CP: Electrostatics February 1, 2010. Electrostatics – Chap. 32.
Polarized hydration shells around proteins and the ...theochemlab.asu.edu/present/trieste10.pdf ·...
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Polarized hydration shells around proteins and the electrostatics of
the protein-water interface
Dmitry Matyushov
Arizona State University, Center for Biological Physics
Frontiers in Water Biophysics, May 25, 2010
Photosynthetic reaction centerwith its first solvation layer
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Electrostatics of redox proteins
Observables:
Plastocyanin, electron carrier inphotosynthetic systems of plants
Bacterial reaction center in a detergent miccelle
e
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Why electrostatics?
●Control enzymetic reactions●Sensitive to the orientational structure of water around proteins●Probed by optical (Stokes shift dynamics) and dielectric spectroscopies
Gaussianity of fluctuations
Water reorganization energy:
Gaussian fluctuations:
Stokes-shift dynamics:
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Non-Gaussian electrostatics above the dynamical transition
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Time-scale issues
~300-500 ps is the time-scale of developing non-Gaussianity
Average electrostatic potential is produced by fast water motions
Taking averages over partsof the trajectory
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Non-Gaussianity: hydration shell dipole moment
Ubiq = ubiquitinLys = lysozymePC = plastocyaninRC = bacterial reaction center
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Polar domains
For plastocyanin redox-activeprotein the first solvation layerbreaks into two oppositely oriented polar domains
For redox-inactive ubiquitin andlysozyme the distribution is closeto Maxwellian
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Polarized ferroelectric domains in the hydration layer
Dielectric constantof the first hydration layer:
Lys.................... 23 Ubiq.................. 28PC...................... 2.5 x 103
10-15 A, penetration into the bulk
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How far does it go?
Small dipoles per water add up into large dipolar fluctuations!
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Terahertz spectroscopy of protein solutions
Hydrated proteins:one needs a dramatic increase of an effective dipole of the proteinto get experimental points.
Gruebele + Havenith,Protein polarizes water 20 A awayfrom its surface (PNAS’07)!
DM, PRE'10
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Not only proteins ...
Kihara sphere in SPC/E water:
High polarity layer penetrates the bulk to ~ the cavity radius!
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Conclusions
Redox-active proteins, large polarity of the hydration shell (correlated with protein dipole's variance).
Non-Gaussian statistics of the electrostatic potential.
Statistics return to Gaussian below the temperature of dynamical transition, ~ 200-240 K.
Dynamics of ferroelectric domains are slow, hundreds of picoseconds.
The length-scale of polarized (ferroelectric) domains is10-15 A into the bulk.
Breaking into domains occurs as a weak first-order transition in a sub-ensemble of hydration layer.
⟨M 2⟩≫Nm2
var≫
T tr≈200−240K
rel≈100 ps
l≈10−15 A
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David LeBard
$$ NSF, BES
Allan Friesen
JPCB 2008, 112, 5218 JPCB 2008, 112, 10322
PRE 2008, 78, 061901.
JPCB 2009, 113, 12424.
JCP 2009, 130, 164522.
PRE 2010, 81, 021914.
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Lengthscale of fluctuations
Dependence of the first and second cumulants on the cutoff distance from the protein surface.
Different length-scales for the first and second cumulants!
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About 10 time higher energetic efficiency of biological machines in the picture of non-Gaussian electrostatic fluctuations!
Gaussianpicture
=s=St
Non-Gaussian picture
eff=St 2
s
Number of electron hops in the non-Gaussian paradigm per one hop in the Gaussian picture:
Electron transport in molecular chains
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Terahertz spectroscopy: Input from simulations
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Gigantic reorganization energy: other studies