Structural and spectroscopic characterization of a HdrA-like subunit from Hyphomicrobium denitrificans.
FEBS J
; 288(5): 1664-1678, 2021 03.
Article
en En
| MEDLINE
| ID: mdl-32750208
ABSTRACT
Many bacteria and archaea employ a novel pathway of sulfur oxidation involving an enzyme complex that is related to the heterodisulfide reductase (Hdr or HdrABC) of methanogens. As a first step in the biochemical characterization of Hdr-like proteins from sulfur oxidizers (sHdr), we structurally analyzed the recombinant sHdrA protein from the Alphaproteobacterium Hyphomicrobium denitrificans at 1.4 Å resolution. The sHdrA core structure is similar to that of methanogenic HdrA (mHdrA) which binds the electron-bifurcating flavin adenine dinucleotide (FAD), the heart of the HdrABC-[NiFe]-hydrogenase catalyzed reaction. Each sHdrA homodimer carries two FADs and two [4Fe-4S] clusters being linked by electron conductivity. Redox titrations monitored by electron paramagnetic resonance and visible spectroscopy revealed a redox potential between -203 and -188 mV for the [4Fe-4S] center. The potentials for the FADHâ¢/FADH- and FAD/FADH⢠pairs reside between -174 and -156 mV and between -81 and -19 mV, respectively. The resulting stable semiquinone FADH⢠species already detectable in the visible and electron paramagnetic resonance spectra of the as-isolated state of sHdrA is incompatible with basic principles of flavin-based electron bifurcation such that the sHdr complex does not apply this new mode of energy coupling. The inverted one-electron FAD redox potentials of sHdr and mHdr are clearly reflected in the different FAD-polypeptide interactions. According to this finding and the assumption that the sHdr complex forms an asymmetric HdrAA'B1C1B2C2 hexamer, we tentatively propose a mechanism that links protein-bound sulfane oxidation to sulfite on HdrB1 with NAD+ reduction via lipoamide disulfide reduction on HdrB2. The FAD of HdrA thereby serves as an electron storage unit. DATABASE Structural data are available in PDB database under the accession number 6TJR.
Palabras clave
Texto completo:
1
Base de datos:
MEDLINE
Asunto principal:
Oxidorreductasas
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Proteínas Bacterianas
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Hyphomicrobium
/
Flavina-Adenina Dinucleótido
/
NAD
Tipo de estudio:
Prognostic_studies
Idioma:
En
Revista:
FEBS J
Asunto de la revista:
BIOQUIMICA
Año:
2021
Tipo del documento:
Article
País de afiliación:
Alemania