Effect of hydration on protein dynamics by incoherent neutron inelastic scattering

Nakagawa, Hiroshi   ; Kataoka, Mikio

Effects of hydration on dynamics of Staphylococcal nuclease were examined by inelastic neutron scattering. At cryogenic temperatures, hydration affected the collective motions with energies lower than 5 meV, whereas the high-energy localized motions were independent of hydration. The frequency-upshift of the boson peak was also observed with hydration. These results suggest hardening of harmonic potential at local minima on the energy landscape. The 240 K transition was observed only for the hydrated protein, but not for the partially hydrated protein. On the other hand, partial hydration is sufficient to affect the harmonic nature of protein dynamics. The interesting and important finding is that there is a threshold hydration level to activate the anharmonic motions. Thus, hydration water controls both the harmonic and anharmonic protein dynamics by different mechanisms.