title: Computer simulations of the translocation and unfolding of a protein pulled mechanically through a pore.
abstract: Protein degradation by ATP-dependent proteases and protein import into the mitochondrial matrix involve the unfolding of proteins upon their passing through narrow constrictions. It has been hypothesized that the cellular machinery accomplishes protein unfolding by pulling mechanically at one end of the polypeptide chain. Here, we use Langevin dynamics simulations of a minimalist off-lattice model to examine this hypothesis and to study the unfolding of a protein domain pulled mechanically through a long narrow pore. We compute the potential of mean force (PMF) experienced by the domain as a function of its displacement along the pore and identify the unfolding intermediates corresponding to the local minima of the PMF. The observed unfolding mechanism is different from that found when the two termini are pulled apart, as in single-molecule mechanical unfolding experiments. It depends on the pore diameter, the magnitude of the pulling force, and on whether the force is applied at the N- or the C-terminus of the chain. Consequently, the translocation time exhibits a pulling force dependence that is more complex than a simple exponential function expected on the basis of simple phenomenological models of translocation.
authors.affiliation: Department of Chemistry and Biochemistry, Institute for Theoretical Chemistry, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Serdal
authors.initials: S
authors.lastname: Kirmizialtin
authors.forename: Dmitrii E
authors.initials: DE
authors.lastname: Makarov
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D001703:Biophysics / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods*; D003198:Computer Simulation; D008928:Mitochondria / Q000378:metabolism; D015233:Models, Statistical; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D013816:Thermodynamics
chemical_list: D010455:Peptides; D011108:Polymers; D000255:Adenosine Triphosphate