TY - JOUR
T1 - Solvent-Slaved Dynamic Processes Observed by Tryptophan Phosphorescence of Human Serum Albumin
AU - Draganski, Andrew R.
AU - Friedman, Joel M.
AU - Ludescher, Richard D.
N1 - Funding Information: This research was supported by an Agriculture and Food Research Initiative grant (no. 2014-67017-21649) from the USDA National Institute of Food and Agriculture, Improving Food Quality–A1361 (to R.D.L.) and by National Institutes of Health grant P01-HL110900 (to J.M.F.). Publisher Copyright: © 2017 Biophysical Society
PY - 2017/3/14
Y1 - 2017/3/14
N2 - Despite extensive experimental and computational efforts to understand the nature of the hierarchy of protein fluctuations and the modulating role of the protein hydration shell, a detailed microscopic description of the dynamics of the protein-solvent system has yet to be achieved. By using single tryptophan protein phosphorescence, we follow site-specific internal protein dynamics over a broad temperature range and demonstrate three independent dynamic processes. Process I is seen at temperatures below the bulk solvent Tg, has low activation energy, and is likely due to fast vibrations that may be enabled by water mobility on the protein surface. Process II is observed above 170 K, with activation energy typical of β relaxations in a glass; it has the same temperature dependence as fluctuations of hydration shell waters. Process III is observed at T > 200 K; it has super-Arrhenius temperature dependence and closely follows the primary relaxation of the bulk. The fluorescence of pyranine bound to the protein reports on the mobility of water in the hydration shell; it reveals a shift in emission spectra with increasing temperature, indicative of a changing H-bond network at the surface of the protein. These results support a model of solvent-slaved protein dynamics.
AB - Despite extensive experimental and computational efforts to understand the nature of the hierarchy of protein fluctuations and the modulating role of the protein hydration shell, a detailed microscopic description of the dynamics of the protein-solvent system has yet to be achieved. By using single tryptophan protein phosphorescence, we follow site-specific internal protein dynamics over a broad temperature range and demonstrate three independent dynamic processes. Process I is seen at temperatures below the bulk solvent Tg, has low activation energy, and is likely due to fast vibrations that may be enabled by water mobility on the protein surface. Process II is observed above 170 K, with activation energy typical of β relaxations in a glass; it has the same temperature dependence as fluctuations of hydration shell waters. Process III is observed at T > 200 K; it has super-Arrhenius temperature dependence and closely follows the primary relaxation of the bulk. The fluorescence of pyranine bound to the protein reports on the mobility of water in the hydration shell; it reveals a shift in emission spectra with increasing temperature, indicative of a changing H-bond network at the surface of the protein. These results support a model of solvent-slaved protein dynamics.
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U2 - https://doi.org/10.1016/j.bpj.2016.12.048
DO - https://doi.org/10.1016/j.bpj.2016.12.048
M3 - Article
C2 - 28297647
SN - 0006-3495
VL - 112
SP - 881
EP - 891
JO - Biophysical Journal
JF - Biophysical Journal
IS - 5
ER -