The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)1897-1910
Number of pages14
JournalFEBS Open Bio
Volume8
Issue number12
DOIs
Publication statusPublished - 1 Dec 2018

Fingerprint

Cytochromes
Heme
Oxidation-Reduction
Geobacter
Nitrate Reductase
Magnetic Resonance Spectroscopy
Nuclear magnetic resonance
Titration
Electrodes
Electrons
Oxidation
Environmental Biodegradation
Gene encoding
Bioremediation
Poisons
Chemical shift
Operon
Circular Dichroism
Ammonia
Nitrates

Keywords

  • electron transfer
  • Geobacter metallireducens
  • multiheme c-type cytochrome PpcF
  • NMR

Cite this

@article{7ec2ad075e214a00a04786ecca00992e,
title = "The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties",
abstract = "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.",
keywords = "electron transfer, Geobacter metallireducens, multiheme c-type cytochrome PpcF, NMR",
author = "Ferreira, {Marisa R.} and Dantas, {Joana M.} and Salgueiro, {Carlos A.}",
note = "info:eu-repo/grantAgreement/FCT/SFRH/SFRH{\%}2FBD{\%}2F89701{\%}2F2012/PT# info:eu-repo/grantAgreement/FCT/5876/147258/PT# This work was supported by Fundacao para a Ciencia e a Tecnologia (FCT-MCTES) through the following grants: SFRH/BD/132969/2017 (to MRF); SFRH/BD/89701/2012 (to JMD); PTDC/BBB-BQB/3554/2014 (to CAS). This work was also supported by Unidade de Ciencias Biomoleculares Aplicadas-UCIBIO which is financed by national funds from FCT/MEC (UID/Multi/04378/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007728). The NMR spectrometers are part of the National NMR Network (PTNMR) and are supported by Infrastructure Project No 022161 (co-financed by FEDER through COMPETE 2020, POCI, and PORL and FCT through PIDDAC).",
year = "2018",
month = "12",
day = "1",
doi = "10.1002/2211-5463.12505",
language = "English",
volume = "8",
pages = "1897--1910",
journal = "FEBS Open Bio",
issn = "2211-5463",
publisher = "WILEY-BLACKWELL",
number = "12",

}

TY - JOUR

T1 - The triheme cytochrome PpcF from Geobacter metallireducens exhibits distinct redox properties

AU - Ferreira, Marisa R.

AU - Dantas, Joana M.

AU - Salgueiro, Carlos A.

N1 - info:eu-repo/grantAgreement/FCT/SFRH/SFRH%2FBD%2F89701%2F2012/PT# info:eu-repo/grantAgreement/FCT/5876/147258/PT# This work was supported by Fundacao para a Ciencia e a Tecnologia (FCT-MCTES) through the following grants: SFRH/BD/132969/2017 (to MRF); SFRH/BD/89701/2012 (to JMD); PTDC/BBB-BQB/3554/2014 (to CAS). This work was also supported by Unidade de Ciencias Biomoleculares Aplicadas-UCIBIO which is financed by national funds from FCT/MEC (UID/Multi/04378/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007728). The NMR spectrometers are part of the National NMR Network (PTNMR) and are supported by Infrastructure Project No 022161 (co-financed by FEDER through COMPETE 2020, POCI, and PORL and FCT through PIDDAC).

PY - 2018/12/1

Y1 - 2018/12/1

N2 - 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.

AB - 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.

KW - electron transfer

KW - Geobacter metallireducens

KW - multiheme c-type cytochrome PpcF

KW - NMR

UR - http://www.scopus.com/inward/record.url?scp=85056208076&partnerID=8YFLogxK

U2 - 10.1002/2211-5463.12505

DO - 10.1002/2211-5463.12505

M3 - Article

VL - 8

SP - 1897

EP - 1910

JO - FEBS Open Bio

JF - FEBS Open Bio

SN - 2211-5463

IS - 12

ER -