title: Redox- and pH-linked conformational changes in triheme cytochrome PpcA from Geobacter sulfurreducens.
abstract: 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 pKavalues of the redox-Bohr center, providing insights into the e-/H+coupling molecular mechanisms driven by PpcA in G. sulfurreducens.
authors.affiliation: UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Leonor
authors.initials: L
authors.lastname: Morgado
authors.affiliation: Departamento de Química Física Biológica, Instituto de Química-Física 'Rocasolano', CSIC, Serrano 119, 28006 Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Bruix
authors.affiliation: Biosciences Division, Argonne National Laboratory, Lemont, IL 60439, U.S.A.
authors.forename: P Raj
authors.initials: PR
authors.lastname: Pokkuluri
authors.affiliation: UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal csalgueiro@fct.unl.pt turner@itqb.unl.pt.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Salgueiro
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade NOVA de Lisboa, Av. da República, 2780-157 Oeiras, Portugal csalgueiro@fct.unl.pt turner@itqb.unl.pt.
authors.forename: David L
authors.initials: DL
authors.lastname: Turner
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D045304:Cytochromes c / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004583:Electrons; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D045302:Geobacter / Q000737:chemistry* / Q000201:enzymology; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D054730:Protein Interaction Domains and Motifs; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D011522:Protons; D011994:Recombinant Proteins; D006418:Heme; D045304:Cytochromes c
keywords: Geobacter; NMR; electron transfer; multiheme cytochrome; solution structure