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Title: Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens

Periplasmic cytochrome A (PpcA) is a representative of a broad class of multiheme cytochromes functioning as protein “nanowires” for storage and extracellular transfer of multiple electrons in the δ-proteobacterium Geobacter sulfurreducens. PpcA contains three bis-His coordinated hemes held in a spatial arrangement that is highly conserved among the multiheme cytochromes c 3 and c 7 families, carries low potential hemes, and is notable for having one of the lowest number of amino acids utilized to maintain a characteristic protein fold and site-specific heme function. Low temperature X-band electron paramagnetic resonance (EPR) spectroscopy has been used to characterize the electronic configuration of the Fe(III) and the ligation mode for each heme. The three sets of EPR signals are assigned to individual hemes in the three-dimensional crystal structure. The relative energy levels of the Fe(III) 3d orbitals for individual hemes were estimated from the principal g-values. The observed g-tensor anisotropy was used as a probe of electronic structure of each heme, and differences were determined by specifics of axial ligation. To ensure unambiguous assignment of highly anisotropic low-spin (HALS) signal to individual hemes, EPR analyses of iron atom electronic configurations have been supplemented with investigation of porphyrin macrocycles by one-dimensional 1H NMRmore » chemical shift patterns for the methyl substituents. In conclusion, within optimized geometry of hemes in PpcA, the magnetic interactions between hemes were found to be minimal, similar to the c 3 family of tetraheme cytochromes.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [2] ;  [1] ;  [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Division
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Biosciences Division
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Biochemistry
Additional Journal Information:
Journal Volume: 57; Journal Issue: 11; Journal ID: ISSN 0006-2960
Publisher:
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 1H NMR; Geobacter sulfurreducens; Periplasmic cytochrome A; PpcA; X-band EPR; heme coordination; triheme cytochrome
OSTI Identifier:
1427531

Ponomarenko, Nina, Niklas, Jens, Pokkuluri, P. Raj, Poluektov, Oleg, and Tiede, David M.. Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens. United States: N. p., Web. doi:10.1021/acs.biochem.7b00917.
Ponomarenko, Nina, Niklas, Jens, Pokkuluri, P. Raj, Poluektov, Oleg, & Tiede, David M.. Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens. United States. doi:10.1021/acs.biochem.7b00917.
Ponomarenko, Nina, Niklas, Jens, Pokkuluri, P. Raj, Poluektov, Oleg, and Tiede, David M.. 2018. "Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens". United States. doi:10.1021/acs.biochem.7b00917. https://www.osti.gov/servlets/purl/1427531.
@article{osti_1427531,
title = {Electron Paramagnetic Resonance Characterization of the Triheme Cytochrome from Geobacter sulfurreducens},
author = {Ponomarenko, Nina and Niklas, Jens and Pokkuluri, P. Raj and Poluektov, Oleg and Tiede, David M.},
abstractNote = {Periplasmic cytochrome A (PpcA) is a representative of a broad class of multiheme cytochromes functioning as protein “nanowires” for storage and extracellular transfer of multiple electrons in the δ-proteobacterium Geobacter sulfurreducens. PpcA contains three bis-His coordinated hemes held in a spatial arrangement that is highly conserved among the multiheme cytochromes c3 and c7 families, carries low potential hemes, and is notable for having one of the lowest number of amino acids utilized to maintain a characteristic protein fold and site-specific heme function. Low temperature X-band electron paramagnetic resonance (EPR) spectroscopy has been used to characterize the electronic configuration of the Fe(III) and the ligation mode for each heme. The three sets of EPR signals are assigned to individual hemes in the three-dimensional crystal structure. The relative energy levels of the Fe(III) 3d orbitals for individual hemes were estimated from the principal g-values. The observed g-tensor anisotropy was used as a probe of electronic structure of each heme, and differences were determined by specifics of axial ligation. To ensure unambiguous assignment of highly anisotropic low-spin (HALS) signal to individual hemes, EPR analyses of iron atom electronic configurations have been supplemented with investigation of porphyrin macrocycles by one-dimensional 1H NMR chemical shift patterns for the methyl substituents. In conclusion, within optimized geometry of hemes in PpcA, the magnetic interactions between hemes were found to be minimal, similar to the c3 family of tetraheme cytochromes.},
doi = {10.1021/acs.biochem.7b00917},
journal = {Biochemistry},
number = 11,
volume = 57,
place = {United States},
year = {2018},
month = {1}
}