title: Force-induced unzipping transitions in an athermal crowded environment.
abstract: Using theoretical arguments and extensive Monte Carlo (MC) simulations of a coarse-grained three-dimensional off-lattice model of a β-hairpin, we demonstrate that the equilibrium critical force, Fc, needed to unfold the biopolymer increases nonlinearly with increasing volume fraction occupied by the spherical macromolecular crowding agent. Both scaling arguments and MC simulations show that the critical force increases as Fc ≈ φc(α). The exponent α is linked to the Flory exponent relating the size of the unfolded state of the biopolymer and the number of amino acids. The predicted power law dependence is confirmed in simulations of the dependence of the isothermal extensibility and the fraction of native contacts on φc. We also show using MC simulations that Fc is linearly dependent on the average osmotic pressure (P) exerted by the crowding agents on the β-hairpin. The highly significant linear correlation coefficient of 0.99657 between Fc and P makes it straightforward to predict the dependence of the critical force on the density of crowders. Our predictions are amenable to experimental verification using laser optical tweezers.
authors.affiliation: Institute for Physical Science and Technology, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Pincus
authors.forename: D
authors.initials: D
authors.lastname: Thirumalai
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D009997:Osmotic Pressure; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D011506:Proteins