Li Chen,Wang Zhuan-Hua,Yu Deng-Guang,Williams Gareth R
This manuscript reports a new type of drug-loaded core-shell nanofibers that provide tunable biphasic release of quercetin. The nanofibers were fabricated using a modified coaxial electrospinning process, in which a polyvinyl chloride (PVC)-coated concentric spinneret was employed. Poly (vinyl pyrrolidone) (PVP) and ethyl cellulose (EC) were used as the polymer matrices to form the shell and core parts of the nanofibers, respectively. Scanning and transmission electron microscopy demonstrated that the nanofibers had linear morphologies and core-shell structures. The quercetin was found to be present in the nanofibers in the amorphous physical status, on the basis of X-ray diffraction results. In vitro release profiles showed that the PVP shell very rapidly freed its drug cargo into the solution, while the EC core provided the succedent sustained release. Variation of the drug loading permitted the release profiles to be tuned.
Abstract NAD(H)-dependent 7α-hydroxysteroid dehydrogenase catalyzes the oxidation of chenodeoxycholic acid to 7-oxolithocholic acid. Here, we designed mutations of Ile258 adjacent to the catalytic pocket of Brucella melitensis 7α-hydroxysteroid dehydrogenase. The I258M variant gave a 4.7-fold higher k cat , but 4.5-fold lower K M , compared with the wild type, resulting in a 21.8-fold higher k cat / K M value for chenodeoxycholic acid oxidation. It presented a 2.0-fold lower K M value with NAD + , suggesting stronger binding to the cofactor. I258M produced 7-oxolithocholic acid in the highest yield of 92.3% in 2 h, whereas the wild-type gave 88.4% in 12 h. The I258M mutation increased the half-life from 20.8 to 31.1 h at 30 °C. Molecular dynamics simulations indicated increased interactions and a modified tunnel improved the catalytic efficiency, and enhanced rigidity at three regions around the ligand-binding pocket increased the enzyme thermostability. This is the first report about significantly improved catalytic efficiency, cofactor affinity, and enzyme thermostability through single site-mutation of Brucella melitensis 7α-hydroxysteroid dehydrogenase. Key points • Sequence and structure analysis guided the site mutation design. • Thermostability, catalytic efficiency and 7 - oxo - LCA production were determined . • MD simulation was performed to indicate the improvement by I258M mutation .
Vanillin (VAN) and ethyl vanillin (EVA) are widely used food additives as flavor enhancers, but may have a potential security risk. In this study, the properties of binding of VAN or EVA with calf thymus DNA (ctDNA) were characterized by multi-spectroscopic methods, multivariate curve resolution-alternating least-squares (MCR–ALS) algorithm and molecular simulation. The concentration profiles for the components (VAN or EVA, ctDNA and VAN–ctDNA or EVA–ctDNA complex) by the MCR–ALS analysis showed that VAN or EVA interacted with ctDNA and formed VAN–ctDNA or EVA–ctDNA complex. The groove binding of VAN or EVA to ctDNA was supported by the results from viscosity measurements, melting studies, denaturation experiments, and competitive binding investigations. Analysis of the Fourier transform infrared spectra corroborated the prediction by molecular docking that VAN and EVA preferentially bound to thymine bases region of ctDNA. The circular dichroism and DNA cleavage assays indicated that both VAN and EVA induced conformational change (from B − like DNA structure toward to A − like form), but didn’t lead to a significant damage on DNA. The fluorescence quenching of Hoechst 33,258–ctDNA complex by VAN or EVA was a static quenching, and hydrogen bonding and van der Waals forces were main forces. This study has provided insights into the mechanism of interaction between VAN or EVA with ctDNA, and may also help better understand their potential toxicity with regard to food safety.
VAN or EVA binds to A–T rich regions of ctDNA in the minor groove.
危险品化学品经营许可证（带存储）