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Bioinorganic Chemistry and Applications
Volume 2012, Article ID 298739, 9 pages
http://dx.doi.org/10.1155/2012/298739
Research Article

Fine Tuning of Redox Networks on Multiheme Cytochromes from Geobacter sulfurreducens Drives Physiological Electron/Proton Energy Transduction

1Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal
2Departamento de Espectroscopía y Estructura Molecular, Instituto de Química-Física “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain
3Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
4New England Biolabs, 240 County Road, Ipswich, MA 01938, USA

Received 13 April 2012; Accepted 11 June 2012

Academic Editor: Takao Yagi

Copyright © 2012 Leonor Morgado et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The bacterium Geobacter sulfurreducens (Gs) can grow in the presence of extracellular terminal acceptors, a property that is currently explored to harvest electricity from aquatic sediments and waste organic matter into microbial fuel cells. A family composed of five triheme cytochromes (PpcA-E) was identified in Gs. These cytochromes play a crucial role by bridging the electron transfer from oxidation of cytoplasmic donors to the cell exterior and assisting the reduction of extracellular terminal acceptors. The detailed thermodynamic characterization of such proteins showed that PpcA and PpcD have an important redox-Bohr effect that might implicate these proteins in the e/H+ coupling mechanisms to sustain cellular growth. The physiological relevance of the redox-Bohr effect in these proteins was studied by determining the fractional contribution of each individual redox-microstate at different pH values. For both proteins, oxidation progresses from a particular protonated microstate to a particular deprotonated one, over specific pH ranges. The preferred e/H+ transfer pathway established by the selected microstates indicates that both proteins are functionally designed to couple e/H+ transfer at the physiological pH range for cellular growth.