Exploring the interaction between “site-markers, aspirin and esterase-like activity” ternary systems on the human serum albumin: direct evidence for modulation of catalytic activity of the protein in different inhibition modes

Exploring the binding mechanism and adverse toxic effects of persistent organic pollutant (dicofol) to human serum albumin: A biophysical, biochemical and computational approach

The organochlorine pesticide dicofol (DCF), a persistent organic pollutant, is used as acaricide worldwide. Considering its large consumption in the agriculture sector and potential toxic effects such as endocrine disruption, carcinogenicity, and environmental persistence are detrimental to human health. To take an extensive evaluation of its potential toxicity, the current study was aimed to explore the binding mechanism and adverse effect of DCF on human serum albumin (HSA) by using an array of biophysical techniques (UV-visible, fluorescence, 3D fluorescence, and circular dichroism spectroscopy), isothermal titration calorimetric (ITC), computational methods and biochemical approaches. Fluorescence quenching and UV-Visible spectra of the HSA-DCF system confirmed static quenching mechanism and complex formation between HSA and DCF. The thermodynamics results from ITC revealed DCF-HSA interaction was exothermic and spontaneous and involved hydrophobic interactions and hydrogen bonding. The esterase activity of HSA displayed constant V_max and elevated K_m values confirming DCF-HSA competitive interaction. Circular dichroism spectra results revealed structural changes in HSA protein on interaction with DCF. Furthermore, molecular-specific site marker and molecular modelling results affirmed that the binding Site of DCF is Site I of HSA. A significant carbonyl content level in DCF-HSA system suggested protein structure damage. This work is likely to add a better understanding of DCF toxicity in human health and helpful in fortifying the check on food safety.

Physiological changes in the albumin-bound non-esterified free fatty acids critically influence heme/bilirubin binding properties of the protein: A comparative, in vitro, spectroscopic study using the endogenous biomolecules

Heme and bilirubin (BR), as by-products of red blood cells (and hemoglobin) degradation, show increased plasma concentrations in some diseases. These two toxic hydrophobic molecules are mainly transported in the blood-stream by human serum albumin (HSA) that carries a wide variety of ligands. Under normal physiological conditions, ~3 fatty acid (FA) molecules are bound to each HSA; and its possible effect on BR/heme binding remains to be more clarified. In the present study, to provide deeper insight on this issue, we purified albumin from healthy individuals (as purified non-defatted albumin or PA) with normal plasma levels of FA, then defatted some of the purified protein (as defatted-HSA; or DA). In the next step, using various spectroscopic methods, their interactions with heme and BR were investigated. By 1: 1 binding of the ligands, quenching and thermodynamic analysis of parameters indicated that binding constants (K_b) values of bilirubin and heme for PA and DA are different. It could be perceived that the presence of FAs in high-affinity FA binding sites (FABSs) exerted considerable conformational changes in the structure followed by an improved BR binding while hindered heme interaction. The data was confirmed by determining surface hydrophobicity of the purified albumin (PA) and DA, and then supported by bioinformatics analyses. The physiological and clinical relevance of the observed dynamic interactions is also discussed. This study, also, re-confirmed that the primary BR binding site is subdomain IIA not subdomain IB.

Insights from a combination of theoretical and experimental methods for probing the biomolecular interactions between human serum albumin and clomiphene

In this study, the interaction of clomiphene (CLO), a non-steroidal and ovulatory stimulant drug employed in the treatment of infertility, with human serum albumin (HSA), the most abundant plasma transport protein, was investigated using spectrofluorometric, FT-IR, UV-Vis, and molecular modeling methods. The obtained results indicated that the binding of CLO to HSA led to intense fluorescence quenching of HSA via a static quenching mechanism, and that the process of CLO binding to HSA was enthalpy driven. By using experimental and theoretical methods, it was confirmed that as a result of binding CLO, slight conformational changes in HSA occurred. Also, the negative ΔH of interaction indicated that the binding of CLO with HSA was mainly enthalpy driven. The experimental and computational results suggested that hydrogen bonds and van der Waals interactions played a major role in the binding, with overall binding constants of K = 3.67 × 10⁹ M⁻¹ at 286 K and 6.52 × 10⁵ mol L⁻¹ at 310 K. Moreover, the results of molecular modeling showed that Asp234, Phe228, Leu327, and Arg209 in HSA had the highest interaction energies with the ligand.

In this study, the interaction of clomiphene with human serum albumin (HSA), the most abundant plasma transport protein, was investigated using spectrofluorometric, FT-IR, UV-Vis, and molecular modeling methods.