Neutron scattering study on dynamics of hydration water aroundmuscle contractile proteins
T. Matsuo1, T. Arata2, T. Oda3, and S. Fujiwara1#1

2

Quantum Beam Science Center, JAEA, Ibaraki 319-1195, Japan
Department of Biological Sciences, Osaka University, Osaka 560-0043, Japan
3
Graduate School of Science, University of Hyogo, Hyogo 678-1297, Japan# corresponding author: fujiwara.satoru@jaea.go.jp

In physiological conditions, proteins are surrounded by water molecules as solvent andfluctuating under their influence (in particular, hydration water molecules). It is now widely
accepted that these thermal fluctuations, or the dynamics, of proteins are essential for theirstructural changes indispensable to their functions [1]. Since the dynamics of proteins isstrongly coupled with that of hydration water [2], investigation of the dynamics of thehydration water is important for ultimate understanding of the protein functions.
In the previous study, we studied the density of the hydration shell around F-actin andmyosin subfragment-1 (S1), which are proteins interacting with each other to produce force inmuscle contraction, and found that the hydration shell around F-actin is denser than thataround S1 [3]. This finding has raised the possibility that the dynamics of the hydration wateraround them could be also different. Characterizations of the dynamics of the hydration wateraround F-actin and S1 in addition to their structural properties are crucial for elucidating therole that the hydration water plays in muscle contraction.
Thus, in this study, we investigated the dynamics of the hydration water around F-actin
and S1 by quasielastic neutron scattering (QENS). The QENS measurements were conductedon the solution samples of F-actin (150 mg/ml) and S1 (80 mg/ml) in H2O and D2O using thecold-neutron disk-chopper spectrometer AMATERAS in MLF/J-PARC, Japan. The spectra ofhydration water were obtained by subtracting those of proteins and those of bulk water fromthe measured spectra of H2O samples (the spectra of proteins were obtained by subtracting
those of D2O buffer from those of D2O samples, while the spectra of H2O buffer was used as
those of bulk water) with appropriate scaling factors. The translational diffusion coefficients(DT) and the residence time (τT) were evaluated from the dependence of the half-widths at
half-maximum of the Lorentzian functions fit to the spectra on the momentum transfer.
In the current analysis, it was found that the DT value of the hydration water around S1
was smaller than that of bulk water while the τT value was larger than that of bulk water,suggesting that S1 has typical hydration water, the mobility of which is less than that of bulkwater. On the other hand, both the DT and the τT values of the hydration water around F-actin
were closer to those of bulk water, suggesting that the hydration water around F-actin has
higher mobility than that around other proteins including S1. The results of a more detailed
analysis will be given in the presentation.
References[1] G. Zaccai, Science, 288, 1604-1607 (2000).
[2] S. Fujiwara, et al., Biochem. Biophys. Res. Commun. 431, 542-546 (2013).
[3] T. Matsuo, et al., BIOPHYSICS, 9, 99-106 (2013).