APOBEC3G (A3G) is a DNA cytidine deaminase (CD) that demonstrates antiviral activity against human immunodeficiency virus 1 (HIV-1) and other pathogenic virus. It has an inactive N-terminal CD1 virus ...infectivity factor (Vif) protein binding domain (A3G-CD1) and an actively catalytic C-terminal CD2 deamination domain (A3G-CD2). Although many studies on the structure of A3G-CD2 and enzymatic properties of full-length A3G have been reported, the mechanism of how A3G interacts with HIV-1 single-stranded DNA (ssDNA) is still not well characterized. Here, we reported a crystal structure of a novel A3G-CD2 head-to-tail dimer (in which the N terminus of the monomer H (head) interacts with the C terminus of monomer T (tail)), where a continuous DNA binding groove was observed. By constructing the A3G-CD1 structural model, we found that its overall fold was almost identical to that of A3G-CD2. We mutated the residues located in or along the groove in monomer H and the residues in A3G-CD1 that correspond to those seated in or along the groove in monomer T. Then, by performing enzymatic assays, we confirmed the reported key elements and the residues in A3G necessary to the catalytic deamination. Moreover, we identified more than 10 residues in A3G essential to DNA binding and deamination reaction. Therefore, this dimer structure may represent a structural model of full-length A3G, which indicates a possible binding mode of A3G to HIV-1 ssDNA.
Background: The mechanism for DNA cytidine deaminase APOBEC3G (A3G) interacting with single-stranded DNA (ssDNA) is not well characterized.
Results: The crystal structure of a head-to-tail dimer of the A3G catalytic deamination domain (A3G-CD2) was obtained.
Conclusion: The dimer structure of A3G-CD2 suggests a binding mode of full-length A3G to ssDNA.
Significance: The dimer structure of A3G-CD2 may represent a structural model of full-length A3G.
Due to the excessive contamination of heavy metals pollution, it is very urgent and necessary to develop a real-time detection method for the heavy metals in food. As a target sensing device, a ...paper-based microfluidic device (μPAD) has the advantages of simplicity, low-cost, and portability. In this study, a self-driven microfluidic paper-based chip was first developed for the simultaneous detection of four targets. The channels on the microfluidic chip were prepared by using wax printing and automatic screen printing on the filter paper, where liquid flowed by capillary force without pump assistance. Based on the specific binding ability of aptamers to heavy metals, a “turn-on” fluorescence aptasensor for the simultaneous detection of four heavy metal ions was developed on the proposed multi-channel device via smartphone imaging. The obtained fluorescence images were digitized into RGB color values by Image J software, and an M-mode was established to realize the quantitative detection of heavy metal ions. Under optimal conditions, the limits of detection for lead(II), mercury(II), cadmium(II), and arsenic(III) were 4.20 nM, 1.70 nM, 2.04 nM, and 1.65 nM, respectively. Furthermore, the aptasensor was successfully applied to the quantitative detection of four heavy metal ions in apple and lettuce samples with recovery rates of 84.0%–104.1%.
Schematic diagram of the multi-channel fluorescent paper-based chip detection system for simultaneous detection of four target metal ions. Display omitted
•A paper-based microfluidic chip was developed to detect multi-target simultaneously.•The fluorescent paper-based chip was detected by smartphone imaging technology.•The paper-based chip was portable, environmentally-friendly, and high-throughput.•The detection limit of the paper-based chip was at the nM level.•This work was successfully applied to the detection of apple and lettuce samples.
A turn-on fluorescent aptasensor based on a paper-based microfluidic chip was developed to detect arsenite via aptamer competition strategy and smartphone imaging. The chip was prepared by ...wax-printing hydrophilic channels on filter paper. It is portable, low-cost, and environmentally friendly. Double-stranded DNA consisting of aptamer and fluorescence-labeled complementary strands was immobilized on the reaction zone of the paper chip. Due to the specific strong binding between aptamer and arsenite, the fluorescent complementary strand was squeezed out and driven by capillary force to the detection area of the paper chip, so that the fluorescent signal arose in the detection area under the excitation wavelength of 488 nm. Arsenite can be quantified by using smartphone imaging and RGB image analysis. Under the optimal conditions, the paper-based microfluidic aptasensor exhibited excellent linear response over a wide range of 1 to 1000 nM, with a detection limit as low as 0.96 nM (3σ).
Graphical Abstract
DNA walking machines have been widely used in rapid and sensitive detection. In this work, we develop a single enzyme-powered DNA cascade machine for the ultrasensitive determination of kanamycin. To ...construct the cascade manner, two types of single-legged three-dimensional DNA walking machine are employed to implement integrated target recognition, signal transduction and signal amplification. Upon adding kanamycin to trigger the upstream machine, the sequential enzymatic cleavage drives the autonomous movement of the walking strand and produces plenty of dye-labeled fragments with fluorescence recovery. Meanwhile, these fragments also serve as walking strands to activate the downstream machine for cascade signal amplification. Taking advantage of this cascade DNA machine, ultrasensitive determination can be accomplished in 60 min. Under the optimum conditions, this method was highly selective toward kanamycin with a detection limit of 28 fM. This cascade signal amplification shows great potential for the rapid screening of antibiotics in food.
ssDNA aptamers have been increasingly used to detect heavy metal ions as recognition elements due to their high affinity and specificity. However, the specific recognition and binding mechanisms ...between aptamers and most heavy metals were still unclear, which limits the development of aptamer-based detection methods. In this work, the interaction mechanisms of CD-2-1 aptamers with Cd2+ in aqueous solutions were investigated using molecular dynamic simulations. The most stable complex was found where Cd2+ binding at aptamer's stem-loop junction and preferred at the phosphate backbone or bases. Noteworthily, two binding modes of Cd2+ combining aptamer in aqueous solution were discovered: direct and indirect. In the former mode, Cd2+ directly coordinated O atoms of bases. For the latter, Cd2+ connected to bases with coordinated water molecules as bridges. Electrostatic interaction was found to be the main driving force, and differences of residues role between two binding modes were elucidated. Buffer molecules in aqueous solutions can stabilize aptamer-Cd2+ complex by hydrogen bonds. This study revealed the specific interaction mechanisms of aptamer with Cd2+ at an atomic level, which provided theoretical references for aptamer-based Cd2+ detection methods establishment as well as an efficient technical route of screening potential aptamers for heavy metal ions.
A novel molecularly imprinted nanomaterial (Eu (BTC)-MPS@MIP) was synthesized on the surface of silanized europium-based metal–organic frameworks (Eu (BTC)-MPS) using 1, 3, 5-benzotrioic acid (H
3
...BTC) as a ligand. The resulting Eu (BTC)-MPS@MIP was applied to constructing a smartphone sensing platform for the sensitive and selective detection of clothianidin (CLT) in vegetables. The synthesized Eu (BTC)-MPS@MIP demonstrated the successful formation of a typical core–shell structure featuring a shell thickness of approximately 70 − 80 nm. The developed sensing platform based on Eu (BTC)-MPS@MIP exhibited sensitivity in CLT detection with a detection limit of 4 µg/L and a linear response in the range 0.01 − 10 mg/L at excitation and emission wavelengths of 365 nm and 617 nm, respectively. The fluorescence sensing platform displayed excellent specificity for CLT detection, as evidenced by a high imprinting factor of 3.1. This specificity is primarily attributed to the recognition sites in the molecularly imprinted polymer (MIP) layer. When applied to spiked vegetable samples, the recovery of CLT ranged from 78.9 to 102.0%, with relative standard deviation (RSD) values falling between 2.2 and 6.2%. The quenching mechanism of Eu (BTC)-MPS@MIP toward CLT can be attributed to the inner filter effect (IFE), resulting from the optimal spectral overlap between the absorption spectrum of CLT and the excitation spectra of Eu (BTC)-MPS@MIP. The proposed method has the potential for extension to the detection of other pesticides by replacing the MIP recognition probes.
Graphical abstract
Photodynamic therapy (PDT) can destroy local tumor cells and induce effective antitumor immune responses, and has been applied in the treatment of patients with superficial solid tumors. Numerous ...systemic side effects of PDT, such as pain and skin photosensitivity, however, limit this therapeutic option. In addition, the immunosuppressive tumor microenvironment has been found to be another critical barrier for the antitumor immunity induced by PDT. Therefore, effectively enhancing the cytotoxicity to tumor cells of low-dose PDT and inhibiting the tumor immunosuppressive tumor microenvironment may be a feasible strategy to overcome these drawbacks of PDT. Here, a sorafenib and chlorin e6 co-loaded reactive oxygen species (ROS)-responsive nanoparticle (NP-sfb/ce6) is developed to improve antitumor responses by intratumoral release of sorafenib at the time of PDT. Under 660-nm laser irradiation, ROS produced by chlorin e6 (ce6) destruct the nanoparticles, resulting in boosted sorafenib cascade release. The rapidly released sorafenib acts synergistically with the low-dose PDT to inhibit tumor growth by inducing strong T cell-dependent local and systemic antitumor immune responses, reprograming the tumor immune microenvironment, and limiting the interaction between cytotoxic CD8+ T cells and immunosuppressive cells. This study provides new avenues for cascade-amplifying antitumor effects of photodynamic therapy.
Aims and objectives
To investigate turnover intention among newly licensed registered nurses and to clarify the impact pathways of organisational justice, work engagement and nurses’ perception of ...care quality on turnover intention.
Background
Nurse shortage is an ongoing and urgent issue worldwide, in which nurse turnover could exacerbate the situation. Newly licensed registered nurses will become the main nursing workforce in the future; however, previous studies have not revealed the specific reasons underlying their turnover intentions.
Design
A descriptive cross‐sectional design.
Methods
A total of 569 newly licensed registered nurses undertaking direct care were recruited from thirteen hospitals from October to November 2018 across Beijing, China. Based on the job demands–resources model, we advanced a hypothetical model, linking the paths between organisational justice, work engagement, nurses’ perception of care quality and turnover intention. Structural equation modelling was used to examine the hypothetical model. The study adhered to the STROBE statement for observational studies.
Results
In total, 22.3% of newly licensed registered nurses had a high turnover intention. The final model had an acceptable fit and could explain 58% of the variance in turnover intention. The organisational justice was directly related to high work engagement, great nurses’ perception of care quality and low turnover intention. Additionally, organisational justice also had indirect effects on great nurses’ perception of care quality and low turnover intention, which were partially mediated by work engagement. However, the effect of nurses’ perception of care quality on turnover intention was not significant.
Conclusion
The improvement of organisational justice could enhance work engagement, and nurses’ perception of care quality, and reduce turnover intention, which is crucial to improving care quality and addressing the shortage of nurses.
Relevance to clinical practice
This study provides evidence for policymakers and hospital administrators to take targeted measures to enhance work engagement, foster high‐quality care and create better defences against losing nurses.
In this study, biochar from the thermal pyrolysis of biomass was introduced into electrolysis to enhance the electrochemical degradation of nitrobenzene (NB). The biochar assisted electrolysis showed ...significantly enhanced NB removal in addition to the adsorption, where the TOC removal reached over 85%. The reaction rate for the electrolysis with 1 g l−1 of biochar (1.81 × 10−3 g mg−1·min−1) was much higher than the test without biochar (0.93 × 10−3 g mg−1·min−1). The four level L16 (44) orthogonal array test confirmed that the biochar played significant roles in NB degradation. Three cycles of adsorption-electrolysis test demonstrated the biochar undergone electroylsis for removing NB could be recycled. The cyclic voltammetry analysis, ·OH free radical scavenging test and NB degradation product analysis suggested that NB on the biochar surface was likely reduced to aniline and the aniline was subsequently mineralized by the hydroxyl radicals which were generated by the electrode. The results of this study highlight the potential of using biochar to assist the electrochemical degradation of organic contaminants in water.
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•Biochar enhanced NB removal during electrolysis.•Over 85% of TOC were removed with the aid of biochar.•Biochar undergone electrolysis could be recycled.•Biochar promoted NB reduction and subsequent mineralization.
Owing to advantage in high sensitivity and fast response, aptamer based electrochemical biosensors have attracted much more attention. However, inappropriate interfacial engineering strategy leads to ...poor recognition performance, which ascribe to the following factors of immobilized oligonucleotide strand including steric hindrance, interchain entanglement, and unfavorable conformation. In this work, we proposed a DNA tetrahedron based diblock aptamer immobilized strategy for the construction of label-free electrochemical biosensor. The diblock aptamer sequence is composite of T-rich anchor domain and recognition domain, where T-rich domain enabling anchored on the edge of DNA tetrahedron via Hoogsteen hydrogen bond at neutral condition. The DNA tetrahedron scaffold offers an appropriate lateral space for target recognition of diblock aptamer. More importantly, this trivalent aptamer recognition interface can be regenerated by simply adjusting the pH environment to alkaline, resulting in the dissociation of diblock aptamer. Under the optimum condition, proposed electrochemical aptasensor manifested a satisfied sensitivity for aminoglycosides antibiotic, kanamycin with a limit of detection of 0.69 nM, which is 45-fold lower than traditional Au–S immobilization strategy. Moreover, the proposed aptasensor had also successfully been extended to ampicillin detection by changing the sequence of recognition domain in diblock aptamer. This work paves a new way for the rational design of aptamer-based electrochemical sensor.
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