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Structure of HdrA-like subunit from Hyphomicrobium denitrificans
Structural highlights
Publication Abstract from PubMedMany Bacteria and Archaea employ a novel pathway of sulfur oxidation involving an enzyme complex that is related to the heterodisulfide reductase (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 A 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 FADH*/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 EPR 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. Structural and spectroscopic characterization of a HdrA-like subunit from Hyphomicrobium denitrificans.,Ernst C, Kayastha K, Koch T, Venceslau SS, Pereira IAC, Demmer U, Ermler U, Dahl C FEBS J. 2020 Aug 4. doi: 10.1111/febs.15505. PMID:32750208[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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