Thermal Stability Of Human Serum Albumin Research Articles

Understanding the intricacy of protein in hydrated deep eutectic solvent: Solvation dynamics, conformational fluctuation dynamics, and stability

Deep eutectic solvents (DESs) are potential biocatalytic media due to their easy preparation, fine-tuneability, biocompatibility, and most importantly, due to their ability to keep protein stable and active. However, there are many unanswered questions and gaps in our knowledge about how proteins behave in these alternate media. Herein, we investigated solvation dynamics, conformational fluctuation dynamics, and stability of human serum albumin (HSA) in 0.5 Acetamide/0.3 Urea/0.2 Sorbitol (0.5Ac/0.3Ur/0.2Sor) DES of varying concentrations to understand the intricacy of protein behaviour in DES. Our result revealed a gradual decrease in the side-chain flexibility and thermal stability of HSA beyond 30 % DES. On the other hand, the associated water dynamics around domain-I of HSA decelerate only marginally with increasing DES content, although viscosity rises considerably. We propose that even though macroscopic solvent properties are altered, a protein feels only an aqueous type of environment in the presence of DES. This is probably the first experimental study to delineate the role of the associated water structure of the enzyme for maintaining its stability inside DES. Although considerable effort is necessary to generalize such claims, it might serve as the basis for understanding why proteins remain stable and active in DES.

Comparative investigation on interaction mechanism and native conformation of human serum albumin with organometallic iridium(III) complexes via spectroscopic and electrochemical approaches

Organometallic iridium(III) complexes, as high-efficient phototherapic drugs for cancer therapy and tumor treatment, have attracted widespread interest in diverse areas. To further clarify the biological functions of iridium(III) complexes, the interaction mechanism and native conformation of human serum albumin (HSA) affected by three organometallic iridium(III) complexes containing curcuminoid ligands were systematically and comparably investigated via various spectroscopic and electrochemical approaches. The results revealed that three iridium(III) complexes reacted with HSA tightly at its Sudlow's site I under the binding forces of van der Waals interaction, protonation, and hydrogen bond, leading to the hypochromic effect in the absorption spectrum of HSA and the static quenching in the intrinsic fluorescence of HSA. Three iridium(III) complexes disturbed the native conformation of HSA by reducing its α-helical content, finally reducing the melting temperature and the thermal stability of HSA. In comparison, the iridium(III) complex containing curcuminoid ligand with bigger spatial steric-hindrance effect and stronger chemical polarity was prone to binding with HSA more tightly and subsequently affecting its native conformation and biological function more prominently. This research finding reveals the interaction mechanisms of organometallic iridium(III) complexes with HSA and evaluates the function of curcuminoid ligands during their binding interactions, which pays the way for the targeted design and the potential application of novel iridium(III) complexes in biological fields.

The influence of sodium phosphate buffer on the stability of various proteins: Insights into protein-buffer interactions

Present study delineates the effects of sodium phosphate buffer (PBS) solutions on the stability of various proteins including lysozyme (Lys), bromelain (BM), hemoglobin (Hb), and human serum albumin (HSA). Different spectroscopic methods such as UV–visible, steady state fluorescence, temperature dependent fluorescence spectroscopy, Fourier transforms infrared spectroscopy (FTIR), circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) show that PBS buffer protects protein structures. Efficacy of PBS stabilization from external additive factors follows order as lysozyme > BM > Hb. The thermal stability of HSA in PBS buffer solution was not detected, since no distinct and clear fluorescence transition was observed. However, results from other biophysical techniques reveal the native structure of HSA stabilized in presence of PBS. Moreover, increasing concentration of PBS also provides structural stabilization of HSA. This confirms the potentiality of PBS buffer as protecting agents for the proteins/enzymes. However, in case of Hb structure perturbed with the addition of higher concentrations of PBS. Our study confirms that efficacy of protein stabilization depends on type and concentration of buffer used. The present study is very useful for providing the alternative media to replace traditional volatile organic compounds or expensive modern solvents for biochemical applications.

Conformational structure variation of human serum albumin after binding interaction with black phosphorus quantum dots

Herein, binding interaction between black phosphorus quantum dots (BPQDs) and human serum albumin (HSA) was systematically characterized for deep illustration of conformational structure variation of HSA affected by BPQDs. The results confirmed that the intrinsic fluorescence of HSA was statically quenched by BPQDs mainly through van der Waals interaction and hydrogen bond. BPQDs bound strongly with the site I of HSA to form ground state complex with molar ratio of 1 to 1. The secondary structure of HSA was changed obviously after its binding interaction with BPQDs, and the α-helix structure of HSA was transformed to the β-sheet structure. The melting temperature of HSA was decreased after its binding interaction with BPQDs, suggesting that BPQDs promoted the thermal denaturation process of HSA. BPQDs could also reduce the molar enthalpy change and the thermal stability of HSA. These results explored the exact conformational structure variation of HSA after its binding interaction with BPQDs, which provides vital information for possible biological influence of BPQDs on human beings.

Elucidation of energetics and mode of recognition of green tea polyphenols by human serum albumin

Green tea is rich in several polyphenols which has many beneficial biological effects. We have done a detailed qualitative and quantitative study on binding of two polyphenol (−)-epicatechin (EC) and (−)-epigallocatechin-3-gallate (EGCG) with human serum albumin (HSA) by using a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), steady-state fluorescence, and circular dichroism spectroscopies. The binding constants obtained from isothermal titration calorimetry for EC-HSA and EGCG-HSA complexes are (2.09 ± 0.08) × 104 and (1.84 ± 0.30) × 105, respectively. The effects of ionic strength and additives of polar and non-polar characters indicate contribution of a mix of ionic, hydrogen bonding and hydrophobic interactions in the polyphenol-HSA association process. The 3D fluorescence analysis and circular dichroism (CD) studies reveal that the complexation of EGCG induces significant conformational change in HSA. The DSC results also show that the binding of EGCG is stronger compared to that of EC and provides quantitative information on the effect of these polyphenols on the thermal stability of HSA. Such studies play a crucial role in understanding the mechanism of drug-protein interactions and optimization of various binding parameters for successful drug delivery.

Binding of Tolperisone Hydrochloride with Human Serum Albumin: Effects on the Conformation, Thermodynamics, and Activity of HSA

Tolperisone hydrochloride (TH) has muscle relaxant activity and has been widely used for several years in clinical practice to treat pathologically high skeletal muscle tone (spasticity) and related pains. The current study was designed to explore the binding efficacy of TH with human serum albumin (HSA) using multispectrscopic, calorimetric approach, FRET, esterase-like activity, and a molecular docking method. A reduction in fluorescence emission at 340 nm of HSA was attributed to fluorescence quenching by TH via a static quenching type. Binding constants ( Kb) were evaluated at different temperatures, and obtained Kb values were ∼104 M-1, which demonstrated moderately strong affinity of TH for HSA. A calculated negative Δ G° value indicated spontaneous binding of TH to HSA. Far-UV CD spectroscopy revealed that the α-helix content was increased after TH binding. The binding distance between donor and acceptor was calculated to be 2.11 nm based on Förster's resonance energy transfer theory. ITC results revealed TH interacted with HSA via hydrophobic interactions and hydrogen bonding. The thermal stability of HSA was studied using DSC, and results showed that in the presence of TH the structure of HSA was significantly more thermostable. The esterase-like activity of HSA showed fixed Vmax and increased Km suggesting that TH binds with HSA in a competitive manner. Furthermore, molecular docking results revealed TH binds in the cavity of HSA, that is, subdomain IIA (Sudlow site I), and that it hydrogen bonds with K199 and H242 of HSA. Binding studies of drugs with HSA are potentially useful for elucidating chemico-biological interactions that can be utilized in the drug design, pharmaceutical, pharmacology, and biochemistry fields. This extensive study provides additional insight of ligand binding and structural changes induced in HSA relevant to the biological activity of HSA in vivo.