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Publication Abstract from PubMed

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.

Redox- and pH-linked conformational changes in triheme cytochrome PpcA from Geobacter sulfurreducens.,Morgado L, Bruix M, Pokkuluri PR, Salgueiro CA, Turner DL Biochem J. 2017 Jan 15;474(2):231-246. doi: 10.1042/BCJ20160932. Epub 2016 Nov, 14. PMID:28062839^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.