Binding of all-trans retinoic acid to human serum albumin:: Fluorescence, FT-IR and circular dichroism studies

All-trans retinoic acid derived from vitamin A is an essential component for the modulation of angiogenesis, the process of blood vessel formation. We have investigated the binding of all-trans retinoic acid to the carrier protein, human serum albumin (HSA) under physiological conditions. Fluorescence quenching methods in combination with Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy were used for the biophysical Studies. The binding parameters were determined by a Scatchard plot and the results found to be consistent with those obtained from a modified Stern-Volmer equation. From the thermodynamic parameters calculated according to the van't Hoff equation. the enthalpy change Delta H-0 and entropy change Delta S-0 are found to be 106.17 and 106.14 J/mol K, respectively. These values suggest that apart front hydrophobic interactions electrostatic interactions are present. Changes in the CD spectra and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. Docking studies performed substantiated our experimental findings and it was observed that all-trans retinoic acid hydrogen bonded with Trp 214 and Asp 45 1 residues of subdomain IIA and IIIA of HSA. respectively. (c) 2006 Elsevier B.V. All rights reserved.