Hydrophobicity Is the Governing Factor in the Interaction
of Human Serum Albumin with Bile Salts
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Abstract
The present study demonstrates a
detailed characterization of the
interaction of a series of bile salts, sodium deoxycholate (NaDC),
sodium cholate (NaC), and sodium taurocholate (NaTC), with a model
transport protein, human serum albumin (HSA). Here, steady-state and
time-resolved fluorescence spectroscopic techniques have been used
to characterize the interaction of the bile salts with HSA. The binding
isotherms constructed from steady-state fluorescence intensity measurements
demonstrate that the interaction of the bile salts with HSA can be
characterized by three distinct regions, which were also successfully
reproduced from the significant variation of the emission wavelength
(λ<sub>em</sub>) of the intrinsic tryptophan (Trp) moiety of
HSA. The time-resolved fluorescence decay behavior of the Trp residue
of HSA was also found to corroborate the steady-state results. The
effect of interaction with the bile salts on the native conformation
of the protein has been explored in a circular dichroism (CD) study,
which reveals a decrease in α-helicity of HSA induced by the
bile salts. In accordance with this, the esterase activity of the
protein–bile salt aggregates is found to be reduced in comparison
to that of the native protein. Our results exclusively highlight the
fact that it is the hydrophobic character of the bile salt that governs
the extent of interaction with the protein. Isothermal titration calorimetry
(ITC) and molecular docking studies further substantiate our other
experimental findings
