Interaction studies of aristolochic acid I with human serum albumin and the binding site of aristolochic acid I in subdomain IIA

Investigations on the complexation and binding mechanism of bovine serum albumin with Ag-doped TiO2 nanoparticles

It is essential to study the interactions between nanoparticles and proteins to better understand the biological interactions of nanoparticles. In this study, we studied the protein adsorption mode on the surface of Ag-doped TiO2 nanoparticles (NPs) using a model protein, bovine serum albumin (BSA). The mechanism of binding BSA to the Ag-doped TiO2 NPs was studied by applying fluorescence quenching, absorbance measurements, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy techniques. The strong binding between BSA and Ag-doped TiO2 NPs was confirmed by a high value of binding constant (K = 2.65 × 105 L mol-1). We also studied the thermal stability of BSA in the presence of the Ag-doped TiO2 NPs. Thermodynamic parameters indicated that the adsorption of BSA on the Ag-doped TiO2 NPs was a spontaneous, natural and exothermic process. The effect of Ag-doped TiO2 NPs on the transportation function of BSA was also studied using a fluorescence spectroscopic technique. Fluorescence spectroscopic data suggested the existence of a strong interaction between BSA and the surface of the Ag-doped TiO2 NPs, which indicated that the binding affinities of some selected amino acids in BSA changed. This, in turn, clearly confirms that the Ag-doped TiO2 NPs affect the transportation capability of BSA in blood.

Structural and mechanistic insights into the transport of aristolochic acids and their active metabolites by human serum albumin

Aristolochic acids I and II (AA-I/II) are carcinogenic principles of Aristolochia plants, which have been employed in traditional medicinal practices and discovered as food contaminants. While the deleterious effects of AAs are broadly acknowledged, there is a dearth of information to define the mechanisms underlying their carcinogenicity. Following bioactivation in the liver, N-hydroxyaristolactam and N-sulfonyloxyaristolactam metabolites are transported via circulation and elicit carcinogenic effects by reacting with cellular DNA. In this study, we apply DNA adduct analysis, X-ray crystallography, isothermal titration calorimetry, and fluorescence quenching to investigate the role of human serum albumin (HSA) in modulating AA carcinogenicity. We find that HSA extends the half-life and reactivity of N-sulfonyloxyaristolactam-I with DNA, thereby protecting activated AAs from heterolysis. Applying novel pooled plasma HSA crystallization methods, we report high-resolution structures of myristic acid-enriched HSA (HSAMYR) and its AA complexes (HSAMYR/AA-I and HSAMYR/AA-II) at 1.9 Å resolution. While AA-I is located within HSA subdomain IB, AA-II occupies subdomains IIA and IB. ITC binding profiles reveal two distinct AA sites in both complexes with association constants of 1.5 and 0.5 · 106 M-1 for HSA/AA-I versus 8.4 and 9.0 · 105 M-1 for HSA/AA-II. Fluorescence quenching of the HSA Trp214 suggests variable impacts of fatty acids on ligand binding affinities. Collectively, our structural and thermodynamic characterizations yield significant insights into AA binding, transport, toxicity, and potential allostery, critical determinants for elucidating the mechanistic roles of HSA in modulating AA carcinogenicity.

Decoding the binding interaction of steroidal pyridines with bovine serum albumin using spectroscopic and molecular docking techniques

The present study reports a comprehensive and conformational aspect of binding of steroidal pyridines (1-6) with a model transport protein, bovine serum albumin (BSA) by fluorescence, UV-visible, circular dichroism, and molecular docking techniques. Quenching of BSA emission was attributed to the formation of the ground state complex after the compound (1-6) binds to the backbone of the protein. Synchronous fluorescence spectra reveals changes in the microenvironment of the aromatic residues. UV-visible absorption spectra further reiterate the quenching mechanism to be static and binding of compound (1-6) results in the formation of a ground-state complex. Circular dichroism spectra indicated that compound 1-3 causes unfolding and compound 4-6 leads to the stabilization of the protein structure. In addition, a molecular docking study revealed the binding pocket for the formation of the ligand-protein complex through hydrogen bonding and hydrophobic interactions. Furthermore, hemolytic activity suggested that the compounds (1-6) are biocompatible in nature. Evaluation of such steroid-protein interaction helps in better understanding of the biomolecular interaction of steroidal compounds with biomacromolecule and opens up new approaches in steroid based drug-design process.

The recognition of aristolochic acid I based on fluorescence quenching of bovine serum albumin-stabilized gold nanoclusters

Aristolochic acid I (AAI) is one of the nephrotoxic derivatives present in genera Aristolochia and Asarum. Although some detection strategies for monitoring AAI have been reported, the application of these methods is limited because they involve tedious preparation and require professional operation. In this work, bovine serum albumin (BSA) has been introduced as a reducing agent and stabilizing agent to synthesize gold nanoclusters with strong red fluorescence for the rapid and effective detection of AAI. Under excitation at 328 nm, the fluorescence intensity at the maximum emission wavelength of the bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) decreased with the addition of AAI, and the degree of quenching showed a linear relationship with the concentration of AAI from 0.1-12.8 μg mL^-1. The obtained BSA-AuNCs were stable, and quenching in the presence of AAI could be achieved within 10 seconds. Here, we have focused on the application of these gold nanoclusters as an optical sensing material for AAI in rat urine samples, including a discussion on the detection mechanism. The detection result of the fluorescent probe was consistent with that of the HPLC method. In view of this reality, the reported protein-AuNCs sensing platform can serve as a convenient detection strategy in toxicological analyses.

Involvement of 5-HT2 serotonin receptors in cognitive defects induced by aristolochic acid I in mice

Aristolochic acids (AAs) are a natural bioactive substance found in Chinese herbs, which are widely used for treating diseases. Many studies have demonstrated that AAs have various pharmacological function, while increasing reports indicated its toxicity. However, the role AAs in cognition remains poorly understood. This study explored the neurotoxic effect of aristolochic acid I (AAI), the most toxic component of the AAs family, on hippocampal synaptic plasticity and spatial cognition in mice. C57BL/6 mice were exposed to 5 mg/kg AAI for 4 weeks. After chronic treatment, AAI considerably increased the level of anxiety and the degree of behavioral despair in mice. Working and reference error rates were higher in the AAI exposed mice than in the control. This was further validated by the molecular docking studies, which AAI might interact with 5-HT₂ serotonin receptor (5-HT_2AR). Mechanism investigation indicated that AAI triggered inflammation in the hippocampus of mice through increasing the activity of Tnf-α-NF-κB-IL-6 signaling pathway. Conclusively, chronic AAI administration causes inflammation, and it possibly also serves as a potential antagonist of 5-HT_2AR to influence the cognition function in C57BL/6 mice.

Exploring the inhibitory mechanism of piceatannol on α-glucosidase relevant to diabetes mellitus

Due to their association with type 2 diabetes mellitus treatment, α-glucosidase inhibitors have attracted increasing attention of researchers. In this study, we systemically investigated the kinetics and inhibition mechanism of piceatannol on α-glucosidase. Enzyme kinetics analyses showed that piceatannol exhibited strong inhibition on α-glucosidase in a non-competitive manner. Spectroscopy analyses indicated that piceatannol could bind with α-glucosidase to form complexes via high affinity. Further, computational molecular dynamics and molecular docking studies validated that the binding of piceatannol was outside the catalytic site of α-glucosidase, which would induce conformational changes of α-glucosidase and block the entrance of substrate, causing declines in α-glucosidase activities. Our results provide useful information not only for the inhibition mechanism of piceatannol against α-glucosidase but also for a novel target site for developing novel α-glucosidase inhibitors as potential therapeutic agents in the treatment of type 2 diabetes mellitus.

The non-competitive inhibition of piceatannol on α-glucosidase. A combination of dynamic and static process with one binding site. The involvement of hydrophobic interactions and hydrogen bonding. Dietary recommendations for diabetes or potential antidiabetic drug.

Biotransformation and Toxicities of Aristolochic Acids

Environmental and iatrogenic exposures contribute significantly to human diseases, including cancer. The list of known human carcinogens has recently been extended by the addition of aristolochic acids (AAs). AAs occur primarily in Aristolochia herbs, which are used extensively in folk medicines, including Traditional Chinese Medicine. Ingestion of AAs results in chronic renal disease and cancer. Despite importation bans imposed by certain countries, herbal remedies containing AAs are readily available for purchase through the internet. With recent advancements in mass spectrometry, next generation sequencing, and the development of integrated organs-on-chips, our knowledge of cancers associated with AA exposure, and of the mechanisms involved in AA toxicities, has significantly improved. DNA adduction plays a central role in AA-induced cancers; however, significant gaps remain in our knowledge as to how cellular enzymes promote activation of AAs and how the reactive species selectively bind to DNA and kidney proteins. In this review, I describe pathways for AAs biotransformation, adduction, and mutagenesis, emphasizing novel methods and ideas contributing to our present understanding of AA toxicities in humans.

BSA binding and antibacterial studies of newly synthesized 5,6-Dihydroimidazo[2,1-b]thiazole-2-carbaldehyde

A new heterocyclic compound, 5,6-Dihydroimidazo[2,1-b]thiazole-2-carbaldehyde (ITC) was synthesized and its antibacterial activity and also its interaction with bovine serum albumin (BSA) were studied. The structure of the synthesized compound was confirmed by ¹H NMR, ¹³C NMR and IR spectroscopic techniques. The antibacterial activity was carried out by minimum inhibitory concentration (MIC) method. The compound showed a good antibacterial activity. The mechanism of interaction between the BSA and ITC under physiological conditions was investigated by various molecular spectroscopic techniques like, fluorescence, circular dichroism (CD), UV absorption and FT-IR. The interaction between ITC and BSA was followed by studying the quenching of intrinsic fluorescence of BSA upon the addition of ITC at three different temperatures. The binding constant (K), Stern-Volmer quenching constant (K_sv) and number of binding sites were determined. The separation distance between BSA and ITC was evaluated based on the fluorescence resonance energy transfer theory. The conformational changes in BSA upon binding of ITC were also confirmed. The interference of some metal ions on interaction was studies. The displacement studies with site specific markers confirm that the site III was the binding site for ITC on BSA.

Steroidal thiazolidinone derivatives: Design, synthesis and their molecular interaction with human serum albumin

A series of steroidal thiazolidinone derivatives have been synthesized through one-pot multicomponent reaction involving steroidal ketone, thiosemicarbazide/methyl-thiosemicarbazide and DMAD in presence of AlCl₃ as a Lewis acid catalyst. Among all the synthesized steroidal thiazolidinone derivatives, compound 7-9 (ST 7-9) were investigated for their in vitro molecular interaction with human serum albumin. Intrinsic fluorescence spectroscopy, constant wavelength synchronous fluorescence spectroscopy, circular dichroism and UV-visible absorption techniques have been exploited to characterize the binding phenomena in phosphate buffer solution at pH 7.4. The experimental results indicated that ST 7-9 bind to HSA and the intrinsic fluorescence of HSA was quenched through static quenching mechanism. The binding parameters were calculated and the binding constants obtained were 1.44 × 10⁵ M^-1 for ST 7, 0.84 × 10⁵ M^-1 for ST 8 and 1.06 × 10⁵ M^-1 for ST 9. Circular dichroism analysis confirms that the presence of ST 7-9, altered the secondary structure of HSA due to partial unfolding of the polypeptide chain. Furthermore, hemolytic activity assay demonstrated that the synthesized steroidal thiazolidinone derivatives have good compatibility towards human red blood cells. Finally, molecular docking studies revealed that the steroidal thiazolidinones can bind in the hydrophobic cavity of HSA, by hydrophobic and hydrogen bonding interaction. These results provided valuable information about the binding mechanism of ST 7-9 with HSA and play a pivotal role in the development of steroidal heterocycle inspired compounds.

Comparative investigation of binding interactions between three steroidal compounds and human serum albumin: Multispectroscopic and molecular modeling techniques

Steroidal compounds have attracted great attentions in biomedical and pharmacological areas. The investigation of structural influences during protein-compound interactions helps in understanding both the biological effects and the mechanism behind bioactivities of steroidal compounds. Herein, the structural influences of three steroidal complexes were investigated based on their binding interactions with human serum albumin (HSA) by multispectroscopic methods and molecular modeling techniques. Three steroidal compounds bonded with HSA to form three HSA-compound complexes, and van der Waals force and hydrogen bond played major roles in stabilizing these complexes. Detailed binding conformation of three steroidal compounds and HSA was further investigated by molecular modeling techniques. The changes of microenvironments and conformations of HSA were significant and the biological activity of HSA was weakened in the present of three steroidal compounds. The space steric hindrance was responsible for differences in the binding interactions between HSA and three steroidal compounds. These results provided the molecular understanding of binding interactions of protein with steroidal compounds and the strategy for research of structural influences.

Interaction studies of copper complex containing food additive carmoisine dye with human serum albumin (HSA): Spectroscopic investigations

In this study, the interaction between human serum albumin (HSA) and a copper complex of carmoisine dye; [Cu(carmoisine)₂ (H₂ O)₂ ], was studied in vitro using multi-spectroscopic methods. It was found that the intrinsic fluorescence of HSA was quenched by the addition of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex and the quenching mechanism was considered as static quenching by formation of a [Cu(carmoisine)₂ (H₂ O)₂ ]-HSA complex. The binding constant was about 10⁴  M^-1 at room temperature. The values of the calculated thermodynamic parameters (ΔH < 0 and ΔS > 0) suggested that both hydrogen bonds and the hydrophobic interactions were involved in the binding process. The site marker competitive experiments revealed that the binding of [Cu(carmoisine)₂ (H₂ O)₂ ] to HSA primarily occurred in subdomain IIIA (site II) of HSA. The results of circular dichroism (CD) and UV-vis spectroscopy showed that the micro-environment of amino acid residues and the conformation of HSA were changed after addition of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex. Finally, the binding of the [Cu(carmoisine)₂ (H₂ O)₂ ] complex to HSA was modelled by a molecular docking method. Excellent agreement was obtained between the experimental and theoretical results with respect to the binding forces and binding constant.

Probing the mechanism of interaction of metoprolol succinate with human serum albumin by spectroscopic and molecular docking analysis

In the present work, the mechanism of the interaction between a β1 receptor blocker, metoprolol succinate (MS) and human serum albumin (HSA) under physiological conditions was investigated by spectroscopic techniques, namely fluorescence, Fourier transform infra-red spectroscopy (FT-IR), fluorescence lifetime decay and circular dichroism (CD) as well as molecular docking and cyclic voltammetric methods. The fluorescence and lifetime decay results indicated that MS quenched the intrinsic intensity of HSA through a static quenching mechanism. The Stern-Volmer quenching constants and binding constants for the MS-HSA system at 293, 298 and 303 K were obtained from the Stern-Volmer plot. Thermodynamic parameters for the interaction of MS with HSA were evaluated; negative values of entropy change (ΔG°) indicated the spontaneity of the MS and HSA interaction. Thermodynamic parameters such as negative ΔH° and positive ΔS° values revealed that hydrogen bonding and hydrophobic forces played a major role in MS-HSA interaction and stabilized the complex. The binding site for MS in HSA was identified by competitive site probe experiments and molecular docking studies. These results indicated that MS was bound to HSA at Sudlow's site I. The efficiency of energy transfer and the distance between the donor (HSA) and acceptor (MS) was calculated based on the theory of Fosters' resonance energy transfer (FRET). Three-dimensional fluorescence spectra and CD results revealed that the binding of MS to HSA resulted in an obvious change in the conformation of HSA. Cyclic voltammograms of the MS-HSA system also confirmed the interaction between MS and HSA. Furthermore, the effects of metal ions on the binding of MS to HSA were also studied.

Synthesis, characterization and serum albumin binding studies of vitamin K3 derivatives

Synthesis, characterization and bovine serum albumin (BSA) binding properties of three derivatives of vitamin K3 have been described. Results of UV-Vis and fluorescence spectra indicate complexation between BSA and the ligands with conformational changes in protein, which is strongly supported by synchronous and three dimensional fluorescence studies. Addition of the ligands quenches the fluorescence of BSA which is accompanied by reduction in quantum yield (Ф) from 0.1010 to 0.0775-0.0986 range. Thermodynamic investigations reveal that hydrophobic interaction is the major binding force in the spontaneous binding of these ligands with BSA. The binding constants obtained depend on the substituent present in the quinone ring, which correlates linearly with the Taft's field substituent constant (σ_F). The results show that compound with strong electron withdrawing nitro-group forms relatively stronger complex with BSA than amino and thioglycolate substituted ones. Circular dichroism studies show that the α-helical content of the protein, upon complexation with the ligands, decreases in the case of amino and nitro substituted vitamin K3 while increases in thioglycolate substituted compound. Molecular docking studies indicated that the vitamin K3 derivatives are surrounded by hydrophobic residues of the BSA molecule, which is in good agreement with the results of fluorescence spectral and thermodynamic studies.

Mass Spectrometric and Spectrofluorometric Studies of the Interaction of Aristolochic Acids with Proteins

Aristolochic acid (AA) is a potent carcinogen and nephrotoxin and is associated with the development of "Chinese herb nephropathy" and Balkan endemic nephropathy. Despite decades of research, the specific mechanism of the observed nephrotoxicity has remained elusive and the potential effects on proteins due to the observed toxicity of AA are not well-understood. To better understand the pharmacotoxicological features of AA, we investigated the non-covalent interactions of AA with proteins. The protein-binding properties of AA with bovine serum albumin (BSA) and lysozyme were characterized using spectrofluorometric and mass spectrometric (MS) techniques. Moreover, the protein-AA complexes were clearly identified by high-resolution MS analyses. To the best of our knowledge, this is the first direct evidence of non-covalently bound protein-AA complexes. An analysis of the spectrofluorometric data by a modified Stern-Volmer plot model also revealed that both aristolochic acid I (AAI) and aristolochic acid II (AAII) were bound to BSA and lysozyme in 1:1 stoichiometries. A significantly stronger protein binding property was observed in AAII than in AAI as evidenced by the spectrofluorometric and MS analyses, which may explain the observed higher mutagenicity of AAII.

Enhancement of the binding affinity of methylene blue to site I in human serum albumin by cupric and ferric ions

In this work, the binding characteristics of methylene blue (MB) to human serum albumin (HSA) and the influence of Cu(2+) and Fe(3+) on the binding affinity of MB to HSA were investigated using fluorescence, absorption, circular dichroism (CD) spectroscopy and molecular modelling. The results of competitive binding experiments using the site probes ketoprofen and ibuprofen as specific markers suggested that MB was located in site I within sub-domain IIA of HSA. The molecular modelling results agreed with the results of competitive site marker experiments and the results of CD spectra indicated that the interaction between MB and HSA caused the conformational changes in HSA. The binding affinity of MB to HSA was enhanced but to a different extent in the presence of Cu(2+) and Fe(3+), respectively, which indicated that the influence of different metal ions varied. Enhancement of the binding affinity of MB to HSA in the presence of Cu(2+) is due to the formation of Cu(2+)-HSA complex leading to the conformational changes in HSA, whereas in the presence of Fe(3+), enhancement of the binding affinity is due to the greater stability of the Fe(3+)-HSA-MB complex compared with the MB-HSA complex.

Competitive binding of Chlorin p6 and Dansyl-l-Proline to Sudlow's site II of human serum albumin

The binding of chlorin p6, a model photosensitizer for photodynamic therapy (PDT), to the Sudlow's site II of Human Serum Albumin (HSA) has been monitored by different spectroscopic methods. Displacement of Dansyl-l-Proline (DP) from its conjugate with HSA is manifested in the spectral shift and decrease in its fluorescence intensity as well as the emergence of component with lifetime of 2-3ns, which is characteristic of free DP. As DP is known to bind specifically to the Sudlow's site II of human serum albumin, its displacement by chlorin p6 indicates the residence of the photosensitizer in the same site, in addition to Sudlow's site I. The binding constants for Sudlow's site II, determined by the stopped-flow technique, are found to be two orders of magnitude smaller than that for Sudlow's site I.

Binding studies of L-3,4-dihydroxyphenylalanine with human serum albumin

L-Dopa has been used to increase dopamine concentrations in the treatment of Parkinson's disease and dopamine-responsive dystonia. The binding interaction between L-dopa (phytochemical) and human serum albumin (HSA) under simulated physiological conditions was investigated by spectroscopic and molecular modeling methods. The results revealed that L-dopa caused fluorescence emission quenching of HSA through a static quenching procedure and the binding constant obtained was 2.3 ± 0.01 × 10(4) M(-1), which is corresponding to -5.9 kcal M(-1) of free energy at 25 °C. Interestingly, L-dopa is not binding to the α-1-acidglycoprotein, which is also a plasma protein and an acute phase protein. Furthermore, circular dichroism results confirm that in the presence of L-dopa the secondary structure of HSA is altered due to partial unfolding of the protein. Importantly, the displacement experiment with site specific probes, phenylbutazone (site I) and ibuprofen (site II), depicts that L-dopa binds particularly to site II of HSA. In addition, the molecular modeling results also confirmed that L-dopa is binding to the subdomain IIIA of HSA and is stabilized by hydrogen bonds and hydrophilic forces. Additionally, the molecular dynamic simulation studies showed that the HSA-L-dopa complex reaches an equilibration state at around 2 ns, which indicates that the HSA-L-dopa complex is very stable. These results provided valuable information of pharmacological mechanisms of L-dopa under in vivo conditions and play a pivotal role in the development of L-dopa-inspired drugs.

Binding of dihydromyricetin and its metal ion complexes with bovine serum albumin

The binding mechanisms of the interaction of three dihydromyricetin (DMY)–metal complexes (DMY–Cu (II) complex, DMY–Mn (II) complex, DMY–Zn (II) complex) and DMY with bovine serum albumin (BSA) were investigated using fluorescence and ultraviolet spectroscopy at different temperatures. The results indicated some differences in the binding process between different DMY–metal complexes and BSA compared with that of free DMY. All of the complexes and DMY quenched the fluorescence of BSA based on static mode combined with radiationless energy transfer, yet having different binding distance based on the Förster theory. Different DMY–metal complexes can change the binding constants. The binding constants increase for DMY–Cu (II) and DMY–Mn (II) complexes, whereas the opposite is true for the DMY–Zn (II) complex compared to the one with free DMY. The DMY–metal complexes can also affect the types of the interaction. The van der Waals forces and hydrogen bonding may play a major role in the interaction of free DMY with BSA, while for the three complexes, the nature of the binding forces lies in hydrophobic forces and hydrogen bonding based on the thermodynamic parameters.

Investigation of interaction of antibacterial drug sulfamethoxazole with human serum albumin by molecular modeling and multi-spectroscopic method

Interaction of sulfamethoxazole (SMX) with human serum albumin (HSA) was investigated by molecular modeling and multi-spectroscopic methods under physiological conditions. The interaction mechanism was firstly predicted through molecular modeling that confirmed the interaction between SMX and HSA. The binding parameters and the thermodynamic parameters at different temperatures for the reaction had been calculated according to the Stern-Volmer, Hill, Scatchard and the Van't Hoff equations, respectively. One independent class of binding site existed during the interaction between HSA and SMX. The binding constants decreased with the increasing temperatures, which meant that the quenching mechanism was a static quenching. The thermodynamic parameters of the reaction, namely standard enthalpy ΔH(0) and entropy ΔS(0), had been calculated to be -16.40 kJ mol(-1) and 32.33 J mol(-1) K(-1), respectively, which suggested that the binding process was exothermic, enthalpy driven and spontaneous. SMX bound to HSA was mainly based on electrostatic interaction, but hydrophobic interactions and hydrogen bonds could not be excluded from the binding. The conformational changes of HSA in the presence of SMX were confirmed by the three-dimensional fluorescence spectroscopy, UV-vis absorption spectroscopy and circular dichroism (CD) spectroscopy. CD data suggested that the protein conformation was altered with the reduction of α-helices from 55.37% to 41.97% at molar ratio of SMX/HSA of 4:1.

Binding and conformational changes of human serum albumin upon interaction with 4-aminoantipyrine studied by spectroscopic methods and cyclic voltammetry

The interactions of 4-aminoantipyrine (AAP) with human serum albumin (HSA) have been studied by UV-visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. The binding of 4-aminoantipyrine quenches the HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 10(5) M(-1). The experimental results showed that AAP effectively quenched the intrinsic fluorescence of HSA via dynamic type of quenching. In addition, according to the synchronous fluorescence spectra of HSA in presence of 4-aminoantipyrine, the tryptophan residue of the proteins are most perturbed by the binding process. The number of binding sites, the binding constant, site probe study, some common metal ions effect and the thermodynamic parameters were calculated.

Studies of the interaction between demeclocycline and human serum albumin by multi-spectroscopic and molecular docking methods

This study was designed to examine the interaction of demeclocycline (DMCTC) with human serum albumin (HSA) by multi-spectroscopic and molecular docking methods. The inner filter effect was corrected before we calculated the binding parameters. Fluorescence and UV-vis spectroscopy revealed that DMCTC induced the fluorescence quenching of HSA though a static quenching procedure. Thermodynamic analysis by Van Hoff equation found enthalpy change (ΔH) and entropy change (ΔS) were -53.01 kJ mol(-1) and -65.13 J mol(-1)K(-1), respectively, which indicated hydrogen bond and van der Waals force were the predominant force in the binding process. According to fluorescence resonance energy transfer (FRET), the specific binding distances between Trp-214 (donor) and DMCTC (acceptor) were 3.18 nm. Through site marker competitive experiments, subdomain IIA of HSA has been assigned to possess the high-affinity binding site of DMCTC. The three dimensional fluorescence showed that the conformation of HSA was changed after its complexation with DMCTC, and the alternations of protein secondary structure were quantitatively calculated from FT-IR with reduction of α-helices content about 4.8%, β-sheet from 30.3% to 21.6% and with increases of β-turn from 15.6% to 22.2%. Furthermore, the binding details between DMCTC and HSA were further confirmed by molecular docking studies, which revealed that DMCTC was bound at subdomain IIA through multiple interactions, such as hydrophobic effect, polar forces and π-π interactions. Moreover, the coexist metal ions such as Al(3+), Fe(3+), Cu(2+), Cr(3+) and Cd(2+) can decrease the binding constants of DMCTC-HSA.