The interactions of bovine serum albumin (BSA) with urea/water were investigated by computer simulation. It was revealed that the BSA-hydrophobic residues in urea solutions favored contact with urea more than with water. Energy decomposition analysis showed that van der Waals energy was the dominant driving force behind urea affinity for hydrophobic residues, whereas coulombic attraction was largely responsible for water affinity for these residues. Meanwhile, urea-BSA hydrogen bond energies were found to be weaker than water-BSA hydrogen bond energies. The greater strength of water-BSA hydrogen bonds than urea-BSA hydrogen bonds, and the opposing preferential interaction between the BSA and urea suggest that disruption of hydrophobic interaction predominates urea-protein denaturation. In pure water, hydrophobic residues showed aggregation tendencies at 323 K, suggesting an increase in hydrophobicity, while at 353 K the residues were partly denatured due to loss of hydrogen bonds; thus, disruption of hydrophobic interactions appeared to contribute less to thermal denaturation.
Keywords: Bovine serum albumin; Computer simulation; Coulombic attraction; Entropic contributions; Hydrogen bond energies.