High-energy channeling in protein folding.
Recent controversy about the role of populated intermediates in protein folding emphasizes the need to better characterize other events on the folding pathway. A complication is that these involve high-energy states which are difficult to target experimentally since they do not accumulate kinetically. Here, we explore the energetics of high-energy states and map out the shape of the free-energy profile for folding of the two-state protein U1A. The analysis is based on nonlinearities in the GdnHCl dependence of the activation energy for unfolding, which we interpret in terms of structural changes of the protein-folding transition state. The result suggests that U1A folds by high-energy channeling where most of the conformational search takes place isoenergetically at transition-state level. This is manifested in a very broad and flat activation barrier, the top of which covers more than 60% of the reaction coordinate. The interpretation favors a folding mechanism where the pathway leading to the native protein is determined by the sequence's ability to stabilize productive transition states.
Silow
M
M
Biochemistry, Chemical Centre, Lund, Sweden.
Oliveberg
M
M
D019791:Guanidine; D006146:Guanidines / Q000737:chemistry; D006801:Humans; D017510:Protein Folding; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000737:chemistry*; D013816:Thermodynamics
D006146:Guanidines; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; C075339:U1A protein; D019791:Guanidine