Structure and dynamical properties of hydrated F-actin investigated by X-ray scattering

Abstract

Structure and dynamical properties of hydrated actin filament (F-actin) are revealed by X-ray diffraction and inelastic X-ray scattering (IXS) in a temperature range of 180–298 K, respectively. We assigned the peaks in the radial distribution functions of the hydrated F-actin by molecular dynamics (MD) simulation for F-actin in water. Although the hydration water of F-actin does not freeze in the temperature range measured, the hydrogen-bonded network where hydration water molecules mediate the hydrophilic groups of F-action becomes enhanced with decreasing temperature, as previously seen for many hydrated proteins. By applying a damped harmonic oscillator model to the dynamical structure factor obtained from the IXS spectra of hydrated F-actin, we investigated the intensity and energy of the phonon excitation as a function of temperature. The phonon excitation energy decreased and the phonon population which is proportional to the intensity of the phonon excitation increased with increasing temperature as previously reported for hydrated lysozyme and could be related to the conformational flexibility of the protein regarding the intraprotein short-time collective vibrational motions. In contrast to hydrated lysozyme, these phenomena for hydrated F-actin were observed at ~11 nm−1 of momentum transfer, Q, indicating that they arise from water dimer mediating the hydrophilic parts of F-actin.