title: Probing the effect of ionic strength on the functional robustness of the triheme cytochrome PpcA from Geobacter sulfurreducens: a contribution for optimizing biofuel cell's power density.
abstract: The increase of conductivity of electrolytes favors the current production in microbial fuel cells (MFCs). Adaptation of cell cultures to higher ionic strength is a promising strategy to increase electricity production. The bacterium Geobacter sulfurreducens is considered a leading candidate for MFCs. Therefore, it is important to evaluate the impact of the ionic strength on the functional properties of key periplasmic proteins that warrants electron transfer to cell exterior. The effect of the ionic strength on the functional properties of triheme cytochrome PpcA, the most abundant periplasmic cytochrome in G. sulfurreducens, was investigated by NMR and potentiometric methods. The redox properties of heme IV are the most affected ones. Chemical shift perturbation measurements on the backbone NMR signals, at increasing ionic strength, also showed that the region close to heme IV is the most affected due to the large number of positively charged residues, which confer a highly positive electrostatic surface around this heme. The shielding of these positive charges at high ionic strength explain the observed decrease in the reduction potential of heme IV and shows that PpcA was designed to maintain its functional mechanistic features even at high ionic strength.
authors.affiliation: Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , Campus Caparica, 2829-516 Caparica, Portugal.
authors.forename: Joana M
authors.initials: JM
authors.lastname: Dantas
authors.forename: Leonor
authors.initials: L
authors.lastname: Morgado
authors.forename: Ana C
authors.initials: AC
authors.lastname: Marques
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Salgueiro
mesh_terms: D001674:Bioelectric Energy Sources; D003580:Cytochromes / Q000737:chemistry* / Q000378:metabolism*; D004579:Electron Transport; D045302:Geobacter / Q000201:enzymology*; D006418:Heme; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D011487:Protein Conformation
chemical_list: D003580:Cytochromes; D006418:Heme