title: Distinguishing between two-state and three-state models for ubiquitin folding.
abstract: Conflicting results exist regarding whether the folding of mammalian ubiquitin at 25 degrees C is a simple, two-state kinetic process or a more complex, three-state process with a defined kinetic intermediate. We have measured folding rate constants up to about 1000 s(-1) using conventional rapid mixing methods in single-jump, double-jump, and continuous-flow modes. The linear dependence of folding rates on denaturant concentration and the lack of an unaccounted "burst-phase" change for the fluorescence signal indicate that a two-state folding model is adequate to describe the folding pathway. This behavior also is seen for folding in the presence of the stabilizing additives 0.23 M sodium sulfate and 1 M sodium chloride. These results stress the need for caution in interpreting deviations from ideal two-state "chevron" behavior when folding is heterogeneous or folding rate constants are near the detection limit.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Chicago, 920 East 58th Street, Chicago, Illinois 60637, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Krantz
authors.forename: T R
authors.initials: TR
authors.lastname: Sosnick
mesh_terms: D002942:Circular Dichroism; D019791:Guanidine / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D011489:Protein Denaturation; D017510:Protein Folding; D013050:Spectrometry, Fluorescence / Q000379:methods; D013431:Sulfates / Q000737:chemistry; D013816:Thermodynamics; D014452:Ubiquitins / Q000737:chemistry*
chemical_list: D013431:Sulfates; D014452:Ubiquitins; C012036:sodium sulfate; D019791:Guanidine