Since the CHARMM36 force field was parametrized with the TIP3P water model, simulations were performed with TIP4P/2005 to get a more appropriate rotational diffusion constant of ubiquitin. The simulations with the CHARMM36 and AMBER force fields yielded very similar isotropic rotational diffusion constants of 3.90 ± 0.32 and 3.93 ± 0.18 • 10 7 s -1 , respectively, corresponding to tumbling correlation times of 4.27 ± 0.39 and 4.24 ± 0.20 ns, respectively. These values are in line with our previous simulations 62). We note in passing that due to the large volume of the simulation box used in this work (ca. 500 nm 3 ), the correction to the rotational diffusion constant due to the finite size of the simulation box is smaller than 5% in the present case. This is comparable to the statistical uncertainty, and thus this correction was not applied here.