Effects of taurine on the ion solvation scenario and its counteraction against the urea-induced denaturation of protein.

Molecular dynamics (MD) simulations have carried out to investigate the solvation scenario of ions (Na+, K+, Cl-, I-, NH4+, CH3COO-) in the binary water-taurine and ternary water-taurine-urea mixtures at 308 K. The hydrogen bond (H-bond) properties and dynamics of water‒water, taurine‒water, and ammonium/acetate ion‒water are also explored. Our study revealed that monovalent cations have a higher tendency towards oxygen of taurine than water. NH4+ preferably interacts with the oxygen of the sulfonate group, whereas acetate ions are attributed towards the amino-hydrogens of taurine compared to the oxygen and hydrogens of water. It is found that taurine forms stronger H-bonds with water molecules through its amino group indicating the higher donating tendency of taurine. The translational and orientational relaxation dynamics of water molecules are slowed down in both the binary and ternary mixtures. The average lifetime of the water's H-bonds is higher in the ternary mixtures than the binary mixtures. Addition of urea enhances the overall lifetime of the ammonium ion-water (HAMM…OWAT) and acetate ion-water (OACE…HWAT) H-bonds. We have also observed that taurine counteracts the denaturation effect of urea on human islet amyloid polypeptide (hIAPP), as evidenced by the secondary structure. The α-helix content of hIAPP is restored with the addition of 0.45 M taurine in 5.60 M urea concentrations.