One role of hydration water in proteins: key to the "softening" of short time intraprotein collective vibrations of a specific length scale.
High resolution inelastic X-ray scattering (IXS) experiments show that the "phonon energy softening" and "phonon population enhancement" observed in a hydrated native protein when increasing the temperature from 200 K to physiological temperature are not directly related to the protein structure. Such phenomena were also observed in a denatured sample without a defined tertiary structure and with a limited residual secondary structure. However, in a dry sample, such "softening" is strongly suppressed. These facts suggest that the above-mentioned protein "softening" phenomenon is water-induced. In addition, increasing the hydration level can also induce "phonon energy softening" at room temperature, but not at 200 K. This change may be due to a qualitative difference in the dynamics of hydration water at 200 K and at room temperature.
Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. sowhsin@mit.edu.
Zhe
Z
Wang
Wei-Shan
WS
Chiang
Peisi
P
Le
Emiliano
E
Fratini
Mingda
M
Li
Ahmet
A
Alatas
Piero
P
Baglioni
Sow-Hsin
SH
Chen
D002919:Chymotrypsinogen / Q000737:chemistry*; D009113:Muramidase / Q000737:chemistry*; D060739:Phonons; D011487:Protein Conformation; D011489:Protein Denaturation; D014732:Vibration; D014867:Water / Q000737:chemistry*
D014867:Water; D002919:Chymotrypsinogen; D009113:Muramidase