Thermal Stability of Human Serum Albumin: the Dependence on the Protein Concentration, Scan Rate, and the Presence of Fatty Acids and Low-Weight Molecular Ligands

Abstract

Human serum albumin (HSA) is the most abundant protein in human plasma with ascribed ligand binding and transport properties. Design of this molecule provides a variety of binding sites for many physiological important ligands, including a wide variety of drugs. In this work, the dependence of the thermal denaturation of HSA on the protein concentration, scan rate, and the presence of fatty acids and low-molecular weight drugs (warfarin, ibuprofen, hypericin, emodin) have been thoroughly investigated by means of differential scanning calorimetry (DSC). Our results show that the presence of fatty acids in HSA significantly stabilizes the structure of this protein. Further, DSC curves exhibit a significant dependence on the protein concentration in both fatty acid containing and fatty acids free HSA. From the linear dependence of 1/Tm on albumin concentration follows that HSA tends to form dimers during denaturation process. The obtained DSC data show only a slight increase of Tm and ΔHcal with a scan rate increase. Interactions of the studied low-molecular weight drugs with HSA lead to a significant enhancement of the protein thermal stability (higher temperature and enthalpy of the denaturation in comparison with those thermodynamic parameters determined for HSA alone). However, in the presence of emodin at high concentration ratios (emodin:HSA>10:1), a decrease of the stabilization effect is observed. This is probably caused by the ability of emodin to bind both folded and unfolded states of HSA.AcknowledgementsThis work has been supported by the contract APVV-0242-11, the project CELIM (316310) funded by 7 FP EU, and by the EU Structural Funds (ITMS 26240120040 and ITMS 26220220107(50%)).