Subdomain IIIA Research Articles

Understanding the mode of binding mechanism of doripenem to human serum albumin: Spectroscopic and molecular docking approaches.

The infections caused by multidrug resistant bacteria are widely treated with carabapenem antibiotics as a drug of choice, and human serum albumin (HSA) plays a vital role in binding with drugs and affecting its rate of delivery and efficacy. So, we have initiated this study to characterize the mechanism of doripenem binding and to locate its site of binding on HSA by using spectroscopic and docking approaches. The binding of doripenem leads to alteration of the environment surrounding Trp-214 residue of HSA as observed by UV spectroscopic study. Fluorescence spectroscopic study revealed considerable interaction and complex formation of doripenem and HSA as indicated by Ksv and Kq values of the order of 104 M-1 and 1012 M-1 s-1 , respectively. Furthermore, doripenem quenches the fluorescence of HSA spontaneously on a single binding site with binding constant of the order of 103 M-1 , through an exothermic process. Van der Waals forces and hydrogen bonding are the major forces operating to stabilize HSA-doripenem complex. Circular dichroism spectroscopic study showed changes in the structure of HSA upon doripenem binding. Drug displacement and molecular docking studies revealed that the binding site of doripenem on HSA is located on subdomain IB and III A. This study concludes that, due to significant interaction of doripenem on either subdomain IB or IIIA of HSA, the availability of doripenem on the target site may be compromised. Hence, there is a possibility of unavailability of threshold amount of drug to be reached to the target; consequently, resistance may develop in the bacterial population.

Comparative studies on the human serum albumin binding of the clinically approved EGFR inhibitors gefitinib, erlotinib, afatinib, osimertinib and the investigational inhibitor KP2187

Binding interactions between human serum albumin (HSA) and four approved epidermal growth factor receptor (EGFR) inhibitors gefitinib (GEF), erlotinib (ERL), afatinib (AFA), osimertinib (OSI), as well as the experimental drug KP2187, were investigated by means of spectrofluorometric and molecular modelling methods. Steady-state and time resolved spectrofluorometric techniques were carried out, including direct quenching of protein fluorescence and site marker displacement measurements. Proton dissociation processes and solvent dependent fluorescence properties were investigated as well. The EGFR inhibitors were predominantly presented in their single protonated form (HL+) at physiological pH except ERL, which is charge-neutral. Significant solvent dependent fluorescence properties were found for GEF, ERL and KP2187, namely their emission spectra show strong dependence on the polarity and the hydrogen bonding ability of the solvents.The inhibitors proved to be bound at site I of HSA (in subdomain IIA) in a weak-to-moderate fashion (logK’ 3.9–4.9) using spectrofluorometry. OSI (logK’ 4.3) and KP2187 can additionally bind in site II (in subdomain IIIA), while GEF, ERL and AFA clearly show no interaction here. Docking methods qualitatively confirmed binding site preferences of compounds GEF and KP2187, and indicated that they probably bind to HSA in their neutral forms. Binding constants calculated on the basis of the various experimental data indicate a weak-to-moderate binding on HSA, only OSI exhibits somewhat higher affinity towards this protein. However, model calculations performed at physiological blood concentrations of HSA resulted in high (ca. 90%) bound fractions for the inhibitors, highlighting the importance of plasma protein binding.

Elucidation of intermolecular interaction of bovine serum albumin with Fenhexamid: A biophysical prospect

Fenhexamid, as a hydroxyanilide, is widely applied to control Botrytis cinerea for protecting crops and fruits. But it could adversely affect human and animals health due to accumulation of residues in food production. Here, the affinity characteristics of fenhexamid on bovine serum albumin (BSA) was studied via a series of spectroscopic methods such as steady-state fluorescence spectroscopy, ultraviolet spectroscopy (UV), synchronous fluorescence spectroscopy (SFS), 3D fluorescence spectroscopy, and fourier transform infrared spectroscopy (FT-IR). The experimental results illustrated that the fluorescence quenching mechanism of BSA induced by fenhexamid was a static quenching. The binding constant (Kb) of fenhexamid with BSA was 2.399 × 104 M−1 at 298 K and the combination ratio was about 1:1. The competitive experiment demonstrated that fenhexamid was binding on the BSA at site II (subdomain IIIA), which was confirmed by the molecular docking studies. The negative values of thermodynamic parameter (ΔH0, ΔS0 and ΔG0) revealed that the reaction of fenhexamid with BSA could proceed spontaneously, the van der Waals force and hydrogen bonding interaction conducted the main effect, and the binding process was enthalpy-driven. What's more, the 8-Anilino-1-naphthalenesulfonate (ANS) and sucrose binding studies were also performed and further verified the binding force between BSA and fenhexamid.

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin.

Saikosaponin D (SSD) and paeoniflorin (PF) are the major active constituents of Bupleuri Radix and Paeonia lactiflora Pall, respectively, and have been widely used in China to treat liver and other diseases for many centuries. We explored the binding of SSD/PF to human serum albumin (HSA) by using fluorospectrophotometry, circular dichroism (CD) and molecular docking. Both SSD and PF produced a conformational change in HSA. Fluorescence quenching was accompanied by a blue shift in the fluorescence spectra. Co-binding of PF and SSD also induced quenching and a conformational change in HSA. The Stern-Volmer equation showed that quenching was dominated by static quenching. The binding constant for ternary interaction was below that for binary interaction. Site-competitive experiments demonstrated that SSD/PF bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for the binary association. Also, there was energy transfer upon binary interaction. Molecular docking supported the experimental findings in conformation, binding sites and binding forces.

Simultaneous Binding of Folic Acid and Methotrexate to Human Serum Albumin: Insights into the Structural Changes of Protein and the Location and Competitive Displacement of Drugs.

Protein structure can be flexible to adopt multiple conformations to house small molecules. In this paper, we have attempted to experimentally figure out how the structure of a transport protein steer the drug–drug competition (DDC) by maintaining the equilibrium distribution of the bound and unbound fractions of drugs. This understanding is an important facet in biophysical and medicinal chemistry to ascertain the effectiveness of drugs. It is important to note that majority of studies involving small-molecule–transport protein interaction aimed at characterizing the binding process, and because these proteins can interact with thousands of molecules, there are hundreds of reports on such interactions. This ultimately led to an impression among the readers that any studies involving serum albumin may not lead to any new findings except for traditional binding explorations. However, in the present paper, we would like to draw the attention of the readers that our findings are very surprising, new, and important, involving the phenomenon of ligand–protein interaction. Here, we have studied two structurally similar drugs methotrexate (MTX) and folic acid (FA), which attempt to bind the primary binding site (subdomain IIA), one at a time, of human serum albumin. Details of binding analyses reveal that when both of the drugs are present, the single-site binding mode of FA prefers to occupy the primary binding site and hence pushes the primary-site-bound MTX to another location (subdomain IIIA), which is the second binding site of MTX. The structural analysis indicates that DDC has occurred in a cooperative fashion so that the loss of the protein secondary structure is minimum when both drugs are bound to the protein, which means that in the case of duo-drug binding, the conventional interaction between the drug and the protein is altered to undergo restoration of the protein structure. This can indeed regulate the DDC by modifying the bound and unbound fractions of MTX in plasma. The present study emphasizes that in vitro structural characterizations of the transport protein provide important information to improve the molecular-level understanding of DDC for further therapeutic applications with combination drug.

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches.

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level.

Elucidating the interaction of letrozole with human serum albumin by combination of spectroscopic and molecular modeling techniques.

Human serum albumin (HSA) is the most abundant protein found in human blood and is extensively employed in clinical applications such as hypovolemic shock treatment. Also, there has been a lot of attempt to use HSA as a carrier to deliver various drugs to their specific targets. Thus, clarify of structure, dynamics, functions, and features of HSA-drug complexes play an important role from the viewpoint of pharmaceutical and/or biochemical sciences. In this study, the interaction of letrozole, as a non-steroidal aromatase inhibitor, with HSA has been studied by combining different techniques such as UV-Vis, fluorescence spectroscopy, and computational methods. The binding of letrozole quenches the serum albumin fluorescence intensities. A clear decrease in fluorescence intensities of letrozole-HSA complex with the increase in temperature showed the static mode of fluorescence quenching. The results of Stern-Volmer procedure analysis showed that letrozole is bound only to a site from the HSA. The results of thermodynamic analysis showed that reaction between HSA and letrozole is spontaneous and exothermic. Furthermore, by monitoring the intrinsic fluorescence and using site markers competitive measurement, the binding of letrozole in the neighborhood of Sudlow's site I of HSA has been proved. Finally, computational methods substantiated the experimental findings and it was revealed that letrozole was bound to Arg-209, Trp-214, Ala-350, and Gly-238 residues of subdomain IIA and IIIA of HSA, respectively.

Quinolinesulfonamides: Interaction between bovine serum albumin, molecular docking analysis, and antiproliferative activity against human breast carcinoma cells

ABSTRACTThe complex formation of bovine serum albumin (BSA) with library of all seven regioisomeric quinolinesulfonamides (QSAs) under physiological condition is studied in this paper. The fluorescence quenching mechanism of BSA by QSAs was discussed and the association constants, as well as the number of binding sites, were calculated. In addition, a molecular docking study of the tested sulfamoylquinolines on the active site of serum albumin is performed. The experimental data and molecular docking studies reveal that sulfamoylquinolines bind in the large hydrophobic cavity of subdomain IB, and in the hydrophobic pockets of BSA subdomains IIA and IIIA by hydrophobic interactions with tryptophanyl (Trp-213) and tyrosyl residues. Moreover, the antiproliferative activity of QSAs against two human breast cancer cell lines (human adenocarcinoma (MCF-7) and human ductal carcinoma (MDA-MB-231)) and a human normal fibroblast is also studied in this paper. The antiproliferative activity of the tested QSAs was comparable to those of cisplatin. The returned data indicate that some of the tested quinolinesulfamoyl derivatives display significant cytotoxic activity.

Is the Sudlow site I of human serum albumin more generous to adopt prospective anti-cancer bioorganic compound than that of bovine: A combined spectroscopic and docking simulation approach

A comparative biophysical study on the individual conformational adaptation embraced by two homologous serum albumins (SA) (bovine and human) towards a potential anticancer bioorganic compound 2-(6-chlorobenzo[d] thiazol-2-yl)-1H-benzo[de] isoquinoline-1,3(2H)- dione (CBIQD) is apparent from the discrimination in binding behavior and the ensuing consequences accomplished by combined in vitro optical spectroscopy, in silico molecular docking and molecular dynamics (MD) simulation. The Sudlow site I of HSA although anion receptive, harbors neutral CBIQD in Sudlow site I (subdomain IIA, close to Trp) of HSA, while in BSA its prefers to snugly fit into Sudlow site II (subdomain IIIA, close to Tyr). Based on discernable diminution of HSA mean fluorescence lifetime as a function of biluminophore concentration, facile occurrence of fluorescence resonance energy transfer (FRET) is substantiated as the probable quenching mechanism accompanied by structural deformations in the protein ensemble. CBIQD establishes itself within HSA close to Trp214, and consequently reduces the micropolarity of the cybotactic environment that is predominantly constituted by hydrophobic amino acid residues. The stronger association of CBIQD with HSA encourages an allosteric modulation leading to slight deformation in its secondary structure whereas for BSA the association is comparatively weaker. Sudlow site I of HSA is capable to embrace a favorable conformation like malleable gold to provide room for incoming CBIQD, whereas for BSA it behaves more like rigid cast-iron which does not admit any change thus forcing CBIQD to occupy an altogether different binding location i.e. the Sudlow site II. The anticancer CBIQD is found to be stable within the HSA scaffold as vindicated by root mean square deviation (RMSD) and root mean square fluctuation (RMSF) obtained by MD simulation. A competitively inhibited esterase-like activity of HSA upon CBIQD binding to Lys199 and Arg257 residues, plausibly envisions that similar naphthalimide based prodrugs, bearing ester functionality, can be particularly activated by Sudlow site I of HSA. The consolidated spectroscopic research described herein may encourage design of naphthalimide based pro-drugs for effective in vivo biodistribution using HSA-based drug delivery systems.

Biophysical and In Silico Studies of the Interaction between the Anti-Viral Agents Acyclovir and Penciclovir, and Human Serum Albumin.

Acyclovir (ACV) and penciclovir (PNV) have been commonly used during the last few decades as potent antiviral agents, especially for the treatment of herpes virus infections. In the present research their binding properties with human serum albumin (HSA) were studied using different advanced spectroscopic and in-silico methods. The interactions between ACV/PNV and HSA at the three investigated temperatures revealed a static type of binding. Extraction of the thermodynamic parameters of the ACV-HSA and PNV-HSA systems from the measured spectrofluorimetric data demonstrated spontaneous interactions with an enthalpy change (∆H0) of −1.79 ± 0.29 and −4.47 ± 0.51 kJ·mol−1 for ACV and PNV, respectively. The entropy change (∆S0) of 79.40 ± 0.95 and 69.95 ± 1.69 J·mol−1·K−1 for ACV and PNV, respectively, hence supported a potential contribution of electrostatic binding forces to the ACV-HSA and PNV-HSA systems. Putative binding of ACV/PNV to HSA, using previously reported site markers, showed that ACV/PNV were bound to HSA within subdomains IIA and IIIA (Sudlow sites I and II). Further confirmation was obtained through molecular docking studies of ACV-HSA and PNV-HSA binding, which confirmed the binding site of ACV/PNV with the most stable configurations of ACV/PNV within the HSA. These ACV/PNV conformers were shown to have free energies of −25.61 and −22.01 kJ·mol−1 for ACV within the HSA sites I and II and −22.97 and −26.53 kJ·mol−1 for PNV in HSA sites I and II, with hydrogen bonding and electrostatic forces being the main binding forces in such conformers.

Identification of a peptide-peptide binding motif in the coating of nab-paclitaxel nanoparticles with clinical antibodies: bevacizumab, rituximab, and trastuzumab

Antibody directed chemotherapy (ADC) takes advantage of the selectivity of the monoclonal antibody to increase the efficacy of the chemotherapeutic agent, while reducing toxicity. Previously we described three nab-paclitaxel (Abraxane) nanoparticles coated with commercial monoclonal antibodies. Identifying the binding sites responsible for these particles could allow reverse engineering of nab-paclitaxel binding antibodies, creating a modular platform for antibody directed chemotherapeutic nanoparticles. Herein, Biacore surface plasmon resonance is used to identify an antibody binding site, HSA Peptide 40, on human serum albumin with nanomolar affinity for all three monoclonal antibodies. This 18-mer peptide, which lies in Subdomain IIIA of human serum albumin, blocks binding of all three antibodies to nab-paclitaxel when added in excess. We furthermore show the complementary binding region on all three monoclonal antibodies to be the CDR H3 loop of the Fab region, and show that they all have nano to micromolar affinity for HSA Peptide 40 and nab-paclitaxel nanoparticles. The presented data identify the nature of the critical protein-protein interaction that enables antibody coating of nab-paclitaxel.

Toxic interaction mechanism of two fluoroquinolones with serum albumin by spectroscopic and computational methods

ABSTRACTTo evaluate the toxicity of two fluoroquinolones (FQs), ciprofloxacin (CPFX), and enrofloxacin (ENFX), at the protein level, their binding modes with bovine serum albumin (BSA) were characterized by multiple spectroscopic and molecular docking methods under simulated physiological conditions. On the basis of fluorescence spectra, we concluded that both FQs greatly quenched the fluorescence intensity of BSA, which was attributed to the formation of a moderately strong complex mainly through electrostatic interactions. Besides, CPFX posed more of an affinity threat than ENFX. The molecular docking methods further illustrated that both CPFX and ENFX could bind into the subdomain IIIA of BSA and interact with Arg 508 and Lys 437, the positively charged residues in protein. Furthermore, as shown by the synchronous fluorescence, UV-Visible absorption and circular dichroism data, both CPFX and ENFX could lead to the conformational and microenvironmental changes of BSA, which may affect its physiological function.

A New Pathway for Protein Haptenation by β-Lactams.

The covalent binding of β-lactams to proteins upon photochemical activation has been demonstrated by using an integrated approach that combines photochemical, proteomic and computational studies, selecting human serum albumin (HSA) as a target protein and ezetimibe (1) as a probe. The results have revealed a novel protein haptenation pathway for this family of drugs that is an alternative to the known nucleophilic ring opening of β-lactams by the free amino group of lysine residues. Thus, photochemical ring splitting of the β-lactam ring, following a formal retro-Staudinger reaction, gives a highly reactive ketene intermediate that is trapped by the neighbouring lysine residues, leading to an amide adduct. For the investigated 1/HSA system, covalent modification of residues Lys414 and Lys525, which are located in sub-domains IIIA and IIIB, respectively, occurs. The observed photobinding may constitute the key step in the sequence of events leading to photoallergy. Docking and molecular dynamics simulation studies provide an insight into the molecular basis of the selectivity of 1 for these HSA sub-domains and the covalent modification mechanism. Computational studies also reveal positive cooperative binding of sub-domain IIIB that explains the experimentally observed modification of Lys414, which is located in a barely accessible pocket (sub-domain IIIA).

Study of the Interactions of Bovine Serum Albumin with the New Anti-Inflammatory Agent 4-(1,3-Dioxo-1,3-dihydro-2H-isoindol-2-yl)-N'-[(4-ethoxy-phenyl)methylidene]benzohydrazide Using a Multi-Spectroscopic Approach and Molecular Docking.

The lipophilic derivative of thalidomide (4-(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)-N′-[(4-ethoxyphenyl)methylidene]benzohydrazide, 6P) was synthesized to enhance its characteristics and efficacy. Earlier studies have proved the immunomodulatory and anti-inflammatory effects of 6P. In this study the interaction between bovine serum albumin (BSA) and 6P was studied using a multi-spectroscopic approach which included UV spectrophotometry, spectrofluorimetry and three dimensional spectrofluorometric and molecular docking studies. Static quenching was involved in quenching the fluorescence of BSA by 6P, because a complex formation occurred between the 6P and BSA. The binding constant decreased with higher temperature and was in the range of 2.5 × 105–4.8 × 103 L mol−1 suggesting an unstable complex at higher temperatures. A single binding site was observed and the the site probe experiments showed site II (sub-domain IIIA) of BSA as the binding site for 6P. The negative values of ∆G0, ∆H0 and ∆S0 at (298/303/308 K) indicated spontaneous binding between 6P and BSA as well as the interaction was enthalpy driven and van der Waals forces and hydrogen bonding were involved in the interaction. The docking results and the results from the experimental studies are complimentary to each other and confirm that 6P binds at site II (sub-domain IIIA) of BSA.

Multi-spectroscopic and molecular modeling approaches to elucidate the binding interaction between bovine serum albumin and darunavir, a HIV protease inhibitor

Darunavir (DRV), a second-generation HIV protease inhibitor, is widely used across the world as an important component of HIV therapy. The interaction of DRV with bovine serum albumin (BSA), a major carrier protein, has been studied under simulated physiological conditions (pH7.4) by multi-spectroscopic techniques in combination with molecular modeling. Fluorescence data revealed that the intrinsic fluorescence of BSA was quenched by DRV in terms of a static quenching procedure due to the formation of the DRV-BSA complex. The results indicated the presence of single weak affinity binding site (~103M−1, 310K) on protein. The thermodynamic parameters, namely enthalpy change (ΔH0), entropy change (ΔS0) and Gibbs free energy change (ΔG0) were calculated, which signified that the binding reaction was spontaneous, the main binding forces were hydrogen bonding and van der Waals forces. Importantly, competitive binding experiments with three site probes, phenylbutazone (in sub-domain IIA, site I), ibuprofen (in sub-domain IIIA, site II) and artemether (in the interface between sub-domain IIA and IIB, site II’), suggested that DRV was preferentially bound to the hydrophobic cavity in site II’ of BSA, and this finding was validated by the docking results. Additionally, synchronous fluorescence, three-dimensional fluorescence and Resonance Rayleigh Scattering (RRS) spectroscopy gave qualitative information on the conformational changes of BSA upon adding DRV, while quantitative data were obtained with Fourier transform infrared spectroscopy (FT-IR).

Red-emitting benzo[e]indolium probes for HSA based on the TICT characteristics

Human serum albumin (HSA) is the most abundant protein in human blood plasma. It plays an important role in many physiological functions, and the increase or decrease of HSA can exhibit the conditions of human health. Therefore, the accurate detection of HSA with high selectivity and sensitivity has a great clinical importance. We herein developed four red-emitting benzo[e]indolium fluorescent dyes, L1-L4, for probing HSA in a physiological buffer or human urine. Satisfactorily, L2 and L4 showed high selectivity and excellent sensitivity for HSA in both PBS buffer and human urine. L2 was completely embedded in the α-helices from subdomain IIA (Sudlow site I) of HSA, and the limit of detection (LOD) was 13.43mgL−1 in PBS and 8.91mgL−1 in urine, respectively. However, L4 inserted into the α-helices from subdomain IIA and IIIA (Sudlow site II) of HSA, and exhibited a lower LOD (1.75mgL−1 in PBS, 1.50mgL−1 in urine). Furthermore, the high tolerance of environmental pH and anti-interference of L2 and L4 enabled us to develop the promising molecular probes for HSA.

Synthesis of triangular silver nanoprisms and spectroscopic analysis on the interaction with bovine serum albumin.

The interactions of triangular silver nanoprisms (TAgNPrs) with bovine serum albumin (BSA) were investigated using multiple spectroscopic techniques. A noticeable absorbance increase was noted in the peak ranges of 250 to 300nm for BSA, and the intensity increased with the increasing concentration of TAgNPrs. Furthermore, a slight blue shift of the surface plasmon resonance band of TAgNPrs occurred, indicating that the protein absorbed on the TAgNPrs surface to form a bio-nano interface. Analysis of fluorescence quenching data using the Stern-Volmer method revealed that static quenching takes place with complex formation. Evaluation of thermodynamic parameter ΔG θ for the binding processes indicated that the binding reaction was exothermic. Furthermore, the values of binding constant K revealed that the size of nanoparticles can affect the binding degree. The order of binding affinity is 43.7nm>36.2nm>25.1nm. The competitive experiments of site markers (flufenamic acid and phenylbutazone) suggested that the binding site of TAgNPrs on BSA was located in the region of subdomain IIIA (Sudlow site II). In addition, the conformational changes of BSA by TAgNPrs were analyzed by using synchronous fluorescence spectra, circular dichroism, and three-dimensional fluorescence spectra. Graphical abstract The protein absorbed on the TAgNPrs surface to form a nanoparticle-protein corona.

A detailed study on the interaction of a novel water-soluble glycine bridged zinc(II) Schiff base coordination polymer with BSA: Synthesis, crystal structure, molecular docking and cytotoxicity effect against A549, Jurkat and Raji cell lines

A novel water-soluble glycine bridged zinc(II) Schiff base coordination polymer was synthesized by the condensation of 2,6-diformyl-4-methylphenol, glycine, and zinc(II) chloride. The complex was characterized by 1HNMR, FT-IR, elemental analyses and X-ray crystallography. The polymeric complex was built up of two glycine-bridged Zn/L moieties, where L denotes the Schiff base containing 2,6-diformyl-4-methylphenol and glycine in 1:1M ratio. The carboxylic group of L was coordinated to the Zn atoms of the neighboring moieties; thus each Zn center was five-coordinated. The interaction between polymeric Zn(II) complex and bovine serum albumin (BSA) was studied by UV–Vis, fluorescence, and synchronous fluorescence spectroscopic techniques. By considering the sign and values of the thermodynamic parameters (ΔH and ΔS), it is clear that the binding between BSA and complex was exothermic and entropy-driven and electrostatic interactions between the complex and BSA was supposed. Site-selective binding studies revealed that the complex were mainly located in the region of site II (subdomain IIIA) in BSA. From the synchronous fluorescence spectroscopic studies, it is concluded that complex could bind to tyrosine and tryptophan residues simultaneously. The Kb values indicated a high binding affinity of the complex to BSA. In vitro anticancer activity of the polymeric Zn(II) complex was evaluated against A549, Jurkat, and Raji cell lines by MTT assay. The complex was remarkably active against the cell lines and can be a good candidate for an anticancer therapy. Theoretical docking studies were performed to further investigate the BSA binding interactions.

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.

Crystallographic analysis of the ternary complex of octanoate and N-acetyl-l-methionine with human serum albumin reveals the mode of their stabilizing interactions

During pasteurization and storage of albumin products, Sodium octanoate (Oct) and N-acethyl-l-tryptophan (N-AcTrp) are used as the thermal stabilizer and the antioxidant for human serum albumin (HSA), respectively. We recently reported that N-acethyl-l-methionine (N-AcMet) is an antioxidant for HSA, which is superior to N-AcTrp when it is especially exposed to light during storage. The objective of the present study is to clarify the molecular mechanism responsible for the HSA protective effect of Oct and N-AcMet based on their ternary complex structure. Crystal structure of the HSA–Oct–N-AcMet complex showed that one N-AcMet molecule is bound to the entrance of drug site 1 of HSA, and its side chain, which is susceptible to the oxidation, is exposed to the solvent. At the same time, two Oct binding sites are observed in drug sites 1 and 2 of HSA, respectively, and each Oct molecule occupies the hydrophobic cavity in them. These results indicate the molecular mechanism responsible for the HSA stabilization by these small molecules as follows. N-AcMet seals the entrance of drug site 1 while it acts as an antioxidant for HSA. Oct is chiefly bound to drug site 2 of HSA and it increases the thermal stability of HSA because of the occupying the largest intra-cavity of sub-domain IIIA in HSA. These findings suggest that N-AcMet acts positively as useful stabilizer for albumin formulated products such as functionalized HSA and HSA fusion proteins.