CONFORMATIONAL STABILITY OF THE ESCHERICHIA-COLI HPR PROTEIN - TEST OF THE LINEAR EXTRAPOLATION METHOD AND A THERMODYNAMIC CHARACTERIZATIONOF COLD DENATURATION
Em. Nicholson et Jm. Scholtz, CONFORMATIONAL STABILITY OF THE ESCHERICHIA-COLI HPR PROTEIN - TEST OF THE LINEAR EXTRAPOLATION METHOD AND A THERMODYNAMIC CHARACTERIZATIONOF COLD DENATURATION, Biochemistry, 35(35), 1996, pp. 11369-11378
The conformational stability of the histidine-containing phosphocarrie
r protein (HPr) from Escherichia coli has been determined using a comb
ination of thermal unfolding and urea denaturation experiments. The an
alysis of the denaturation data provides a measure of the changes in c
onformational free energy, enthalpy, entropy, and heat capacity that a
ccompany the equilibrium folding of HPr over a wide range of temperatu
re and urea concentrations, In moderate concentrations of urea, HPr un
dergoes both high- and low-temperature unfolding, allowing for a relia
ble determination of the change in heat capacity for the conformationa
l transition, The data are consistent with the linear free energy rela
tionship commonly employed to analyze protein denaturation data, even
over a relatively large temperature and urea concentration range. Furt
hermore, we find that a temperature-independent Delta C-p is adequate
to describe HPr stability over the accessible temperature range. Final
ly, our data allow us to evaluate the energetics of the urea-protein i
nteraction. For HPr, the changes in excess enthalpy and entropy of the
denaturant-protein interaction(s) make only minor contributions to th
e observed Delta H and Delta S terms, presumably due in some part to t
he small size of the HPr protein.