Redox- and pH-linked conformational changes in triheme cytochrome PpcA from Geobacter sulfurreducens

Leonor Morgado, Marta Bruix, P. Raj Pokkuluri, Carlos A. Salgueiro, David L. Turner

Research output: Contribution to journalArticle

14 Citations (Scopus)

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 pKa values of the redox-Bohr center, providing insights into the e-/H+ coupling molecular mechanisms driven by PpcA in G. sulfurreducens.

Original languageEnglish
Pages (from-to)231-246
Number of pages16
JournalBiochemical Journal
Volume474
Issue number2
DOIs
Publication statusPublished - 15 Jan 2017

Keywords

  • C-TYPE CYTOCHROMES
  • HEME ELECTRONIC-STRUCTURE
  • AROMATIC RESIDUE F-15
  • ESCHERICHIA-COLI
  • DESULFOVIBRIO-VULGARIS
  • PARAMAGNETIC NMR
  • AXIAL LIGANDS
  • ELECTROCHEMICAL CHARACTERIZATION
  • STRUCTURAL-CHARACTERIZATION
  • MAGNETIC-PROPERTIES

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