title: Force-clamp experiments reveal the free-energy profile and diffusion coefficient of the collapse of protein molecules.
abstract: We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ∼ 100 nm(2) s(-1) is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.
authors.affiliation: Department of Physics and Center for Soft Matter Research, New York University, 4 Washington Place, New York, New York 10003, USA.
authors.forename: H
authors.initials: H
authors.lastname: Lannon
authors.affiliation: Department of Chemical and Biological Sciences, Polytechnic Institute of NYU, Brooklyn, New York 11201, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Haghpanah
authors.affiliation: Department of Chemical and Biological Sciences, Polytechnic Institute of NYU, Brooklyn, New York 11201, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Montclare
authors.affiliation: Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, New York 10012, USA.
authors.forename: E
authors.initials: E
authors.lastname: Vanden-Eijnden
authors.affiliation: Department of Physics and Center for Soft Matter Research, New York University, 4 Washington Place, New York, New York 10003, USA.
authors.forename: J
authors.initials: J
authors.lastname: Brujic
mesh_terms: D004058:Diffusion; D018625:Microscopy, Atomic Force; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics; D025801:Ubiquitin / Q000737:chemistry
chemical_list: D011506:Proteins; D025801:Ubiquitin