Protein conformational stabilities can be determined from hydrogen exchange
rates
Beatrice M.P. Huyghues-Despointes, J. Martin Scholtz
& C. Nick Pace
Departments of Medical Biochemistry and Genetics, and
of Biochemistry and Biophysics, Center for Macromolecular Design, Texas A
& M University, College Station, Texas,
77843, USA.
Measuring protein conformational stability is one key to solving the protein
folding problem. The conformational stability is the free energy change of
the unfolding reaction, F U, under ambient conditions, G
U = GU - GF. Traditional methods of measuring G
U are solvent (urea or guanidinium chloride (GdmCl)) or thermal denaturation1. Solvent denaturation curves are generally analyzed using the linear
extrapolation method (LEM):
G = G
U(H2O) - m[denaturant] (1)
where m is
a measure of the dependence of G on denaturant, and GU
(H2O) is an estimate of the conformational stability that
assumes that the linear dependence of G on denaturant observed in the
transition region continues to 0 M denaturant. Thermal denaturation experiments
yield the melting temperature, Tm, the enthalpy change at T
m, Hm, and the heat capacity change, C
p, which can then be used to calculate GU at any temperature
T, GU(T), with the Gibbs−Helmholtz equation:
U, under ambient conditions, 
G
U = GU - GF. Traditional methods of measuring 
