Molecular Dynamics Simulation and Binding Studies of β-Sitosterol with Human Serum Albumin and Its Biological Relevance

Abstract

Beta-sitosterol is a naturally occurring phytosterol that is widely used to cure atherosclerosis, diabetes, cancer, and inflammation and is also an antioxidant. Here, we studied the interaction of beta-sitosterol, isolated from the aerial roots of Ficus bengalensis, with human serum albumin (HSA) at physiological pH 7.2 by using fluorescence, circular dichroism (CD), molecular docking, and molecular dynamics simulation methods. The experimental results show that the intrinsic fluorescence of HSA is quenched by addition of beta-sitosterol through a static quenching mechanism. The binding constant of the compound to HSA, calculated from fluorescence data, was found to be K(beta-sitosterol) = 4.6 +/- 0.01 x 10(3) M(-1), which corresponds to -5.0 kcal M(-1) of free energy. Upon binding of beta-sitosterol to HSA, the protein secondary structure was partially unfolded. Specifically, the molecular dynamics study makes an important contribution to understanding the effect of the binding of beta-sitosterol on conformational changes of HSA and the stability of a protein-drug complex system in aqueous solution. Molecular docking studies revealed that the beta-sitosterol can bind in the large hydrophobic cavity of subdomain IIA, mainly by the hydrophobic interaction but also by hydrogen bond interactions between the hydroxyl (OH) group of carbon-3 of beta-sitosterol to Arg(257), Ser(287), and Ala(261) of HSA, with hydrogen bond distances of 1.9, 2.4, and 2.2 A, respectively.

Molecular dynamics simulation studies of betulinic acid with human serum albumin

“…Thus, the free energy change is−8.5 kcal M −1 at 25°C. These results were fully supported by computational calculation which was obtained as−8.49 kcal M −1 (Table 1) [25][26][27][28]. Further, we performed computational studies like molecular docking and simulations to understand more details of its binding and also stable conformation of protein.…”

“…We have also shown that there are conformational changes in protein due to binding of BA to HSA. Also, it is shown in a recent report from our group on different phytomedicines like maslinic acid, trimethoxyflavone, and coumaroyltyramine, sitosterol, strongly binds to HSA leading to change in protein conformation [25][26][27][28].…”

“…2a and b). It binds various endogenous and exogenous ligands including hormones, fatty acids and foreign molecules such as drugs [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Recently our group has shown that HSA binds to BA with a binding constant of K BA = 1.685±0.01×10 6 M −1 [24].…”

β-Carotene and astaxanthin with human and bovine serum albumins

“…HSA is composed by three homologous a-helical domains (I, II, and III): I (residues 1-195), , and III (384-585), each of which includes 10 helices that are divided into six-helix and four-helix subdomains (A and B) (Sudhamalla, Gokara, Ahalawat, Amooru, & Subramanyam, 2010). The native conformation of HSA has two principal hydrophobic binding sites, called sites I and II (Sudlow, Birkett, & Wade, 1975), located in subdomains IIA and IIIA (He & Carter, 1992) and it is generally assumed that in BSA and HSA these sites are homologous.…”

Studies on the interaction between promethazine and human serum albumin in the presence of flavonoids by spectroscopic and molecular modeling techniques

“…Fluorescence spectroscopy is an effective method to study the interactions between small molecule compounds and proteins [38,39]. The fluorescence spectra of HSA and HSA-PMT mixed solutions are shown in Fig.…”