An extended dynamical hydration shell around proteins.
The focus in protein folding has been very much on the protein backbone and sidechains. However, hydration waters make comparable contributions to the structure and energy of proteins. The coupling between fast hydration dynamics and protein dynamics is considered to play an important role in protein folding. Fundamental questions of protein 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? We show here that Terahertz spectroscopy directly probes such solvation dynamics around proteins, and determines the width of the dynamical hydration layer. We also investigate the dependence of solvation dynamics on protein concentration. We observe an unexpected nonmonotonic trend in the measured terahertz absorbance of the five helix bundle protein lambda(6-85)* 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 approximately 10 A. At higher protein concentrations such that solvation layers overlap, the calculated absorption spectrum varies nonmonotonically, qualitatively consistent with the experimental observations. The experimental data suggest an influence on the correlated water network motion beyond 20 A, greater than the pure structural correlation length usually observed.
Ebbinghaus
Simon
S
Lehrstuhl für Physikalische Chemie II, Ruhr-Universität Bochum 44780 Bochum, Germany.
Kim
Seung Joong
SJ
Heyden
Matthias
M
Yu
Xin
X
Heugen
Udo
U
Gruebele
Martin
M
Leitner
David M
DM
Havenith
Martina
M
D001671:Biochemistry / Q000379:methods*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015233:Models, Statistical; D009154:Mutation; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics; D012997:Solvents / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature; D054334:Viral Regulatory and Accessory Proteins / Q000737:chemistry / Q000235:genetics; D014867:Water / Q000737:chemistry
D004268:DNA-Binding Proteins; D011506:Proteins; D012097:Repressor Proteins; D012997:Solvents; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D014867:Water