Diffusion control in an elementary protein folding reaction.
The cold-shock protein CspB (from Bacillus subtilis), a very small protein of 67 residues, folds extremely fast in a reversible N &lrharr; U two-state reaction. Both unfolding and refolding are strongly decelerated when the viscosity of the solvent is increased by adding ethylene glycol or sucrose. The folding of CspB thus seems to follow Kramers' model for reactions in which the reactants must diffuse together. It indicates that the compaction of the protein chain occurs in the rate-limiting step of folding. Chain diffusion to a productively collapsed form and the crossing of a high energy barrier are thus tightly coupled in this folding reaction, and the measured reaction rate depends on both the diffusion of the protein chain in the solvent and the magnitude of the activation energy. We suggest that in protein folding an energetic barrier is essential to separate the native from the unfolded conformations of a protein. This barrier protects the ordered structure of a native protein against continuous unfolding by diffusive chain motions and leads to apparent two-state behavior.
Jacob
M
M
Laboratorium für Biochemie, Universität Bayreuth, D-95440 Bayreuth, Germany.
Schindler
T
T
Balbach
J
J
Schmid
F X
FX
D001412:Bacillus subtilis; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D004058:Diffusion; D019855:Ethylene Glycol; D005026:Ethylene Glycols; D019791:Guanidine; D006146:Guanidines; D006360:Heat-Shock Proteins; D007700:Kinetics; D007768:Lactalbumin / Q000737:chemistry* / Q000378:metabolism*; D008962:Models, Theoretical; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D012997:Solvents; D014783:Viscosity
D001426:Bacterial Proteins; D002352:Carrier Proteins; D005026:Ethylene Glycols; D006146:Guanidines; D006360:Heat-Shock Proteins; D012997:Solvents; C077188:cold-shock protein CspB, Bacteria; D007768:Lactalbumin; D019855:Ethylene Glycol; D019791:Guanidine