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Long-Range Modulations of Electric Fields in Proteins
Citation key ISI:000444355100003
Author Biava, Hernan and Schreiber, Toni and Katz, Sagie and Voeiler, Jan-Stefan and Stolarski, Michael and Schulz, Claudia and Michael, Norbert and Budisa, Nediljko and Kozuch, Jacek and Utesch, Tillmann and Hildebrandt, Peter
Pages 8330-8342
Year 2018
ISSN 1520-6106
DOI 10.1021/acs.jpcb.8b03870
Journal JOURNAL OF PHYSICAL CHEMISTRY B
Volume 122
Number 35
Month SEP 6
Abstract Electrostatic interactions are essential for controlling the protein structure and function. Whereas so far experimental and theoretical efforts focused on the effect of local electrostatics, this work aims at elucidating the long-range modulation of electric fields in proteins upon binding to charged surfaces. The study is based on cytochrome c (Cytc) variants carrying nitrile reporters for the vibrational Stark effect that are incorporated into the protein via genetic engineering and chemical modification. The Cytc variants were thoroughly characterized with respect to possible structural perturbations due to labeling. For the proteins in solution, the relative hydrogen bond occupancy and the calculated electric fields, both obtained from molecular dynamics (MD) simulations, and the experimental nitrile stretching frequencies were used to develop a relationship for separating hydrogen-bonding and non-hydrogen-bonding electric field effects. This relationship provides an excellent description for the stable Cytc variants in solution. For the proteins bound to Au electrodes coated with charged self-assembled monolayers (SAMs), the underlying MD simulations can only account for the electric field changes Delta E-ads due to the formation of the electrostatic SAM-Cytc complexes but not for the additional contribution, Delta E-int, representing the consequences of the potential drops over the electrode/SAM/protein interfaces. Both Delta E-ads and Delta E-int, determined at distances between 20 and 30 angstrom with respect to the SAM surface, are comparable in magnitude to the non-hydrogen-bonding electric field in the unbound protein. This long-range modulation of the internal electric field may be of functional relevance for proteins in complexes with partner proteins (E-ads) and attached to membranes (Delta E-ads + Delta E-int).
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