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Physics Colloquium - Friday, March 6th, 2009,
Center; Refreshments at 3:30 P.M. in
The THz dance of the protein with the water
Department of Physical Chemistry II
Ruhr University Bochum
The focus in protein folding has been very
much on the protein backbone and sidechains.
Yet hydration waters make comparable
contributions to the structure and energy of
proteins. Although the dynamics of the
hydration water occurs on the picosecond time
scale, 'slaving' to fast solvent modes
profoundly affects the slower but larger-scale
protein motions. In return the protein
influences the structure and dynamics of
surrounding water molecules. Fundamental
questions of biomolecule hydration include,
how far out into the solvent does the
influence of the biomolecule reach, how is the
water affected, and how are the properties of
the hydration water influenced by the
separation between protein molecules in
solution? Terahertz spectroscopy is shown to
directly probe such solvation dynamics, and
the width of the dynamic hydration layer .
Solvation of the five helix bundle protein
λ*6-85 leads to an unexpected non-monotonic trend in
the measured terahertz absorbance as a
function of the protein:water molar ratio.
The trend can be explained by overlapping
solvation layers around the proteins .
Molecular dynamics simulations indicate water
dynamics in the solvation layer around one
protein to be distinct from bulk water out to
about 10Å. At higher protein concentrations
such that solvation layers overlap, the
calculated absorption spectrum varies
non-monotonically, qualitatively consistent
with the experimental observations. The
experimental data suggest an influence on the
correlated water motion beyond 20Å, greater
than the structural correlation length usually
observed. Most recent results demonstrate that
the long range hydration layer is protein
sequence and pH dependent. Whereas the native
wildtype shows the most pronounced effect on
the fast water dynamics, the denaturated
protein have much less influence on the fast
water network motions .
U. Heugen, G. Schwaab, E. Bründermann, M. Heyden, X. Yu, D.M. Leitner, M. Havenith, Solute-induced retardation of water dynamics probed directly by THz spectroscopy, PNAS 103, 12301 (2006).
S. Ebbinghaus, S.J. Kim, M. Heyden, X. Yu, U. Heugen, M. Gruebele, D.M. Leitner, and M. Havenith, An extended dynamical solvation shell around proteins PNAS 104, 20749 (2007).
S. Ebbinghaus, S.J. Kim, M. Heyden, X. Yu, M. Gruebele, D.M. Leitner, M. Havenith, Protein sequence- and pH dependend hydration probed by THz spectroscopy, JACS 130 (8), 2374 (2008).