title: Hidden dynamics in the unfolding of individual bacteriorhodopsin proteins.
abstract: Protein folding occurs as a set of transitions between structural states within an energy landscape. An oversimplified view of the folding process emerges when transiently populated states are undetected because of limited instrumental resolution. Using force spectroscopy optimized for 1-microsecond resolution, we reexamined the unfolding of individual bacteriorhodopsin molecules in native lipid bilayers. The experimental data reveal the unfolding pathway in unprecedented detail. Numerous newly detected intermediates-many separated by as few as two or three amino acids-exhibited complex dynamics, including frequent refolding and state occupancies of <10 μs. Equilibrium measurements between such states enabled the folding free-energy landscape to be deduced. These results sharpen the picture of the mechanical unfolding of membrane proteins and, more broadly, enable experimental access to previously obscured protein dynamics.
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA.
authors.forename: Hao
authors.identifier: 0000-0003-1589-7781
authors.initials: H
authors.lastname: Yu
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA.|Department of Physics, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Matthew G W
authors.identifier: 0000-0001-7345-6971
authors.initials: MG
authors.lastname: Siewny
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA.
authors.forename: Devin T
authors.identifier: 0000-0002-2612-9561
authors.initials: DT
authors.lastname: Edwards
authors.affiliation: Radio Frequency Technology Division, National Institute of Standards and Technology, Boulder, CO 80305, USA.
authors.forename: Aric W
authors.identifier: 0000-0003-3371-8054
authors.initials: AW
authors.lastname: Sanders
authors.affiliation: JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA. tperkins@jila.colorado.edu.|Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Thomas T
authors.identifier: 0000-0003-4826-9490
authors.initials: TT
authors.lastname: Perkins
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D018625:Microscopy, Atomic Force; D000072757:Protein Conformation, beta-Strand; D058767:Protein Unfolding; D000072760:Single Molecule Imaging
chemical_list: D008051:Lipid Bilayers; D001436:Bacteriorhodopsins