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Modeling the Solvation of Nonpolar Amino Acids in Guanidinium Chloride Solutions
journal contribution
posted on 2014-09-11, 00:00 authored by Paul Cohen, Ken A. Dill, Sheila S. JaswalIt is common to denature proteins
by using high temperatures or
by adding guanidinium chloride (GdmCl). However, the physical mechanism
of denaturation is not well understood. Based on extensive experimental
data, we developed a thermodynamic binding-polynomial model for the
process of transferring nonpolar amino acids from water into GdmCl
solutions, as a function of temperature and GdmCl concentration. To
mimic nonpolar amino acids, we utilized the model compound, N-acetyl-tryptophanamide (NATA). We find that all nonpolar
amino acids behave like NATA, with a scale factor linearly dependent
on the surface area. Our model with three thermodynamic parameters
fully captures the nonlinear dependencies on both the temperature
and GdmCl concentration: binding the first guanidinium ion (Gdm+) to NATA has favorable entropy and unfavorable enthalpy of
desolvation (ΔS = +11.7 cal/mol, ΔH = +3.9 kcal/mol), while cooperativity of binding a second
Gdm+ has a small contribution (K = 0.032
± 0.003). This model may be useful for a better understanding
of protein denaturation by temperature and GdmCl.