EPL Association, EPL, 6(79), p. 66003
The temperature- dependent conformations of alanine-rich polypeptides are investigated using generalized ensemble Monte Carlo simulations. Pure polyalanines form a helices at low temperature, but exhibit an intermediate beta-sheet structure below the coil transition. For the substituted peptide WA(13), the simulation predicts the beta conformation to be more stable than helices already at low temperatures, and the beta motif is further favored by entropy. Measurements of the electric dipole of this peptide do not provide evidence for helical structures even at room temperature. These experimental observations are thus compatible with our suggestion of beta conformations, even though random-coil structures cannot be ruled out. Finally, we show how to stabilize a helices by an intense electric field, possibly leading to electrofreezing behavior. Copyright (C) EPLA, 2007.