title: Sampling the Denatured State of Polypeptides in Water, Urea, and Guanidine Chloride to Strict Equilibrium Conditions with the Help of Massively Parallel Computers.
abstract: The denatured state of polypeptides and proteins, stabilized by chemical denaturants like urea and guanidine chloride, displays residual secondary structure when studied by nuclear-magnetic-resonance spectroscopy. However, these experimental techniques are weakly sensitive, and thus molecular-dynamics simulations can be useful to complement the experimental findings. To sample the denatured state, we made use of massively-parallel computers and of a variant of the replica exchange algorithm, in which the different branches, connected with unbiased replicas, favor the formation and disruption of local secondary structure. The algorithm is applied to the second hairpin of GB1 in water, in urea, and in guanidine chloride. We show with the help of different criteria that the simulations converge to equilibrium. It results that urea and guanidine chloride, besides inducing some polyproline-II structure, have different effect on the hairpin. Urea disrupts completely the native region and stabilizes a state which resembles a random coil, while guanidine chloride has a milder effect.
authors.affiliation: Department of Physics, Università degli Studi di Milano , via Celoria 16, 20133 Milano, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Meloni
authors.affiliation: Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Carlo
authors.initials: C
authors.lastname: Camilloni
authors.affiliation: Department of Physics, Università degli Studi di Milano, and INFN , via Celoria 16, 20133 Milano, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Tiana