Molecular dynamics studies of the inhibitory mechanism of copper(Ⅱ) on aggregation of amyloid β-peptide

The inhibitory mechanism of copper（Ⅱ） on the aggegation of amyloid β-peptide （Aβ） was investigated by molecular dynamics simulations. The binding mode ofcopper（Ⅱ） with Aβ is characterized by the imidazole nitrogen atom, Nπ, of the histidine residue H 13, acting as the anchoring site, and the backbone＇s deprotoned amide nitogen atoms as the main binding sites. Drove by the coordination bonds and their induced hydrogen bond net, the conformations of Aβ converted from β-sheet non-β-sheet conformations, which destabilized the aggregation of Aβ into fibrils.

Molecular modeling of the inhibitory mechanism of copper(II) on aggregation of amyloidβ-peptide

Aggregation of amyloid ?-peptide (A?) into insoluble fibrils is a key pathological event in Alzheimer’s disease (AD). Under certain conditions, Cu(II) exhibits strong inhibitory ef-fect on the Zn(II)-induced aggregation, which occurs significantly even at nearly physiological concentrations of zinc ion in vitro. Cu(II) is considered as a potential factor in the normal brain preventing A? from aggregating. The possible mechanism of the inhibitory effect of Cu(II) is in-vestigated for the first time by molecular modeling method. In the mono-ring mode, the Y10 residue promotes typical quasi-helix conformations of A?. Specially, [Cu-H13(Np)-Y10(OH)] complex forms a local 3.010 helix conformation. In the multi-ring mode, the side chains of Q15 and E11 residues collaborate harmoniously with other chelating ligands producing markedly low energies and quasi-helix conformations. [Cu-3N-Q15(O)-E11(O1)] and [Cu-H13(Np)-Y10(OH)] complex with quasi-helix conformations may prefer soluble forms in solution. In addition, hydro-gen-bond interactions may be the main driving force for A? aggregation. All the results will pro-vide helpful clues for an improved understanding of the role of Cu(II) in the pathogenesis of AD and contribute to the development of an “anti-amyloid” therapeutic strategy.

Discovery of human pancreatic lipase inhibitors from root of Rhodiola crenulata via integrating bioactivity-guided fractionation,chemical profiling and biochemical assay

Although herbal medicines(HMs)are widely used in the prevention and treatment of obesity and obesity-associated disorders,the key constituents exhibiting anti-obesity activity and their molecular mechanisms are poorly understood.Recently,we assessed the inhibitory potentials of several HMs against human pancreatic lipase(hPL,a key therapeutic target for human obesity),among which the root-extract of Rhodiola crenulata(ERC)showed the most potent anti-hPL activity.In this study,we adopted an integrated strategy,involving bioactivity-guided fractionation techniques,chemical profiling,and biochemical assays,to identify the key anti-hPL constituents in ERC.Nine ERC fractions(retention time=12.5e35 min),obtained using reverse-phase liquid chromatography,showed strong anti-hPL activity,while the major constituents in these bioactive fractions were subsequently identified using liquid chromatography-quadrupole time-of-flight mass spectrometry(LC-Q-TOF-MS/MS).Among the identified ERC constituents,1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose(PGG)and catechin gallate(CG)showed the most potent anti-hPL activity,with pIC50 values of 7.59±0.03 and 7.68±0.23,respectively.Further investigations revealed that PGG and CG potently inhibited hPL in a non-competitive manner,with inhibition constant(Ki)values of 0.012 and 0.082 mM,respectively.Collectively,our integrative analyses enabled us to efficiently identify and characterize the key anti-obesity constituents in ERC,as well as to elucidate their anti-hPL mechanisms.These findings provide convincing evidence in support of the anti-obesity and lipid-lowering properties of ERC.

Enzymatic properties of phenoloxidase from Pieris rapae （Lepidoptera） larvae

The kinetic parameters of partially purified phenoloxidase （PO, EC. 1.14.18.1） from the 5th instar larvae of Pieris rapae （Lepidoptera） were determined, using L-3, 4- dihydroxyphenylalanine （L-DOPA） as substrate. The optimal pH and temperature of the enzyme for the oxidation of L-DOPA were determined to be at pH 7.0 and at 42℃, respectively. The enzyme was stable between pH 6.5 and 7.4 and at temperatures lower than 37℃. At pH 6.8 and 37℃, the Michaelis constant （Kin） and maximal velocity （V） of the enzyme for the oxidation of L-DOPA were determined to be 0.80 mmol/L and 1.84 μmol/ L/min, respectively. Tetra-hexylresorcinol and 4-dodecylresorcinol effectively inhibited activity of phenoloxidase and this inhibition was reversible and competitive, with the IC50 of 1.50 and 1.12 μmol/L, respectively. The inhibition constants were estimated to be 0.50 and 0.47μmol/L, respectively.

Delphinidin-3-O-sambubioside: a novel xanthine oxidase inhibitor identified from natural anthocyanins

Objectives:This study was conducted to investigate the xanthine oxidase(XO)inhibitory activities of 18 monomeric anthocyanins from berry fruits and roselle,and to illustrate the underlying mechanism of the most active anthocyanin delphinidin-3-O-sambubioside.Materials and Methods:Eighteen monomeric anthocyanins were prepared and purified in our laboratory.The inhibitory properties of anthocyanins were investigated by in vitro inhibitory activity studies and fluorescence quenching studies;the inhibitory mechanism was explored through kinetic studies,fluorescence quenching studies,circular dichroism analysis and computational docking simulations.Results:XO inhibitory activities of anthocyanins were related to the structures of B rings and glycosides.Among all the tested anthocyanins,delphinidin-3-O-sambubioside showed the most potent inhibitory activity with an IC_(50) of 17.1μmol/L,which was comparable to the positive control allopurinol.Spectroscopic results revealed that delphinidin-3-O-sambubioside could spontaneously interact with XO and induce conformational changes.Computational docking study indicated that delphinidin-3-O-sambubioside could bind to XO with a proper orientation,stably formed π-π interactions and hydrogen bonds with key residues,thus preventing the substrate from entering the active pocket.Conclusions:In brief,our study identified delphinidin-3-O-sambubioside as a potent XO inhibitor from natural anthocyanins,which is potentially applicable for prevention and treatment of hyperuricemia.