Comprehensive study on the structure of the BSA from extended-to aged form in wide (2-12) pH range

In this work we studied the structure of the bovine serum albumin (BSA) and the protein-ligand interactions since researchers prefer to use them as carriers in drug delivery systems. Systematic study (between pH 2-12, in double distilled water and physiological salt solution) was carried out to determine the changes in the secondary and the tertiary structures of the BSA, the apparent molecular weight (Mw), the size (dLS) and the electrokinetic potential (ζ). At pH 7, the BSA has higher stability in the absence (ζ = −69 mV, dLS = 2.2 nm, A2 = 1.4 × 10−3 mlmol/g2) than in the presence of salt solution (ζ = −2.4 mV, dLS = 5.3 nm, A2 = −3.2 × 10−4 mlmol/g2). The Mw strongly depends on the pH and the ionic strength (at pH 3 in the absence of salt, the Mw is 54.6 kDa while in the presence of salt is 114 kDa) which determines the geometry of the protein. The protein-ligand interactions were characterized by fluorescence (FL) and isothermal microcalorimetry (ITC) methods; these independent techniques provided similar thermodynamic parameters such as the binding constant (K) and the Gibbs free energy (ΔG).