TY - JOUR
T1 - Protein response to external electric fields
T2 - Relaxation, hysteresis, and echo
AU - Xu, Dong
AU - Phillips, James Christopher
AU - Schulten, Klaus
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 1996/7/18
Y1 - 1996/7/18
N2 - Dipole moments induced in proteins by external electric fields are studied by molecular dynamics simulations and described in terms of analytical models based on ensembles of Langevin oscillators and Fokker-Planck equations. We investigate through simulations of the protein bovine pancreatic trypsin inhibitor (BPTI) (1) the distribution p(M) of dipole moments as well as the dipole moment autocorrelation function CM,M(t) at thermal equilibrium, (2) the dielectric constant ∈, (3) the dipole moment ΔM(t) induced by cyclic (piecewise linear or sinusoidally periodic in time) spatially homogeneous fields, demonstrating significant hysteresis behavior, and (4) the dipolar response to a constant homogeneous field applied for about a picosecond. Through a comparison between an analytical model and simulations, we show that the dipolar response (4) can be described by a relaxation characterized by VM,M(t) in addition to a significant pulse-shaped component, termed the dipole echo. The dipole echo arises from a memory effect of transient increases or decreases of protein vibrational frequencies induced by an external field. The hysteresis behavior (3) under a weak external field is related to the equilibrium properties p(M), CM,M(t), and ∈; however, discrete structural transitions induced by a strong field also contribute to hysteresis, as demonstrated in a model evoking stochastic motion in a periodically driven bistable potential. In the case of electric fields arising through charge displacements in proteins, e.g., through electronic excitation or photoinduced electron transfer, concomitant dipolar responses in real proteins should resemble those reported here and should be observable by means of sub-picosecond spectroscopy.
AB - Dipole moments induced in proteins by external electric fields are studied by molecular dynamics simulations and described in terms of analytical models based on ensembles of Langevin oscillators and Fokker-Planck equations. We investigate through simulations of the protein bovine pancreatic trypsin inhibitor (BPTI) (1) the distribution p(M) of dipole moments as well as the dipole moment autocorrelation function CM,M(t) at thermal equilibrium, (2) the dielectric constant ∈, (3) the dipole moment ΔM(t) induced by cyclic (piecewise linear or sinusoidally periodic in time) spatially homogeneous fields, demonstrating significant hysteresis behavior, and (4) the dipolar response to a constant homogeneous field applied for about a picosecond. Through a comparison between an analytical model and simulations, we show that the dipolar response (4) can be described by a relaxation characterized by VM,M(t) in addition to a significant pulse-shaped component, termed the dipole echo. The dipole echo arises from a memory effect of transient increases or decreases of protein vibrational frequencies induced by an external field. The hysteresis behavior (3) under a weak external field is related to the equilibrium properties p(M), CM,M(t), and ∈; however, discrete structural transitions induced by a strong field also contribute to hysteresis, as demonstrated in a model evoking stochastic motion in a periodically driven bistable potential. In the case of electric fields arising through charge displacements in proteins, e.g., through electronic excitation or photoinduced electron transfer, concomitant dipolar responses in real proteins should resemble those reported here and should be observable by means of sub-picosecond spectroscopy.
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U2 - 10.1021/jp960076a
DO - 10.1021/jp960076a
M3 - Article
AN - SCOPUS:0030197735
VL - 100
SP - 12108
EP - 12121
JO - Journal of Physical Chemistry
JF - Journal of Physical Chemistry
SN - 0022-3654
IS - 29
ER -