Hydration-coupled protein boson peak measured by incoherent neutron scattering

Nakagawa, Hiroshi   ; Kataoka, Mikio*; Jochi, Yasumasa*; Kitao, Akio*; Shibata, Kaoru  ; Tokuhisa, Atsushi*; Tsukushi, Itaru*; Go, Nobuhiro

The boson peak of a protein was examined in relation to hydration using staphylococcal nuclease. Although the boson peak is commonly observed in synthetic polymers, glassy materials and amorphous materials, the origin of the boson peak is not fully understood. The motions that contribute to the peak are harmonic vibrations. Upon hydration the peak frequency shifts to a higher frequency and the effective force constant of the vibration increases at low temperatures, suggesting that the protein energy surface is modified. Hydration of the protein leads to a more rugged surface and the vibrational motions are trapped within the local minimum at cryogenic temperatures. The origin of the protein boson peak may be related to this rugged energy surface.