Bacterial sulfite respiration: structure, function and biogenesis of the Mcc system
Final Report Abstract
Despite its reactivity and toxicity to living cells, sulfite is readily converted by microorganisms, and both assimilatory and dissimilatory sulfite reduction to sulfide are key reactions in the biogeochemical sulfur cycle. In this project, a bacterial respiratory sulfite reduction system, termed Mcc, was investigated, which uses the multihaem cytochrome c sulfite reductase MccA as the terminal enzyme of a dedicated electron transport chain. This respiratory system differs significantly from previously characterised systems using sirohaem-containing sulfite reductases. The following key results were obtained based on the characterisation of the Wolinella succinogenes Mcc system, encoded by the eight-gene mcc cluster. (I) The determination of the high-resolution crystal structure of W. succinogenes MccA revealed a novel arrangement of 24 haem c groups in the MccA sulfite reductase homotrimer and a highly unusual haem c-copper sulfite reduction site. The enzymatic activity of MccA in sulfite and nitrite reduction was characterised. (II) The response regulator MccR was found to be involved in the up-regulation of the Mcc system in response to sulfite. (III) Characterisation of non-polar mutants lacking either the ironsulfur protein MccC or the putative quinol dehydrogenase MccD, a member of the PsrC/NrfD family, indicated that these two proteins contribute to electron transport to MccA. (IV) Cells of W. succinogenes ∆mqnK lacking 8-methylmenaquinone (8-MMK) were found to be severely impaired in sulfite turnover, indicating that 8-MMK plays a role in sulfite respiration. (V) The enzyme MqnK was found to be responsible for the methylation of menaquinone to 8-MMK. MqnK is a novel radical S- adenosylmethionine (SAM) methyltransferase that can be used as a biomarker for MMK-producing microorganisms. (VI) Several members of the phylogenetically widespread MenK/MqnK/MenK2 family were shown to catalyse specific MK methylation reactions at position C-8 (MqnK/MenK) or C-7 (MenK2) to synthesise 8-MMK, 7-MMK and 7,8-dimethylmenaquinone (DMMK). MqnK, MenK and MenK2 from organisms such as W. succinogenes, Adlercreutzia equolifaciens, Collinsella tanakaei, Ferrimonas marina and Syntrophus aciditrophicus were functionally produced in Escherichia coli, allowing extensive quinone/quinol pool engineering of the native quinone/quinol pool. (VII) A model of the radical reaction mechanism of menaquinone methyltransferases was proposed. Overall, the project has largely elucidated Mcc-dependent bacterial sulfite respiration and thoroughly characterised the newly discovered family of MenK/MqnK/MenK2 menaquinone methyltransferases.
Publications
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Microbial Sulfite Respiration. Advances in Microbial Physiology, 45-117.
Simon, Jörg & Kroneck, Peter M.H.
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The octahaem MccA is a haem c–copper sulfite reductase. Nature, 520(7549), 706-709.
Hermann, Bianca; Kern, Melanie; La Pietra, Luigi; Simon, Jörg & Einsle, Oliver
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A class C radical S‐adenosylmethionine methyltransferase synthesizes 8‐methylmenaquinone. Molecular Microbiology, 104(3), 449-462.
Hein, Sascha; Klimmek, Oliver; Polly, Markus; Kern, Melanie & Simon, Jörg
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Two dedicated class C radical S-adenosylmethionine methyltransferases concertedly catalyse the synthesis of 7,8-dimethylmenaquinone. Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1859(4), 300-308.
Hein, Sascha; von Irmer, Jonas; Gallei, Markus; Meusinger, Reinhard & Simon, Jörg
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Significance of MccR, MccC, MccD, MccL and 8-methylmenaquinone in sulfite respiration of Wolinella succinogenes. Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1860(1), 12-21.
Eller, Jakob; Hein, Sascha & Simon, Jörg
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Sequence analysis and specificity of distinct types of menaquinone methyltransferases indicate the widespread potential of methylmenaquinone production in bacteria and archaea. Environmental Microbiology, 23(3), 1407-1421.
Wilkens, Dennis; Meusinger, Reinhard; Hein, Sascha & Simon, Jörg
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The missing enzymatic link in syntrophic methane formation from fatty acids. Proceedings of the National Academy of Sciences, 118(40).
Agne, Michael; Estelmann, Sebastian; Seelmann, Carola S.; Kung, Johannes; Wilkens, Dennis; Koch, Hans-Georg; van der Does, Chris; Albers, Sonja V.; von Ballmoos, Christoph; Simon, Jörg & Boll, Matthias
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Biosynthesis and function of microbial methylmenaquinones. Advances in Microbial Physiology, 1-58.
Wilkens, Dennis & Simon, Jörg
