Effect of molecular parameters on the binding of phenoxyacetic acid derivatives to albumins

Fluorescence spectroscopy and molecular docking analysis of the binding of Lactobacillus acidophilus GIM1.208 β-glucosidase with quercetin glycosides

Lactobacillus acidophilus is an important probiotic. The β-glucosidase produced by L. acidophilus GIM1.208 can transform quercetin glycosides of Rosa roxburghii Tratt to release quercetin and improve the functional activity of raw materials. Understanding the interaction and the characteristics of the two will lay a theoretical foundation for the site-directed transformation and functional application of the catalytic active site of enzymes. In our study, using the heterologously expressed and highly stable, purified L. acidophilus GIM1.208 BGL as the strain, the representative quercetin in β-glucosidase and Rosa roxburghii Tratt was preliminarily predicted and explored using ultraviolet-visible absorption spectroscopy. Fluorescence spectroscopy combined with molecular docking was used to determine the interaction characteristics of the glycoside substrates, rutin (Rut) and isoquercitrin (Iso). Results from molecular docking showed that Asp159, Arg56, Iso294, Phe292, and Gly25 were the main residues of β-glucosidase and Rut. Arg56 was found to be the most crucial residue of β-glucosidase and isoquercitrin; the interaction between Rut and Iso and β-glucosidase was mainly driven by hydrogen bonding. The combined free energy of β-glucosidase and Iso was found to be -182.10 kcal/mol, while that of β-glucosidase and Rut was -32.37 kcal/mol. The results of fluorescence spectroscopy showed that the fluorescence intensity of β-glucosidase decreased with an increase in Rut and Iso concentrations. This interaction made β-glucosidase quench endogenous fluorescence, which was static quenching. The binding constants of Rut and Iso with β-glucosidase were determined to be 0.50×10⁷ and 0.31×10⁷ L/mol, respectively, indicating that rutin had a stronger affinity when interacting with β-glucosidase. These findings were consistent with our prediction results determined using molecular docking studies.

Phenoxyherbicides induce production of free radicals in human erythrocytes: Oxidation of dichlorodihydrofluorescine and dihydrorhodamine 123 by 2,4-D-Na and MCPA-Na

Although it is known that phenoxyacetic herbicides significantly affect the oxidative status of human erythrocytes, there is no direct evidence of their ability to induce free radical production. To demonstrate this phenomenon we investigated the effect of two commonly used phenoxyherbicides-sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D-Na) and sodium salt of 4-chloro-2-methylphenoxyacetic acid (MCPA-Na) on oxidation of dihydrorhodamine 123 and H(2)DCFDA as well as on carbonyl group content in cellular proteins. Moreover, haemoglobin denaturation was also measured. The rate of fluorescent probe oxidation was significantly higher for 2,4-D-Na, while both compounds exerted similar effects on protein carbonyl group (an increase in their content) and on denaturation of haemoglobin (no changes were observed). These results and the previous data led us to a conclusion that pro-oxidative action of phenoxyherbicides is strongly dependent on the localization of the substituent in the phenol ring. We also proposed a metabolic reaction chain that explains the mechanism of action of 2,4-D-Na in vivo.

Contribution of ionization and lipophilicity to drug binding to albumin: a preliminary step toward biodistribution prediction

Understanding the molecular mechanisms governing albumin binding is a major challenge in absorption-distribution-metabolism-excretion prediction. To gain insight into this complex field, an ultracentrifugation method to measure the drug fraction bound to bovine serum albumin [%B(DAB)] is presented. The second part of the study shows the dependence of the experimental binding parameter on ionization and lipophilicity descriptors (pK(a) and log D(oct)(7.4) for a series of 14 structurally diverse drugs. Finally, a docking strategy is used to rationalize the findings; the results confirm the mostly nonspecific nature of the interaction of albumin with neutral ligands.

Binding of low molecular mass compounds to proteins studied by liquid chromatographic techniques

The newest achievements in the application of miscellaneous liquid chromatographic techniques such as size-exclusion, ion-exchange and reversed-phase high-performance liquid chromatography, and thin-layer chromatography for the elucidation of the various aspects of the binding of ligands to proteins are compiled and briefly discussed. Examples of employment in pharmaceutical and clinical chemistry, drug design, enzyme kinetic studies and environmental protection are presented.

Piezoelectric quartz crystal impedance and electrochemical impedance study of HSA-diazepam interaction by nanogold-structured sensor

Human serum albumin (HSA) was immobilized on the surface of colloidal Au and exposed to diazepam. Colloidal Au were at first self-assembled on the gold electrode through the thiol groups of a 1,6-hexanedithiol monolayer. The real-time course of the resonant frequency and equivalent circuit parameters of the sensor during the protein-diazepam binding was determined for the first time by piezoelectric quartz crystal impedance (PQCI). On the basis of the multidimensional information provided by the PQCI analysis, it was concluded that the decrement of the observed frequency was mainly ascribable to the mass loading on the sensor surface. Compared with a bare gold electrode, the gold electrode self-assembled from nanogold colloids exhibits maintained biocompatibility, increased capacity, and more bioactivity. Cyclic voltammetry and electrochemical impedance techniques were used to investigate the immobilization of HSA and the interaction between HSA and diazepam. Results testified that gold colloid could play the role of an efficient electron-conducting tunnel and have a very high ratio of surface to volume. Additionally, the kinetics of the binding process was investigated. The estimated binding constant (K) and the number of binding site (n) on one HSA molecule were 1.66 x 10(6) mol l(-1) and 1.28, respectively.