MD simulations were carried out with GROMACS 5.0.6 52 using the X-ray crystal structure of ubiquitin (PDB code 1UBQ) as a starting structure. The simulation details are described elsewhere and shall thus only be summarized briefly here. The protein was centered in a periodic cubic box with a volume of about 500 nm 3 . Crystal waters were kept during the setup, and the system was solvated with 16235 TIP4P/2005 21 water molecules. The AMBER ff99SB*-ILDN and CHARMM36 54 protein force fields with the reparametrized methyl rotation barriers of Hoffmann and coworkers were used (scripts for modifying the methyl rotation barriers in GROMACS protein force field topology (.top or .itp) files are available at ). Sodium and chloride ions were added to the system at 0.15 mol/l concentration, ensuring an overall neutral (uncharged) simulation box. After energy minimization, the system was equilibrated in the NPT ensemble for 200 ps with harmonic position restraints on the protein heavy atoms.