Locating The Binding Sites Of Citric Acid And Gallic Acid On Milk Beta-Lactoglobulin

beta-Lactoglobulin (beta-LG) is a member of lipocalin superfamily of transporters for small hydrophobic and hydrophilic molecules. We located the binding sites of citric acid and gallic acid on beta-lactoglobulin (beta-LG) in aqueous solution at physiological conditions, using spectroscopic methods, thermodynamic analysis and molecular modeling. Thermodynamic parameters Delta H-0-9.5 to -6.9 (kJ mol(-1)), Delta S(0)23.9 to 13.6 (J mol(-1)K(-1)) and Delta G(0)-14.5 to -13.6 (kJ mol(-1)) showed that acid binds protein via ionic contacts with gallic acid forming stronger protein conjugates consistent with theoretical modeling. Different amino acids are involved in gallic acid and citric acid complexation. Protein conformation was altered with reduction of beta-sheet from 58% (free protein) to 46-43% and a major increase in alpha-helix from 11% (free protein) to 29-23% and random coil structure in the acid-protein, indicating a partial protein destabilization. Communicated by Ramaswamy H. Sarma