Reconstruction the feedback regulation of amino acid metabolism to develop a non-auxotrophic L-threonine producing Corynebacterium glutamicum.

L-Threonine is an important feed additive with the third largest market size among the amino acids produced by microbial fermentation. The GRAS (generally regarded as safe) industrial workhorse Corynebacterium glutamicum is an attractive chassis for L-threonine production. However, the present L-threonine production in C. glutamicum cannot meet the requirement of industrialization due to the relatively low production level of L-threonine and the accumulation of large amounts of by-products (such as L-lysine, L-isoleucine, and glycine). Herein, to enhance the L-threonine biosynthesis in C. glutamicum, releasing the aspartate kinase (LysC) and homoserine dehydrogenase (Hom) from feedback inhibition by L-lysine and L-threonine, respectively, and overexpressing four flux-control genes were performed. Next, to reduce the formation of by-products L-lysine and L-isoleucine without the cause of an auxotrophic phenotype, the feedback regulation of dihydrodipicolinate synthase (DapA) and threonine dehydratase (IlvA) was strengthened by replacing the native enzymes with heterologous analogues with more sensitive feedback inhibition by L-lysine and L-isoleucine, respectively. The resulting strain maintained the capability of synthesizing enough amounts of L-lysine and L-isoleucine for cell biomass formation but exhibited almost no extracellular accumulation of these two amino acids. To further enhance L-threonine production and reduce the by-product glycine, L-threonine exporter and homoserine kinase were overexpressed. Finally, the rationally engineered non-auxotrophic strain ZcglT9 produced 67.63 g/L (17.2% higher) L-threonine with a productivity of 1.20 g/L/h (108.0% higher) in fed-batch fermentation, along with significantly reduced by-product accumulation, representing the record for L-threonine production in C. glutamicum. In this study, we developed a strategy of reconstructing the feedback regulation of amino acid metabolism and successfully applied this strategy to de novo construct a non-auxotrophic L-threonine producing C. glutamicum. The main end by-products including L-lysine, L-isoleucine, and glycine were almost eliminated in fed-batch fermentation of the engineered C. glutamicum strain. This strategy can also be used for engineering producing strains for other amino acids and derivatives.

Pyridine-Based Covalent Organic Frameworks with Pyridyl-Imine Structures for Boosting Photocatalytic H2O2 Production via One-Step 2e- Oxygen Reduction.

Bipyridine-based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one-step two-electron (2e-) route to a two-step 2e- oxygen reduction pathway. In this work, we introduce 3,3'-bipyridine units into imine-based COF skeletons, creating a pyridyl-imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine-like architecture can effectively suppress the two-step 2e- ORR process at the single imine-nitrogen site, facilitating a more efficient one-step 2e- pathway. Consequently, the optimized pyridyl-imine COF (PyIm-COF) exhibits a remarkable H2O2 production rate of up to 5850 µmol h-1 g-1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Construction of an autofluorescence interference-free phosphorescence biosensor for the specific detection of TK1 mRNA.

The anti-interference ability of biosensors is critical for detection in biological samples. Fluorescence-based sensors are subject to interference from self-luminescent substances in biological matrices. Therefore, phosphorescent sensors stand out among biosensors due to their lack of self-luminescence background. In this study, a phosphorescent sensor was constructed, which can accurately detect thymidine kinase 1 (TK1) mRNA in biological samples and avoid autofluorescence interference. When there is no target, polydopamine (PDA) is used as the phosphorescence resonance energy transfer (PRET) acceptor to quench the phosphorescence of the persistently luminescent (PL) nanomaterial. When there is a target, the DNA modified by the PL nanomaterial is replaced by the hairpin H and removed away from the PDA, resulting in a rebound in phosphorescence. The phosphorescent sensor exhibits a good linear relationship in the TK1 mRNA concentration range of 0-200 nM, and the detection limit was 1.74 nM. The sensor fabricated in this study can effectively avoid interference from spontaneous fluorescence in complex biological samples, and sensitively and precisely detect TK1 mRNA in serum samples, providing a powerful tool to more accurately detect biomarkers in biological samples.

Small variation induces a big difference: the effect of polymerization kinetics of graphitic carbon nitride on its photocatalytic activity.

Graphitic carbon nitride (g-CN) has emerged as a promising visible-light-responsive photocatalyst, and its activity is highly sensitive to synthesis conditions. In this work, we attempt to correlate the photocatalytic activity of g-CN with its production yield, which is kinetically determined by the specific condensation process. Bulk g-CN samples were synthesized by the conventional condensation procedure, but in static air and flowing air, respectively. The one synthesized in static air showed a lower production yield with an increased specific surface area and preferential surface chemical states, corresponding to a significantly improved activity for photocatalytic hydrogen evolution (PHE) and dye degradation. We further synthesized a series of g-CN samples by merely changing the synthetic atmosphere, the ramping rate, and the loading amount of the precursor, and the difference in their PHE performance was found to be as high as 7.05 times. The notable changes in their production yields as well as the photocatalytic activities have been discussed from the point of view of polymerization reaction kinetics, and the self-generated NH3 atmosphere plays a crucial role.

Detection of long mRNA sequences by a Y-shaped DNA probe with three target-binding segments.

Tumor-related mRNA detection is significant and interesting. The current mRNA detection method has the challenge of quantifying long mRNA sequences. Herein, a Y-shaped DNA probe with three target-binding segments was developed to detect tumor-related mRNA. This Y-shaped DNA probe (Y-probe) was assembled by six single DNA strands. Among these DNA strands, two DNA strands contained the split G-quadruplex sequence, and two DNA strands were modified with a pair of fluorophore and quencher, which were used to produce the detectable signal. In the presence of a long target mRNA sequence, target mRNA was hybridized with the three target-binding segments of the Y-probe, resulting in the increased fluorescence of G-quadruplex specific dye Thioflavin T and the decreased fluorescence of fluorophore, which could achieve the ratio detection of target mRNA. The Y-probe exhibited a low detection limit of 17.53 nM. Moreover, this probe showed high accuracy due to the benefits of three target-binding segments.

Tensor Learning Meets Dynamic Anchor Learning: From Complete to Incomplete Multiview Clustering.

Multiview clustering (MVC), which can dexterously uncover the underlying intrinsic clustering structures of the data, has been particularly attractive in recent years. However, previous methods are designed for either complete or incomplete multiview only, without a unified framework that handles both tasks simultaneously. To address this issue, we propose a unified framework to efficiently tackle both tasks in approximately linear complexity, which integrates tensor learning to explore the inter-view low-rankness and dynamic anchor learning to explore the intra-view low-rankness for scalable clustering (TDASC). Specifically, TDASC efficiently learns smaller view-specific graphs by anchor learning, which not only explores the diversity embedded in multiview data, but also yields approximately linear complexity. Meanwhile, unlike most current approaches that only focus on pair-wise relationships, the proposed TDASC incorporates multiple graphs into an inter-view low-rank tensor, which elegantly models the high-order correlations across views and further guides the anchor learning. Extensive experiments on both complete and incomplete multiview datasets clearly demonstrate the effectiveness and efficiency of TDASC compared with several state-of-the-art techniques.

Construction of Covalent Organic Framework Nanofiber Membranes for Efficient Adsorption of Antibiotics.

Techniques beyond crystal engineering are critical for manufacturing covalent organic frameworks (COFs) and to explore them for advanced applications. However, COFs are normally obtained as insoluble, unmeltable, and thus nonprocessible microcrystalline powders. Therefore, it is a significant challenge to implement COFs into larger architectures and structural control on different length scales. Herein, a facile strategy is presented to prepare flexible COF nanofiber membranes by in-situ growth of COFs on polyacrylonitrile (PAN) nanofiber substrates via a reversible polycondensation-termination approach. The obtained PAN@COF nanofiber membranes with vertically aligned COF nanoplates combine a large functional surface with efficient mass transport, thus making it a promising adsorbent, for example, for water purification. The antibiotic pollutant ofloxacin (OFX) is removed from water with a superior absorption capacity of ≈236 mg g-1 and removal efficiency as high as 98%. The here presented in-situ growth of COFs on nanofiber membranes can be extended to various Schiff base-derived COF materials with different compositions, providing a highly efficient way to construct flexible COF-based membranes for several applications.

Molecular dynamics simulation study of DNA conformation changes caused by the dinuclear platinum(II) complexes with the bisphosphonate group.

Bisphosphonate (BP) has been widely used as a bone-targeting group, and the BP-modified platinum(II) complexes have shown potential to as anticancer drugs against bone-related diseases, such as osteosarcoma. DNA conformation changes induced by the BP-modified dinuclear platinum(II) complexes have been investigated using molecular dynamics simulations. The results indicated that the BP-modified dinuclear platinum(II) complexes coordinated to DNA results in DNA structural distortions, including twisting, unwinding and bending. Furthermore, the rigidity of the bridging linkers in the BP-modified platinum(II) complex may induce more significant DNA structural distortions with same spans. The results provide the detail information of DNA conformational changes induced by the BP-modified platinum(II) complexes with different flexibility of bridging linkers, and are helpful for exploring novel platinum-based antitumor drugs.

A covalent organic framework/graphene aerogel electrocatalyst for enhanced overall water splitting.

The rational design of covalent organic framework (COF) based hybrid materials is of paramount importance to address the fundamental challenges of COFs with respect to their poor electron mobilization and the limited number of accessible active sites. Herein, we propose a new strategy for the fabrication of covalently bonded COF grafted graphene aerogel hybrid materials for electrocatalytic application. An in situ step-growth polymerization approach was developed to achieve the hybridization of COFs along the surface of amino-functionalized graphene nanosheets. By taking advantage of the three-dimensional conductive networks and highly accessible active sites, the cobalt-incorporated COF/graphene hybrid aerogel shows high oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances with an overpotential of 300 and 275 mV at 10 mA cm-2, respectively, under alkaline conditions. When applied to an electrochemical water-splitting electrolyzer, it is able to produce hydrogen and oxygen at competitive rates of 1.14 and 0.58 µL s-1, respectively, under ambient conditions, demonstrating its potential for practical applications.

pH-activated DNA nanomachine for miRNA-21 imaging to accurately identify cancer cell.

MicroRNA (miRNA) imaging has been employed to distinguish cancer cells from normal cells by exploiting the overexpression of miRNA in cancer. Inspired by the acidic extracellular tumor microenvironment, we designed a pH-activated DNA nanomachine to enable the specific detection of cancer cells using miRNA imaging. The DNA nanomachine was engineered by assembling two hairpins (Y1 and Y2) onto the surface of a ZIF-8 metal-organic framework (MOF), which decomposed under acidic conditions to release the adsorbed DNA hairpin molecules in situ. The released hairpins were captured by the target miRNA-21 and underwent catalytic hairpin assembly amplification between Y1 and Y2. The detection limit for miRNA assays using the DNA nanomachine was determined to be 27 pM, which is low enough for sensitive detection in living cells. Living cell imaging of miRNA-21 further corroborated the application of the DNA nanomachine in the identification of cancer cell.

Ultralight Magnetic and Dielectric Aerogels Achieved by Metal-Organic Framework Initiated Gelation of Graphene Oxide for Enhanced Microwave Absorption.

HIGHLIGHTS: Metal-organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal-organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal-oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe3O4@C/rGO and Ni-doped Fe3O4@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (- 58.1 dB and 6.48 GHz) and 2.8 mm (- 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

CRISPR-assisted rational flux-tuning and arrayed CRISPRi screening of an L-proline exporter for L-proline hyperproduction.

Development of hyperproducing strains is important for biomanufacturing of biochemicals and biofuels but requires extensive efforts to engineer cellular metabolism and discover functional components. Herein, we optimize and use the CRISPR-assisted editing and CRISPRi screening methods to convert a wild-type Corynebacterium glutamicum to a hyperproducer of L-proline, an amino acid with medicine, feed, and food applications. To facilitate L-proline production, feedback-deregulated variants of key biosynthetic enzyme γ-glutamyl kinase are screened using CRISPR-assisted single-stranded DNA recombineering. To increase the carbon flux towards L-proline biosynthesis, flux-control genes predicted by in silico analysis are fine-tuned using tailored promoter libraries. Finally, an arrayed CRISPRi library targeting all 397 transporters is constructed to discover an L-proline exporter Cgl2622. The final plasmid-, antibiotic-, and inducer-free strain produces L-proline at the level of 142.4 g/L, 2.90 g/L/h, and 0.31 g/g. The CRISPR-assisted strain development strategy can be used for engineering industrial-strength strains for efficient biomanufacturing.

Covalent organic frameworks (COFs) for electrochemical applications.

Covalent organic frameworks are a class of extended crystalline organic materials that possess unique architectures with high surface areas and tuneable pore sizes. Since the first discovery of the topological frameworks in 2005, COFs have been applied as promising materials in diverse areas such as separation and purification, sensing or catalysis. Considering the need for renewable and clean energy production, many research efforts have recently focused on the application of porous materials for electrochemical energy storage and conversion. In this respect, considerable efforts have been devoted to the design and synthesis of COF-based materials for electrochemical applications, including electrodes and membranes for fuel cells, supercapacitors and batteries. This review article highlights the design principles and strategies for the synthesis of COFs with a special focus on their potential for electrochemical applications. Recently suggested hybrid COF materials or COFs with hierarchical porosity will be discussed, which can alleviate the most challenging drawback of COFs for these applications. Finally, the major challenges and future trends of COF materials in electrochemical applications are outlined.

An enzyme-free probe based on G-triplex assisted by silver nanocluster pairs for sensitive detection of microRNA-21.

A sensitive ratiometric fluorescence probe based on hybridization chain reaction (HCR) was constructed for sensitive detection of miRNA-21 by using G-triplex and silver nanocluster pairs (AgNC pairs) as an enzyme-free and label-free signal output group. miRNA-21 was used as the primer for the hybridization chain reaction of molecular beacon 1 (MB1) containing the locked G-triplex sequence and molecular beacon 2 (MB2) with intact AgNC pairs at the 5' and 3' end activation. The double-stranded product was obtained along with the opening of the G-triplex and the separation of the AgNC pairs. A detection limit of 67 pM and a linear detection range of 0.1-300 nM were obtained for miRNA-21 determination. The proposed strategy enabled the monitoring of miRNA-21 levels in at least three cell lines, indicating that it provided new ideas for detecting miRNA in real samples. MB1 and MB2 contained the locked G-triplex sequence and silver nanocluster pairs (AgNC pairs), respectively. In the presence of target, the hybridization chain reaction (HCR) between MB1 and MB2 was initiated. At the same time, the locked G-triplex was released and combined to the dye thioflavin T (THT) to increase fluorescence, while the separation of the AgNC pairs caused the fluorescence to decrease. The double-stranded (ds) DNA product was generated to form a ratiometric signal to be detected.

Positron emission tomography/computed tomography dual imaging using 18-fluorine flurodeoxyglucose and 11C-labeled 2-ß-carbomethoxy-3-ß-(4-fluorophenyl) tropane for the severity assessment of Parkinson disease.

The value of dual imaging mode for the severity assessment of Parkinson disease (PD) is explored by conducting positron emission tomography computed tomography (PET/CT) double imaging using combined 18-fluorine flurodeoxyglucose (F-FDG) brain metabolism and 11C-2ß-carbomethoxy-3ß-(4-fluorophenyl) tropane (C-CFT) brain dopamine transporter (DAT).A total of 102 patients with PD and 50 healthy people in the control group are enrolled for the PET/CT dual imaging of F-FDG brain metabolism and C-CFT brain DAT. The characteristics of F-FDG PET/CT and C-CFT PET/CT imaging are analyzed by delineating the region of interest. Differences in the glucose metabolism and DAT distribution in the basal ganglia of patients with PD and healthy control group in the PET/CT imaging and the radioactive distribution characteristics of cerebral cortex in glucose metabolism imaging are compared. The characteristics of PET/CT imaging of C-CFT brain DAT in the ganglion region in absorbing C-CFT in different PD groups are analyzed.Compared with the healthy control group, changes in the cerebral glucose metabolism in the PD group mainly occur due to the increased symmetry metabolism of the nucleus of bilateral basal ganglia and the decreased metabolism of the cerebral cortex as shown in the F-FDG PET/CT images. With disease progression, the bilateral parietal, frontal, temporal, and occipital leaves showed different degrees of FDG metabolism. Statistically significant difference is observed for theC-CFT absorption among the caudate nucleus and the anterior, middle, and posterior nuclei of the bilateral basal ganglia of the PD and healthy control groups. In the PD group, the bilateral caudate nucleus and the anterior, middle, and posterior parts of the putamen show decreased DAT distribution. Regardless of unilateral or bilateral symptoms, the DAT distribution in the nucleus of the contralateral basal ganglia and in the posterior part of the nucleus is substantially reduced.PET/CT dual imaging by F-FDG PET/CT combined with C-CFT PET/CT features high application value for the severity assessment of PD.

DNA Structural Distortions Induced by a Monofunctional Trinuclear Platinum Complex with Various Cross-Links Using Molecular Dynamics Simulation.

The monofunctional trinuclear platinum complex (MTPC), as a promising antitumor agent, can form MTPC-DNA adducts via bifunctional and trifunctional cross-links. Molecular dynamics simulations were used to investigate DNA structural distortions of the MTPC-DNA adducts. MTPC coordinating to DNA results in the decrease of base-pair thermal stability and DNA structural distortions. It is found that there are more significant DNA structural distortions in the trifunctional cross-link than in the bifunctional cross-link, in the 1,4-GG than in the 1,3-GG cross-link, and in the intrastrand than in the interstrand cross-link with the same spans. The results provide a better understanding of DNA structural distortions induced by MTPC with various cross-links at the nucleotide level and are helpful for exploring novel Pt-based anticancer drugs.

Cobalt-Exchanged Poly(Heptazine Imides) as Transition Metal-Nx Electrocatalysts for the Oxygen Evolution Reaction.

Poly(heptazine imides) hosting cobalt ions as countercations are presented as promising electrocatalysts for the oxygen evolution reaction (OER). A facile mixed-salt melt-assisted condensation is developed to prepare such cobalt poly(heptazine imides) (PHI-Co). The Co ions can be introduced in well-controlled amounts using this method, and are shown to be atomically dispersed within the imide-linked heptazine matrix. When applied to electrocatalytic OER, PHI-Co shows a remarkable activity with an overpotential of 324 mV and Tafel slope of 44 mV dec-1 in 1 m KOH.

Cyclometalated Iridium Complex as Off-On-Off Reversible Photoluminescence Probe for Redox Cycle HSO3-/H2O2 in Living Cells.

The development of new methods for the detection of redox cycle is important for biological and clinical diagnoses. Here, a new cyclometalated iridium complex, (4-(2-pyridyl) benzaldehyde)2Ir (5-chloro-1,10-phenanthroline) ([(4-pba)2Ir(5-Cl-phen)]PF6, probe 1), has been synthesized and applied to rapid, sensitive, and reversible detection and imaging of redox cycle HSO3-/H2O2 in living cells. The probe 1 is synthesized by using 4-(2-pyridyl) benzaldehyde as main ligand and 5-chloro-1,10-phenanthroline as ancillary ligand. Probe 1 exhibited "off-on-off" photoluminescence (PL) signal change in response to HSO3- and H2O2 in aqueous solution within 1 min. The change of PL intensity is proportional to HSO3- concentration from 40 µM to 300 µM and to H2O2 concentration from 40 µM to 260 µM. The detection limit is 10 µM for HSO3- and 20 µM for H2O2. Additionally, probe 1 was applied to detect HSO3- in food samples with satisfactory results. More importantly, PL imaging of HeLa cells indicates that probe 1 is able to image redox cycle HSO3-/H2O2 in living cells.

Macro/Microporous Covalent Organic Frameworks for Efficient Electrocatalysis.

Covalent organic frameworks (COFs) are of interest for many applications originating from their mechanically robust architectures, low density, and high accessible surface area. Depending on their linkers and binding patterns, COFs mainly exhibit microporosity, even though COFs with small mesopores have been reported using extended linkers. For some applications, especially when fast mass transport is desired, hierarchical pore structures are an ideal solution, e.g., with small micropores providing large surface areas and larger macropores providing unhindered transport to and from the materials surface. Herein, we have developed a facile strategy for the fabrication of crystalline COFs with inherent microporosity and template-induced, homogeneously distributed, yet tunable, macroporous structures. This method has been successfully applied to obtain various ß-ketoenamine-based COFs with interconnected macro-microporous structures. The as-synthesized macroporous COFs preserve high crystallinity with high specific surface area. When bipyridine moieties are introduced into the COF backbone, metals such as Co2+ can be coordinated within the hierarchical pore structure (macro-TpBpy-Co). The resulting macro-TpBpy-Co exhibits a high oxygen evolution reaction (OER) activity, which is much improved compared to the purely microporous COF with a competitive overpotential of 380 mV at 10 mA/cm2. This can be attributed to the improved mass diffusion properties in the hierarchically porous COF structures, together with the easily accessible active Co2+-bipyridine sites.

Molecular dynamics simulation on the allosteric analysis of the c-di-GMP class I riboswitch induced by ligand binding.

Riboswitches are RNA molecules that regulate gene expression using conformation change, affected by binding of small molecule ligands. Although a number of ligand-bound aptamer complex structures have been solved, it is important to know ligand-free conformations of the aptamers in order to understand the mechanism of specific binding by ligands. In this paper, we use dynamics simulations on a series of models to characterize the ligand-free and ligand-bound aptamer domain of the c-di-GMP class I (GEMM-I) riboswitch. The results revealed that the ligand-free aptamer has a stable state with a folded P2 and P3 helix, an unfolded P1 helix and open binding pocket. The first Mg ions binding to the aptamer is structurally favorable for the successive c-di-GMP binding. The P1 helix forms when c-di-GMP is successive bound. Three key junctions J1/2, J2/3 and J1/3 in the GEMM-I riboswitch contributing to the formation of P1 helix have been found. The binding of the c-di-GMP ligand to the GEMM-I riboswitch induces the riboswitch's regulation through the direct allosteric communication network in GEMM-I riboswitch from the c-di-GMP binding sites in the J1/2 and J1/3 junctions to the P1 helix, the indirect ones from those in the J2/3 and P2 communicating to P1 helix via the J1/2 and J1/3 media.