Schwefeltransferasen als essentielle Komponenten der dissimilatorischen Schwefeloxidation
Zusammenfassung der Projektergebnisse
In A. vinosum the dsr operon consists of 15 genes (dsrABEFHCMKLJOPNRS) the first two of which (rdsrAB) encode dissimilatory sulfite reductase which is thought to act in the reverse i.e. in the sulfite-producing direction. At the onset of our project, individual functions and interplay of the various Dsr proteins proteins were largely unclear. In the first period of the project, detailed investigations were performed on the sulfur transfer reactions occurring in the cytoplasm of A. vinosum during degradation of sulfur globules with special focus on the Dsr system. These studies firmly established proteins Rhd_2599 (Alvin_2599), TusA (Alvin_2600), DsrE2A (Alvin_2601) and DsrEFH as parts of a sulfur relay system that finally transfers sulfane sulfur to the substrate binding protein DsrC which then serves as the substrate for reverse-acting sulfite reductase DsrAB. Comparative genome analysis, genome wide-transcriptional profiling, differential expression proteomics and metabolomics profiling further allowed us to conclude important roles not only for enzymes we had previously identified by biochemical approaches and reverse genetics but also for a number of further players in the cellular sulfur transfer network. In the second period of the project, we confirmed in more detail that sulfur trafficking is an indispensable part of different sulfur-oxidizing pathways and described TusA homologous proteins as central and common elements in these processes. We contributed to the finding that a DsrC trisulfide, in which a sulfur atom is bridging the two conserved cysteine residues, is released as the product of sulfite reduction catalyzed by DsrAB from a sulfate reducer. We propose that the membrane-bound DsrMKJOP electron-transporting complex catalyzes the formation of the DsrC trisulfide in sulfur oxidizers and that it then serves as the substrate for reverse operating sulfite reductase. We proved that A. vinosum rDsrAB forms a tight complex with the iron-sulfur flavoprotein DsrL. The latter is essential for sulfur oxidation. In vitro, the rDsrABL complex effectively catalyzes NADH- dependent sulfite reduction. DsrL is not confined to sulfur oxidizers but also occurs in a number of (probable) sulfate/sulfur-reducing bacteria. We characterized two DsrL proteins from sulfur oxidizers and one from a thiosulfate and sulfur reducer and in conjuction with detailed phylogenetic analyses it appears that NAD+ as well as NADP+ are suitable in vivo electron acceptors for DsrABL-catalysed sulfur oxidation, while NADPH is required as electron donor for sulfite reduction.
Projektbezogene Publikationen (Auswahl)
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(2015) A protein trisulfide couples dissimilatory sulfate reduction to energy conservation. Science 350, 1541-1545
Santos, A. A., Venceslau, S. S., Grein, F., Leavitt, W. D., Dahl, C., Johanston, D. T., Pereira, I. A.
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(2015) Cytoplasmic sulfur trafficking in sulfur-oxidizing prokaryotes. IUBMB Life 67, 268-274
Dahl, C.
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(2017) Sulfur metabolism in phototrophic bacteria. In Modern topics in the phototrophic prokaryotes. Metabolism, bioenergetics and omics (Hallenbeck, P. C., ed.) Springer, Cham, 27-66
Dahl, C.
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(2019) The functional diversity of the prokaryotic sulfur carrier protein TusA. Adv. Microb. Physiol. 75, 233-277
Tanabe, T. S., Leimkühler, S., & Dahl, C.
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(2020) Bacterial Intracellular Sulphur Globules. In: Jendrossek D. (eds) Bacterial Organelles and Organelle-like Inclusions. Microbiology Monographs, vol 34. Springer, Cham. S. 19-51
Dahl, C.
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(2020) DsrL mediates electron transfer between NADH and rDsrAB in Allochromatium vinosum. Environm. Microbial. 22, 783-795
Löffler, M, Feldhues, J., Venceslau, S. S., Kammler, L. Grein, F., Pereira, I. A.C. & Dahl, C.
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(2020): A biochemical view on the biological sulfur cycle. In: Piet N. L. Lens (Hg.): Environmental Technologies to Treat Sulphur Pollution: Principles and Engineering: IWA Publishing, S. 55–96
Dahl, C.
