Identification of FX in the heliobacterial reaction center as a [4Fe-4S] cluster with an S = 3/2 ground spin state

Mark Heinnickel, Rufat Agalarov, Nina Svensen, Carsten Krebs, John H. Golbeck

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Type I homodimeric reaction centers, particularly the class present in heliobacteria, are not well understood. Even though the primary amino acid sequence of PshA in Heliobacillus mobilis has been shown to contain an FX binding site, a functional Fe-S cluster has not been detected by EPR spectroscopy. Recently, we reported that PshB, which contains FA- and FB-like Fe-S clusters, could be removed from the Heliobacterium modesticaldum reaction center (HbRC), resulting in 15 ms lifetime charge recombination between P798+ and an unidentified electron acceptor [Heinnickel, M., Shen, G., Agalarov, R., and Golbeck, J. H. (2005) Biochemistry 44, 9950-9960]. We report here that when a HbRC core is incubated with sodium dithionite in the presence of light, the 15 ms charge recombination is replaced with a kinetic transient in the sub-microsecond time domain, consistent with the reduction of this electron acceptor. Concomitantly, a broad and intense EPR signal arises around g = 5 along with a minor set of resonances around g = 2 similar to the spectrum of the [4Fe-4S]+ cluster in the Fe protein of Azotobacter vinelandii nitrogenase, which exists in two conformations having S = 3/2 and S = 1/2 ground spin states. The Mössbauer spectrum in the as-isolated HbRC core shows that all of the Fe is present in the form of a [4Fe-4S]2+ cluster. After reduction with sodium dithionite in the presence of light, approximately 65% of the Fe appears in the form of a [4Fe-4S]+ cluster; the remainder is in the [4Fe-4S]2+ state. Analysis of the non-heme iron content of HbRC cores indicates an antenna size of 21.6 ±1.1 BChl g molecules/P798. The evidence indicates that the HbRC contains a [4Fe-4S] cluster identified as Fx that is coordinated between the PshA homodimer; in contrast to FX in other type I reaction centers, this [4Fe-4S] cluster exhibits an S = 3/2 ground spin state.

Original languageEnglish (US)
Pages (from-to)6756-6764
Number of pages9
JournalBiochemistry
Volume45
Issue number21
DOIs
StatePublished - May 30 2006

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Dithionite
Genetic Recombination
Paramagnetic resonance
Electrons
Azotobacter vinelandii
Light
Nitrogenase
Biochemistry
Conformations
Amino Acid Sequence
Spectrum Analysis
Iron
Binding Sites
Spectroscopy
Antennas
Amino Acids
Molecules
Kinetics
Proteins

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

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title = "Identification of FX in the heliobacterial reaction center as a [4Fe-4S] cluster with an S = 3/2 ground spin state",
abstract = "Type I homodimeric reaction centers, particularly the class present in heliobacteria, are not well understood. Even though the primary amino acid sequence of PshA in Heliobacillus mobilis has been shown to contain an FX binding site, a functional Fe-S cluster has not been detected by EPR spectroscopy. Recently, we reported that PshB, which contains FA- and FB-like Fe-S clusters, could be removed from the Heliobacterium modesticaldum reaction center (HbRC), resulting in 15 ms lifetime charge recombination between P798+ and an unidentified electron acceptor [Heinnickel, M., Shen, G., Agalarov, R., and Golbeck, J. H. (2005) Biochemistry 44, 9950-9960]. We report here that when a HbRC core is incubated with sodium dithionite in the presence of light, the 15 ms charge recombination is replaced with a kinetic transient in the sub-microsecond time domain, consistent with the reduction of this electron acceptor. Concomitantly, a broad and intense EPR signal arises around g = 5 along with a minor set of resonances around g = 2 similar to the spectrum of the [4Fe-4S]+ cluster in the Fe protein of Azotobacter vinelandii nitrogenase, which exists in two conformations having S = 3/2 and S = 1/2 ground spin states. The M{\"o}ssbauer spectrum in the as-isolated HbRC core shows that all of the Fe is present in the form of a [4Fe-4S]2+ cluster. After reduction with sodium dithionite in the presence of light, approximately 65{\%} of the Fe appears in the form of a [4Fe-4S]+ cluster; the remainder is in the [4Fe-4S]2+ state. Analysis of the non-heme iron content of HbRC cores indicates an antenna size of 21.6 ±1.1 BChl g molecules/P798. The evidence indicates that the HbRC contains a [4Fe-4S] cluster identified as Fx that is coordinated between the PshA homodimer; in contrast to FX in other type I reaction centers, this [4Fe-4S] cluster exhibits an S = 3/2 ground spin state.",
author = "Mark Heinnickel and Rufat Agalarov and Nina Svensen and Carsten Krebs and Golbeck, {John H.}",
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Identification of FX in the heliobacterial reaction center as a [4Fe-4S] cluster with an S = 3/2 ground spin state. / Heinnickel, Mark; Agalarov, Rufat; Svensen, Nina; Krebs, Carsten; Golbeck, John H.

In: Biochemistry, Vol. 45, No. 21, 30.05.2006, p. 6756-6764.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Identification of FX in the heliobacterial reaction center as a [4Fe-4S] cluster with an S = 3/2 ground spin state

AU - Heinnickel, Mark

AU - Agalarov, Rufat

AU - Svensen, Nina

AU - Krebs, Carsten

AU - Golbeck, John H.

PY - 2006/5/30

Y1 - 2006/5/30

N2 - Type I homodimeric reaction centers, particularly the class present in heliobacteria, are not well understood. Even though the primary amino acid sequence of PshA in Heliobacillus mobilis has been shown to contain an FX binding site, a functional Fe-S cluster has not been detected by EPR spectroscopy. Recently, we reported that PshB, which contains FA- and FB-like Fe-S clusters, could be removed from the Heliobacterium modesticaldum reaction center (HbRC), resulting in 15 ms lifetime charge recombination between P798+ and an unidentified electron acceptor [Heinnickel, M., Shen, G., Agalarov, R., and Golbeck, J. H. (2005) Biochemistry 44, 9950-9960]. We report here that when a HbRC core is incubated with sodium dithionite in the presence of light, the 15 ms charge recombination is replaced with a kinetic transient in the sub-microsecond time domain, consistent with the reduction of this electron acceptor. Concomitantly, a broad and intense EPR signal arises around g = 5 along with a minor set of resonances around g = 2 similar to the spectrum of the [4Fe-4S]+ cluster in the Fe protein of Azotobacter vinelandii nitrogenase, which exists in two conformations having S = 3/2 and S = 1/2 ground spin states. The Mössbauer spectrum in the as-isolated HbRC core shows that all of the Fe is present in the form of a [4Fe-4S]2+ cluster. After reduction with sodium dithionite in the presence of light, approximately 65% of the Fe appears in the form of a [4Fe-4S]+ cluster; the remainder is in the [4Fe-4S]2+ state. Analysis of the non-heme iron content of HbRC cores indicates an antenna size of 21.6 ±1.1 BChl g molecules/P798. The evidence indicates that the HbRC contains a [4Fe-4S] cluster identified as Fx that is coordinated between the PshA homodimer; in contrast to FX in other type I reaction centers, this [4Fe-4S] cluster exhibits an S = 3/2 ground spin state.

AB - Type I homodimeric reaction centers, particularly the class present in heliobacteria, are not well understood. Even though the primary amino acid sequence of PshA in Heliobacillus mobilis has been shown to contain an FX binding site, a functional Fe-S cluster has not been detected by EPR spectroscopy. Recently, we reported that PshB, which contains FA- and FB-like Fe-S clusters, could be removed from the Heliobacterium modesticaldum reaction center (HbRC), resulting in 15 ms lifetime charge recombination between P798+ and an unidentified electron acceptor [Heinnickel, M., Shen, G., Agalarov, R., and Golbeck, J. H. (2005) Biochemistry 44, 9950-9960]. We report here that when a HbRC core is incubated with sodium dithionite in the presence of light, the 15 ms charge recombination is replaced with a kinetic transient in the sub-microsecond time domain, consistent with the reduction of this electron acceptor. Concomitantly, a broad and intense EPR signal arises around g = 5 along with a minor set of resonances around g = 2 similar to the spectrum of the [4Fe-4S]+ cluster in the Fe protein of Azotobacter vinelandii nitrogenase, which exists in two conformations having S = 3/2 and S = 1/2 ground spin states. The Mössbauer spectrum in the as-isolated HbRC core shows that all of the Fe is present in the form of a [4Fe-4S]2+ cluster. After reduction with sodium dithionite in the presence of light, approximately 65% of the Fe appears in the form of a [4Fe-4S]+ cluster; the remainder is in the [4Fe-4S]2+ state. Analysis of the non-heme iron content of HbRC cores indicates an antenna size of 21.6 ±1.1 BChl g molecules/P798. The evidence indicates that the HbRC contains a [4Fe-4S] cluster identified as Fx that is coordinated between the PshA homodimer; in contrast to FX in other type I reaction centers, this [4Fe-4S] cluster exhibits an S = 3/2 ground spin state.

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