify the biosynthetic gene cluster of beticolin 1 in Cercospora. It contains an anthraquinone moiety and an unusual halogenated xanthone moiety connected by a bicyclo[3.2.2]nonane. During elucidation of the biosynthetic pathway of beticolin 1, a novel non-heme iron oxygenase BTG13 responsible for anthraquinone ring cleavage was discovered. More importantly, the discovery of non-heme iron oxygenase BTG13 is well supported by experimental evidence: (i) crystal structure and the inductively coupled plasma mass spectrometry revealed that its reactive site is built by an atypical iron ion coordination, where the iron ion is uncommonly coordinated by four histidine residues, an unusual carboxylated-lysine (Kcx377) and water; (ii) Kcx377 is mediated by His58 and Thr299 to modulate the catalytic activity of BTG13. Therefore, we believed this study updates our knowledge of metalloenzymes.

Characterization of Multifunctional and Non-stereoselective Oxidoreductase RubE7/IstO, Expanding the Functional Diversity of the Flavoenzyme Superfamily.

Flavin-dependent enzymes enable a broad range of redox transformations and generally act as monofunctional and stereoselective catalysts. Herein, we report the investigation of a multifunctional and non-stereoselective FMN-dependent oxidoreductase RubE7 from the rubrolone biosynthetic pathway. Our study outlines a single RubE7-catalysed sequential reduction of three spatially distinct bonds in a tropolone ring and a reversible double-bond reduction and dehydrogenation. The crystal structure of IstO (a RubE7 homologue) with 2.0 Šresolution reveals the location of the active site at the interface of two monomers, and the size of active site is large enough to permit both flipping and free rotation of the substrate, resulting in multiple nonselective reduction reactions. Molecular docking and site mutation studies demonstrate that His106 is oriented towards the substrate and is important for the reverse dehydrogenation reaction.

Donut-like MOFs of copper/nicotinic acid and composite hydrogels with superior bioactivity for rh-bFGF delivering and skin wound healing.

BACKGROUND: Skin injury and the resultant defects are common clinical problems, and usually lead to chronic skin ulcers and even life-threatening diseases. Copper, an essential trace element of human body, has been reported to promote the regeneration of skin by stimulating proliferation of endothelial cell and enhance angiogenesis. RESULTS: Herein, we have prepared a new donut-like metal-organic frameworks (MOF) of copper-nicotinic acid (CuNA) by a simple solvothermal reaction. The rough surface of CuNA is beneficial for loading/release basic fibroblast growth factor (bFGF). The CuNAs with/without bFGF are easily processed into a light-responsive composite hydrogel with GelMA, which not only show excellent mechanical properties, but also display superior biocompatibility, antibacterial ability and bioactivity. Moreover, in the in vivo full-thickness defect model of skin wound, the resultant CuNA-bFGF@GelMA hydrogels significantly accelerate the wound healing, by simultaneously inhibiting the inflammatory response, promoting the new blood vessels formation and the deposition of collagen and elastic fibers. CONCLUSIONS: Considering the superior biocompatibility, antibacterial ability and bioactivity, the CuNA and its composite light-responsive hydrogel system will be promising in the applications of skin and even other tissue regeneration.

Consumption of Wild Rice (Zizania latifolia) Prevents Metabolic Associated Fatty Liver Disease through the Modulation of the Gut Microbiota in Mice Model.

Metabolic associated fatty liver disease (MAFLD) due to excess weight and obesity threatens public health worldwide. Gut microbiota dysbiosis contributes to obesity and related diseases. The cholesterol-lowering, anti-inflammatory, and antioxidant effects of wild rice have been reported in several studies; however, whether it has beneficial effects on the gut microbiota is unknown. Here, we show that wild rice reduces body weight, liver steatosis, and low-grade inflammation, and improves insulin resistance in high-fat diet (HFD)-fed mice. High-throughput 16S rRNA pyrosequencing demonstrated that wild rice treatment significantly changed the gut microbiota composition in mice fed an HFD. The richness and diversity of the gut microbiota were notably decreased upon wild rice consumption. Compared with a normal chow diet (NCD), HFD feeding altered 117 operational taxonomic units (OTUs), and wild rice supplementation reversed 90 OTUs to the configuration in the NCD group. Overall, our results suggest that wild rice may be used as a probiotic agent to reverse HFD-induced MAFLD through the modulation of the gut microbiota.

Effect of statins on blood pressure: Analysis on adverse events released by FDA.

OBJECTIVE: As a class of cholesterol-lowering drugs, statins have been reported to cause unexpected decrease in blood pressure (BP). However, most studies in this issue were subject to inadequate study design or very small sample size. The present study was designed to examine the BP-lowering effect of various statins. METHODS: Here we retrieved 5.9 million clinical reports submitted to FDA Adverse Event Reporting System (FAERS) from 2004 to 2015. Meta-analysis was performed to estimate the overall reporting odds ratio (ROR) of hypotension adverse events concurrent with various statins (i.e., atorvastatin, simvastatin, and rosuvastatin). RESULTS: Comparing the reporting rate of hypotension event between statins and other drugs found that atorvastatin (pooled ROR = 1.26, adjusted p-value = 8.60 × 10-4) and simvastatin (pooled ROR = 1.94, adjusted p-value = 4.16 × 10-45) were significantly associated with reduction in BP. On the other hand, the association between rosuvastatin and hypotension was observed to be nonsignificant (adjusted p-value = 0.65). CONCLUSION: To our knowledge, this is the first pooled analysis on large-scale data of adverse events to identify the BP-lowering effect of statins. The results will contribute to the development of novel statin-based antihypertensive therapies. In addition, the differential effects of individual statins can warrant subsequent research on the underlying mechanisms of BP control.

Genome-Wide Analysis of Long Non-Coding RNAs in Potato and Their Potential Role in Tuber Sprouting Process.

Sprouting is a key factor affecting the quality of potato tubers. The present study aimed to compare the differential expression of long non-coding RNAs (lncRNAs) in the apical meristem during the dormancy release and sprouting stages by using lncRNA sequencing. Microscopic observations and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed the changes in the morphology and expression of lncRNAs in potato tubers during sprouting. Meristematic cells of potato tuber apical buds divided continuously and exhibited vegetative cone bulging and vascularisation. In all, 3175 lncRNAs were identified from the apical buds of potato tubers, among which 383 lncRNAs were up-regulated and 340 were down-regulated during sprouting. The GO enrichment analysis revealed that sprouting mainly influenced the expression of lncRNAs related to the cellular components of potato apical buds (e.g., cytoplasm and organelles) and cellular metabolic processes. The KEGG enrichment analysis also showed significant enrichment of specific metabolic pathways. In addition, 386 differentially expressed lncRNAs during sprouting were identified as putative targets of 235 potato miRNAs. Quantitative real-time polymerase chain reaction results agreed with the sequencing data. Our study provides the first systematic study of numerous lncRNAs involved in the potato tuber sprouting process and lays the foundation for further studies to elucidate their precise functions.

Chemical Basis of the Fungicidal Activity of Tobacco Extracts against Valsa mali.

Under pressure from social criticism and an unclear future, tobacco researchers have begun to seek alternative uses for the product. Here, we present our study on isolating tobacco compounds with fungicidal activity, which could be used as plant-derived pesticides. Using Valsa mali as the target fungus, agar plate tests were conducted to evaluate the fungicidal activity of various tobacco extracts, including tobacco leaves extracts prepared with different solvents, extracts of different tobacco cultivars, and samples from different tobacco organs. Fungal growth morphology was used as the criterion to evaluate the fungicidal activity of tobacco extracts. Correlation analyses between the fungicidal activities and the chemical components of tobacco extracts indicated the major chemical constituents with fungicidal activity. Then, the active compounds were isolated and their effects on the ultra-microstructures of V. mali was analyzed using scanning- and transmission-electron microscopy. The results suggested that tobacco extracts prepared with solvents of weaker polarity had higher fungicidal activity, and the inhibitory activity of tobacco extracts against V. mali was also cultivar dependent. Furthermore, the fungicidal effects of tobacco flower extracts were higher than those of the leaf extracts. Chemical analysis indicated that cembranoids were the main fungicidal substances, which act by destroying the endometrial structure of the fungus. Tobacco cembranoids at 80 µg/mL could completely inhibit the growth of V.mali, with an EC50 value of 13.18 µg/mL. Our study therefore suggests that tobacco leaves and inflorescences are excellent plant resources for the biological control of V. mali.

Chemical structures, biosynthesis, bioactivities, and utilisation values for the diterpenes produced in tobacco trichomes.

Cembranoids and labdanes are two important types of diterpenes in tobacco (Nicotiana genus) that are predominantly found in the leaf and flower glandular trichome secretions. This is the first systematic review of the biosynthesis, chemical structures, bioactivities, and utilisation values of cembranoid and labdane diterpenes in tobacco. A total of 131 natural cembranoid diterpenes have been reported in tobacco since 1962; these were summarised and classified according to their chemical structure characteristics as isopropyl cembranoids (1-88), seco-cembranoids (89-103), chain cembranoids (104-123), and polycyclic cembranoids (124-131). Forty natural labdane diterpenes reported since 1961 were also summarised and divided into epoxy side chain labdanes (132-150) and epoxy-free side chain labdanes (151-171). Tobacco cembranoid and labdane diterpenes are both formed via the methylerythritol 4-phosphate pathway and are synthesised from geranylgeranyl diphosphate. Their biosynthetic pathways and the four key enzymes (cembratrienol synthase, cytochrome P450 hydroxylase, copalyl diphosphate synthase, and Z-abienol cyclase) that affect their biosynthesis have been described in detail. A systematic summary of the bioactivity and utilisation values of the cembranoid and labdane diterpenes is also provided. The agricultural bioactivities associated with cembranoid and labdane diterpenes include antimicrobial and insecticidal activities as well as induced resistance, while the medical bioactivities include cytotoxic and neuroprotective activities. Further research into the cembranoid and labdane diterpenes will help to promote their development and utilisation as plant-derived pesticides and medicines.

Comparison of anterior cervical diskectomy with fusion (ACDF) and laminoplasty treating multilevel cervical spondylotic myelopathy with developmental canal stenosis: a retrospective study.

PURPOSE: To evaluate clinical effectiveness and radiologic results of anterior cervical diskectomy with fusion (ACDF) comparing with laminoplasty (LP) in treating multilevel cervical spondylotic myelopathy (MCSM) with developmental canal stenosis (DCS). METHODS: This was a retrospective analysis of 41 patients who had MCSM with DCS treated with ACDF or LP from December 2018 to April 2023. Patients were split into ACDF and LP groups for comparison, and patients were further separated into subgroups based on whether or not a reserving canal space was present. The operation time, hemoglobin, hospital stay, modified Japanese Orthopaedic Association (mJOA) score, and visual analog scale (VAS) score were used to assess clinical efficacy. The C2-C7 Cobb angle, C2-C7 sagittal vertical axis, T1 slope, and cervical range of motion were applied to evaluate imaging changes. RESULTS: Of the 41 patients, 19 received ACDF, and 22 received LP. At the final follow-up, both groups' mJOA scores significantly improved, and the intercomparison showed no differences; the VAS score was much lower in the ACDF group but remained unchanged in the LP group. At the final follow-up, the C2-C7 Cobb angle and T1 slope had significantly increased in the ACDF group, while the LP group showed no change; the cervical range of motion had significantly decreased in both groups, with the ACDF group exhibiting a more marked reduction. Within the ACDF subgroup, there was no postoperative symptom improvement for those with reserving space, whereas there was postoperative symptom resolution for those with non-reserving space; however, postoperative symptom in the LP subgroup was resolved. CONCLUSIONS: Both ACDF and LP were efficacious for MCSM patients with DCS. While ACDF could improve cervical lordosis and alleviate neck pain more effectively, it can also result in cervical sagittal imbalance and decreased mobility. Furthermore, the recovery from LP was superior to that from ACDF for patients with reserving space. In contrast, the recovery from both decompression techniques was comparable for individuals in non-reserving space.

Comparison of Laminectomy with Fusion and Laminoplasty Treating Multilevel Cervical Spondylotic Myelopathy: A Single-Center Retrospective Study.

OBJECTIVE: Comparing laminectomy with fusion (LF) and laminoplasty (LP) for treating multilevel cervical spondylotic myelopathy (MCSM) and comparative analysis of neck pain and sagittal cervical parameters. METHODS: This single-center study retrospectively analyzed MCSM patients treated with LF or LP in our department between June 2018 and January 2023, with at least a 12-month follow-up. T-tests were used to identify operation time, hemoglobin, hospital stay, modified Japanese Orthopaedic Association (mJOA) score, C2-C7 Cobb angle, C2-C7 sagittal vertical axis, T1 slope, cervical range of motion (cROM), and C4/5 anterior and posterior spinal canal diameter (A-P diameter) and area. Nonparametric tests were used to identify visual analog scale (VAS) score (assessing neck pain). Pearson correlation analyses were used to identify the neck pain. RESULTS: Of all 67 patients (LF: 24, LP: 43), both groups' mJOA scores significantly improved (P < 0.001). The VAS scores had both significantly decreased, with the LF group exhibiting a more marked reduction (LF: P < 0.001, LP: P = 0.037). Both groups' C4/5 A-P diameters and areas increased significantly (P < 0.001). The cROM had both significantly decreased, with the LF group exhibiting a greater reduction. At the last follow-up, the LF group's T1 slope and C2-C7 Cobb angle considerably increased, and pain VAS scores substantially correlated with the C2-C7 Cobb angle (R = -0.451, P < 0.001). CONCLUSIONS: LF and LP were efficacious for MCSM. LF relieved neck pain better but caused greater reduction in cervical mobility. Cervical lordosis improvement was significantly correlated with neck pain alleviation.

Selective synthesis of rebaudioside M2 through structure-guided engineering of glycosyltransferase UGT94D1.

Rebaudioside M2 (Reb M2), a novel steviol glycoside derivative, has limited industrial applications due to its low synthetic yield and selectivity. Herein, we identify UGT94D1 as a selective glycosyltransferase for rebaudioside D (Reb D), leading to the production of a mono ß-1,6-glycosylated derivative, Reb M2. A variant UGT94D1-F119I/D188P was developed through protein engineering. This mutant exhibited a 6.33-fold improvement in catalytic efficiency, and produced Reb M2 with 92% yield. Moreover, molecular dynamics simulations demonstrated that UGT94D1-F119I/D188P exhibited a shorter distance between the nucleophilic oxygen (OH6) of the substrate Reb D and uridine diphosphate glucose, along with an increased Ophosphate-C1-Oacceptor angle, thus improving the catalytic activity of the enzyme. Therefore, this study provides an efficient method for the selective synthesis of Reb M2 and paves the way for its applications in various fields.

Differential Resistance to Acetyl-CoA Carboxylase Inhibitors in Rice: Insights from Two Distinct Target-Site Mutations.

Weeds present a significant challenge to agricultural productivity, and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides have proven to be effective in managing weed populations in rice fields. To develop ACCase-inhibiting herbicide-resistant rice, we generated mutants of rice ACCase (OsACC) featuring Ile-1792-Leu or Gly-2107-Ser substitutions through ethyl methyl sulfonate (EMS) mutagenesis. The Ile-1792-Leu mutant displayed cross-resistance to aryloxyphenoxypropionate (APP) and phenylpyrazoline (DEN) herbicides, whereas the Gly-2107-Ser mutants primarily exhibited cross-resistance to APP herbicides with diminished resistance to the DEN herbicide. In vitro assays of the OsACC activity revealed an increase in resistance to haloxyfop and quizalofop, ranging from 4.84- to 29-fold in the mutants compared to that in wild-type. Structural modeling revealed that both mutations likely reduce the binding affinity between OsACC and ACCase inhibitors, thereby imparting resistance. This study offers insights into two target-site mutations, contributing to the breeding of herbicide-resistant rice and presenting alternative weed management strategies in rice cultivation.

Different interventions for the treatment of patent ductus arteriosus in children: a protocol for a network meta-analysis.

INTRODUCTION: Patent ductus arteriosus (PDA) is one of the most common congenital heart diseases. Once the PDA is diagnosed, it needs to be dealt with in time. At present, main methods include pharmacological treatment, surgical closure, and interventional closure for treatment of PDA. However, the effect of different interventions in PDA management is still controversial. Thus, our study aims to assess the effectiveness of different interventions together and estimate the sequence of these therapies for PDA children. Meanwhile, it is necessary to conduct a Bayesian network meta-analysis to compare the safety of different interventions comprehensively. METHODS AND ANALYSIS: To the best of our knowledge, this is the first Bayesian network meta-analysis comparing the efficacy and safety of different interventions for the treatment of PDA. PubMed, Embase, Cochrane Library, Web of Science, gray literature, and trial registry databases were searched from inception to December 2022. We will extract and report data according to methodological guidelines for Bayesian network meta-analysis by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P). Primary PDA closure, overall PDA closure, technical success, surgical success rate, mortality during hospital stay, operation time, intensive care unit stay, intraoperative radiation dose, radiation exposure time, total postoperative complication rate, and postoperative major complication rate will be defined as the outcomes. The quality of all random studies will be assessed using ROB, and quality of evidence for all outcomes will be judged by using the Grading of Recommendations Assessment, Development and Evaluation (GRADE). ETHICS AND DISSEMINATION: The results will be disseminated through peer-reviewed publication. Since no private and confidential patient data will be contained in the reporting, there are no ethical considerations associated with this protocol. SYSTEMATIC REVIEW REGISTRATION: INPLASY2020110067.

Structural Insight into the Catalytic Mechanisms of an L-Sorbosone Dehydrogenase.

L-Sorbosone dehydrogenase (SNDH) is a key enzyme involved in the biosynthesis of 2-keto-L-gulonic acid , which is a direct precursor for the industrial scale production of vitamin C. Elucidating the structure and the catalytic mechanism is essential for improving SNDH performance. By solving the crystal structures of SNDH from Gluconobacter oxydans WSH-004, a reversible disulfide bond between Cys295 and the catalytic Cys296 residues is discovered. It allowed SNDH to switch between oxidation and reduction states, resulting in opening or closing the substrate pocket. Moreover, the Cys296 is found to affect the NADP+ binding pose with SNDH. Combining the in vitro biochemical and site-directed mutagenesis studies, the redox-based dynamic regulation and the catalytic mechanisms of SNDH are proposed. Moreover, the mutants with enhanced activity are obtained by extending substrate channels. This study not only elucidates the physiological control mechanism of the dehydrogenase, but also provides a theoretical basis for engineering similar enzymes.

Structural analysis of an anthrol reductase inspires enantioselective synthesis of enantiopure hydroxycycloketones and ß-halohydrins.

Asymmetric reduction of prochiral ketones, particularly, reductive desymmetrization of 2,2-disubstituted prochiral 1,3-cyclodiketones to produce enantiopure chiral alcohols is challenging. Herein, an anthrol reductase CbAR with the ability to accommodate diverse bulky substrates, like emodin, for asymmetric reduction is identified. We firstly solve crystal structures of CbAR and CbAR-Emodin complex. It reveals that Tyr210 is critical for emodin recognition and binding, as it forms a hydrogen-bond interaction with His162 and π-π stacking interactions with emodin. This ensures the correct orientation for the stereoselectivity. Then, through structure-guided engineering, variant CbAR-H162F can convert various 2,2-disubstituted 1,3-cyclodiketones and α-haloacetophenones to optically pure (2S, 3S)-ketols and (R)-ß-halohydrins, respectively. More importantly, their stereoselectivity mechanisms are also well explained by the respective crystal structures of CbAR-H162F-substrate complex. Therefore, this study demonstrates that an in-depth understanding of catalytic mechanism is valuable for exploiting the promiscuity of anthrol reductases to prepare diverse enantiopure chiral alcohols.

One-Pot Synthesis of Ruthenium-Based Nanocatalyst Using Reduced Graphene Oxide as Matrix for Electrochemical Synthesis of Ammonia.

Conventional ammonia production consumes significant energy and causes enormous carbon dioxide (CO2) emissions globally. To lower energy consumption and mitigate CO2 emissions, a facile, environmentally friendly, and cost-effective one-pot method for the synthesis of a ruthenium-based nitrogen reduction nanocatalyst has been developed using reduced graphene oxide (rGO) as a matrix. The nanocatalyst synthesis was based on a single-step simultaneous reduction of RuCl3 into ruthenium-based nanoparticles (Ru-based NPs) and graphene oxide (GO) into rGO using glucose as the reducing agent and stabilizer. The obtained ruthenium-based nanocatalyst with rGO as a matrix (Runano-based/rGO) has shown much higher catalytic activity at lower temperatures and pressures for ammonia synthesis than conventional iron catalysts. The rGO worked as a promising promoter for the electrochemical synthesis of ammonia due to its excellent electrical and thermal conductivity. The developed Runano-based/rGO nanocatalyst was characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the size of the Ru-based NPs on the surface of rGO was 1.9 ± 0.2 nm and the ruthenium content was 25.03 wt %. Bulk electrolysis measurements were conducted on thin-layer electrodes at various cathodic potentials in a N2-saturated 0.1 M H2SO4 electrolyte at room temperature. From the chronoamperometric measurements, the maximum faradic efficiency (F.E.) of 2.1% for ammonia production on the nanostructured Runano-based/rGO electrocatalyst was achieved at a potential of -0.20 V vs reversible hydrogen electrode (RHE). This electrocatalyst has attained a superior ammonia production rate of 9.14 µg·h-1·mgcat.-1. The results demonstrate the feasibility of reducing N2 into ammonia under ambient conditions and warrant further exploration of the nanostructured Runano-based/rGO for electrochemical ammonia synthesis.

Crystal Structure of Levansucrase from the Gram-Negative Bacterium Brenneria Provides Insights into Its Product Size Specificity.

Microbial levansucrases (LSs, EC 2.4.1.10) have been widely studied for the synthesis of ß-(2,6)-fructans (levan) from sucrose. LSs synthesize levan-type fructo-oligosaccharides, high-molecular-mass levan polymer or combinations of both. Here, we report crystal structures of LS from the G--bacterium Brenneria sp. EniD 312 (Brs-LS) in its apo form, as well as of two mutants (A154S, H327A) targeting positions known to affect LS reaction specificity. In addition, we report a structure of Brs-LS complexed with sucrose, the first crystal structure of a G--LS with a bound substrate. The overall structure of Brs-LS is similar to that of G-- and G+-LSs, with the nucleophile (D68), transition stabilizer (D225), and a general acid/base (E309) in its active site. The H327A mutant lacks an essential interaction with glucosyl moieties of bound substrates in subsite +1, explaining the observed smaller products synthesized by this mutant. The A154S mutation affects the hydrogen-bond network around the transition stabilizing residue (D225) and the nucleophile (D68), and may affect the affinity of the enzyme for sucrose such that it becomes less effective in transfructosylation. Taken together, this study provides novel insights into the roles of structural elements and residues in the product specificity of LSs.