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Title: Molecular interaction studies revealed the bifunctional behavior of triheme cytochrome PpcA from Geobacter sulfurreducens toward the redox active analog of humic substances

Humic substances (HS) constitute a significant fraction of natural organic matter in terrestrial and aquatic environments and can act as terminal electron acceptors in anaerobic microbial respiration. Geobacter sulfurreducens has a remarkable respiratory versatility and can utilize the HS analog anthraquinone-2,6-disulfonate (AQDS) as a terminal electron acceptor or its reduced form (AH 2QDS) as an electron donor. Previous studies set the triheme cytochrome PpcA as a key component for HS respiration in G. sulfurreducens, but the process is far from fully understood. In this work, NMR chemical shift perturbation measurements were used to map the interaction region between PpcA and AH 2QDS, and to measure their binding affinity. The results showed that the AH 2QDS binds reversibly to the more solvent exposed edge of PpcA heme IV. The NMR and visible spectroscopies coupled to redox measurements were used to determine the thermodynamic parameters of the PpcA:quinol complex. The higher reduction potential of heme IV (- 127 mV) compared to that of AH 2QDS (- 184 mV) explains why the electron transfer is more favorable in the case of reduction of the cytochrome by the quinol. The clear evidence obtained for the formation of an electron transfer complex between AH 2QDSmore » and PpcA, combined with the fact that the protein also formed a redox complex with AQDS, revealed for the first time the bifunctional behavior of PpcA toward an analog of the HS. In conclusion, such behavior might confer selective advantage to G. sulfurreducens, which can utilize the HS in any redox state available in the environment for its metabolic needs.« less
 [1] ;  [2] ;  [3] ;  [1]
  1. Nova Univ.of Lisbon, Caparica (Portugal). Dept. of Chemistry
  2. James Madison Univ., Harrisonburg, VA (United States). Dept. of Chemistry and Biochemistry
  3. Argonne National Lab. (ANL), Argonne, IL (United States). Biosciences Division
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Published Article
Journal Name:
Biochimica et Biophysica Acta - Bioenergetics
Additional Journal Information:
Journal Volume: 1847; Journal Issue: 10; Journal ID: ISSN 0005-2728
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; Electron transfer; Geobacter; Humics; Multiheme cytochromes; NMR