The periplasmic triheme cytochrome PpcA from Geobacter sulfurreducens is highly abundant; it is the likely reservoir of electrons to the outer surface to assist the reduction of extracellular terminal acceptors; these include insoluble metal oxides in natural habitats and electrode surfaces from which electricity can be harvested. A detailed thermodynamic characterization of PpcA showed that it has an important redox-Bohr effect that might implicate the protein in e−/H+ coupling mechanisms to sustain cellular growth. This functional mechanism requires control of both the redox state and the protonation state. In the present study, isotope-labeled PpcA was produced and the three-dimensional structure of PpcA in the oxidized form was determined by NMR. This is the first solution structure of a G. sulfurreducens cytochrome in the oxidized state. The comparison of oxidized and reduced structures revealed that the heme I axial ligand geometry changed and there were other significant changes in the segments near heme I. The pH-linked conformational rearrangements observed in the vicinity of the redox-Bohr center, both in the oxidized and reduced structures, constitute the structural basis for the differences observed in the pKa values of the redox-Bohr center, providing insights into the e−/H+ coupling molecular mechanisms driven by PpcA in G. sulfurreducens.
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January 2017
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Research Article|
January 06 2017
Redox- and pH-linked conformational changes in triheme cytochrome PpcA from Geobacter sulfurreducens
Leonor Morgado;
Leonor Morgado
*
1UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
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Marta Bruix;
Marta Bruix
2Departamento de Química Física Biológica, Instituto de Química-Física ‘Rocasolano’, CSIC, Serrano 119, 28006 Madrid, Spain
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P. Raj Pokkuluri;
P. Raj Pokkuluri
3Biosciences Division, Argonne National Laboratory, Lemont, IL 60439, U.S.A.
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Carlos A. Salgueiro;
1UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
Correspondence: Carlos A. Salgueiro ([email protected]) or David L. Turner ([email protected])
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David L. Turner
4Instituto de Tecnologia Química e Biológica, Universidade NOVA de Lisboa, Av. da República, 2780-157 Oeiras, Portugal
Correspondence: Carlos A. Salgueiro ([email protected]) or David L. Turner ([email protected])
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Publisher: Portland Press Ltd
Received:
October 12 2016
Revision Received:
November 10 2016
Accepted:
November 14 2016
Accepted Manuscript online:
November 14 2016
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 2017 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society
2017
Biochem J (2017) 474 (2): 231–246.
Article history
Received:
October 12 2016
Revision Received:
November 10 2016
Accepted:
November 14 2016
Accepted Manuscript online:
November 14 2016
Citation
Leonor Morgado, Marta Bruix, P. Raj Pokkuluri, Carlos A. Salgueiro, David L. Turner; Redox- and pH-linked conformational changes in triheme cytochrome PpcA from Geobacter sulfurreducens. Biochem J 15 January 2017; 474 (2): 231–246. doi: https://doi.org/10.1042/BCJ20160932
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