Slow cooperative folding of a small globular protein HPr.
The folding of an 85-residue protein, the histidine-containing phosphocarrier protein HPr, has been studied using a variety of techniques including DSC, CD, ANS fluorescence, and NMR spectroscopy. In both kinetic and equilibrium experiments the unfolding of HPr can be adequately described as a two-state process which does not involve the accumulation of intermediates. Thermodynamic characterization of the native and the transition states has been achieved from both equilibrium and kinetic experiments. The heat capacity change from the denatured state to the transition state (3. 2 kJ mol-1 K-1) is half of the heat capacity difference between the native and denatured states (6.3 kJ mol-1 K-1), while the solvent accessibility of the transition state (0.36) indicates that its compactness is closer to that of the native than that of the denatured state. The high value for the change in heat capacity upon unfolding results in the observation of cold denaturation at moderate denaturant concentrations. Refolding from high denaturant concentrations is, however, slow. The rate constant of folding in water, (14.9 s-1), is small compared to that reported for other proteins of similar size under similar conditions. This indicates that very fast refolding is not a universal character of small globular proteins which fold in the absence of detectable intermediates.
Van Nuland
N A
NA
New Chemistry Laboratory, Oxford Centre for Molecular Sciences, University of Oxford, South Parks Road, Oxford OX1 3QT, U.K.
Meijberg
W
W
Warner
J
J
Forge
V
V
Scheek
R M
RM
Robillard
G T
GT
Dobson
C M
CM
D001426:Bacterial Proteins / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D019791:Guanidine; D007700:Kinetics; D008956:Models, Chemical; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D013045:Species Specificity; D013696:Temperature; D013816:Thermodynamics
D001426:Bacterial Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr; D019791:Guanidine