In vacuum, Ala2 exhibits a three-basin free-energy landscape in the Ramachandran plot of the back-bone dihedral angles φ (C-N-Cα-C) and ψ (N-Cα-C-N). Two of the basins occupy the β-strand like structures and are disconnected by only a small free energy barrier. The third, minor basin occupies the region of the Ramachandran plot associated with left-handed helices, and is disconnected from the β-strand states by a large free-free energy barrier > 10k B T in the Amber96-SB forcefield at 300 K (Lindorff-Larsen et al., 2010) All simulations were carried out using the Langevin integrator implemented in OpenMM (v. 8.0) with a time step of 2.0 fs and a collision frequency of 1.0ps -1 . A free energy baseline was established by running 10 simulations of 100 ns each, as depicted in Supp. Figure . To analyze the conformational distribution, we recorded the ψ and φ backbone dihedral angles of each sample. The free energy difference was calculated via Equation with