[Inhibitory effect of icariin on acetylcholinesterase].

Acetylcholinesterase (AChE) inhibitors are mainly used in the treatment of Alzheimer's disease (AD). The inhibitory effect of icariin on the activity of AChE was investigated by inhibition kinetics. The binding interaction and binding sites between icariin and AChE were also studied by using fluorimetry and molecular docking, respectively. The results showed that icariin could potently inhibit the activity of AChE, the IC50 value was determined to be 3.50 x 10(-8) mol x L(-1), and the determined IC50 value to tacrine was 0.75 x 10(-8) mol x L(-1). Kinetic analyses showed that icariin is a reversible and mixed type AChE inhibitor. The inhibition constants K1 and K(IS) were determined to be 2.67 x 10(-8) and 4.43 x 10(-8) mol x L(-1), respectively. Icariin binds selectively to the AChE peripheral anionic site via hydrogen bonds and Van der Waals forces.

Affinity binding-guided fluorescent nanobiosensor for acetylcholinesterase inhibitors via distance modulation between the fluorophore and metallic nanoparticle.

The magnitude of fluorescence enhancement was found to depend strongly on the distance between fluorophores and metal nanostructures in metal-enhanced fluorescence (MEF). However, the precise placement of the particle in front of the molecule with nanometer accuracy and distance control is a great challenge. We describe a method using acetylcholinesterase (AChE) to modulate the distance between a gold nanoparticle (AuNP) and the fluorophore 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) (DDAO). We found that DDAO is a reversible mixed type-I AChE inhibitor. DDAO binds to the peripheral anionic site and penetrates into the active gorge site of AChE via inhibition kinetics test and molecular docking study. The affinity ligand DDAO bound to AChE which was immobilized onto AuNPs, and its fluorescence was sharply enhanced due to MEF. The fluorescence was reduced by distance variations between the AuNP and DDAO, which resulted from other inhibitors competitively binding with AChE and partly or completely displacing DDAO. Experimental results show that changes in fluorescence intensity are related to the concentration of inhibitors present in the solution. In addition, the nanobiosensor has high sensitivity, with detection limits as low as 0.4 µM for paraoxon and 10 nM for tacrine, and also exhibits different reduction efficiencies for the two types of inhibitor. Thus, instead of an inhibition test, a new type of affinity binding-guided fluorescent nanobiosensor was fabricated to detect AChE inhibitors, determine AChE inhibitor binding mode, and screen more potent AChE inhibitors. The proposed strategy may be applied to other proteins or protein domains via changes in the affinity ligand.

[Study on the interaction of quercetin with beta-glucosidase by fluorescence spectroscopy and molecular docking].

Combined with molecular docking model, a fluorescence method was applied to investigate the interaction between quercetin and beta-glucosidase and the acting mechanism. The interaction between beta-glucosidase and quercetin, as well as the enzyme inhibitor 4-nitrophenyl-beta-D-thioglucoside, was studied by the AutoDock4.2 molecular docking model, respectively. The binding reaction was simultaneously studied using fluorescence quenching method. The results showed that these interactions result in the endogenous fluorescence quenching of beta-glucosidase, which belongs to a static quenching mechanism. The calculated binding constants were 4.36 X 10(4), 4.04 x 10(4) and 3.18 x 10(4) L mol(-1) at 17, 27 and 37 degrees C, respectively. The results revealed that quercetin tended to bind with beta-glucosidase mainly by hydrogen bond and hydrophobic interaction, as well as electrostatic forces. Both fluorescence spectroscopy and molecular docking are complementary to each other for the investigation of the interaction between beta-glucosidase and quercetin from the experimental and theoretical view.

[The interaction between genistein and beta-glucosidase].

The interaction between genistein and beta-glucosidase was studied using fluorescence quenching method and synchronous fluorimetry. The binding reaction was simultaneously studied by the AutoDock 4.2 molecular docking model. Data from fluorescence spectroscopy indicated that these interactions resulted in the endogenous fluorescence quenching of beta-glucosidase, which belongs to a static quenching mechanism. The calculated binding constants were 3.69 x 10(4), 3.06 x 10(4) and 2.36 x 10(4) L x mol(-1) at 17, 27 and 37 degrees C, respectively. The evidences from synchronous fluorescence showed the effect of genistein on the microenvironment around beta-glucosidase in aqueous solution. The inhibition test showed that the activity of beta-glucosidase could be inhibited by genistein. The determined bimolecular rate constant (k(i)) was 1.2 x 10(3) (mol x L(-1)(-1) x min(-1). Molecular docking was performed to reveal the possible binding mode or mechanism and suggested that genistein could bind strongly to beta-glucosidase. The results revealed that genistein tended to bind with beta-glucosidase mainly by hydrogen bond and hydrophobic interaction as well as electrostatic forces.