Non-arrhenius behavior in the unfolding of a short, hydrophobic alpha-helix. Complementarity of molecular dynamics and lattice model simulations.
The unfolding of the last, C-terminal residue of AcNH(2)-(l-Leu)(11)-NHMe in its alpha-helical form has been investigated by measuring the variation of free energy involved in the alpha(R) to beta conformational transition. These calculations were performed using large-scale molecular dynamics simulations in conjunction with the umbrella sampling method. For different temperatures ranging from 280 to 370 K, the free energy of activation was estimated. Concurrently, unfolding simulations of a homopolypeptide formed by twelve hydrophobic residues were carried out, employing a three-dimensional lattice model description of the peptide, with a temperature-dependent interaction potential. Using a Monte Carlo approach, the lowest free energy conformation, an analogue of a right-handed alpha-helix, was determined in the region where the peptide chain is well ordered. The free energy barrier separating this state from a distinct, compact conformation, analogue to a beta-strand, was determined over a large enough range of temperatures. The results of these molecular dynamics and lattice model simulations are consistent and indicate that the kinetics of the unfolding of a hydrophobic peptide exhibits a non-Arrhenius behavior closely related to the temperature dependence of the hydrophobic effect. These results further illuminate the necessity to include a temperature dependence in potential energy functions designed for coarse-grained models of proteins.
Collet
Olivier
O
Contribution from the Equipe de Dynamique des Assemblages Membranaires, UMR CNRS/UHP 7565, Institut Nancéien de Chimie Moléculaire, Université Henri Poincaré, BP 239, 54506 Vandoeuvre-lès-Nancy Cedex, France. chipot@lctn.uhp-nancy.fr
Chipot
Christophe
C
D003198:Computer Simulation; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D009010:Monte Carlo Method; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013816:Thermodynamics
D010455:Peptides; C027819:polyleucine