The binding of 3,6-disubstituted bile salts to human serum albumin induces conformational change on the molecule of this protein

Abstract

The binding of 3,6-hydroxy and keto disubstituted bile salts to human serum albumin was studied using differential scanning calorimetry, fluorescence spectroscopy and circular dichroism. The bile salts assayed did not produce any modification in the shape of the albumin thermogram, its thermal unfolding process in their presence being reversible; however, an increase in the enthalpy of unfolding and in the Tm was observed in the presence of 3,6-diketo and 3-hydroxy-6-keto bile salts. These two derivatives induced a negative circular dichroism spectrum of the protein around 280-290 nm, quenched the native fluorescence of the buried tryptophan of albumin and induced energy transfer between 1 aniline-8-naphthalene sulfonate and the buried tryptophan 214 of albumin. The presence of a keto group at C6 in the steroid ring of the bile salts plays an important role in producing slight movement of the albumin domains, increasing the distance between domains I and II.