Probing the interaction of cephalosporin antibiotic–ceftazidime with human serum albumin: A biophysical investigation

Interaction between the antioxidant compound safranal and α-chymotrypsin in spectroscopic fields and molecular modeling approaches

Among various herbal plants, saffron has been the subject of study in various medical and food fields. Among the compounds of saffron, safranal is one of them. Safranal is a monoterpene aldehyde. The precursor of safranal is called picrocrocin, whose hydrolysis leads to the production of safranal. picrocrocin has two sugar components and aglycone. sugar component was separated during the drying process of saffron and safranal is produced. Saffron is the cause of the saffron aroma. Previous studies have shown that safranal offers many benefits such as antioxidants, blood pressure regulation and anti-tumor qualities. On the other hand, α-Chy is an enzyme secreted by the pancreas into the intestine and then acts as an efficient protease. In this study, various methods, such as molecular dynamics (MD) simulation and molecular binding, and different spectroscopic techniques, as well as protein stability techniques, were used to investigate the possible interactions between safranal and α-Chy. UV spectroscopic studies were showing that the existence of safranal decreased α-Chy absorption intensity. safranal caused the intrinsic fluorescence of α-Chy to be quenched too. According to the Stern-Volmer equation, the interaction between safranal and α-Chy was of the static type. In thermodynamic calculations, the interaction between safranal and α-Chy was stabilized by hydrophobic forces. And it was found that this interaction continued spontaneously. These results were, thus, consistent with the Docking data simulation (with the negative ΔG° number and positive changes in enthalpy and entropy). The thermal stability of α-Chy was also measured, showing that its melting point was shifted to a higher threshold as a result of the interaction. also, MD simulation indicated that α-Chy became more stable in the presence of safranal. In this paper, all the results of the laboratory techniques were confirmed by molecular dynamic simulations, so the correctness of the results was confirmed. From this research, we hope to carefully observe the possible changes in the behavior and structure of the enzyme in the presence of safranal.Communicated by Ramaswamy H. Sarma.

Spectroscopy and molecular simulation on the interaction of Nano-Kaempferol prepared by oil-in-water with two carrier proteins: An investigation of protein-protein interaction

In this work, the interaction of human serum albumin (HSA) and human holo-transferrin (HTF) with the prepared Nano-Kaempferol (Nano-KMP) through oil-in-water procedure was investigated in the form of binary and ternary systems by the utilization of different spectroscopy techniques along with molecular simulation and cancer cell experiments. According to fluorescence spectroscopy outcomes, Nano-KMP is capable of quenching both proteins as binary systems by a static mechanism, while in the form of (HSA-HTF) Nano-KMP as the ternary system, an unlinear Stern-Volmer plot was elucidated with the occurrence of both dynamic and static fluorescence quenching mechanisms in the binding interaction. In addition, the two acquired Ksv values in the ternary system signified the existence of two sets of binding sites with two different interaction behaviors. The binding constant values of HSA-Nano KMP, HTF-Nano-KMP, and (HSA-HTF) Nano-KMP complexes formation were (2.54 ± 0.03) × 104, (2.15 ± 0.02) × 104 and (1.43 ± 0.04) × 104M-1at the first set of binding sites and (4.68 ± 0.05) × 104 M-1 at the second set of binding sites, respectively. The data of thermodynamic parameters confirmed the major roles of hydrogen binding and van der Waals forces in the formation of HSA-Nano KMP and HTF-Nano KMP complexes. The thermodynamic parameter values of (HSA-HTF) Nano KMP revealed the dominance of hydrogen binding and van der Waals forces in the first set of binding sites and hydrophobic forces for the second set of binding sites. Resonance light scattering (RLS) analysis displayed the existence of a different interaction behavior for HSA-HTF complex in the presence of Nano-KMP as the ternary system. Moreover, circular dichroism (CD) technique affirmed the conformational changes of the secondary structure of proteins as binary and ternary systems. Molecular docking and molecular dynamics simulations (for 100 ns) were performed to investigate the mechanism of KMP binding to HSA, HTF, and HSA-HTF. Next to observing a concentration and time-dependent cytotoxicity, the down regulation of PI3K/AkT/mTOR pathway resulted in cell cycle arrest in SW480 cells.

Interaction mechanism of a cysteine protease inhibitor, odanacatib, with human serum albumin: In vitro and bioinformatics studies

Odanacatib (ODN) is a selective cathepsin K inhibitor that acts as an anti-resorptive agent to treat osteoporosis. ODN is also found effective in reducing the effect of severe periodontitis. The interaction between ODN and human serum albumin (HSA) was investigated using spectroscopic, microscopic, and in silico approaches to characterize their binding. The fluorescence intensity of HSA increased upon the addition of increasing concentrations of ODN accompanied by blueshift in the fluorescence spectrum, which suggested hydrophobic formation around the microenvironment of the fluorophores upon ODN binding. A moderate binding affinity was obtained for ODN-HSA binding, with binding constant (Ka) values of ∼104 M-1. Circular dichroism results suggested that the overall secondary and tertiary structures of HSA were both only slightly altered upon ODN binding. The surface morphology of HSA was also affected upon ODN binding, showing aggregate formation. Drug displacement and molecular docking results revealed that ODN preferably binds to site III in subdomain IB of HSA, while molecular dynamics simulations indicated formation of a stable protein complex when site III was occupied by ODN. The ODN-HSA complex was mainly stabilized by a combination of hydrogen bonding, hydrophobic interactions, and van der Waals forces. These findings provide additional information to understand the interaction mechanism of ODN in blood circulation and may help in future improvements on the adverse effects of ODN.

Structural change study of pepsin in the presence of spermidine trihydrochloride: Insights from spectroscopic to molecular dynamics methods

Spermidine is an aliphatic polyamine that directs a set of biological processes. This work aimed to use UV-Vis spectroscopy, fluorescence spectroscopy, thermal stability, kinetic methods, docking, and molecular dynamic simulations to examine the influence of spermidine trihydrochloride (SP) on the structure and function of pepsin. The results of the fluorescence emission spectra indicated that spermidine could quench pepsin's intrinsic emission in a static quenching process, resulting in the formation of the pepsin-spermidine complex. The results discovered that spermidine had a strong affinity to the pepsin structure because of its high binding constant. The obtained results from spectroscopy and molecular dynamic approaches showed the binding interaction between spermidine and pepsin, induced micro-environmental modifications around tryptophan residues that caused a change in the tertiary and secondary structure of the enzyme. FTIR analysis showed hypochromic effects in the spectra of amide I and II and redistribution of the helical structure. Moreover, the molecular dynamic (MD) and docking studies confirmed the experimental data. Both experimental and molecular dynamics simulation results clarified that electrostatic bond interactions were dominant forces.

A flaw in applying the FRET technique to evaluate the distance between ligands and tryptophan residues in human serum albumin: Proposal of correction

Due to its primordial function as a drug carrier, human serum albumin (HSA) is extensively studied regarding its binding affinity with developing drugs. Förster resonance energy transfer (FRET) is frequently applied as a spectroscopic molecular ruler to measure the distance between the binding site and the ligand. In this work, we have shown that most of the published results that use the FRET technique to estimate the distance from ligands to the binding sites do not corroborate the crystallography data. By comparing the binding affinity of dansyl-proline with HSA and ovotransferrin, we demonstrated that FRET explains the quenching provoked by the interaction of ligands in albumin. So, why does the distance calculation via FRET not corroborate the crystallography data? We have shown that this inconsistency is related to the fact that a one-to-one relationship between donor and acceptor is not present in most experiments. Hence, the quenching efficiency used for calculating energy transfer depends on distance and binding constant, which is inconsistent with the correct application of FRET as a molecular ruler. We have also shown that the indiscriminate attribution of 2/3 to the relative orientation of transition dipoles of the acceptor and donor (κ²) generates inconsistencies. We proposed corrections based on the experimental equilibrium constant and theoretical orientation of transition dipoles to correct the FRET results.

Comprehensive insights into the interactions of dicyclohexyl phthalate and its metabolite to human serum albumin

Phthalate esters (PAEs) are a type of persistent organic pollutants and have received widespread concerns due to their adverse effects on human health. Dicyclohexyl phthalate (DCHP) and its metabolite monocyclohexyl phthalate (MCHP) were selected to explore the mechanism for interaction of PAEs with human serum albumin (HSA) through molecular docking and several spectroscopic techniques. The results showed that DCHP/MCHP can spontaneously occupy site I to form a binary complex with HSA, and DCHP exhibited higher binding affinity to HSA than MCHP. At 298 K, the binding constants (K_b) of DCHP and MCHP to HSA were 24.82 × 10⁴ and 1.04 × 10⁴ M^-1, respectively. Hydrogen bonds and van der Waals forces were the major driving forces in DCHP/MCHP-HSA complex. The presence of DCHP/MCHP induced the secondary structure changes in HSA, and the pi electrons of the benzene ring skeleton of DCHP/MCHP played a key role in this binding processes. Exposure of DCHP/MCHP to TM4 cells revealed that interactions between PAEs and serum albumin can affect their cytotoxicity; DCHP showed higher toxicity than MCHP. The binding affinity of PAEs with HSA may be a valuable parameter for rapid assessment of their toxicity to organisms.

On the binding reaction of loratadine with human serum acute phase protein alpha 1-acid glycoprotein

Loratadine is an important anti-allergic drug. It is a second generation antihistamine drug used to treat allergic rhinitis, hay fever and urticaria. Human serum alpha 1-acid glycoprotein (AG) is an important acute phase protein and its serum concentration is found to increase in inflammation and acute response.The binding interaction between loratadine and AG is studied using spectroscopy and molecular docking techniques. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of AG is quenched by loratadine. Loratadine was found to bind AG with the binding constant of ≈10⁴ at 298 K. The Gibb's free energy change was found to be negative for the interaction of loratadine with AG indicating the binding process is spontaneous. Binding of loratadine with AG induced ordered structures in the protein. Hydrogen bonding and hydrophobic interactions were the main bonding forces between AG-loratadine as revealed by molecular docking results. This study suggests the importance of binding of anti-allergic drug to AG spatially in the diseases where the plasma concentration of AG increases many folds and interaction with this protein becomes significant. This study will help in design of drug dosage and adjustment accordingly to achieve optimal treatment outcome. Communicated by Ramaswamy H. Sarma.

Interaction of esculetin with aluminium ion by spectroscopic studies and isothermal titration calorimetry: a probable molecule for chelation therapy

The use of aluminium has made significant impact in our life by virtue of its attractive properties. The lack of essentiality of aluminium in biosphere indicated that its accumulation above certain level is undesirous. Esculetin (6,7-dihydroxy coumarin) is an excellent aluminium ion chelator and the chelation interaction was studied by exploiting the absorption and fluorescence behavior of esculetin. In presence of aluminium ion, the absorption band of esculetin was shifted from 350 to 380 nm suggesting the possibility of complex formation. The fluorescence intensity of esculetin at 466 nm was significantly quenched in presence of aluminium ion. The fluorescence quenching was interpreted in terms of chelation-quenched fluorescence (CHQF) mechanism where the strong Lewis acid character of aluminium ion accepts electrons from the chelating catechol moiety of the excited esculetin. From the absorption and fluorescence changes the association constant was estimated in the order of 10⁵ M^-1. The association constant was further evaluated by isothermal titration calorimetry (ITC) and there was close agreement to that of obtained from spectroscopic studies. Form ITC studies, the binding enthalpy and binding entropy were estimated as -20.6 kcal/mol and -46.7 cal/mol/K respectively. The complex was less toxic compared to the individual complexing agents when studied in Chinese hamster ovary cells. Considering the present investigation, esculetin can be a probable molecule for chelation therapy where rapid complex formation ability of esculetin will help to reduce the aluminium accumulation through chelation and water soluble nature of the complex will help for faster elimination from the system.Communicated by Ramaswamy H. Sarma.

Spectroscopic evaluation of Zn (II) complexes with drug analogues: Interactions with BSA and the pH effect on the drug-Zn (II) system

Using UV-Vis, FT-IR, fluorescence spectroscopy and protein-ligand docking, the interactions between the zinc complexes with drug analogues and bovine serum albumin were investigated. In addition, considering the ubiquitous presence of zinc ions in the human system, we studied the interactions between this ion with hymecromone, dihydropyridine analogue, and acetamide, as well as the pH influence on these systems. The complexes were synthesized by interaction between the ligands and the Zn (II) ion in a 2:1 M ratio. Elemental analysis, FT-IR, and UV-Vis spectroscopy studies investigated the structure of the synthesized complexes. Fluorescence spectroscopy, UV-Vis, molecular docking and molecular dynamics were used to study the interactions of the Zn complexes with the BSA. The drug-Zn (II) system's pH effect was investigated using UV-Vis spectroscopy. After the complexation with the zinc, the drug molecules exhibited higher apparent binding affinity to BSA. BSA's fluorescence efficiency by the drug analogues was enhanced. In addition, molecular modelling was used to classify the residue of amino acids in the BSA playing key roles in this binding interaction. An increase in pH appears to contribute to alkaline hydrolysis of the Zn (II) molecules.

Inhibition of human islet amyloid polypeptide aggregation and cellular toxicity by oleuropein and derivatives from olive oil

Loss of β-cell function and β-cell death is the key feature of type 2 diabetes mellitus (T2DM). One hypothesis for the mechanism of this feature is amyloid formation by the human islet amyloid polypeptide (hIAPP). Despite the global prevalence of T2DM, there are no therapeutic strategies for the treatment of or prevention of amylin amyloidosis. Clinical trials and population studies indicate the healthy virtues of the Mediterranean diet, especially the extra virgin olive oil (EVOO) found in this diet. This oil is enriched in phenolic compounds shown to be effective against several aging and lifestyle diseases. Oleuropein (Ole), one of the most abundant polyphenols in EVOO, has been reported to be anti-diabetic. Some of Ole's main derivative have attracted our interest due to their multi-targetted effects, including interference with amyloid aggregation path. However, the structure-function relationship of Ole and its metabolites in T2DM are not yet clear. We report here a broad biophysical approach and cell biology techniques that enabled us to characterize the different molecular mechanisms by which tyrosol (TYR), hydroxytyrosol (HT), oleuropein (Ole) and oleuropein aglycone (OleA) modulate the hIAPP fibrillation in vitro and their effects on cell cytotoxicity. The OleA formed by enolic acid and hydroxytyrosol moiety was found to be more active than the Ole and HT at low micromolar concentrations. We further demonstrated that OleA inhibit the cytotoxicity induced by hIAPP aggregates by protecting more the cell membrane from permeabilization and then from death. These findings highlight the benefits of consuming EVOO and the great potential of its polyphenols, mainly OleA. Moreover, they support the possibility to validate and optimize the possible pharmacological use of EVOO polyphenols for T2DM prevention and therapy and also for many other amyloid related diseases.

Synthesis of two novel pyrazolo[1,5-a]pyrimidine compounds with antibacterial activity and biophysical insights into their interactions with plasma protein

Two novel water-soluble pyrazolo[1,5-a]pyrimidine derivatives, 5-chloro-7-(4-methyl-piperazin -1-yl)-pyrazolo[1,5-a]pyrimidine (CMPS) and N'-(5-chloro-pyrazolo[1,5-a]pyrimidin-7-yl)-N,N-dimethyl -propane-1,3-diamine (NCPS), were synthesized and characterized with antibacterial activity. Then, the interactions of these compounds with bovine serum albumin (BSA) were studied by fluorescence, time-resolved fluorescence, circular dichroism (CD) spectroscopy and molecular docking. The results indicate that both CMPS and NCPS could effectively quench the intrinsic fluorescence of BSA via a static quenching process. The energy transfer from BSA to CMPS and NCPS may occur with high probability. Both CMPS and NCPS bind in the site I of BSA. The hydrophobic force and hydrogen bonds play major roles in the complex formation. Binding constants for both systems show that the affinity of CMPS binding to BSA is stronger than that of NCPS. The results of three-dimensional fluorescence and CD spectra reveal that the binding of CMPS and NCPS to BSA can induce conformational changes of BSA, and the influence of CMPS is slightly stronger than that of NCPS.

Comparative studies on the interaction of spermidine with carboxypeptidase A using multispectroscopic and docking methods

Carboxypeptidase A (CPA) (EC 3.4.17.1) is one of the main members of the M14 family that release one amino acid from the C-terminal region of the polypeptides at each time. The purpose of the present study was to study the effect of spermidine (NH₂(CH₂)₃NH(CH₂)₄NH₂) on the conformation, thermal stability, and activity of native CPA from bovine pancreas, by employing ultraviolet-visible (UV-Vis) spectroscopy, intrinsic fluorescence, thermal stability, circular dichroism (CD), kinetic techniques and molecular docking. It was found that the decrease in the CPA, UV-Vis absorption could be due to the formation of the CPA-spermidine complexes. The results of fluorescence spectroscopic measurements at the temperatures of 308 and 318 K also revealed that spermidine had the capability to quench the intrinsic fluorescence of CPA with the static mode. Further, the thermodynamic parameters, (Gibbs free-energy, enthalpy and entropy changes) showed that the binding process of spermidine to CPA was spontaneous and the main force in stabilizing the complex was the van der Waals and hydrogen interactions, along with the molecular docking results. In addition, CD spectra and fluorescence results revealed that spermidine had a partial effect on the CPA structure, leading to some changes in its secondary structure. The T_m studies of the CPA-spermidine complex also indicated that the T_m values were enhanced with increasing the spermidine concentration. Kinetic studies further showed that by spermidine binding, the V_max value and activity of the enzyme were increased.

Effects of piceatannol on the structure and activities of bovine serum albumin: A multi-spectral and molecular modeling studies

Piceatannol (PIC) displays a wide spectrum of biological activities, such as antioxidation, antibacterial activity and anti-inflammation, but the biochemical and molecular mechanism is not fully understood. In this study, the interaction of PIC with bovine serum albumin (BSA) was studied by fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, circular dichroism spectroscopy and molecular simulation. The effects of PIC on BSA non-enzymatic glycosylation, fibrillation, thermal stability, and structure information were also studied. The results showed that the formation of PIC-BSA complex by mainly hydrogen-bonding forces resulted in the conformational changes of protein. PIC inhibited the formation of β-sheets structures of BSA. BSA still maintained the esterase-like good activity in the presence of PIC. In addition, PIC significantly reduced the degree of BSA glycosylation. These results provided a basis for the molecular interaction between PIC and protein, and suggested the potential effect of PIC in preventing the progression of diabetes mellitus.

Characterizing the interactions of the antipsychotic drug trifluoperazine with bovine serum albumin: Probing the drug-protein and drug-drug interactions using multi-spectroscopic approaches

Trifluoperazine is a potent antipsychotic drug used in the treatment of neurological disorders. The usage of trifluoperazine is often found to be associated with more adverse side effects as compared to other low-potency antipsychotic agents. Plasma proteins play an inevitable role in determining the pharmacokinetic properties of a drug. Hence, this study was conducted with an aim to characterize the interactions of trifluoperazine with bovine serum albumin and determine the influence of other small molecules on its interaction with serum albumin. Trifluoperazine bound to BSA at two independent sites with K_d values of 9.5 and 172.6 μM. Förster resonance energy transfer and computational docking analysis revealed that both the binding sites of trifluoperazine were located closer to TRP 213 in subdomain IIA of BSA. Evaluation of trifluoperazine-BSA interactions at three different temperatures indicated that there was a stable complex formation between the two molecules at the ground state and that the static quenching mechanism was predominant behind these interactions. Binding studies in the presence of pharmaceutically relevant drugs indicated that warfarin, paracetamol, and caffeine negatively influenced the binding of trifluoperazine on BSA. Lastly, Fourier transformed infrared spectroscopy and circular dichroism spectroscopy indicated that the binding of trifluoperazine induced a conformational change by reducing the α-helical content of BSA. The study implicates that the small molecules which prefer binding to the Sudlow site I of BSA might compete with trifluoperazine for its binding site thereby increasing the concentration of free trifluoperazine in the plasma which could lead to adverse side effects in patients.

Serum starvation enhances nonsense mutation readthrough

Of all genetic mutations causing human disease, premature termination codons (PTCs) that result from splicing defaults, insertions, deletions, and point mutations comprise around 30%. From these mutations, around 11% are a substitution of a single nucleotide that change a codon into a premature termination codon. These types of mutations affect several million patients suffering from a large variety of genetic diseases, ranging from relatively common inheritable cancer syndromes to muscular dystrophy or very rare neuro-metabolic disorders. Over the past three decades, genetic and biochemical studies have revealed that certain antibiotics and other synthetic molecules can act as nonsense mutation readthrough-inducing drugs. These compounds bind a specific site on the rRNA and, as a result, the stop codon is misread and an amino acid (that may or may not differ from the wild-type amino acid) is inserted and translation occurs through the premature termination codon. This strategy has great therapeutic potential. Unfortunately, many readthrough agents are toxic and cannot be administered over the extended period usually required for the chronic treatment of genetic diseases. Furthermore, readthrough compounds only restore protein production in very few disease models and the readthrough levels are usually low, typically achieving no more than 5% of normal protein expression. Efforts have been made over the years to overcome these obstacles so that readthrough treatment can become clinically relevant. Here, we present the creation of a stable cell line system that constitutively expresses our dual-reporter vector harboring two cancer initiating nonsense mutations in the adenomatous polyposis coli (APC) gene. This system will be used as an improved screening method for isolation of new nonsense mutation readthrough inducers. Using these cell lines as well as colorectal cancer cell lines, we demonstrate that serum starvation enhances drug-induced readthrough activity, an observation which may prove beneficial in a therapeutic scenario that requires higher levels of the restored protein. KEY MESSAGES: Nonsense mutations affects millions of people worldwide. We have developed a nonsense mutation read-through screening tool. We find that serum starvation enhances antibiotic-induced nonsense mutation read-through. Our results suggest new strategies for enhancing nonsense mutation read-through that may have positive effects on a large number of patients.

Structural dynamics studies on the binding of aflatoxin B1 to chicken egg albumin using spectroscopic techniques and molecular docking

Aflatoxin B₁, a mycotoxin produced by large number of Aspergillus species including Aspergillus flavus and Aspergillus parasiticus, has been described as the most potent carcinogenic mycotoxin. In this study, we have used a multiple spectroscopic and molecular docking approach to investigate the interaction of aflatoxin B₁ (AFB₁) with chicken egg albumin (CEA). Fluorescence spectroscopy, UV-Vis spectroscopy, and three-dimensional fluorescence spectroscopic techniques were employed to gain insight into the conformational changes in CEA in the presence of AFB₁. Fluorescence spectroscopy revealed ligand-induced quenching in the fluorescence emission spectra of CEA upon binding with AFB₁. Hyperchromic effect was observed in case of the ground state complex formation between CEA and AFB₁ by UV-Vis spectroscopy. To gain further comprehension into the site of binding of AFB₁ to CEA, competitive site marker displacement assay was performed using warfarin site marker. The magnitude of ΔG value calculated from fluorescence-based method was negative which confirmed spontaneous process. The results obtained suggest that the binding is enthalpy driven and van der Waals force and hydrogen bonds are stabilizing the AFB₁-CEA complex. Three-dimensional fluorescence studies also confirmed the quenching in the fluorescence intensity around tryptophan residues in CEA. Circular dichroism assessment revealed reduction in the alpha helical content of CEA in the presence of AFB₁. Molecular docking studies showed hydrophobic interaction, van der Waals forces, and hydrogen bonds as major forces present in interaction between CEA and AFB₁. The overall study confirms conformational and structural alteration in the protein due to binding of AFB₁.Communicated by Ramaswamy H. Sarma.

Cytotoxic species in amyloid-associated diseases: Oligomers or mature fibrils

Amyloid diseases especially, Alzheimer's disease (AD), is characterized by an imbalance between the production and clearance of amyloid-β (Aβ) species. Amyloidogenic proteins or peptides can transform structurally from monomers into β-stranded fibrils via multiple oligomeric states. Among various amyloid species, structured oligomers are proposed to be more toxic than fibrils; however, the identification of amyloid oligomers has been challenging due to their heterogeneous and metastable nature. Multiple techniques have recently helped in better understanding of oligomer's assembly details and structural properties. Moreover, some progress on elucidating the mechanisms of oligomer-triggered toxicity has been made. Based on the collection of current findings, there is growing consensus that control of toxic amyloid oligomers could be a valid approach to regulate amyloid-associated toxicity, which could advance development of new diagnostics and therapeutics for amyloid-related diseases. In this review, we have described the recent scenario of amyloid diseases with a great deal of information about the recent understanding of oligomers' assembly, structural properties, and toxicity. Also comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates.

Metal-Biosurfactant Complexes Characterization: Binding, Self-Assembly and Interaction with Bovine Serum Albumin

Studies on the specific and nonspecific interactions of biosurfactants with proteins are broadly relevant given the potential applications of biosurfactant/protein systems in pharmaceutics and cosmetics. The aim of this study was to evaluate the interactions of divalent counterions with the biomolecular anionic biosurfactant surfactin-C₁₅ through molecular modeling, surface tension and dynamic light scattering (DLS), with a specific focus on its effects on biotherapeutic formulations. The conformational analysis based on a semi-empirical approach revealed that Cu²⁺ ions can be coordinated by three amide nitrogens belonging to the surfactin-C₁₅ cycle and one oxygen atom of the aspartic acid from the side chain of the lipopeptide. Backbone oxygen atoms mainly involve Zn²⁺, Ca²⁺ and Mg²⁺. Subsequently, the interactions between metal-coordinated lipopeptide complexes and bovine serum albumin (BSA) were extensively investigated by fluorescence spectroscopy and molecular docking analysis. Fluorescence results showed that metal-lipopeptide complexes interact with BSA through a static quenching mechanism. Molecular docking results indicate that the metal-lipopeptide complexes are stabilized by hydrogen bonding and van der Waals forces. The biosurfactant-protein interaction properties herein described are of significance for metal-based drug discovery hypothesizing that the association of divalent metal ions with surfactin allows its interaction with bacteria, fungi and cancer cell membranes with effects that are similar to those of the cationic peptide antibiotics.

Serum albumin saturation test based on non-esterified fatty acids imbalance for clinical employment

Fatty acids are fundamental as energy and structural source to the human cells. They are not usually found free in human circulation. Alteration in fatty acids metabolism is linked to diseases such as diabetes, preeclampsia, heart disease, and some infectious diseases. Increased levels of non-esterified fatty acids (NEFA) may cause cell dysfunction and lipotoxicity. Since physiologically fatty acids are transported bound to albumin, we propose here a simple and cheap test that consists of albumin isoelectric focusing determination to measure the potential systemic NEFA cytotoxicity. For validation of this method, albumin isoelectric focusing in 51 serum samples from 40 critically ill patients and 11 controls was compared with NEFA/albumin ratios measured by HPLC. We called this approach an albumin saturation test. This test may indicate to physicians the potential NEFA lipotoxicity guiding them throughout better patient management. The albumin saturation test can point out serum albumin-NEFA saturation through a cheap assay that could be performed by any care facility.

Maslinic acid conjugate with 7-amino-4-methylcoumarin as probe to monitor the temperature dependent conformational changes of human serum albumin by FRET

Synthesis, characterization and spectroscopic investigation of maslinic acid labeled with fluorescent 7-amino-4-methylcoumarin is reported. It was found that the coumarin-maslinic derivative (MaCo) forms an excellent fluorescence resonance energy transfer (FRET) pair with the tryptophan (Trp) residue of human serum albumin (HSA). This feature allowed for monitoring HSA conformational alterations by measuring the distance between donor (Trp) and acceptor (MaCo) through Förster energy transfer mechanism. Displacement experiments confirmed that MaCo binds to subdomain IIA of HSA with independence of temperature. It was observed that, in the temperature range 35-45 °C, the fluorescence emission maximum of HSA-MaCo complex decreased, whereas in the range 45 °C-65 °C, an increment was detected. The concomitant change in the polarity of environment surrounding Trp was confirmed by red edge excitation shift experiments. Thermal denaturation of HSA was followed by time-resolved fluorescence spectroscopy. Average lifetime of Trp residue decreased with temperature due to the increment of solvent collisions and changes in the solvent exposure of Trp. To discriminate the importance of each effect, lifetime of N-Acetyl-L-tryptophanamide (NATA) at different temperatures was measured. Circular dichroism (CD) studies confirmed the loss of secondary structure of HSA with increasing temperature and showed a different trend in the conformational transformation below and above 45 °C, in agreement with steady-state and time-resolved fluorescence experiments.

Stabilizing proteins to prevent conformational changes required for amyloid fibril formation

Amyloid fibrillation is associated with several human maladies, such as Alzheimer's, Parkinson's, Huntington's diseases, prions, amyotrophic lateral sclerosis, and type 2 diabetes diseases. Gaining insights into the mechanism of amyloid fibril formation and exploring novel approaches to fibrillation inhibition are crucial for preventing amyloid diseases. Here, we hypothesized that ligands capable of stabilizing the native state of query proteins might prevent protein unfolding, which, in turn, may reduce the propensity of proteins to form amyloid fibrils. We demonstrated the efficient inhibition of amyloid formation of the human serum albumin (HSA) (up to 85%) and human insulin (up to 80%) by a nonsteroidal anti-inflammatory drug, ibuprofen (IBFN). IBFN significantly increases the conformational stability of both HSA and insulin, as confirmed by differential scanning calorimetry (DSC). Moreover, increasing concentration of IBFN boosts its amyloid inhibitory propensity in a linear fashion by influencing the nucleation phase as assayed by thioflavin T fluorescence, transmission electron microscopy, and dynamic light scattering. Furthermore, circular dichroism analysis supported the DSC results, showing that IBFN binds to the native state of proteins and almost completely prevents their tendency to lose secondary and tertiary structures. Cell toxicity assay confirms that species formed in the presence of IBFN are less toxic to neuronal cells (SH-SY5Y). These results demonstrate the feasibility of using a small molecule to stabilize the native state of proteins, thereby preventing the amyloidogenic conformational changes, which appear to be the common link in several human amyloid diseases.

A comprehensive spectroscopic and computational investigation on the binding of the anti-asthmatic drug triamcinolone with serum albumin

Binding study of triamcinolone with BSA through in vitro and in silico approaches, helping in the development of drugs with better therapeutic efficacy.

Amyloid Oligomers, Protofibrils and Fibrils

Amyloid diseases are of major concern all over the world due to a number of factors including: (i) aging population, (ii) increasing life span and (iii) lack of effective pharmacotherapy options. The past decade has seen intense research in discovering disease-modifying multi-targeting small molecules as therapeutic options. In recent years, targeting the amyloid cascade has emerged as an attractive strategy to discover novel neurotherapeutics. Formation of amyloid species, with different degrees of solubility and neurotoxicity is associated with the gradual decline in cognition leading to dementia/cell dysfunction. Here, in this chapter, we have described the recent scenario of amyloid diseases with a great deal of information about the structural features of oligomers, protofibrils and fibrils. Also, comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates. Moreover, a review of the technologies that aid characterisation of oligomer, protofibrils and fibrils as well as various inhibition strategies to overcome protein fibrillation are also discussed.

Reactive oxygen species generation and human serum albumin damage induced by the combined effects of ultrasonic irradiation and brilliant cresyl blue

In this paper, brilliant cresyl blue (BCB) was selected as a sonosensitizer. The sonodynamic damage to human serum albumin (HSA) in the presence of BCB and the mechanism were studied by means of fluorescence and absorption spectra. Firstly, BCB could quench the intrinsic fluorescence of HSA obviously and the quenching mechanism was static quenching due to the formation of HSA-BCB complex. The results of the displacement experiments and the molecular modeling suggested that the binding site of BCB on HSA was site I, and hydrophobic forces and hydrogen bonds played major roles in the interaction between HSA and BCB. Secondly, the damage of HSA induced by the combined effects of ultrasonic irradiation and BCB was more efficient than that only BCB or ultrasound irradiation, which confirmed that BCB had sonodynamic activity. The damage degree of HSA was positively correlated with reactive oxygen species (ROS) produced in the system, which indicated that ultrasound could activate BCB to produce ROS, and the kinds of ROS produced by the combined effects of ultrasonic irradiation and BCB were mainly hydroxyl free radical, singlet oxygen and superoxide anion radical.

Probing the binding of phenolic aldehyde vanillin with bovine serum albumin: Evidence from spectroscopic and docking approach

The interactions of bovine serum albumin (BSA) with vanillin (VAN) were studied using UV-vis absorption, fluorescence, synchronous fluorescence, three dimensional fluorescence spectroscopy (3D), Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and molecular docking techniques. The results revealed that VAN causes the static quenching of BSA by forming BSA-VAN complex. The thermodynamic parameters obtained using isothermal titration calorimetry (ITC) showed that the interaction between BSA and VAN is spontaneous and hydrogen bonding, van der Waals forces are mainly involved in stabilizing the complex. The distance between the donor and the acceptor was analyzed using fluorescence resonance energy transfer (FRET) which showed Forster distance of 2.58 nm. Molecular docking technique was applied to study the modes of interaction between BSA-VAN system and it was found that VAN bound to the sub-domain IIA of BSA. Structural analysis using 3D, synchronous fluorescence FTIR, and CD showed that upon binding of VAN, BSA exhibits small micro-environmental changes around tryptophan amino acid residue.

Binding behavior of trelagliptin and human serum albumin: Molecular docking, dynamical simulation, and multi-spectroscopy

This study aims to investigate the interaction mechanism of a hypoglycemic agent, trelagliptin (TLP), and human serum albumin (HSA) through computer simulation and assisted spectroscopy methods. Computer simulation including molecular docking and molecular dynamics analysis was conducted under physiological conditions. Molecular docking results indicate that TLP bound to HSA at site I, and the binding behavior was mainly governed by hydrophobic force. Competitive experiments further verified the theoretical conclusion from molecular docking. Molecular dynamics simulation revealed that TLP indeed stably bound to site I of HSA in the hydrophobic subdomain IIA. Moreover, TLP presented a certain effect on the structural compactness of HSA. In molecular dynamics simulation, hydrogen bonds appeared, which suggested the reliability and stability of the combination. The binding energy of the stable phase is around -250 kJ/mol. Fluorescence quenching studies and time-resolved fluorescence analysis indicated that the evident fluorescence quenching phenomenon of HSA could be due to TLP binding initiated by static quenching mechanism. The binding constants (K_a) of the complex were found to be around 10⁴ via fluorescence data, and the calculated thermodynamic parameters indicated that hydrophobic force played major role in the binding of TLP to HSA. Synchronous fluorescence and three-dimensional fluorescence results demonstrated that TLP slightly disturbed the microenvironment of amino residues. Circular dichroism spectra showed that TLP affected the secondary structure of HSA. The theoretical and experimental results showed excellent agreement.

Exploration of ligand-induced protein conformational alteration, aggregate formation, and its inhibition: A biophysical insight

The association of protein aggregates with plentiful human diseases has fascinated studies regarding the biophysical characterization of protein misfolding and ultimately their aggregate formation mechanism. Protein-ligand interaction, their mechanism, conformational changes by ligands, and protein aggregate formation have been studied upon exploiting experimental techniques and computational methodologies. Such studies for the exploration of ligand-induced conformational changes in protein, misfolding and aggregation, has confirmed drastic progresses in the study of aggregate formation pathways. This review comprises of an inclusive description of contemporary experimental techniques as well as theoretical improvements in the interpretation of the conformational properties of protein. We have also discussed various factors responsible for the microenvironment change around protein that sequentially causes amyloidoses. Biophysical techniques and cell-based assays to gain comprehensive understandings of protein-ligand interaction, protein folding, and aggregation pathways have also been described. The promising therapeutic methods used to inhibit the protein fibrillogenesis have also been discussed.

Comprehensive insights into the interaction mechanism between perfluorodecanoic acid and human serum albumin

In this investigation, we explored the toxic effects of perfluorodecanoic acid (PFDA) on human serum albumin (HSA), established the interaction mode of PFDA with HSA, and provided a new strategy for the evaluation of toxicity of PFDA on functional proteins.