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Main Title: Quantification of Local Electric Field Changes at the Active Site of Cytochrome c Oxidase by Fourier Transform Infrared Spectroelectrochemical Titrations
Author(s): Baserga, Federico
Dragelj, Jovan
Kozuch, Jacek
Mohrmann, Hendrik
Knapp, Ernst-Walter
Stripp, Sven T.
Heberle, Joachim
Type: Article
Abstract: Cytochrome c oxidase (CcO) is a transmembrane protein complex that reduces molecular oxygen to water while translocating protons across the mitochondrial membrane. Changes in the redox states of its cofactors trigger both O2 reduction and vectorial proton transfer, which includes a proton-loading site, yet unidentified. In this work, we exploited carbon monoxide (CO) as a vibrational Stark effect (VSE) probe at the binuclear center of CcO from Rhodobacter sphaeroides. The CO stretching frequency was monitored as a function of the electrical potential, using Fourier transform infrared (FTIR) absorption spectroelectrochemistry. We observed three different redox states (R4CO, R2CO, and O), determined their midpoint potential, and compared the resulting electric field to electrostatic calculations. A change in the local electric field strength of +2.9 MV/cm was derived, which was induced by the redox transition from R4CO to R2CO. We performed potential jump experiments to accumulate the R2CO and R4CO species and studied the FTIR difference spectra in the protein fingerprint region. The comparison of the experimental and computational results reveals that the key glutamic acid residue E286 is protonated in the observed states, and that its hydrogen-bonding environment is disturbed upon the redox transition of heme a3. Our experiments also suggest propionate A of heme a3 changing its protonation state in concert with the redox state of a second cofactor, heme a. This supports the role of propionic acid side chains as part of the proton-loading site.
Subject(s): vibrational Stark effect
carbon monoxide
proton transfer
electrostatic potential
redox chemistry
electron transfer
infrared spectroscopy
Issue Date: 27-Apr-2021
Date Available: 18-May-2021
Language Code: en
DDC Class: 540 Chemie und zugeordnete Wissenschaften
Sponsor/Funder: DFG, 221545957, SFB 1078: Proteinfunktion durch Protonierungsdynamik
Journal Title: Frontiers in Chemistry
Publisher: Frontiers
Volume: 9
Article Number: 669452
Publisher DOI: 10.3389/fchem.2021.669452
EISSN: 2296-2646
TU Affiliation(s): Fak. 2 Mathematik und Naturwissenschaften » Inst. Chemie » FG Modellierung biomolekularer Systeme
Appears in Collections:Technische Universit├Ąt Berlin » Publications

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