Comparison of the Thermal Denaturing of Human Serum
Albumin in the Presence of Guanidine Hydrochloride and 1‑Butyl-3-methylimidazolium
Ionic Liquids
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Abstract
The
interaction of proteins with aqueous solutions of ionic liquids
(ILs) has attracted considerable recent attention owing to the challenges
of finding biocompatible water-free ILs. These systems remain of great
interest because of the potential for using ILs as designer solvents
for biocatalytic processes. Increasing evidence demonstrates that
aqueous solutions of water-miscible ILs, such as the well-studied
1-alkyl-3-methylimidazolium ILs, disrupt the native fold of proteins
and can drive the formation of non-native aggregates that could negatively
impact catalytic function. Here, we present a study comparing the
thermal unfolding of human serum albumin (HSA) in a 1 M solution of
the protein denaturant guanidine hydrochloride with two 1 M aqueous
solutions of 1-butyl-3-methylimidazolium ILs, namely the chloride
and the acetate. Small-angle neutron scattering (SANS) measurements
found qualitative agreement between the thermally driven unfolding
process for the three denaturants, as well as with a Tris buffer solution.
HSA irreversibly aggregates and unfolds in the three denaturant solutions
upon heating to temperatures below that required to drive the same
process in a simple Tris buffer solution. The results reveal subtle
differences in the interaction of the ILs and guanidine hydrochloride
with the protein, although the final states of the protein were similar
in all cases. The results indicate that the ions of water-miscible
ILs and guanidine hydrochloride have specific roles in disrupting
protein structure and driving aggregation. The experimental approach
employed has the potential to provide new insights into protein interactions
with ionic liquids that may aid in the search for more biocompatible
ionic liquids