Molecular interactions of isoxazolcurcumin with human serum albumin: spectroscopic and molecular modeling studies

Naphthalene-fused (α-alkoxycarbonyl)methylene-γ-butyrolactones: antiproliferative activity and binding to bovine serum albumin and DNA

A naphthalene-fused (α-alkoxycarbonyl)methylene-γ-butyrolactone (methyl 2-[7-hydroxy-2-oxonaphtho[1,2-b]furan-3(2H)-yliden]acetate) has been prepared as a representative compound of a potential class of cytotoxic agents. In vitro cytotoxicity has been evaluated against HCT-15 colon and MCF-7 breast cancer cells and IC(50) was 64-66 μM, causing morphological changes in cells, such as loss of adhesion, rounding, cell shrinkage, and detachment from the substratum. The binding constant K of the complex between the naphthyl lactone with bovine serum albumin (8 × 10(3) M(-1)) suggests a minor change in protein folding. The K of the binding with DNA (1.06 × 10(4) M(-1)) suggests nonspecific electrostatic interactions with DNA and this was confirmed by melting point data (Tm<0.6 °C). Therefore, naphthalene-fused (α-alkoxycarbonyl)methylene-γ-butyrolactone should not be able to intercalate with DNA but its interaction should occur at the level of DNA surface.

Multitargeting by curcumin as revealed by molecular interaction studies

Curcumin (diferuloylmethane), the active ingredient in turmeric (Curcuma longa), is a highly pleiotropic molecule with anti-inflammatory, anti-oxidant, chemopreventive, chemosensitization, and radiosensitization activities. The pleiotropic activities attributed to curcumin come from its complex molecular structure and chemistry, as well as its ability to influence multiple signaling molecules. Curcumin has been shown to bind by multiple forces directly to numerous signaling molecules, such as inflammatory molecules, cell survival proteins, protein kinases, protein reductases, histone acetyltransferase, histone deacetylase, glyoxalase I, xanthine oxidase, proteasome, HIV1 integrase, HIV1 protease, sarco (endo) plasmic reticulum Ca(2+) ATPase, DNA methyltransferases 1, FtsZ protofilaments, carrier proteins, and metal ions. Curcumin can also bind directly to DNA and RNA. Owing to its β-diketone moiety, curcumin undergoes keto-enol tautomerism that has been reported as a favorable state for direct binding. The functional groups on curcumin found suitable for interaction with other macromolecules include the α, β-unsaturated β-diketone moiety, carbonyl and enolic groups of the β-diketone moiety, methoxy and phenolic hydroxyl groups, and the phenyl rings. Various biophysical tools have been used to monitor direct interaction of curcumin with other proteins, including absorption, fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, surface plasmon resonance, competitive ligand binding, Forster type fluorescence resonance energy transfer (FRET), radiolabeling, site-directed mutagenesis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), immunoprecipitation, phage display biopanning, electron microscopy, 1-anilino-8-naphthalene-sulfonate (ANS) displacement, and co-localization. Molecular docking, the most commonly employed computational tool for calculating binding affinities and predicting binding sites, has also been used to further characterize curcumin's binding sites. Furthermore, the ability of curcumin to bind directly to carrier proteins improves its solubility and bioavailability. In this review, we focus on how curcumin directly targets signaling molecules, as well as the different forces that bind the curcumin-protein complex and how this interaction affects the biological properties of proteins. We will also discuss various analogues of curcumin designed to bind selective targets with increased affinity.

Spectroscopic and molecular modeling evidence of clozapine binding to human serum albumin at subdomain IIA

Various spectroscopy and molecular docking methods were used to examine the binding of Clozapine (CLZ) to human serum albumin (HSA) in this paper. By monitoring the intrinsic fluorescence of single Trp214 residue and performing Dansylamide (DNSA) displacement measurement, the specific binding of CLZ in the vicinity of Sudlow's Site I of HSA has been clarified. An apparent distance of 27.3 Å between the Trp214 and CLZ was obtained via fluorescence resonance energy transfer (FRET) method. In addition, the changes in the secondary structure of HSA after its complexation with CLZ ligand were studied with CD spectroscopy, which indicate that CLZ does not has remarkable effect on the structure of the protein. Moreover, thermal denaturation experiment shows that the HSA-CLZ complexes are conformationally more stable. Finally, the binding details between CLZ and HSA were further confirmed by molecular docking studies, which revealed that CLZ was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, van der Waals forces and hydrogen bonding.

Molecular interaction studies of trimethoxy flavone with human serum albumin

BACKGROUND

Human serum albumin (HSA) is the most abundant protein in blood plasma, having high affinity binding sites for several endogenous and exogenous compounds. Trimethoxy flavone (TMF) is a naturally occurring flavone isolated from Andrographis viscosula and used in the treatment of dyspepsia, influenza, malaria, respiratory functions and as an astringent and antidote for poisonous stings of some insects.

METHODOLOGY/PRINCIPAL FINDINGS

The main aim of the experiment was to examine the interaction between TMF and HSA at physiological conditions. Upon addition of TMF to HSA, the fluorescence emission was quenched and the binding constant of TMF with HSA was found to be K(TMF) = 1.0+/-0.01x10(3) M(-1), which corresponds to -5.4 kcal M(-1) of free energy. Micro-TOF Q mass spectrometry results showed a mass increase of from 66,513 Da (free HSA) to 66,823 Da (HAS +Drug), indicating the strong binding of TMF with HSA resulting in decrease of fluorescence. The HSA conformation was altered upon binding of TMF to HSA with decrease in alpha-helix and an increase in beta-sheets and random coils suggesting partial unfolding of protein secondary structure. Molecular docking experiments found that TMF binds strongly with HSA at IIIA domain of hydrophobic pocket with hydrogen bond and hydrophobic interactions. Among which two hydrogen bonds are formed between O (19) of TMF to Arg 410, Tyr 411 and another one from O (7) of TMF to Asn 391, with bond distance of 2.1 A, 3.6 A and 2.6 A, respectively.

CONCLUSIONS/SIGNIFICANCE

In view of the evidence presented, it is imperative to assign a greater role of HSA's as a carrier molecule for many drugs to understand the interactions of HSA with TMF will be pivotal in the design of new TMF-inspired drugs.