Molecular docking study
Molecular docking was conducted by a Surflex Dock program in the Sybyl-X 2.1.1 package. The crystal structure of HSA was obtained from the Protein Data Bank (http://www.pdb.org/, PDB ID: 1H9Z). All H were added randomly and charge applied using the AMBER method. The Protomol was generated in ligand mode with the threshold kept at 0.50 and the bloat 0. The structure of Nar was drawn in the Sybyl-X 2.1.1 package, then Estradiol optimized using a Tripos force field and charged using the Gasteiger–Huckel method.
Results and discussions
Fluorescence characteristics and quenching mechanism of HSA–Nar
Fluorescence spectroscopy is a powerful tool for monitoring microscopic changes in polymer systems due to the high sensitivity and selectivity, short response time, and nondestructive nature of the measurement . Here, Fig. 2 displays the fluorescence spectra of HSA, Nar, and the HSA–Nar complex, all measured under the same buffer and temperature conditions (Tris–HCl buffer, pH 7.4, 298 K). A remarkable decrease in the fluorescence intensity was observed upon addition of Nar to the HSA solution, accompanied with a red shift of the maximum emission wavelength λmax, which suggests an increased polarity (or a decreased hydrophobicity) in the region surrounding the tryptophan site . The inset in Fig. 2 shows that within the investigated concentration range, the fluorescence quenching intensity of HSA was proportional to the concentration of Nar. Curve k shows that Nar alone has no effect on the fluorescence intensity of the HSA–Nar complex.