Before revision:  These data were validated by multi-frequency continuous-wave electron paramagnetic resonance (EPR) measurements, that relying on the frequency dependence of the fast and slow motions of the spin probe were used to distinguish the fast internal motion of the spin label from slow protein tumbling. It was found that the activation loop oscillated between two conformational states separated by 7 Angstrom and the average structures obtained from the MD trajectories showed the MTSL exposed to the solvent and probing the C-lobe of the protein .
After revision:  These data were validated by multi-frequency continuous-wave electron paramagnetic resonance (EPR) measurements, that relying on the frequency dependence of the fast and slow motions of the spin probe were used to distinguish the fast internal motion of the spin probe was determined from 94 GHz measurements that reflect the fast motions .