Abstract
A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding ΔGb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.
Highlights
A comparison with the analysis of other sets of data related to the binding of human serum albumin (HSA) to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomrelease of the condensed counterions presents a strong driving force for binding that is even operative under physiological conditions
Counterion release has been identified as major driving force for enon that always accompanies the binding of proteins to polyelectrolytes the binding of synthetic polyelectrolytes to dominated by counterion release
To ensure that the heat signal is not due to a partial unfolding upon binding, we studied the complex by Fourier transform infrared spectroscopy (FT-IR), where changes in protein secondary structure upon adsorption to the brush layer would show up in the spectra immediately.[36,37]
Summary
A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomrelease of the condensed counterions presents a strong driving force for binding that is even operative under physiological conditions.
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