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 language | English |
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Pages (from-to) | 231-246 |
Number of pages | 16 |
Journal | Biochemical Journal |
Volume | 474 |
Issue number | 2 |
DOIs | |
Publication status | Published - 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