Coupling of the hydration water dynamics and the internal dynamics of actin detected by quasielastic neutron scattering

Fujiwara, Satoru; Plazanet, M.*; Oda, Toshiro*

Quasi-elastic neutron scattering experiments of powder samples of F-actin and G-actin, hydrated either with DO or HO, at hydration ratios of 0.4 and 1.0, were performed. Combined analysis of the quasi-elastic neutron scattering spectra provided the parameters characterizing the water dynamics in the first hydration layer and those outside of the first layer. The translational diffusion coefficients (D) of the hydration water in the first layer were found to be 1.2 10 cm/s and 1.7 10 cm/s for F-actin and G-actin, respectively, while that for bulk water was 2.8 10 cm/s. The residence times were 6.6 ps and 5.0 ps for F-actin and G-actin, respectively, while that for bulk water was 0.63 ps. These differences between F-actin and G-actin, indicating that the hydration water around G-actin is more mobile than that around F-actin, are in concert with the results of the internal dynamics of F-actin and G-actin, showing that G-actin fluctuates more rapidly than F-actin. This implies that the dynamics of the hydration water is coupled to the internal dynamics of the actin molecules. The D values of the water molecules outside of the first hydration layer were found to be similar to that of bulk water though the residence times are strongly affected by the first hydration layer. This supports the recent observation on intracellular water that shows bulk-like behavior.