Deciphering binding mechanism between bovine serum albumin and new pyrazoline compound K4

Abstract

The binding mechanism of a new and possible drug candidate pyrazoline derivative compound K4 and bovine serum albumin (BSA) was investigated in buffer solution (pH 7.4) using ultraviolet-visible light absorption and steady-state and synchronous fluorescence techniques. The fluorescence intensity of BSA was quenched in the presence of K4. The quenching process between BSA and K4 was examined at four different temperatures. Decrease of the quenching constants calculated using the Stern-Volmer equation and at increasing temperature suggested that the interaction BSA-K4 was realized through a static quenching mechanism. Synchronous fluorescence measurements suggested that K4 bounded to BSA at the tryptophan region.Fourier transform infrared spectroscopy results showed that there was no significant change in polarity around the tryptophan residue The forces responsible for the BSA-K4 interaction were examined using thermodynamic parameters. In this study, the calculated negative value of ΔG, the negative value of ΔH and the positive value of ΔS pointed to the interaction being through spontaneous and electrostatic interactions that were dominant for our cases. This study provides a very useful in vitro model to researchers by mimicking in vivo conditions to estimate interactions between a possible drug candidate or a drug and body proteins. K E Y W O R D S bovine serum albumin, fluorescence quenching, FRET, pyrazoline 1 | INTRODUCTION Studies on the interaction between proteins and fluorescent probes are very important as they act as models for biochemical applications in cells. [1-3] Serum albumins are proteins that constitute approximately 60% of total plasma proteins. These proteins play an important role in the transport of exogenous and endogenous substances such as fatty acids, metal ions, drugs, and dyes. Bovine serum albumin (BSA) and human serum albumin (HSA) are proteins that are frequently used in biochemical and biophysical studies. BSA is the 76% structural homologue of HSA. BSA is generally preferred as a model protein due to its ease of use, low cost, stability, and unusual ligand binding properties in laboratory experiments. [4] Spectroscopic techniques such as ultraviolet-visible (UV-vis) light absorption, and steady-state and time-resolved fluorescence measurements are often used to investigate the interactions between BSA or HSA and fluores-cence probes due to their ease of use, accuracy, high precision, and rapid response. [5][6][7] Pyrazoline derivatives are compounds with antimicrobial, [8] antinociceptive, [9] anticancer, [10,11] antidepressant, [12] and anti-inflammatory [13] properties. In addition to the pharmacological importance of these compounds, they are used as fluorescent compounds because of their strong fluorescence properties and high quantum yields. To understand the interaction of these bioactive fluorescent compounds with protein molecules in the cell, studies in the laboratory environment with model systems constitute a marked research area. [14,15] Therefore, it is very importa...