title: Direct observation of an ensemble of stable collapsed states in the mechanical folding of ubiquitin.
abstract: Statistical theories of protein folding have long predicted plausible mechanisms for reducing the vast conformational space through distinct ensembles of structures. However, these predictions have remained untested by bulk techniques, because the conformational diversity of folding molecules has been experimentally unapproachable. Owing to recent advances in single molecule force-clamp spectroscopy, we are now able to probe the structure and dynamics of the small protein ubiquitin by measuring its length and mechanical stability during each stage of folding. Here, we discover that upon hydrophobic collapse, the protein rapidly selects a subset of minimum energy structures that are mechanically weak and essential precursors of the native fold. From this much reduced ensemble, the native state is acquired through a barrier-limited transition. Our results support the validity of statistical mechanics models in describing the folding of a small protein on biological timescales.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA. sergi@biology.columbia.edu
authors.forename: Sergi
authors.initials: S
authors.lastname: Garcia-Manyes
authors.forename: Lorna
authors.initials: L
authors.lastname: Dougan
authors.forename: Carmen L
authors.initials: CL
authors.lastname: Badilla
authors.forename: Jasna
authors.initials: J
authors.lastname: Brujic
authors.forename: Julio M
authors.initials: JM
authors.lastname: Fernández
mesh_terms: D003198:Computer Simulation; D007700:Kinetics; D018625:Microscopy, Atomic Force / Q000379:methods; D008956:Models, Chemical; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D013816:Thermodynamics; D025801:Ubiquitin / Q000737:chemistry*
chemical_list: D025801:Ubiquitin