Sinorhizobium meliloti BR-bodies promote fitness during host colonization.

Biomolecular condensates, such as the nucleoli or P-bodies, are non-membrane-bound assemblies of proteins and nucleic acids that facilitate specific cellular processes. Like eukaryotic P-bodies, the recently discovered bacterial ribonucleoprotein bodies (BR-bodies) organize the mRNA decay machinery, yet the similarities in molecular and cellular functions across species have been poorly explored. Here, we examine the functions of BR-bodies in the nitrogen-fixing endosymbiont Sinorhizobium meliloti, which colonizes the roots of compatible legume plants. Assembly of BR-bodies into visible foci in S. meliloti cells requires the C-terminal intrinsically disordered region (IDR) of RNase E, and foci fusion is readily observed in vivo, suggesting they are liquid-like condensates that form via mRNA sequestration. Using Rif-seq to measure mRNA lifetimes, we found a global slowdown in mRNA decay in a mutant deficient in BR-bodies, indicating that compartmentalization of the degradation machinery promotes efficient mRNA turnover. While BR-bodies are constitutively present during exponential growth, the abundance of BR-bodies increases upon cell stress, whereby they promote stress resistance. Finally, using Medicago truncatula as host, we show that BR-bodies enhance competitiveness during colonization and appear to be required for effective symbiosis, as mutants without BR-bodies failed to stimulate plant growth. These results suggest that BR-bodies provide a fitness advantage for bacteria during infection, perhaps by enabling better resistance against the host immune response.

Simulating arsenic discharge flux at a relic smelting site in Guangxi Zhuang Autonomous Region, China.

Anthropogenic groundwater arsenic (As) pollution is common in many aquifers in Southwest China. It is concerned that long-term random disposal of As smelting slag could induce the transport of high-As groundwater into previously uncontaminated aquifers. Here, we used HELP-MODFLOW-MT3DMS model simulations to integrate the percolation, groundwater flow, and solute transport processes at an aquifer at site scale, constrained by weather, hydrogeology, and monitoring data. Our simulations provide a new method framework of the simulated percolation by HELP model and have induced As spatiotemporal distribution in the aquifer. According to the HELP model simulation results, percolation volume accounts for 24% of rainfall over 18 years. This work determined that the As discharge trend was fitted by double-constants kinetics based on the leaching experiment. And this work calculates total mass distribution of As in the aquifer over 18 years. We have found that the sustained As pollution relies on the rainfall that acts as the primary contributor of elevated As concentrations. Model simulation results suggest that 51.70% of the total As mass (1.96 × 104 kg) was fixed in low permeability solid media. The total As mass discharged into groundwater reached 9.3 × 103 kg, accounting for 24.68%. The accumulative outflow mass of arsenic was 8.0 × 103 kg, accounting for 21.62%.

A protease and a lipoprotein jointly modulate the conserved ExoR-ExoS-ChvI signaling pathway critical in Sinorhizobium meliloti for symbiosis with legume hosts.

Sinorhizobium meliloti is a model alpha-proteobacterium for investigating microbe-host interactions, in particular nitrogen-fixing rhizobium-legume symbioses. Successful infection requires complex coordination between compatible host and endosymbiont, including bacterial production of succinoglycan, also known as exopolysaccharide-I (EPS-I). In S. meliloti EPS-I production is controlled by the conserved ExoS-ChvI two-component system. Periplasmic ExoR associates with the ExoS histidine kinase and negatively regulates ChvI-dependent expression of exo genes, necessary for EPS-I synthesis. We show that two extracytoplasmic proteins, LppA (a lipoprotein) and JspA (a lipoprotein and a metalloprotease), jointly influence EPS-I synthesis by modulating the ExoR-ExoS-ChvI pathway and expression of genes in the ChvI regulon. Deletions of jspA and lppA led to lower EPS-I production and competitive disadvantage during host colonization, for both S. meliloti with Medicago sativa and S. medicae with M. truncatula. Overexpression of jspA reduced steady-state levels of ExoR, suggesting that the JspA protease participates in ExoR degradation. This reduction in ExoR levels is dependent on LppA and can be replicated with ExoR, JspA, and LppA expressed exogenously in Caulobacter crescentus and Escherichia coli. Akin to signaling pathways that sense extracytoplasmic stress in other bacteria, JspA and LppA may monitor periplasmic conditions during interaction with the plant host to adjust accordingly expression of genes that contribute to efficient symbiosis. The molecular mechanisms underlying host colonization in our model system may have parallels in related alpha-proteobacteria.

Porous carbon nanosheets derived from two-dimensional Fe-MOF for simultaneous voltammetric sensing of dopamine and uric acid.

It is of great significance for electrochemical sensors to simultaneously detect dopamine (DA) and uric acid (UA) related to biological metabolism. In this work, two-dimensional (2D) porous carbon nanosheets (CNS) was prepared as electrocatalysts to improve the sensitivity, the selectivity, and the detection limit of the simultaneous detection. First, 2D amorphous iron-metal organic frameworks (Fe-MOF) was synthesized with Fe3+and terephthalic acid via a facile wet chemistry method at room temperature. And then, CNS was prepared by pyrolysis and pickling of Fe-MOF. CNS had large specific surface area, good electrical conductivity and lots of carbon defects. The response currents of the CNS modified electrode was larger than those of the control electrodes in the simultaneous determination. The simultaneous determination was measured via differential pulse voltammetry to reduce the effect of capacitive currents on quantitative analysis. The CNS modified electrodes showed high sensitivity and low detection limit for the simultaneous detection of DA and UA. The modified electrodes have been successfully used to detect DA and UA in normal human serum.

Linking health to geology-a new assessment and zoning model based on the frame of medical geology.

With the growing concerns about the Earth's environment and human health, there has been a surge in research focused on the intersection of health and geology. This study quantitatively assesses the relationship between human health and geological factors using a new framework. The framework considers four key geological environment indicators related to health: soil, water, geological landform, and atmosphere. Results indicate that the atmospheric and water resource indicators in the study area were generally favorable, while the scores of geological landforms varied based on topography. The study also found that the selenium content in the soil greatly exceeded the local background value. Our research underscores the importance of geological factors on human health, establishes a new health-geological assessment model, and provides a scientific foundation for local spatial planning, water resource development, and land resource management. However, due to varying geological conditions worldwide, the framework and indicators for health geology may need to be adjusted accordingly.

Portable hydrogel test kit integrated dual-emission coordination polymer nanocomposite for on-site detection of organophosphate pesticides.

It is of great significance to on-site detection of organophosphate pesticides (OPs) for pollution monitoring and poisoning estimation. Herein, we developed a portable hydrogel test kit for on-site detection of OPs, which is based on the integration of agarose hydrogel with dual-emission coordination polymers (CPs) nanocomposite comprised of Ru(bpy)32+ and zinc (II)-based CPs (ZnCPs) loaded with thioflavin T (ThT). Different from Ru(bpy)32+ with stable fluorescence in acidic environment, ThT@ZnCPs is highly sensitive to H+, which destroys the structure of ZnCPs as a host and quenches ThT@ZnCPs fluorescence. The distinct fluorescence behaviors of Ru(bpy)32+ and ThT@ZnCPs in acidic environment enable the hydrogel test kit to exhibit ratiometric fluorescence responses to acetylcholinesterase (AChE), which hydrolyzes acetylcholine to acetic acid and provides H+. On this basis, combining the inhibition effect of OPs to AChE activity, a ratiometric fluorescence method for OPs detection was established with the hydrogel test kit, and satisfactory results have been achieved in buffered aqueous solutions and apple juice samples. Attractively, by employing smartphone as a signal readout, on-site quantitation of OPs was accomplished with the features of easy to use, portability and low cost, demonstrating a great promising for point-of-care testing in food safety monitoring.

Leaching experiments and risk assessment to explore the migration and risk of potentially toxic elements in soil from black shale.

Black shale is rich in potentially toxic elements (PTEs) that migrate through rock weathering or rainfall, adversely affecting human health and the environment. In this study, simulated rainfall leaching experiments were used to investigate the migration patterns and leaching kinetics of PTEs in black shale from the Lower Cambrian Hetang Formation and to analyze the water quality index (WQI) of PTEs in the leachate. A comparison between the risk of PTEs in the leachate and those in the soil was also made to determine the risk sources, risk status, and distribution characteristics of PTEs in the study area. The WQI of the indoor column experimental leachate indicated the highest As contamination. The geo-accumulation index (Igeo) and potential ecological risk (Er) of soils in the entire region revealed that the risk of Cd was the highest. Furthermore, by mapping the distribution of Igeo and Er in soils, the risk level in the region where black shale is located was found to be significantly higher than that in other areas. Comparing the leaching rate of PTEs with the WQI from leaching experiments, the risk associated with As in soil can be inferred to originate mainly from the leaching of black shale. Previous studies on PTEs in black shale in the study area tended to focus on Cd; however, this study found that the risk of As was not negligible. The health risk assessment also showed that the risk at the location of black shale was beyond the accepted range. Overall, this study provided a new and important evaluation law for the level of pollution by PTEs and health risks in typical black shale regions.

Integrated enzyme with stimuli-responsive coordination polymer for personal glucose meter-based portable immunoassay.

Coordination polymers (CPs) with tunable structures and properties have been extensively explored in a variety of fields. In this work, we demonstrated the potential of stimuli-responsive CPs as a host of integrating enzymes to construct a portable immunoassay. By employing terbium ion (Tb3+) as a metal node and guanine monophosphate (GMP) as a bridge ligand, an alkaline phosphatase (ALP)-responsive Tb/GMP CPs was fabricated, which allows amyloglucosidase (GA) to be integrated to form GA@Tb/GMP composite. Owing to the size-selectivity of Tb/GMP CPs as a host, the loaded GA was physically isolated from its substrate starch. However, Tb/GMP CPs is highly sensitive to ALP, which can hydrolyze the phosphate group of GMP to destroy the structure of Tb/GMP CPs, leading to the release of GA from GA@Tb/GMP composite. The released GA can digest starch to produce glucoses and give a measured signal by personal glucose meter (PGM). This finding leads to a PGM-based portable immunoassay for the quantitative analysis of carcinoembryonic antigen (CEA), and satisfactory results with a detection limit of 0.28 ng/mL have been achieved. The successful determination of CEA in serum samples demonstrates its potential in practical application. We believe that this work can provide a remarkable insight for the rational design of stimuli-responsive CPs for a wide of applications.

Simultaneous electrochemical sensing of heavy metal ions based on a g-C3N4/CNT/NH2-MIL-88(Fe) nanocomposite.

The presence of Cd2+, Pb2+, Cu2+ and Hg2+ in drinking-water can be harmful to human health, even if their concentration is fairly low. Hence, it is significant to detect these heavy metal ions in sewage to evaluate the quality of water. Herein, amino-functionalized metal-organic frameworks (NH2-MIL-88(Fe)) embedded with graphitic carbon nitride (g-C3N4) nanosheets and acid-functionalized carbon nanotubes were prepared via a one-pot synthesis. The composite can be directly modified on the surface of glass carbon electrodes without the assistance of Nafion or other binders. The modified glass carbon electrodes can be used to simultaneously detect Cd2+, Pb2+, Cu2+ and Hg2+ in water via square wave stripping voltammetry. The doping of g-C3N4 in the composite, rich in N-containing functional groups, participates in the adsorption of metal ions on the surface of the electrodes. The porous composite provides accommodation room for metals generated by electro-reduction. The detection limit for Cd2+, Pb2+, Cu2+ and Hg2+ is 39.6 nM, 7.6 nM, 11.9 nM, and 9.6 nM, respectively. And the sensitivity for Cd2+, Pb2+, Cu2+ and Hg2+ is 0.0789 mA µM-1 cm-2, 0.4122 mA µM-1 cm-2, 0.2616 mA µM-1 cm-2, and 0.3251 mA µM-1 cm-2, respectively. This work not only enriches the functional design of Fe-MOF materials, but also develops a method for the determination of metal ions using the adsorption sites in g-C3N4.

Visual detection of alkaline phosphatase based on ascorbic acid-triggered gel-sol transition of alginate hydrogel.

Stimuli-responsive hydrogel has been emerged as a popular tool for chemical sensing due to its unique mechanical properties. In this work, we fabricated an ascorbic acid (AA)-responsive alginate hydrogel for the visual detection of alkaline phosphatase (ALP). This alginate hydrogel (RhB@Alg/Fe3+) was crosslinked with Fe3+, and rhodamine B (RhB) was encapsulated into the hydrogel as an indicating reagent to assistant visual detection. Because of the weak affinity of Fe2+ to alginate, the presence of reductive AA can trigger the dissolution of RhB@Alg/Fe3+ to give an observable red color in the sol solution. On this basis, by using ascorbic acid 2-phosphate as a substrate of ALP, which can be hydrolyzed by ALP to produce AA, the gel-sol transition process of RhB@Alg/Fe3+ was further modulated by ALP. This finding leads to a simple visual method for ALP detection with a low detection limit of 0.37 mU/mL and an excellent selectivity over other proteins. Compared with conventional colorimetric assays, this visual sensor shows the distinct advantages of simple fabrication, cost-effectiveness and easy to implement. We believe that this study can provide a new insight into the fabrication of responsive alginate hydrogel for promising applications in chemical sensing and biomedical fields.

Time-Resolved Fluorescence Detection of Superoxide Anions Based on an Enzyme-Integrated Lanthanide Coordination Polymer Composite.

In this work, we proposed a new strategy of fabricating time-resolved fluorescent nanoprobes by using an enzyme-integrated lanthanide coordination polymer (CP) composite for the detection of superoxide anions (O2•-). This CP composite was constructed with terbium ions (Tb3+) as a metal node, adenosine triphosphate (ATP) as a bridge ligand, and carboxyphenylboronic acid (CPBA) as a sensitizer in which superoxide dismutase (SOD) was encapsulated by a self-adaptive inclusion process. The as-prepared SOD@ATP/Tb-CPBA displays both catalytic and fluorescence properties. Benefiting from the shielding effect of ATP/Tb CP, greatly enhanced catalytic activity and stability against harsh environments can be obtained in the loaded SOD. Meanwhile, the loaded SOD can remove the water molecules on the coordination sphere of Tb3+, leading to a significant increase in the fluorescence intensity and lifetime of SOD@ATP/Tb-CPBA. However, upon the addition of O2•-, the fluorescence of SOD@ATP/Tb-CPBA was quenched significantly. This is because SOD can convert O2•- into H2O2 to induce the deboronation of CPBA, resulting in an intramolecular charge transfer process. On this basis, by taking advantage of Tb3+ in long lifetime emission, a time-resolved fluorescence method was developed for the detection of O2•-, and satisfactory results have been achieved in both buffered aqueous solutions and serum samples. We believe that the presented study will open up a new avenue to develop enzyme-involved fluorescent nanoprobes.

Self-Assembled FRET Nanoprobe with Metal-Organic Framework As a Scaffold for Ratiometric Detection of Hypochlorous Acid.

Metal-organic framework (MOF) has been extensively explored in a number of fields due to its diverse properties. In this work, we demonstrated the potential of MOF in the establishment of a self-assembled fluorescence resonance energy transfer (FRET) system for developing ratiometric fluorescent nanoprobe. For this purpose, zeolitic imidazolate framework-8 (ZIF-8) was selected as a MOF model to entrap carbon dot (CD) and curcumin (CCM) during its self-assembly, which produces CD/CCM@ZIF-8. Benefiting from the confinement effect of ZIF-8, the loaded CD and CCM can be brought in close proximity for energy transfer to occur. Under optimal conditions, a high FRET efficiency of 68.7% can be obtained. Importantly, compared with traditional FRET systems, the fabrication process of CD/CCM@ZIF-8 is much more simple and straightforward, which does not involve the elaborate design and complicated synthesis of molecular linkers. However, in the presence of hypochlorous acid (HClO), the FRET process from CD to CCM will be disrupted, rendering CD/CCM@ZIF-8 to display a ratiometric response to HClO. This finding led to a method for ratiometric fluorescent detection of HClO with a detection limit of 67 nM and excellent selectivity over other reactive oxygen species. We believe that this study can give a new insight into the rational design and application of FRET-based nanoprobes.

Pyrophosphate ion-responsive alginate hydrogel as an effective fluorescent sensing platform for alkaline phosphatase detection.

A pyrophosphate ion (PPi)-responsive alginate hydrogel was fabricated by using Cu2+ as a crosslinker. Benefiting from the ultrahigh affinity of Cu2+ to PPi, which can discriminate PPi from phosphate ions and other anions, the incorporation of carbon dots enables the alginate hydrogel to be an effective fluorescent sensing platform for the detection of alkaline phosphatase.

Luminescent SiO2@Tb/guanosine 5'-monophosphate core-shell nanoscale coordination polymers for superoxide anion detection.

It is of great significance for superoxide anion (O2•-) detection due to its important role in regulation of biological function. The nanoscale coordination polymers (NCPs) core-shell nanostructures have attracted increasing interests for their nanosized-dependent properties. In this study, SiO2@Tb/guanosine 5'-monophosphate (GMP) NCPs with core-shell nanostructures was designed for O2•- detection. The SiO2@Tb/GMP NCPs core-shell nanostructures were produced by using SiO2 nanoparticles (NPs) as template to control their nano-size. First, Tb3+ was adsorbed on the surface of SiO2NPs by coordination with -COOH of SiO2NPs. Then the Tb/GMP NCPs shells were grown along the surface of SiO2NPs. The SiO2@Tb/GMP NCPs core-shell nanostructures were characterized with scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and Zeta potential. The resulted SiO2@Tb/GMP NCPs core-shell nanostructures displayed strong Tb/GMP emission which decreased linearly with the increased O2•- concentration in the range from 5.3 nM to 6.0 µM with a limit detection of 2.18 nM. And the SiO2@Tb/GMP NCPs core-shell nanostructures also exhibited good selectivity and high sensitivity in HEPES buffer at pH 7.4.

Ratiometric fluorescence detection of superoxide anion based on AuNPs-BSA@Tb/GMP nanoscale coordination polymers.

A novel ratiometric fluorescence nanosensor for superoxide anion (O2•- ) detection was designed with gold nanoparticles-bovine serum albumin (AuNPs-BSA)@terbium/guanosine monophosphate disodium (Tb/GMP) nanoscale coordination polymers (NCPs) (AuNPs-BSA@Tb/GMP NCPs). The abundant hydroxyl and amino groups of AuNPs-BSA acted as binding points for the self-assembly of Tb3+ and GMP to form core-shell AuNPs-BSA@Tb/GMP NCP nanosensors. The obtained probe exhibited the characteristic fluorescence emission of both AuNPs-BSA and Tb/GMP NCPs. The AuNPs-BSA not only acted as a template to accelerate the growth of Tb/GMP NCPs, but also could be used as the reference fluorescence for the detection of O2•- . The resulting AuNPs-BSA@Tb/GMP NCP ratiometric fluorescence nanosensor for the detection of O2•- demonstrated high sensitivity and selectivity with a wide linear response range (14 nM-10 µM) and a low detection limit (4.7 nM).

BSA-AuNPs@Tb-AMP metal-organic frameworks for ratiometric fluorescence detection of DPA and Hg2.

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA-AuNPs@Tb-AMP (BSA, bovine serum albumin; AMP, adenosine 5'-monophosphate; AuNPs, Au nanoparticles) metal-organic framework (MOF) nanostructures were synthesized by encapsulating BSA-AuNPs into Tb-AMP MOFs for the detection of 2,6-pyridinedicarboxylic acid (DPA) and Hg2+ . DPA could strongly co-ordinate with Tb3+ to replace water molecules from the Tb3+ center and accordingly enhanced the fluorescence of Tb-AMP MOFs. The fluorescence of BSA-AuNPs at 405 nm remained constant. While the fluorescence of BSA-AuNPs at 635 nm was quenched after Hg2+ was added, the fluorescence of Tb-AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg2+ . The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F545 /F405 linearly increased with increase of DPA concentration in the range of 50 nM to 10 µM with a detection limit as low as 17.4 nM. F635 /F405 increased linearly with increase of Hg2+ concentration ranging from 50 nM to 1 µM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg2+ in running water.

Analysis of a taurine-dependent promoter in Sinorhizobium meliloti that offers tight modulation of gene expression.

BACKGROUND: Genetic models have been developed in divergent branches of the class Alphaproteobacteria to help answer a wide spectrum of questions regarding bacterial physiology. For example, Sinorhizobium meliloti serves as a useful representative for investigating rhizobia-plant symbiosis and nitrogen fixation, Caulobacter crescentus for studying cell cycle regulation and organelle biogenesis, and Zymomonas mobilis for assessing the potentials of metabolic engineering and biofuel production. A tightly regulated promoter that enables titratable expression of a cloned gene in these different models is highly desirable, as it can facilitate observation of phenotypes that would otherwise be obfuscated by leaky expression. RESULTS: We compared the functionality of four promoter regions in S. meliloti (P(araA), P(tauA), P(rhaR), and P(melA)) by constructing strains carrying fusions to the uidA reporter in their genomes and measuring beta-glucuronidase activities when they were induced by arabinose, taurine, rhamnose, or melibiose. P(tauA) was chosen for further study because it, and, to a lesser extent, P(melA), exhibited characteristics suitable for efficient modulation of gene expression. The levels of expression from P(tauA) depended on the concentrations of taurine, in both complex and defined media, in S. meliloti as well as C. crescentus and Z. mobilis. Moreover, our analysis indicated that TauR, TauC, and TauY are each necessary for taurine catabolism and substantiated their designated roles as a transcriptional activator, the permease component of an ABC transporter, and a major subunit of the taurine dehydrogenase, respectively. Finally, we demonstrated that P(tauA) can be used to deplete essential cellular factors in S. meliloti, such as the PleC histidine kinase and TatB, a component of the twin-arginine transport machinery. CONCLUSIONS: The P(tauA) promoter of S. meliloti can control gene expression with a relatively inexpensive and permeable inducer, taurine, in diverse alpha-proteobacteria. Regulated expression of the same gene in different hosts can be achieved by placing both tauR and P(tauA) on appropriate vectors, thus facilitating inspection of conservation of gene function across species.

Effect of particle size on conformation and enzymatic activity of EcoRI adsorbed on CdS nanoparticles.

Better understanding of the interaction between nanoparticles (NPs) and protein is the basis for biological and biomedical applications of NPs. Water-soluble fluorescent CdS NPs have been widely used in the biological and biomedical fields and the study on effect of CdS NPs size on conformation and enzymatic activity of protein might be very important in its application. In this work, the interaction of CdS NPs with different size with type II restriction endonuclease (EcoRI) were investigated by atomic force microscopy, transmission electron microscopy, UV-vis spectroscopy, fluorescence quenching method, CD spectra, laser scanning confocal microscopy and gel electrophoresis. It was found that the equilibrium constant (kD) as well as the cooperativity degree of CdS NPs-EcoRI binding (Hill constant, n) strongly depended on the CdS NPs size. The different curvature of CdS NPs surface could result in different changes of EcoRI conformation. The gel electrophoresis indicated that the decrease in α-helix content more or less affected the activity of EcoRI.

Investigation of the association behaviors between bovine serum albumin and 2-(4-methylphenyl)-3-(N-acetyl)-5-(2,4-dichlorophenoxymethyl)-1,3,4-oxodiazoline.

The study was designed to examine the interaction between 2-(4-methylphenyl)-3-(N-acetyl)-5-(2,4-dichlorophenoxymethyl)-1,3,4-oxodiazoline (MPNDO) and bovine serum albumin (BSA) under physiological conditions by using fluorescence spectroscopy, ultraviolet absorption spectroscopy, FT-IR spectroscopy and circular dichroism spectroscopy and atomic force microscope. Spectroscopic analysis of the fluorescence emission quenching and ultraviolet absorption revealed that the quenching mechanism of bovine serum albumin by MPNDO was static quenching procedure. The binding constant and binding sites number at different temperatures were measured. The average binding distances between donor (BSA) and acceptor (MPNDO) was estimated to be 1.46 nm (301 K), based on the Föster non-radioactive energy transfer theory. An average size of 3.1 nm had a high proportion and these dots might be ascribed to BSA, some other dots with an average size of 6.6 nm might result from BSA-MPNDO bioconjugates while the average diameter of MPNDO was 1.6 nm, which was reasonable to conclude that one BSA-MPNDO bioconjugates consisted of one BSA and one MPNDO. The thermodynamic parameters, enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG) were calculated, which indicated that the action force was mainly van der Waals forces. The data collected through synchronous fluorescence, FT-IR spectroscopy and circular dichroism spectroscopy demonstrated that the conformation of BSA was not affected obviously in the presence of MPNDO.

Spectroscopic studies on the interaction between EcoRI and CdS QDs and conformation of EcoRI in EcoRI-CdS QDs bioconjugates.

Water-soluble fluorescent quantum dots (QDs) have been widely used in biological and biomedical fields, and the interaction between QDs and proteins and the conformational structure of the protein in the bioconjugate has attracted increasing attention. In this study, UV-Vis spectroscopy, fluorescence quenching, CD spectra, gel electrophoresis and Fourier transform infrared (FTIR) spectroscopic techniques were used to systematically investigate the interaction between type II restriction endonuclease (EcoRI) and CdS QDs and the conformational structure of EcoRI in the EcoRI-CdS QDs bioconjugates. The results indicated that electrostatic interactions played a major role in the binding reaction at pH 6.0, and the nature of quenching was static, resulting in forming CdS QDs-EcoRI bioconjugates. FTIR and CD spectra studies indicated a decrease of α-helical and turn structures accompanied by the increase of ß-sheet structures of EcoRI in the bioconjugates. This study showed that the interaction between EcoRI and CdS QDs resulted in a change in the secondary structure of EcoRI after it was conjugated with CdS QDs, but the enzyme activity was maintained.