The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties
Electrogenic bacteria, such as Geobacter, can couple the oxidation of carbon sources to the reduction of extracellular electron acceptors; such acceptors include toxic and radioactive metals, as well as electrode surfaces, making Geobacter a suitable candidate for applied use in bioremediation and b...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Wiley
2018-12-01
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| Series: | FEBS Open Bio |
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| Online Access: | https://doi.org/10.1002/2211-5463.12505 |
| _version_ | 1797870985113763840 |
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| author | Marisa R. Ferreira Joana M. Dantas Carlos A. Salgueiro |
| author_facet | Marisa R. Ferreira Joana M. Dantas Carlos A. Salgueiro |
| author_sort | Marisa R. Ferreira |
| collection | DOAJ |
| description | Electrogenic bacteria, such as Geobacter, can couple the oxidation of carbon sources to the reduction of extracellular electron acceptors; such acceptors include toxic and radioactive metals, as well as electrode surfaces, making Geobacter a suitable candidate for applied use in bioremediation and bioenergy generation. Geobacter metallireducens is more promising in this regard than the better studied Geobacter sulfurreducens, as it has more efficient Fe (III) reduction rates and can convert nitrate to ammonia. The operon responsible for nitrate reductase activity in G. metallireducens includes the gene encoding the cytochrome PpcF, which was proposed to exchange electrons with nitrate reductase. In the present work, we perform a biochemical and a biophysical characterization of PpcF. Spectroscopic techniques, including circular dichroism (CD), UV‐visible, and nuclear magnetic resonance (NMR), revealed that the cytochrome is very stable (Tm > 85 °C), contains three low‐spin hemes, and is diamagnetic (S = 0) and paramagnetic (S = 1/2) in the reduced and oxidized states, respectively. The NMR chemical shifts of the heme substituents were assigned and used to determine the heme core architecture of PpcF. Compared to the PpcA‐family from G. sulfurreducens, the spatial disposition of the hemes is conserved, but the functional properties are clearly distinct. In fact, potentiometric titrations monitored by UV‐visible absorption reveal that the reduction potential values of PpcF are significantly less negative (−56 and −64 mV, versus the normal hydrogen electrode at pH 7.0 and 8.0, respectively). NMR redox titrations showed that the order of oxidation of the hemes is IV‐I‐III, a feature not observed for G. sulfurreducens. The different redox properties displayed by PpcF, including the small redox‐Bohr effect and low reduction potential value of heme IV, were structurally rationalized and attributed to the lower number of positively charged residues located in the vicinity of heme IV. Overall, the redox features of PpcF suggest that biotechnological applications of G. metallireducens may require less negative working functional redox windows than those using by G. sulfurreducens. |
| first_indexed | 2024-04-10T00:37:05Z |
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| institution | Directory Open Access Journal |
| issn | 2211-5463 |
| language | English |
| last_indexed | 2024-04-10T00:37:05Z |
| publishDate | 2018-12-01 |
| publisher | Wiley |
| record_format | Article |
| series | FEBS Open Bio |
| spelling | doaj.art-122b6644899b41418984e251f2efa4d22023-03-14T13:06:01ZengWileyFEBS Open Bio2211-54632018-12-018121897191010.1002/2211-5463.12505The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox propertiesMarisa R. Ferreira0Joana M. Dantas1Carlos A. Salgueiro2UCIBIO‐Requimte Departamento de Química Faculdade de Ciências e Tecnologia Universidade NOVA de Lisboa Caparica PortugalUCIBIO‐Requimte Departamento de Química Faculdade de Ciências e Tecnologia Universidade NOVA de Lisboa Caparica PortugalUCIBIO‐Requimte Departamento de Química Faculdade de Ciências e Tecnologia Universidade NOVA de Lisboa Caparica PortugalElectrogenic bacteria, such as Geobacter, can couple the oxidation of carbon sources to the reduction of extracellular electron acceptors; such acceptors include toxic and radioactive metals, as well as electrode surfaces, making Geobacter a suitable candidate for applied use in bioremediation and bioenergy generation. Geobacter metallireducens is more promising in this regard than the better studied Geobacter sulfurreducens, as it has more efficient Fe (III) reduction rates and can convert nitrate to ammonia. The operon responsible for nitrate reductase activity in G. metallireducens includes the gene encoding the cytochrome PpcF, which was proposed to exchange electrons with nitrate reductase. In the present work, we perform a biochemical and a biophysical characterization of PpcF. Spectroscopic techniques, including circular dichroism (CD), UV‐visible, and nuclear magnetic resonance (NMR), revealed that the cytochrome is very stable (Tm > 85 °C), contains three low‐spin hemes, and is diamagnetic (S = 0) and paramagnetic (S = 1/2) in the reduced and oxidized states, respectively. The NMR chemical shifts of the heme substituents were assigned and used to determine the heme core architecture of PpcF. Compared to the PpcA‐family from G. sulfurreducens, the spatial disposition of the hemes is conserved, but the functional properties are clearly distinct. In fact, potentiometric titrations monitored by UV‐visible absorption reveal that the reduction potential values of PpcF are significantly less negative (−56 and −64 mV, versus the normal hydrogen electrode at pH 7.0 and 8.0, respectively). NMR redox titrations showed that the order of oxidation of the hemes is IV‐I‐III, a feature not observed for G. sulfurreducens. The different redox properties displayed by PpcF, including the small redox‐Bohr effect and low reduction potential value of heme IV, were structurally rationalized and attributed to the lower number of positively charged residues located in the vicinity of heme IV. Overall, the redox features of PpcF suggest that biotechnological applications of G. metallireducens may require less negative working functional redox windows than those using by G. sulfurreducens.https://doi.org/10.1002/2211-5463.12505electron transferGeobacter metallireducensmultiheme c‐type cytochrome PpcFNMR |
| spellingShingle | Marisa R. Ferreira Joana M. Dantas Carlos A. Salgueiro The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties FEBS Open Bio electron transfer Geobacter metallireducens multiheme c‐type cytochrome PpcF NMR |
| title | The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties |
| title_full | The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties |
| title_fullStr | The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties |
| title_full_unstemmed | The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties |
| title_short | The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties |
| title_sort | triheme cytochrome ppcf from geobacter metallireducens exhibits distinct redox properties |
| topic | electron transfer Geobacter metallireducens multiheme c‐type cytochrome PpcF NMR |
| url | https://doi.org/10.1002/2211-5463.12505 |
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