HSA Binding Sites Research Articles

Spectroscopic investigation and structural simulation in human serum albumin with hydroxychloroquine/Silybum marianum and a possible potential COVID-19 drug candidate.

In this study, the interaction between human serum albumin (HSA) and the hydroxychloroquine/Silybum marianum (HCQ/SM) mixture was investigated using various techniques. The observed high binding constant (Kb) and Stern-Volmer quenching constant (KSV) indicate a strong binding affinity between the HCQ/SM mixture and HSA. The circular dichroism (CD) analysis revealed that HCQ/SM induced conformational changes in the secondary structure of HSA, leading to a decrease in the α-helical content. UV-Vis analysis exhibited a slight redshift, indicating that the HCQ/SM mixture could adapt to the flexible structure of HSA. The experimental results demonstrated the significant conformational changes in HSA upon binding with HCQ/SM. Theoretical studies were carried out using molecular dynamics simulation via the Gromacs simulation package to explore insights into the drug interaction with HSA-binding sites. Furthermore, molecular docking studies demonstrated that HCQ/SM-HSA exhibited favorable docking scores with the receptor (5FUZ), suggesting a potential therapeutic relevance in combating COVID-19 with a value of -6.24 kcal mol-1. HCQ/SM exhibited stronger interaction with both SARS-CoV-2 virus main proteases compared to favipiravir. Ultimately, the experimental data and molecular docking analysis presented in this research offer valuable insights into the pharmaceutical and biological properties of HCQ/SM mixtures when interacting with serum albumin.

Hsa_circ_0001326 inhibited the proliferation, migration, and invasion of trophoblast cells via miR-145-5p/TGFB2 axis.

Preeclampsia (PE) is an obstetric disease involving multiple systems, which account for maternal and fetal complications and increased mortality. Circular RNAs (circRNAs) were recently deemed to associate with the pathogenesis of PE. This study aims to clarify the correlation between circRNA hsa_circ_0001326 and PE and explore its biological function in PE. The expression of hsa_circ_0001326 in PE placentas was detected by real-time quantitative PCR (qRT-PCR). After overexpressing or inhibiting hsa_circ_0001326 in trophoblast cells, the cell growth, migration, and invasion were evaluated by Cell Counting Kit-8 (CCK-8) and transwell assays. Western blot assay was applied to detect the epithelial-mesenchymal transition (EMT) proteins, E-cadherin and Vimentin. Furthermore, a dual-luciferase reporter assay was applied to verify the binding sites of hsa_circ_0001326, miR-145-5p, and transforming growth factor beta 2 (TGFB2). Hsa_circ_0001326 was found to be higher expressed in PE placentas than in normal placentas. Furthermore, hsa_circ_0001326 played a negative regulating role in trophoblast cell viability, migration, and invasion. Overexpression of hsa_circ_0001326 inhibited the viability, migration, and invasion of trophoblast cells, while inhibition of hsa_circ_0001326 showed opposite effects. Mechanistically, hsa_circ_0001326 sponged miR-145-5p to elevate TGFB2 expression in trophoblast cells. This study provided evidence that the up-regulated hsa_circ_0001326 in PE restrained trophoblast cells proliferation, migration, and invasion by sponging miR-145-5p to elevate TGFB2 expression. Our results might provide a novel insight into the role of hsa_circ_0001326 in the pathogenesis of PE.

Exploring the Molecular Level Interaction of Human Serum Albumin with Calcium Oxalate Monohydrate Crystals.

Human serum albumin (HSA) is one of the most abundant proteins in the blood plasma, urine as well as in the organic matrix of renal calculi. Macromolecules present in the urine modulate kidney stone formation either by stimulating or inhibiting the crystallization process. In the present study, the effect of HSA protein on the growth of calcium oxalate monohydrate crystal (COM) was investigated. Crystal growth assay was used to measure oxalate depletion in the crystal seeded solution in the presence of HSA. HSA concentrations exhibiting effect on crystal growth were selected for FTIR and XRD analysis. In silico docking was performed on seven different binding sites of HSA. Albumin plays dual role in the growth of calcium oxalate crystallization. FTIR and XRD studies further revealed HSA exerted strain over crystal thus affecting its structure by interacting with amino acids of its pocket 1. Docking results indicate that out of 7 binding pocket in protein, calcium oxalate interacts with Arg-186 and Lys-190 amino acids of pocket 1. Our study confirms the role of HSA in calcium oxalate crystallization where acidic amino acids arginine and lysine bind to COM crystals, revealing molecular interaction of macromolecule and crystal in urolithiasis.

Barbiturate squaraine dyes as fluorescent probes for serum albumins detection

Three indolenine-based barbiturate squaraine dyes were synthesized, characterized and subjected to photophysical studies, including their affinity with human serum albumin and bovine serum albumin as protein models in phosphate buffer solution. All dyes successfully interact with both proteins with high affinity binding constants. It was found that dyes with hydrophobic substituents had superior binding constants with both proteins. The fluorescence intensity of all dyes increased in the presence of both proteins which allowed the determination of detection and quantifications limits in the tens of nanomolar, using a protein concentration of 0–3.5 μM. Concerning to the study on the binding sites of the synthesized dyes using the warfarin and ibuprofen markers, the results of this study suggest that, one dye binds to both BSA binding sites while the two others dyes binds only to site I, and that all three dyes bind to both HSA binding sites.

Circular RNA hsa_circ_103809 promotes cell migration and invasion of gastric cancer cells by binding to microRNA-101-3p.

Studies have found that hsa_circ_103809, a newly discovered circRNA in recent years, can serve as an oncogene involved in the progression of hepatocellular carcinoma. However, its role in gastric cancer (GCa) remains elusive. The aim of this study was to reveal the molecular mechanism of hsa_circ_103809 affecting the process of GCa, thus providing new ideas for its treatment. Hsa_circ_103809 expression in GCa and adjacent tissues specimens were studied by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) analysis, and its effect on the prognosis of GCa patients was analyzed. In GCa cells lines, hsa_circ_103809 was knocked down by small interfering RNA, and GCa cell metastasis ability was detected by cell wound healing test and transwell assay. Finally, the potential target gene of hsa_circ_103809 was predicted through bioinformatics website and verified by Luciferase assay. Hsa_circ_103809 showed an increased expression both in GCa tissues and cell lines, predicting a poor prognosis of GCa patients. Meanwhile, the invasive and migration capacities of GCa cells were remarkably reduced after the knockdown of hsa_circ_103809. Bioinformatics website predicted that there existed binding sites of hsa_circ_103809 on microRNA-101-3p, and Luciferase assay verified that hsa_circ_103809 can adsorb microRNA-101-3p. In GCa tissues, qPCR detected a significantly reduced expression of microRNA-101-3p, which was negatively correlated with that of hsa_circ_103809. In addition, the knockdown of hsa_circ_103809 enhanced microRNA-101-3p expression in GCa cell lines. Subsequent in vitro experiments further detected that the overexpression of hsa_circ_103809 partially reversed the inhibitory effect of microRNA-101-3p overexpression on GCa cell migration ability and invasiveness. Hsa_circ_103809, highly expressed in GCa, may promote the migration capacity of GCa cells by adsorbing microRNA-101-3p and thus become a new therapeutic target for GCa.

Perfluoroalkane sulfonyl fluorides non-covalently bind to human serum albumin at Sudlow’s sites

Perfluorooctane sulfonyl fluoride (PFOSF) has been defined as persistent organic pollutant in the Stockholm Convention in 2009. Currently PFOSF and its substitutes (structural analogues in which octyl group is substituted for other aliphatic chains) are still scarcely studied. HSA is a main carrier for drugs in blood, and the influence of exogenous compounds including pollutants on HSA is of particular interest. In this work, the binding sites of HSA to Perfluoroalkane sulfonyl fluoride (PFASFs) were determined by fluorescence technique. The results demonstrated that PFASFs competitively bind to HSA at Sudlow’s site I against warfarin and at Sudlow’s site II against dansyl-proline and the related association constants were determined. The association constants of PFOSF, perfluorohexane sulfonyl fluoride (PFHSF) and perfluorobutane sulfonyl fluoride (PFBSF) were determined to be 2.59 × 10−3 μM-1, 4.65 × 10−3 μM-1 and 2.85 × 10−3 μM-1 at Sudlow’s site I and 8.68 × 10−4 μM-1, 3.43 × 10−2 μM-1 and 1.92 × 10−2 μM-1 at Sudlow’s site II, respectively. The results showed that PFASFs can bind tightly to HSA and thus migrate to all parts of the body through vascular system. Non-covalent interaction between HSA and PFASFs was confirmed with tryptic digestion experiment. The mass spectra results indicated that other binding sites of HSA are also involved in the binding of PFHSF and PFBSF. The total binding numbers of PFOSF, PFHSF and PFBSF on HSA are 2, 6 and 3, respectively.

2D photonic crystal protein hydrogel coulometer for sensing serum albumin ligand binding.

Bovine and human serum albumin (BSA and HSA) are globular proteins that function as bloodstream carriers of hydrophobes such as fatty acids and drugs. We fabricated novel photonic crystal protein hydrogels by attaching 2D colloidal arrays onto pure BSA and HSA hydrogels. The wavelengths of the diffracted light sensitively report on the protein hydrogel surface area. The binding of charged species to the protein hydrogel gives rise to Donnan potentials that change the hydrogel volume causing shifts in the diffraction. These photonic crystal protein hydrogels act as sensitive Coulometers that monitor the hydrogel charge state. We find multiple high-affinity BSA and HSA binding sites for salicylate, ibuprofen and picosulfate by using these sensors to monitor binding of charged drugs. We demonstrate proof-of-concept for utilizing protein hydrogel sensors to monitor protein-ionic species binding.

Species-dependent binding of tocainide analogues to albumin: Affinity chromatography and circular dichroism study

A series of novel tocainide analogues were characterized for their HSA and RSA binding, by using high-performance liquid affinity chromatography (HPLAC) and circular dichroism (CD). In this HPLAC study, HSA and RSA were covalently immobilized to the silica matrix of HPLC columns, with a procedure that maintained unaltered the binding properties of the proteins. The tocainide analogues were ranked for their affinity to HSA and RSA on the basis of their bound fractions measured by the two albumin-based columns. This technique was also applied to characterize the high affinity binding sites of these tocainide analogues to the protein. For this purpose displacement experiments were carried out by means of increasing concentrations in the mobile phase of competitors known to bind selectively to the main binding sites of HSA. The results obtained with the immobilized proteins were confirmed by investigating the same drug-protein systems in solution by circular dichroism. The comparison of the data collected with both methodologies highlighted the dramatic effect of small differences in the amino acidic sequences of the two proteins. In fact, despite their similar primary and secondary structures, a small difference in the amino acidic sequence leads to significant differences in their three-dimensional structure reflecting their different binding capacity and their stereoselectivity. Therefore, this study confirms how it is crucial to consider the significant differences among the animal models when performing pharmacokinetic studies. It is also clear that the knowledge of serum carrier binding parameters at an early stage of drug discovery represents a great advantage that may help to save time and efforts.

Molecular Dynamics Simulations of Human Serum Albumin and Role of Disulfide Bonds

Atomistic molecular dynamics simulations of human serum albumin in the presence and absence of disulfide bonds are presented. Simulations of 70 ns duration provide information on the relevance of disulfide bonds in the dynamics and structural conformation of HSA. Significant conformational changes are observed in the absence of disulfide bonds after 35 ns that could impact the functionality and stability of the protein. Changes in the secondary structure, hydrogen bonds, B factors, and cross-correlations reveal which disulfide bonds are important for keeping the secondary and tertiary structure and dynamics of the protein (e.g., Cys168-Cys177, Cys278-Cys289) and which have little effect on the local structure and dynamics (e.g., Cys200-Cys246, Cys461-Cys477). Removing all disulfide bonds in the protein appears to be a practical prescreening tool for identifying disulfide bonds relevant to structure and dynamics. In the absence of disulfide bonds, certain hydrogen bonds and correlated motions vanish, affecting the structure of neighboring residues. The structure of the primary binding sites of HSA is partially affected when disulfide bonds are removed. For the native structure, simulations clearly reveal the conformational changes that allow the only free cysteine to be exposed on the protein surface to form intermolecular disulfide bonds; this information could not be resolved from the static crystal structure alone. The absence of specific disulfide bonds could lead to partially unfolded structures; such structures are known to be prone to protein aggregation. Removing disulfide bonds could have similar consequences in other proteins of interest, such as immunoglobulin G.

Serum-protein interactions with anticancer Ru(III) complexes KP1019 and KP418 characterized by EPR

The compounds imidazolium [trans-[RuCl(4)(1H-imidazole)(2)] (KP418) and indazolium [trans-RuCl(4)(1H-indazole)(2)] (KP1019) both show significant anticancer activity, with the latter recently having completed phase I clinical trials. An important component of this success has been associated with targeted delivery of the complexes to cancer cells by serum proteins. In this study, electron paramagnetic resonance (EPR) measurements, combined with incubation under physiological conditions, and separation of protein-bound fractions, have been used to characterize the interactions of these complexes with human serum albumin (hsA), human serum transferrin (hsTf) apoprotein, and whole human serum. The strong EPR signals observed in these experiments demonstrate that both complexes are primarily retained in the 3+ oxidation state in the presence of serum components. Rapid, noncovalent binding of KP1019 was observed in the presence of both hsA and serum, indicating that the predominant interactions occur within the hydrophobic binding sites of hsA. This sequestering process correlates with the low levels of side effects observed in clinical trials of the complex. At longer incubation times, the noncovalently bound complexes are converted slowly to a protein-coordinated form. Noncovalent interactions are not observed in the presence apo-hsTf, where only slow binding of KP1019 via ligand exchange with the protein occurs. By contrast, hydrophobic interactions of KP418 with hsA only occur with the aquated products of the complex, a process that also dominates in serum. In the presence of apo-hsTf, KP418 interacts directly with the protein through exchange of ligands, as observed with KP1019.

HSA binding of HIV protease inhibitors: a high‐performance affinity chromatography study

The binding of HIV protease inhibitors, drugs important for anti-HIV chemotherapy, to HSA was examined by high-performance affinity chromatography. Frontal analysis was first used to determine the amount of anchored protein and the binding capacity for selected markers on this column. Zonal elution experiments then ranked the HSA bound fraction of the examined compounds. Information on the binding region was obtained by competitive zonal elution experiments using probe compounds with known sites on HSA. An allosteric competition between HIV protease inhibitors (PIs) and valproate (a probe for the bilirubin site) was detected, consistent with a noncooperative binding mechanism. No significant competition was observed between the examined compounds and salicylate or ibuprofen, probes for sites I and II, respectively. The observations were confirmed by circular dichroism spectroscopy, based on the change in the induced circular dichroism signals of selected markers for the main binding sites of HSA when ritonavir was added as the competitor. These results were in good agreement with previous literature reports and provide more details on how PIs are transported in plasma and how they may compete with other drugs in the body.

A molecular dynamics study of human serum albumin binding sites

A 2.0 ns unrestrained Molecular Dynamics was used to elucidate the geometric and dynamic properties of the HSA binding sites. The structure is not stress affected and the rmsds calculated from the published crystallographic data are almost constant for all the simulation time, with an averaged value of 2.4Å. The major variability is in the C-terminus region. The trajectory analysis of the IIA binding site put in evidence fast oscillations for the Cγ@Leu203···Cγ@Leu275 and Cγ@Leu219···Cγ@Leu260 distances, with fluctuations around 250 ps, 1000 ps and over for the first, while the second is smoothly increasing with the simulation time from 7 to 10Å. These variations are consistent with a volume increase up to 20% confirmed by the inter-domain contacts analysis, in particular for the pair O@Pro148···Oγ@Ser283, representing the change of distance between IB-h9 and IIA-h6, O@Glu149···Oγ@Ser189 for sub-domains IB-h9/IIA-h1 and N@Val339···Oδ2@Asp447 sub-domains IIB-h9/IIIA-h1. These inter-domain motions confirm the flexibility of the unfatted HSA with possible binding site pre-formation.

Binding of 99mTc to human serum albumin

The specificity of 99m Tc-MDP binding to HSA was examined , the results showed that the non specific binding was 21-23% of the total binding . The range of optimum pH for the binding was 7.4-7.6 . The most suitable amounts for HSA to give maximum binding was (70mg)per incubation medium , binding seemed to be affected by 99m Tc- MDP concentration and also mono and divalent metal chloride salts. The association constants (ka) and maximum binding capacity (Bmax) of 99m Tc-MDP binding to its binding sites of HSA was determined from scatchard and double reciprocal plots , the results revealed that (ka) and (Bmax) values were temperature dependant.

Anti-coagulant rodenticide binding properties of human serum albumin: a biochromatographic approach

In this paper, the anti-coagulant rodenticide-human serum albumin (HSA) binding was investigated using a perturbation method to calculate the solute distribution isotherms. It was shown that rodenticide can bound either on the benzodiazepine HSA site with low affinity (site I) or on the warfarin HSA site with high affinity (site II). The thermodynamic parameters of this association were calculated for the two HSA binding sites. For the site II, the rodenticide-HSA association was governed enthalpically whereas for the site I, this one was driven entropically. Moreover, the role of the magnesium (Mg 2+) and calcium (Ca 2+) on this association was carried out. It was clearly demonstrated that the rodenticide affinity for the site I was not affected by modifying the bulk solvent surface tension whereas for the site II the association constant increased strongly with the Mg 2+ or the Ca 2+ concentration in the bulk solvent. These results showed that the rodenticide-HSA affinity and thus the rodenticide toxicological effect depends on the Mg 2+ or Ca 2+ concentration.

A re-evaluation of the HSA-piroxicam interaction

Piroxicam binding to HSA was studied using equilibrium dialysis and fluorescence methods. It was shown that this drug, like its analogs isoxicam and tenoxicam, binds to the apazone locus (site I area) and to a lesser extent to the diazepam site (site II). The piroxicam binding to HSA can be modulated by various specific ligands--apazone, warfarin, diazepam, ibuprofen--and these drug interactions have to be considered not only as potential displacement from the HSA binding sites but also in terms of induced allosteric effects.

Blood distribution of tenoxicam in humans: a particular HSA drug interaction.

Blood binding of tenoxicam was studied in vitro by equilibrium dialysis. Isolated human plasma proteins and blood cells were checked, and the distribution of the bound form was then calculated. The results showed that tenoxicam is mainly bound to HSA and that binding percentages are not different when measured in plasma (98.4%) and in an HSA solution at physiological concentration (704 microM, 98.15%). In these conditions, within the range of 1-150 microM, the tenoxicam binding percentage remained constant, evidence of a nonsaturable process. When a lower HSA concentration (10 microM) was used, the binding parameters of the tenoxicam interaction were calculated by using the same equilibrium dialysis data, by 3 methods of analysis- a stoichiometric method and site-oriented methods, fixing or not the number of HSA binding sites (n) as integer values. The best fit was observed with the first method, suggesting that two main interactions occurred. The site-oriented method gave lesser fits, the better being observed when n was not fixed. Its value, 1.77, suggest the possibility of two binding sites, one of them not preformed. The effects of known markers of site I, warfarin and apazone, of site II, diazepam and ibuprofen and of palmitic acid showed that tenoxicam is bound simultaneously to both sites I and II. The binding capacity of site I for tenoxicam is enhanced by diazepam: as this compound alone is bound to site II, this result suggests that the two HSA binding sites are not independent.

Human serum albumin as a 'silent receptor' for drugs and endogenous substances.

Most drugs are bound to human serum albumin (HSA) via a few high affinity binding sites and several sites of much lower affinity. There is now increasing evidence that the actual number of high affinity drug-binding sites of HSA is rather small. Thus, each of these binding sites binds several drugs of very different chemical and pharmacological properties with relative high affinity. On the other hand these drug-binding sites can in some cases be very specific and even stereoselective, as demonstrated by the stereospecific binding of drugs to some of these binding sites. The discrepancy between both observations can be explained by the conformational adaptability of the HSA-binding sites.

Fluorescence of 4-Methyl-7-substituted Aminocoumarin in a Variety of Organic Solvents and Aqueous Protein Solutions

Some organic compounds fluorescence intensely when dissolved in less-polar solvents or bound to proteins but have extremely low fluorescence intensity in aqueous solutions. When the fluorescence quantum yield, emission maximum, or emission band width are related to the polarity of the environment around the fluorescent species, these compounds can serve as probes for hydrophobic sites in proteins. To provide new types of the effective hydrophobic probe for investigation of hydrophobic regions in proteins and micelle of surfactants, the fluorescence of ten 4-methyl-7-substituted aminocoumarin in a variety of solvents has been measured. When the amino groups on the coumarin are anilino, diethylamino, and morphorino, the fluorescence of the coumarin derivatives is varied significantly with polarity of solvents and hence the compounds seem to be applicable as the hydrophobic probe. On the other hand, the primary and secondary alkyl aminocoumarins are inadequate for the hydrophobic probe. Among the coumarin derivatives 4-methyl-7-anilino coumarin (MAC) has extremely low fluorescence in aqueous solutions. In less-polar solvents, however, the fluorescence increases. The increase is remarkable especially in solvents whose dielectric constant is below twenty. Furthermore, the wavenumber of emission maximum changes as a function of polarity of the solvents. Therefore the fluorescence characteristics of MAC make this compound a new type of useful reagent for the hydrophobic probe. The fluorescence of MAC was measured in aqueous solutions of human and bovine serum albumin (HSA, BSA respectively) and the results of the fluorescence measurement were referred to the results of the above experiments. The binding sites of HSA and BSA for MAC are estimated to have such high hydrophobicity as 7-10 and 6-.9, respectively, in units of dielectric constant.