Difference in the hydration water mobility around F-actin and myosin subfragment-1 studied by quasielastic neutron scattering

Hydration water is essential for a protein to perform its biological function properly. In this study, the dynamics of hydration water around F-actin and myosin subfragment-1 (S1), which are the partner proteins playing a major role in various cellular functions related to cell motility including muscle contraction, was characterized by incoherent quasielastic neutron scattering (QENS). The QENS measurements on the D2O- and H2O-solution samples of F-actin and S1 provided the spectra of hydration water, from which the translational diffusion coefficient (DT), the residence time (τT), and the rotational correlation time (τR) were evaluated. The DT value of the hydration water of S1 was found to be much smaller than that of the hydration water of F-actin while the τT values were similar between S1 and F-actin. On the other hand, the τR values of the hydration water of S1 was found to be larger than that of the hydration water of F-actin. It was also found that the DT and τR values of the hydration water of F-actin are similar to those of bulk water. These results suggest a significant difference in mobility of the hydration water between S1 and F-actin: S1 has the typical hydration water, the mobility of which is reduced compared with that of bulk water, while F-actin has the unique hydration water, the mobility of which is close to that of bulk water rather than the typical hydration water around proteins.