Hydration affects both harmonic and anharmonic nature of protein dynamics
Hiroshi Nakagawa 1, Yasumasa Joti 2, Akio Kitao 3 and Mikio Kataoka 4*
1 Japan Atomic Energy Agency
2 Institute of Molecular and Cellular Biosciences, University of Tokyo
3 University of Tokyo
4 Nara Inst. of Science & Technology
* To whom correspondence should be addressed. E-mail: kataoka{at}ms.naist.jp.
Submitted on December 27, 2007
Revised on March 15, 2008
Accepted on 27 May 2008
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Abstract |
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To understand the effect of hydration on protein dynamics, inelastic neutron scattering experiments were carried out on Staphylococcal nuclease samples at differing hydration levels: dehydrated, partially hydrated and hydrated. At cryogenic temperatures, hydration affected the collective motions with energies lower than 5 meV, while the high energy localized motions were independent of hydration. The prominent change was a shift of boson peak toward higher energy by hydration, suggesting hardening of harmonic potential at local minima on the energy landscape. The 240 K transition was observed only for the hydrated protein. Significant quasi-elastic scattering at 300 K was observed only for the hydrated sample, indicating that the origin of the transition is the motion activated by hydration water. The neutron scattering profile of the partially hydrated sample was quite similar to that of the hydrated sample at 100 and 200 K, while it was close to the dehydrated sample at 300 K, indicating that partial hydration is sufficient to affect the harmonic nature of protein dynamics, and that there is a threshold hydration level to activate the anharmonic motions. Thus, hydration water controls both the harmonic and anharmonic protein dynamics, by differing means.
Key Words:
boson peak, dynamical transition, hydration, neutron scattering, protein dynamics, staphylococcal nuclease
