Conjugation of citric acid and gallic acid with serum albumins: Acid binding sites and protein conformation

We studied the effect of citric acid and gallic acid on the solution structures of bovine serum albumin (BSA) and human serum albumins (HSA) at pH 7.2. Thermodynamic parameters Delta H-0-13.30 to -5.60 (kJ mol(-1)), Delta S-0 2735 to 2.40 (J mol(-1) K-1) and Delta G(0)-14.80 to -13.75 (kJ mol(-1)) showed that acid binds protein via ionic contacts with gallic acid forming stronger protein conjugates. Different amino acids are involved in gallic acid and citric acid complexation, while HSA forming more stable acid complexes. Protein conformation was altered with major reduction of alpha-helix and an increase of random coil and turn structures, indicating a partial protein destabilization. (C) 2019 Elsevier B.V. All rights reserved.