Spectroscopic evidence for an all-ferrous 4Fe–4S0 cluster in the superreduced activator of 2-hydroxyglutaryl-CoA dehydratase from Acidaminococcus fermentansReport as inadecuate

Spectroscopic evidence for an all-ferrous 4Fe–4S0 cluster in the superreduced activator of 2-hydroxyglutaryl-CoA dehydratase from Acidaminococcus fermentans - Download this document for free, or read online. Document in PDF available to download.

JBIC Journal of Biological Inorganic Chemistry

, Volume 13, Issue 4, pp 563–574

First Online: 15 February 2008Received: 02 November 2007Accepted: 28 January 2008


The key enzyme of the fermentation of glutamate by Acidaminococcus fermentans, 2-hydroxyglutarylcoenzyme A dehydratase, catalyzes the reversible syn-elimination of water from R-2-hydroxyglutaryl-coenzyme A, resulting in E-glutaconylcoenzyme A. The dehydratase system consists of two oxygen-sensitive protein components, the activator HgdC and the actual dehydratase HgdAB. Previous biochemical and spectroscopic studies revealed that the reduced 4Fe–4S cluster containing activator transfers one electron to the dehydratase driven by ATP hydrolysis, which activates the enzyme. With a tenfold excess of titaniumIII citrate at pH 8.0 the activator can be further reduced, yielding about 50% of a superreduced 4Fe–4S cluster in the all-ferrous state. This is inferred from the appearance of a new Mössbauer spectrum with parameters δ = 0.65 mm-s and ΔEQ = 1.51–2.19 mm-s at 140 K, which are typical of FeIIS4 sites. Parallel-mode electron paramagnetic resonance EPR spectroscopy performed at temperatures between 3 and 20 K showed two sharp signals at g = 16 and 12, indicating an integer-spin system. The X-band EPR spectra and magnetic Mössbauer spectra could be consistently simulated by adopting a total spin St = 4 for the all-ferrous cluster with weak zero-field splitting parameters D = −0.66 cm and E-D = 0.17. The superreduced cluster has apparent spectroscopic similarities with the corresponding 4Fe–4S cluster described for the nitrogenase Fe-protein, but in detail their properties differ. While the all-ferrous Fe-protein is capable of transferring electrons to the MoFe-protein for dinitrogen reduction, a similar physiological role is elusive for the superreduced activator. This finding supports our model that only one-electron transfer steps are involved in dehydratase catalysis. Nevertheless we discuss a common basic mechanism of the two diverse systems, which are so far the only described examples of the all-ferrous 4Fe–4S cluster found in biology.

Keywords2-Hydroxyglutaryl-coenzyme A dehydratase Activator Iron–sulfur protein Superreduced All-ferrous In memory of Prof. Helmut Beinert 1913–2007, who was a pioneer in spectroscopy and biochemistry of iron–sulfur clusters.

Electronic supplementary materialThe online version of this article doi:10.1007-s00775-008-0345-z contains supplementary material, which is available to authorized users.

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Author: Marcus Hans - Wolfgang Buckel - Eckhard Bill

Source: https://link.springer.com/

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