Investigation of the interactions of quercetin and morin with trypsin

Interaction between Caffeic Acid Phenethyl Ester (CAPE) and Protease: Monitoring by Spectroscopic and Molecular Docking Approaches

The interaction of one anticancer drug (caffeic acid phenethyl ester, CAPE) with three proteases (trypsin, pepsin and α-chymotrypsin) has been investigated with multispectral methods and molecular docking. As an active components in propolis, the findings are of great benefit to metabolism, design and stuctural modification of drugs. The results show that CAPE has an obvious ability to quench the trypsin, pepsin, or α-chymotrypsin fluorescence mainly through a static quenching procedure. Trypsin has the largest binding affinity to CAPE, and α-chymotrypsin has the smallest binding affinity to CAPE. The data obtained from thermodynamic parameters and molecular docking prove that the spontaneously interaction between CAPE and each protease is mainly due to a combination of Van der Waals (vdW) force and hydrogen bond (H-bond), controlled by enthalpy-driven process. The binding force, strength, position, and the number of H-bond are further obtained from the results of molecular docking. Through ultraviolet spectroscopy, dynamic light scattering (DLS) and circular dichroism (CD) experiments, the change in the protease secondary structure induced by CAPE was observed. Additionally, the addition of protease had a positive impact on the antioxidative activity of CAPE, and α-chymotrypsin has the greatest impact on the removal of DPPH free radicals by CAPE.

A Study of the Interaction, Morphology, and Structure in Trypsin-Epigallocatechin-3-Gallate Complexes

Understanding the interaction between proteins and polyphenols is of significance to food industries. The aim of this research was to investigate the mode of aggregation for trypsin-EGCG (Epigallocatechin-3-gallate) complexes. For this, the complex was characterized by fluorescence spectroscopy, circular dichroism (CD) spectra, small-angel X-ray scattering (SAXS), and atomic force microscope (AFM) techniques. The results showed that the fluorescence intensity of trypsin-EGCG complexes decreased with increasing the concentration of EGCG, indicating that the interaction between trypsin and EGCG resulted in changes in the microenvironment around fluorescent amino acid residues. The results of CD analysis showed conformational changes in trypsin after binding with EGCG. The results from SAXS analysis showed that the addition of EGCG results in the formation of aggregates of trypsin-EGCG complexes, and increasing the concentration of EGCG resulted in larger aggregates. AFM images showed that the trypsin-EGCG complex formed aggregates of irregular ellipsoidal shapes with the size of about 200 × 400 × 200 nm, with EGCG interconnecting the trypsin particles. Overall, according to these results, it was concluded that the large aggregates of trypsin-EGCG complexes are formed from several small aggregates that are interconnected. The results of this study shed some light on the interaction between digestive enzymes and EGCG.

Comparative studies on the interaction of nine flavonoids with trypsin

In this study, the interaction between nine classic flavonoids (including baicalin, quercetin, myricetin, rutin, puerarin, daidzein, liquiritin and isoliquiritin) and trypsin was investigated by fluorescence spectroscopy and molecular modeling methods. The results reveal that all flavonoids can interact with trypsin to form flavonoid-trypsin complexes. The binding parameters obtained from the data at different temperatures indicate that all flavonoids can spontaneously bind with trypsin with one binding site. The binding constants of trypsin with nine classic flavonoids are in the following order as: baicalin > myricetin > rutin > isoliquiritin > hesperidin > puerarin > quercetin > daidzein > liquiritin. The interaction forces between flavonoids and trypsin may be electrostatic forces (except for rutin/puerarin/daidzein), hydrophobic interactions as well as van der Waals forces. Synchronous fluorescence spectroscopy shows that the interaction between flavonoids and trypsin changes the hydrophobicity of the microenvironment of tryptophan (Trp) residues. All flavonoids close to tyrosine (Tyr) residues but have no effect on the microenvironment around Tyr residues except for hesperidin and liquiritin. Molecular modeling displays that all flavonoids bind directly into trypsin cavity site and lead to a decrease in enzyme activity.

Study of Binding Properties Between Two New Ibuprofen and Naproxen Based Acyl Hydrazone Derivatives and Trypsin

Two acyl hydrazone derivatives, AHI and AHN,made from ibuprofen and naproxen-derived hydrazides, were prepared and studied of binding properties with serine protease trypsin by UV-vis absorption and fluorescence quenching at pH 7.4. The results suggest that both hydrazones can interact strongly with trypsin and there are the formation of trypsin-hydrazone complexes. The Stern-Volmer constants, binding constants,binding sites and the corresponding thermodynamic parameters ΔH°, ΔS° and ΔG° were calculated at different temperatures.The effect of common metal ions on the constants was also discussed. The binding modes can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance(r) ~3 nm between the donor (trypsin) and acceptors (AHI and AHN) was obtained according to Förster's non-radiative energy transfer theory. Moreover, LOD and LOQ of hydrazones were calculated in the presence of trypsin.

Binding characteristics of psoralen with trypsin: Insights from spectroscopic and molecular modeling studies

Psoralen (PSO) is a naturally occurring furanocoumarin with a variety of pharmacological activities, however very limited information on the interaction of PSO with trypsin is available. In this study, the binding characteristics between PSO and trypsin at physiological pH were investigated using a combination of fluorescence, UV-vis absorption, circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopic, chemometric and molecular modeling approaches. It was found that the fluorescence quenching of trypsin by PSO was a static quenching procedure, ascribing the formation of a PSO-trypsin complex. The binding of PSO to trypsin was driven mainly by hydrophobic forces as the positive enthalpy change and entropy change values. The molecular docking showed that PSO inserted into the active site pocket of trypsin to interact with the catalytic residues His57, Asp102 and Ser195 and may cause a decrease in trypsin activity. The results of CD and FT-IR spectra along with the temperature-induced denaturation studies indicated that the addition of PSO to trypsin led to the changes in the secondary structure of the enzyme. The concentration profiles and spectra of the three components (PSO, trypsin, and PSO-trypsin complex) obtained by multivariate curve resolution-alternating least squares analysis exhibited the kinetic processes of PSO-trypsin interaction. This study will be helpful to understand the mechanism of PSO that affects the conformation and activity of trypsin in biological processes.

Interaction of gallic acid with trypsin analyzed by spectroscopy

The interactions between trypsin and gallic acid (GA) were investigated by means of fluorescence spectroscopy, UV-vis absorption spectroscopy, resonance light scattering (RLS) spectroscopy, synchronous fluorescence spectroscopy, and enzymatic inhibition assay. It was found that GA can cause the fluorescence quenching of trypsin during the process of formation of GA-trypsin complex, resulting in inhibition of trypsin activity (IC₅₀ = 3.9 × 10⁻⁶ mol/L). The fluorescence spectroscopic data showed that the quenching efficiency can reach about 80%. The binding constants were 1.9371 × 10⁴ L/mol, 1.8192 × 10⁴ L/mol, and 1.7465 × 10⁴ L/mol at three temperatures, respectively. The thermodynamic parameters revealed that hydrogen bonds, van der Waals, hydrophobic, and electrostatic interactions were involved in the binding process of GA to trypsin. Molecular modeling studies illustrated a specific display of binding information and explained most of the experiment phenomena. The microenvironments of tryptophan and tyrosine residue in trypsin were changed by the GA. Results indicated that GA was a strong quencher and inhibitor of trypsin.

Structure Activity Relationships of Flavonoids as Potent α-Amylase Inhibitors

The effects of three flavonoids (quercetin, luteolin, diosmetin) on α-amylase were examined by enzymatic kinetics and fluorescence spectroscopy. The three test flavonoids were non-competitive inhibitors of the enzyme. Addition of flavonoids led to fluorescence quenching of α-amylase. The quenching was initiated from the formation of a complex between the flavonoids and the enzyme, corresponding to a static quenching process. An α-amylase molecule provides a binding site for the test flavonoid. The main binding force was hydrophobic. The decreasing order of inhibition of α-amylase by flavonoids and the binding force was luteolin, diosmetin, and quercetin. It is demonstrated that hydroxylation in ring C and methylation of the hydroxyl group in ring B of flavonoids may weaken the binding affinities to α-amylase.

Study on the bindings of dichlorprop and diquat dibromide herbicides to human serum albumin by spectroscopic methods

The interactions of dichlorprop (DCP) and diquat dibromide (DQ) herbicides with human serum albumin (HSA) protein were studied by UV absorption, fluorescence, synchronous fluorescence and circular dichroism (CD) spectroscopy. Both DCP and DQ quenched the fluorescence emission spectrum of HSA through the static quenching mechanism. The Stern-Volmer quenching constant, binding constant, the number of binding sites and thermodynamic parameters were determined at 288K, 298K, 310K and 318K. In HSA-DCP and HSA-DQ systems, an increase in temperature led to a decrease in the Stern-Volmer quenching constant and binding constant. One binding site was obtained for DCP and DQ on HSA. It was found that DCP can bind to HSA with higher affinity than DQ. Negative ΔH and positive ΔS values were obtained for the binding processes between protein and herbicide molecules. This result displayed that electrostatic interactions play a major role in the formation of HSA-DCP and HSA-DQ complexes. The binding processes were exothermic reactions and spontaneous. In addition, synchronous fluorescence and CD spectra of HSA revealed that the binding of DCP to HSA did not cause a significant conformational change in protein, but the interaction of DQ with HSA led to an alteration in the protein structure.

Mechanism of cinnamic acid-induced trypsin inhibition: a multi-technique approach

In order to investigate the association of the protease trypsin with cinnamic acid, the interaction was characterized by using fluorescence, UV-vis absorption spectroscopy, molecular modeling and an enzymatic inhibition assay. The binding process may be outlined as follows: cinnamic acid can interact with trypsin with one binding site to form cinnamic acid-trypsin complex, resulting in inhibition of trypsin activity; the spectroscopic data show that the interaction is a spontaneous process with the estimated enthalpy and entropy changes being -8.95 kJ mol(-1) and 50.70 J mol(-1) K(-1), respectively. Noncovalent interactions make the main contribution to stabilize the trypsin-cinnamic acid complex; cinnamic acid can enter into the primary substrate-binding pocket and alter the environment around Trp and Tyr residues.

Spectroscopic and molecular modeling studies of the interaction between morin and polyamidoamine dendrimer

Interactions between the polyamidoamine (PAMAM) dendrimer and drug molecules are of interest for their potential biomedical applications. The goal of this work is to examine the interaction of PAMAM-C12 25% dendrimer with morin. The ultraviolet-visible, fluorescence spectroscopic methods as well as molecular modeling were used to analyze drug-binding mode, binding constants and binding sites, etc. The experimental data showed that the binding constant of morin-PAMAM-C12 25% is about 10(5) L/mol. The interaction of morin with PAMAM-C12 25% is mainly driven by the hydrophobic, electrostatic, hydrogen bonds and van der Waals forces. There are mainly three classes of binding site of morin at the interface of PAMAM-C12 25%. These results provided some useful information for self-assembling and disassembling the PAMAM dendrimer as well as efficient drug delivery and therapeutic applications.

The interactions of glutathione-capped CdTe quantum dots with trypsin

Due to their unique fluorescent properties, quantum dots present a great potential for biolabelling applications; however, the toxic interactions of quantum dots with biopolymers are little known. The toxic interactions of glutathione-capped CdTe quantum dots with trypsin were studied in this paper using synchronous fluorescence spectroscopy, fluorescence emission spectra, and UV-vis absorption spectra. The interaction between CdTe quantum dots and trypsin resulted in structure changes of trypsin and inhibited trypsin's activity. Fluorescence emission spectra revealed that the quenching mechanism of trypsin by CdTe quantum dots was a static quenching process. The binding constant and the number of binding sites at 288 and 298 K were calculated to be 1.98 × 10(6) L mol(-1) and 1.37, and 6.43 × 10(4) L mol(-1) and 1.09, respectively. Hydrogen bonds and van der Waals' forces played major roles in this process.

Mechanisms of tannin-induced trypsin inhibition: a molecular approach

Association of procyanidins with enzymes has drawn attention over the past few years. This work aimed to bring insights on interaction of the protease trypsin with the procyanidin dimer (B3). This interaction was characterized by fluorescence quenching, saturation transfer difference (STD) NMR, molecular modeling, and through an enzymatic inhibition assay. Further studies were conducted regarding the influence of pectin on the binding process. A general overview of the binding process may be outlined as follows: a) at low procyanidin concentrations (below the critical micellar concentration-(CMC)) a specific interaction probably driven by hydrogen bonds between the protein backbone and the procyanidin occurs and is associated with the reduction of both enzyme activity and fluorescence; b) at high procyanidin concentration (above the CMC) the interaction becomes nonspecific. This variation in both nature and extent of the interaction with the variation of procyanidin concentration shows how tannin self-association may affect the interaction between tannins and proteins. It was also shown that the mechanism through which pectin affects the interaction between procyanidin B3 and trypsin is of a competitive type.

The electrostatic interactions between nano-TiO(2) and trypsin inhibit the enzyme activity and change the secondary structure of trypsin

In this work, the interaction between nano-TiO(2) and trypsin was investigated, and the mechanisms of the interaction were explored by the methods of UV-vis detection, circular dichroism (CD), and fluorescence. The results clearly demonstrated that nano-TiO(2) had an inhibitory effect on the enzyme activity. The activity was decreased to 64% of the untreated trypsin in the presence of 300 μg/ml nano-TiO(2). UV spectrometry proved that nano-TiO(2) had a strong physical absorption effect on trypsin, and the CD spectra revealed that the secondary structure of trypsin was partly destroyed while bound together with nano-TiO(2). The ratio of α-helix increased from 7.9% to 12.8% in the presence of 100 μg/ml TiO(2) while the ratio of β-sheet decreased from 48.7% to 36.4%. Furthermore, the fluorescence spectrometry indicated that nano-TiO(2) could quench the intrinsic fluorescence of trypsin through static quenching. Meanwhile, the binding constant was calculated to be 1, and the process of binding of trypsin on nano-TiO(2) was a spontaneous molecular interaction procedure in which electrostatic interaction plays a major role. Our study was to provide a useful approach for evaluating the health risk of nanomaterials on level of proteins.

Biological relevance of the interaction between procyanidins and trypsin: a multitechnique approach

The interactions between the digestive protease trypsin type IX-S from porcine pancreas and grape seed procyanidins were monitorized by fluorescence quenching, dynamic light scattering, nephelometry, circular dichroism, and enzymatic inhibition assay. This work reports that the inhibition of trypsin activity by grape seed procyanidins and the respective quenching of intrinsic protein fluorescence are closely related. These two phenomena increase with the molecular weight of the tested procyanidins. The interaction between procyanidins and enzyme was shown to involve a specific interaction as inferred from the fluorescence assays. It was also shown by fluorescence spectroscopy that the binding of procyanidin molecules to the enzyme does not induce significant structural modifications. A relationship between aggregate formation, using dynamic light scattering and nephelometry, and fluorescence quenching was observed with maxima achieved for similar stoichiometric ratios. The binding of procyanidins to trypsin affects only slightly protein structure as seen by circular dichroism.

Investigation of the interactions of lysozyme and trypsin with biphenol A using spectroscopic methods

The interaction between bisphenol A (BPA) and lysozyme (or trypsin) was investigated by UV-vis absorption, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. BPA effectively quenched the intrinsic fluorescence of lysozyme and trypsin via static quenching. H-bonds and van der Waals interactions played a major role in stabilizing the BPA-proteinase complex. The distance r between donor and acceptor was obtained to be 1.65 and 2.26 nm for BPA-lysozyme and BPA-trypsin complexes, respectively. The effect of BPA on the conformation of lysozyme and trypsin was analyzed using synchronous fluorescence and three-dimensional fluorescence spectra.