Resveratrol binding to human serum albumin

Resveratrol (Res), a polyphenolic compound found largely in the skin of red grape and wine, exhibits a wide range of pharmaceutical properties and plays a role in prevention of human cardiovascular diseases [Pendurthi et al., Arterioscler. Thromb. Vasc. Biol. 19, 419-426 (1999)]. It shows a strong affinity towards protein binding and used as inhibitor for cyclooxygenase and ribonuclease reductase. The aim of this study was to examine the interaction of resveratrol with human serum albumin (HSA) in aqueous solution at physiological conditions, using a constant protein concentration (0.3 mM) and various pigment contents (microM to mM). FTIR, UV-Visible, CD, and fluorescence spectroscopic methods were used to determine the resveratrol binding mode, the binding constant and the effects of pigment complexation on protein secondary structure. Structural analysis showed that resveratrol bind non-specifically (H-bonding) via polypeptide polar groups with overall binding constant of K(Res) = 2.56 x 10(5) M(-1). The protein secondary structure, analysed by CD spectroscopy, showed no major alterations at low resveratrol concentrations (0.125 mM), whereas at high pigment content (1 mM), major increase of alpha-helix from 57% (free HSA) to 62% and a decrease of beta-sheet from 10% (free HSA) to 7% occurred in the resveratrol-HSA complexes. The results indicate a partial stabilization of protein secondary structure at high resveratrol content.     

Human serum albumin complexes with chlorophyll and chlorophyllin

Porphyrins and their metal derivatives are strong protein binders. Some of these compounds have been used for radiation sensitization therapy of cancer and are targeted to interact with cellular DNA and protein. The presence of several high-affinity binding sites on human serum albumin (HSA) makes it possible target for many organic and inorganic molecules. Chlorophyll a and chlorophyllin (a food-grade derivative of chlorophyll), the ubiquitous green plant pigment widely consumed by humans, are potent inhibitors of experimental carcinogenesis and interact with protein and DNA in many ways. This study was designed to examine the interaction of HSA with chlorophyll (Chl) and chlorophyllin (Chln) in aqueous solution at physiological conditions. Fourier transform infrared, UV-visible, and CD spectroscopic methods were used to determine the pigment binding mode, the binding constant, and the effects of porphyrin complexation on protein secondary structure. Spectroscopic results showed that chlorophyll and chlorophyllin are located along the polypeptide chains with no specific interaction. Stronger protein association was observed for Chl than for Chln, with overall binding constants of K(Chl) = 2.9 x 10(4)M(-1) and K(Chln) = 7.0 x 10(3)M(-1). The protein conformation was altered (infrared data) with reduction of alpha-helix from 55% (free HSA) to 41-40% and increase of beta-structure from 22% (free HSA) to 29-35% in the pigment-protein complexes. Using the CDSSTR program (CD data) also showed major reduction of alpha-helix from 66% (free HSA) to 58 and 55% upon complexation with Chl and Chln, respectively.     

Resveratrol Binding to Human Serum Albumin

Abstract

Resveratrol (Res), a polyphenolic compound found largely in the skin of red grape and wine, exhibits a wide range of pharmaceutical properties and plays a role in prevention of human cardiovascular diseases [Pendurthi et al., Arterioscler. Thromb. Vasc. Biol. 19, 419–426 (1999)]. It shows a strong affinity towards protein binding and used as inhibitor for cyclo- oxygenase and ribonuclease reductase. The aim of this study was to examine the interaction of resveratrol with human serum albumin (HSA) in aqueous solution at physiological conditions, using a constant protein concentration (0.3 mM) and various pigment contents μM to mM). FTIR, UV-Visible, CD, and fluorescence spectroscopic methods were used to determine the resveratrol binding mode, the binding constant and the effects of pigment complexation on protein secondary structure.

Structural analysis showed that resveratrol bind non-specifically (H-bonding) via polypeptide polar groups with overall binding constant of K_Res = 2.56× 10⁵ M^?1. The protein secondary structure, analysed by CD spectroscopy, showed no major alterations at low resveratrol concentrations (0.125 mM), whereas at high pigment content (1 mM), major increase of α-helix from 57% (free HSA) to 62% and a decrease of β-sheet from 10% (free HSA) to 7% occurred in the resveratrol-HSA complexes. The results indicate a partial stabilization of protein secondary structure at high resveratrol content.     

Interaction of taxol with human serum albumin

Taxol (paclitaxel) is an anticancer drug, which interacts with microtuble proteins, in a manner that catalyzes their formation from tubulin and stabilizes the resulting structures (Nogales et al., Nature 375 (1995) 424-427). This study was designed to examine the interaction of taxol with human serum albumin (HSA) in aqueous solution at physiological pH with drug concentrations of 0.0001-0.1 mM, and HSA (fatty acid free) concentration of 2% w/v. Gel electrophoresis, absorption spectra and Fourier transform infrared (FTIR) spectroscopy with self-deconvolution and second-derivative resolution enhancement were used to determine the drug binding mode, binding constant and the protein secondary structure in the presence of taxol in aqueous solution. Spectroscopic evidence showed that taxol-protein interaction results into two types of drug-HSA complexes with overall binding constant of K=1.43 x 10(4) M(-1). The molar ratios of complexes were of taxol/HSA 30/1 (30 mM taxol) and 90/1 (90 mM taxol) with the complex ratios of 1.9 and 3.4 drug molecules per HSA molecule, respectively. The taxol binding results in major protein secondary structural changes from that of the alpha-helix 55 to 45% and beta-sheet 22 to 26%, beta-anti 12 to 15% and turn 11 to 16%, in the taxol-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of taxol in aqueous solution.     

Polyamine analogues bind human serum albumin

Polyamine analogues show antitumor activity in experimental models, and their ability to alter activity of cytotoxic chemotherapeutic agents in breast cancer is well documented. Association of polyamines with nucleic acids and protein is included in their mechanism of action. The aim of this study was to examine the interaction of human serum albumin (HSA) with several polyamine analogues, such as 1,11-diamino-4,8-diazaundecane (333), 3,7,11,15-tetrazaheptadecane.4HCl (BE-333), and 3,7,11,15,19-pentazahenicosane.5HCl (BE-3333), in aqueous solution at physiological conditions using a constant protein concentration and various polyamine contents (microM to mM). FTIR, UV-visible, and CD spectroscopic methods were used to determine the polyamine binding mode and the effects of polyamine complexation on protein stability and secondary structure. Structural analysis showed that polyamines bind nonspecifically (H-bonding) via polypeptide polar groups with binding constants of K333 = 9.30 x 10(3) M(-1), KBE-333 = 5.63 x 10(2) M(-1), and KBE-3333 = 3.66 x 10(2) M(-1). The protein secondary structure showed major alterations with a reduction of alpha-helix from 55% (free protein) to 43-50% and an increase of beta-sheet from 17% (free protein) to 29-36% in the 333, BE-333, and BE-3333 complexes, indicating partial protein unfolding upon polyamine interaction. HSA structure was less perturbed by polyamine analogues compared to those of the biogenic polyamines.     

Interactions of human serum albumin with chlorogenic acid and ferulic acid

The interactions of chlorogenic acid and ferulic acid with human serum albumin (HSA) have been investigated by fluorescence and Fourier transformed infrared (FT-IR) spectrometry. Fluorescence results showed that one molecule of protein combined with one molecule of drugs at the molar ratio of drug to HSA ranging from 1 to 10, and their binding affinities (KA) are 4.37 x 10(4) M(-1) and 2.23 x 10(4) M(-1) for chlorogenic acid and ferulic acid, respectively. The primary binding site for chlorogenic acid is most likely located on IIA and that for ferulic acid in IIIA. The main mechanism of protein fluorescence quenching was static quenching process. Combining the curve-fitting results of infrared amide I and amide III bands, the alterations of protein secondary structure after drug complexation were estimated. With increasing the drug concentration, the protein alpha-helix structure decreased gradually and the reduction of protein alpha-helix structure reached about 7% and 5% for protein binding with chlorogenic acid and ferulic acid individually at the drug to protein molar ratio of 30. This indicated a partial unfolding of HSA in the presence of the two acids. From the fluorescence and FT-IR results, the binding mode was discussed.     

Retinol and retinoic acid bind human serum albumin: stability and structural features

Vitamin A components, retinol and retinoic acid, are fat-soluble micronutrients and critical for many biological processes, including vision, reproduction, growth, and regulation of cell proliferation and differentiation. The cellular uptake of Vitamin A is through specific interaction of a plasma membrane receptor with serum retinol-binding protein. Human serum albumin (HSA), as a transport protein, is the major target of several micronutrients in vivo. The aim of present study was to examine the interaction of retinol and retinoic acid with human serum albumin in aqueous solution at physiological conditions using constant protein concentration and various retinoid contents. FTIR, UV–vis, CD and fluorescence spectroscopic methods were used to determine retinoid binding mode, the binding constant and the effects of complexation on protein secondary structure.

Structural analysis showed that retinol and retinoic acid bind non-specifically (H-bonding) via protein polar groups with binding constants of K_ret = 1.32 (±0.30) × 10⁵ M⁻¹ and K_retac = 3.33 (±0.35) × 10⁵ M⁻¹. The protein secondary structure showed no alterations at low retinoid concentrations (0.125 mM), whereas at high retinoid content (1 mM), an increase of -helix from 55% (free HSA) to 60% and a decrease of β-sheet from 22% (free HSA) to 18% occurred in the retinoid–HSA complexes. The results point to a partial stabilization of protein secondary structure at high retinoid content.     

Study on the binding of Arsenazo-TB to human serum albumin by Rayleigh light scattering technique and FT-IR

The interaction between Arsenazo-TB and human serum albumin (HSA) was studied by Rayleigh light scattering (RLS) technique and Fourier transformed IR (FT-IR). The binding parameters of Arsenazo-TB with HSA were studied at different temperature of 288, 298, 308, 318 K under the optimum conditions. It is indicated by the Scatchard plots that the binding constant K decreased from 5.03 x 10(7) to 7.13 x 10(6) and the maximum binding number N reduced from 53 to 36 with the increasing of the temperature. The binding process was exothermic, enthalpy driven and spontaneous, as indicated by the thermodynamic analyses, and the major part of the binding energy is hydrophobic interaction. The free energy change deltaG0, the enthalpy change deltaH0 and the entropy change deltaS0 of 288 K were calculated to be -42.46 kJ/mol, -49.17 kJ/mol and 318.15 J/mol K, respectively. The alterations of protein secondary structure in the presence of Arsenazo-TB in aqueous solution were quantitatively calculated from FT-IR spectroscopy with reductions of alpha-helix from 57% to 40% and with increases of beta-sheet from 36% to 39%, beta-turn from 7% to 21%.     

Interaction of cisplatin drug with Na,K-ATPase: drug binding mode and protein secondary structure

cis-Pt(NH(3))(2)Cl(2) (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic changes associated with its mechanism of action. This study was designed to examine the interaction of cisplatin drug with the Na(+), K(+)-dependent adenosine triphosphatase (Na,K-ATPase) in H(2)O and D(2)O solutions at physiological pH, using drug concentrations of 0.1 microM to 1 mM. UV absorption spectra and Fourier transform infrared difference spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were applied to characterize the drug binding mode, the drug binding constant and the protein secondary structure in the cisplatin-ATPase complexes. Spectroscopic evidence showed that at low drug concentration (0.1 microM), cisplatin binds mainly to the lipid portion of the enzyme, whereas at higher drug contents, the Pt cation interaction is through the polypeptide C==O and C-N groups with overall binding constant of K=1.93 x 10(4) M(-1). At high cisplatin concentration (1 mM), drug binding results in protein secondary structural changes from that of the alpha-helix 19.8%; beta-pleated 25.6%; turn 9.1%; beta-antiparallel 7.5% and random 38%, in the free Na,K-ATPase to that of the alpha-helix 22.2%; beta-pleated 23.2%; turn 9.4%; beta-antiparallel 2.2% and random 43%, in the cis-Pt-ATPase complexes.     

Interaction between hesperetin and human serum albumin revealed by spectroscopic methods

Hesperetin (5,7,3'-trihydroxyl-4'-methoxyl-flavanone) is an important bioactive compound in Chinese traditional medicine and has multiple biological and pharmacological activities. The interaction of hesperetin with human serum albumin (HSA) has been investigated by UV absorption, fluorescence and Fourier transformed infrared spectrometry. Fluorescence results showed that one molecule of protein combined with one molecule of drug at the molar ratio of drug to HSA ranging from 0.3 to 7 and the binding affinity (K(A)) was 8.11x10(4) M(-1). The primary binding site was most likely located on subdomain IIA. The binding ability of the drug to protein decreased from pH 6.4 to 8.4 in the drug to protein molar ratio of 1. Combining the curve-fitting results of infrared amide I band in D2O and H2O phosphate buffers, the alterations of protein secondary structure after drug complexation were estimated. With increasing the drug concentration, the percentage of protein alpha-helix structure decreased gradually. The reduction of protein alpha-helix structure reached about 7-9% after the protein interacted with hesperetin in D2O and H2O buffer solution at pH 7.4 when the drug to protein molar ratio was 10. This indicated a partial unfolding of HSA in the presence of the drug. From the results of UV absorption, fluorescence and Fourier transformed infrared spectrometry, the binding mode was discussed. The main mechanism of protein fluorescence quenching was a static quenching process and the hydroxyl groups of the drug in its neutral part played an important role in the binding process.     

Interaction of rhein with human serum albumin investigation by optical spectroscopic technique and modeling studies

The binding of rhein with human serum albumin (HSA) has been studied in detail by spectroscopic method including circular dichroism (CD), Fourier transformation infrared spectra (FT-IR), fluorescence spectra. The binding parameters for the reaction have been calculated according to Scatchard equation at different temperatures. The plots indicated that the binding of HSA to rhein at 303, 310 and 318 K is characterized by one binding site with the affinity constant K at (4.93+/-0.16)x10(5), (4.02+/-0.16)x10(5) and (2.69+/-0.16)x10(5) M-1, respectively. The secondary structure compositions of free HSA and its rhein complexes were estimated by the FT-IR spectra. FT-IR and curve-fitted results of amide I band are in good agreement with the analyses of CD spectra. Molecular Modeling method was used to calculate the interaction modes between the drug and HSA.     

Effects of organic and inorganic polyamine cations on the structure of human serum albumin

The presence of several high affinity binding sites on human serum albumin (HSA) makes it a possible target for many organic and inorganic molecules. Organic polyamines are widely distributed in living cells and their biological roles have been associated with their physical and chemical interactions with proteins, nucleic acids, and lipids. This study is designed to examine the effects of spermine, spermidine, putrescine, and cobalt [Co(III)]-hexamine cations on the solution structure of HSA using Fourier transform IR, UV-visible, and circular dichroism (CD) spectroscopic methods. The spectroscopic results show that polyamine cations are located along the polypeptide chains with no specific interaction. The order of perturbations is associated with the number of positive charges of the polyamine cation: spermine > Co(III)-hexamine > spermidine > putrescine. The overall binding constants are 1.7 x 10(4), 1.1 x 10(4), 5.4 x 10(3), and 3.9 x 10(3)M(-1), respectively. The protein conformation is altered (IR and CD data) with reductions of alpha helices from 60 to 55% for free HSA to 50-40% and with increases of beta structures from 22 to 15% for free HSA to 33-23% in the presence of polyamine cations.     

Interaction of cisplatin drug with RNase A.

cis-Pt(NH3)2Cl2 (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic structural changes associated with its mechanism of action. This study is designed to examine the interaction of cisplatin drug with ribonuclease A (RNase A) in aqueous solution at physiological pH, using drug concentration of 0.0001 mM to 0.1 mM with final protein concentration of 2% w/v. Absorption spectra and Fourier transform infrared (FTIR) spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were used to characterize the drug binding mode, association constant and the protein secondary structure in the cisplatin-RNase complexes. Spectroscopic results show that at low drug concentration (0.0001 mM), no interaction occurs between cisplatin and RNase, while at higher drug concentrations, cisplatin binds indirectly to the polypeptide C=O, C-N (via H2O or NH3 group) and directly to the S-H donor atom with overall binding constant 5.66 x 10(3)M(-1). At high drug concentration, major protein secondary structural changes occur from that of the alpha-helix 29% (free enzyme) to 20% and beta-sheet 39% (free enzyme) to 45% in the cisplatin-RNase complexes. The observed structural changes indicate a partial protein unfolding in the presence of cisplatin at high drug concentration.     

The effects of drug complexation on the stability and conformation of human serum albumin

We report different analytical methods used to study the effects of 3\'-azido-3\'-deoxythymidine, aspirin, taxol, cisplatin, atrazine, 2,4-dichlorophenoxyacetic, biogenic polyamines, chlorophyll, chlorophyllin, poly(ethylene glycol), vanadyl cation, vanadate anion, cobalt-hexamine cation, and As2O3, on the stability and secondary structure of human serum albumin (HSA) in aqueous solution, using capillary electrophoresis, Fourier transform infrared, ultraviolet visible, and circular dichroism (CD) spectroscopic methods. The concentrations of HSA used were 4% to 2% or 0.6 to 0.3 mM, while different ligand concentrations were 1 microM to 1 mM. Structural data showed drugs are mostly located along the polypeptide chains with both specific and nonspecific interactions. The stability of drug-protein complexes were in the order K(VO(2+)) 1.2 x 10(8) M(-1) > K(AZT) 1.9 x 10(6) M(-)1 > K(PEG) 4.1 x 10(5) M(-1) > K(atrazine) 3.5 x 10(4) M(-1) > K(chlorophyll) 2.9 x 10(4) M(-1) > K2,4-D 2.5 x 10(4) M-1 > K(spermine) 1.7 x 10(4) M(-1) > K(taxol) 1.43 x 10(4) M(-1) > K(Co(3+)) > 1.1 x 10(4) M(-1) > K(aspirin) 1.04 x 10(4)i(-1) > K(chlorophyllin) 7.0 x 10(3) M(-1) > K(VO(3)(-)) 6.0 x 103 M(-1) > K(spermidine) 5.4 x 10(3) M(-1) > K(putrescine) 3.9 x 10(3) M(-1) > K(As(2)O(3)) 2.2 x 10(3) M(-1)> K(cisplatin) 1.2 x 10(2) M(-1). The protein conformation was altered (infrared and CD results) with major reduction of alpha-helix from 60 to 55% (free HSA) to 49 to 40% and increase of beta-structure from 22 to 15% (free HSA) to 33 to 23% in the drug-protein complexes. The alterations of protein secondary structure are attributed to a partial unfolding of HSA on drug complexation.     

Interactions of atrazine and 2,4-D with human serum albumin studied by gel and capillary electrophoresis, and FTIR spectroscopy.

The herbicides 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine) and 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practice to fight dicotyledon weeds mainly in maize, cereals, and lucerne. As a result, these compounds are found not only in the plants, soil, and water, but also in the cultivated ground in the following years as well as in agricultural products such as fruits, milk, butter, and sugar beet. The toxicological effects of herbicides occur in vivo, when transported to the target organ through the bloodstream. It has been suggested that human serum albumin (HSA) serves as a carrier protein to transport 2,4-D to molecular targets. This study was designed to examine the interaction of atrazine and 2,4-D with HSA in aqueous solution at physiological pH with herbicide concentrations of 0.0001-1 mM, and final protein concentration of 1% w/v. Gel and capillary electrophoresis, UV-visible and Fourier transform infrared spectroscopic methods were used to determine the drug binding mode, the drug binding constant, and the protein secondary structure in aqueous solution. Structural analysis showed that different types of herbicide-HSA complexes are formed with stoichiometric ratios (drug/protein) of 3:1 and 11:1 for atrazine and 4.5:1 and 10:1 for 2,4-D complexes. Atrazine showed a weak binding affinity (K=3.50 x 10(4) M(-1)), whereas two bindings (K(1)=2.50 x 10(4) M(-1) and K(2)=8.0 x 10(3) M(-1)) were observed for 2,4-D complexes. The herbicide binding results in major protein secondary structural changes from that of the alpha-helix 55% to 45--39% and beta-sheet 22% to 24--32%, beta-anti 12% to 10--22% and turn 11% to 12--15%, in the drug-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of herbicides in aqueous solution.     

Effect of Chinese medicine alpinetin on the structure of human serum albumin

Alpinetin (7-hydroxy-5-methoxyflavanone), one of the main constituents from the seeds of Alpinia katsumadai Hayata, belongs to flavonoids with its usefulness as antibacterial, anti-inflammatory and other important therapeutic activities of significant potency and low systemic toxicity. In this paper, the interaction of alpinetin to human serum albumin (HSA) has been studied for the first time by spectroscopic method including Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD), and UV-absorption spectroscopy in combination with fluorescence quenching study under physiological conditions with drug concentrations of 3.3 x 10(-6)-2.0 x 10(-5)mol/L. The results of spectroscopic measurements and the thermodynamic parameters obtained (the enthalpy change DeltaH(0) and the entropy change DeltaS(0) were calculated to be -10.20 kJ/mol and 53.97 J/molK(-1) according to the Van't Hoff equation) suggest that hydrophobic interaction is the predominant intermolecular forces stabilizing the complex, which is also good agreement with the results of molecule modeling study. The alterations of protein secondary structure in the presence of alpinetin in aqueous solution were quantitatively estimated by the evidences from FT-IR and CD spectroscopy with reductions of alpha-helices about 24%, decreases of beta-sheet structure about 2%, and increases of beta-turn structure about 21%. The quenching mechanism and the number of binding site (n approximately 1) were obtained by fluorescence titration data. Fluorescent displacement measurements confirmed that alpinetin bind HSA on site III. In addition, the effects of common ions on the constants of alpinetin-HSA complex were also discussed.     

Mutational analysis of the interaction between albumin-binding domain from streptococcal protein G and human serum albumin

Streptococcal protein G (SpG) is a bacterial cell surface receptor exhibiting affinity to both human immunoglobulin (IgG) and human serum albumin (HSA). Interestingly, the serum albumin and immunoglobulin-binding activities have been shown to reside at functionally and structurally separated receptor domains. The binding domain of the HSA-binding part has been shown to be a 46-residue triple alpha-helical structure, but the binding site to HSA has not yet been determined. Here, we have investigated the precise binding region of this bacterial receptor by protein engineering applying an alanine-scanning procedure followed by binding studies by surface plasmon resonance (SPR). The secondary structure as well as the HSA binding of the resulting albumin-binding domain (ABD) variants were analyzed using circular dichroism (CD) and affinity blotting. The analysis shows that the HSA binding involves residues mainly in the second alpha-helix.     

Conformation and stability of Sendai virus fusion protein

The conformation and stability of Sendai virus fusion (F) protein were studied by circular dichroism spectroscopy, and the protein predictive models of Chou and Fasman and Robson and Suzuki were used to elucidate the secondary structure of Sendai virus F protein. The F protein conformation is predicted to contain 33% alpha-helix, 53% beta-sheet and 15% beta-turn by the Chou and Fasman model, and 30% alpha-helix, 55% beta-sheet, 9% beta-turn and 7% random coil by the Robson and Suzuki model. C.d. studies of F protein purified in the presence of the non-ionic detergent, n-octylglucoside, indicated the presence of 49% alpha-helix and 31% beta-sheet at pH 7.0, 54% alpha-helix and 28% beta-sheet at pH 9.0 and 50% alpha-helix and 23% beta-sheet at pH 5.4. A small change in conformation of the protein occurred when the pH was titrated from 7.0 to 5.4 and from 7.0 to 9.0 and a more pronounced conformational change occurred when the pH was changed from 9.0 to 5.4. The F protein in 0.2% n-octylglucoside was resistant to denaturation by 4 M guanidine hydrochloride, the reducing agent 20 mM mercaptoethanol, and to increases in temperature from 5 to 80 degrees C. Monoclonal anti-F protein antibody showed an increased binding to whole virus when the pH was changed from 7.0 to 9.0. The antibody binding was decreased when the pH was shifted from 9.0 to 5.4 Maximum haemolytic activity was observed with virus that was preincubated at pH 8.0.(ABSTRACT TRUNCATED AT 250 WORDS)     

Specific interaction of chalcone-protein: cardamonin binding site II on the human serum albumin molecule

Cardamonin (2',4'-dihydroxy-6'-methoxychalcone), one of the main constituents from the seeds of Alpinia katsumadai Hayata, belongs to chalcone with its antibacterial, antiinflammatory and other important therapeutic activities of significant potency and low systemic toxicity. In this article, the interaction of cardamonin to human serum albumin (HSA) has been studied for the first time by spectroscopic methods including Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD), and UV-absorption spectroscopy in combination with fluorescence quenching under physiological conditions with drug concentrations of 0.67-4.0 microM. The results of the spectroscopic measurements and the thermodynamic parameters obtained (the enthalpy change DeltaH(0) and the entropy change DeltaS(0) were calculated to be -25.312 and 7.040 J.mol(-1).K(-1) according to the van't Hoff equation) suggest that hydrophobic interaction is the predominant intermolecular forces stabilizing the complex, which is also in good agreement with the results of the molecule modeling study. The alterations of protein secondary structure in the presence of cardamonin in aqueous solution were quantitatively calculated by the evidence from CD and FTIR spectroscopes with reductions of alpha-helices of about 20%, decreases of beta-sheet structures of about 14%, and increases of beta-turn structures of about 15%. The quenching mechanism and the number of binding sites (n approximately 1) were obtained by fluorescence titration data. Fluorescent displacement measurements confirmed that cardamonin binds HSA on site II. In addition, the effects of common ions on the constants of the cardamonin-HSA complex were also discussed.