title: Localizing internal friction along the reaction coordinate of protein folding by combining ensemble and single-molecule fluorescence spectroscopy.
abstract: Theory, simulations and experimental results have suggested an important role of internal friction in the kinetics of protein folding. Recent experiments on spectrin domains provided the first evidence for a pronounced contribution of internal friction in proteins that fold on the millisecond timescale. However, it has remained unclear how this contribution is distributed along the reaction and what influence it has on the folding dynamics. Here we use a combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, microfluidic mixing and denaturant- and viscosity-dependent protein-folding kinetics to probe internal friction in the unfolded state and at the early and late transition states of slow- and fast-folding spectrin domains. We find that the internal friction affecting the folding rates of spectrin domains is highly localized to the early transition state, suggesting an important role of rather specific interactions in the rate-limiting conformational changes.
authors.affiliation: Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Borgia
authors.forename: Beth G
authors.initials: BG
authors.lastname: Wensley
authors.forename: Andrea
authors.initials: A
authors.lastname: Soranno
authors.forename: Daniel
authors.initials: D
authors.lastname: Nettels
authors.forename: Madeleine B
authors.initials: MB
authors.lastname: Borgia
authors.forename: Armin
authors.initials: A
authors.lastname: Hoffmann
authors.forename: Shawn H
authors.initials: SH
authors.lastname: Pfeil
authors.forename: Everett A
authors.initials: EA
authors.lastname: Lipman
authors.forename: Jane
authors.initials: J
authors.lastname: Clarke
authors.forename: Benjamin
authors.initials: B
authors.lastname: Schuler
mesh_terms: D004058:Diffusion; D031541:Fluorescence Resonance Energy Transfer; D017276:Friction; D007700:Kinetics; D044085:Microfluidics; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D012997:Solvents / Q000737:chemistry; D013049:Spectrin / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*; D014783:Viscosity
chemical_list: D011506:Proteins; D012997:Solvents; D013049:Spectrin