Graduate Students Mini Symposium I 2022

Graduate Students Mini-Symposium


16:00 h Kangli Guo, RG Liesack
"Stress response and stress relief mechanisms of Methylocystis sp. strain SC2"

The only known biological sink for the greenhouse gas methane in soils is oxidation by methanotrophic bacteria, among those by alphaproteobacterial Methylocystis spp. These methanotrophs can utilize methane as sole source of carbon and energy. However, their methane-oxidizing activity is sensitive to environmental stressors such as NaCl-induced salt stress. In particular, ammonium can act as a methanotroph-specific stressor due to its pMMO-based oxidation to toxic hydroxylamine. Here I will present cellular stress response and stress relief mechanisms of Methylocystis sp. strain SC2, unraveled by a combination of growth experiments, global proteomics, targeted metabolomics, and NOx measurements.

16:30 h Evgenij Protasov, RG Brune
"Methanogenesis in Methanomassiliicoccales – a case of evolutionary tinkering ?"

Methanomassiliicoccales (phylum “Thermoplasmatota”) is a lineage of obligately methylotrophic methanogens that presumably arose from non-methanogenic ancestors. It has only a single cultured representative. Using metagenome assembled genomes (MAGs) from termite guts and other environments, we conducted a comprehensive comparative analysis of this peculiar group. Although all lineages in the order utilize the same truncated version of the methanogenic pathway, they differ in their potential substrate range, presumably reflecting adaptations to particular habitats. Most importantly, phylogenetic analysis of the core enzymes of methanogenesis revealed a complex evolutionary history of the pathway that apparently involved horizontal gene transfers in the ancestral Methanomassiliicoccales.

17:00 h Manuel Gehl, RG Shima
"Extension of the substrate spectrum of the [Fe]-hydrogenase Hmd"

In the hydrogenotrophic methanogenesis, methenyl-tetrahydromethanopterin (methenyl-H4MPT+) is sequentially reduced to methylene-H4MPT and methyl-H4MPT. The H2-forming methylene-H4MPT dehydrogenase ([Fe]-hydrogenase or Hmd) catalyzes the reduction of methenyl-H4MPT to methylene-H4MPT using H2 as the electron donor, whereas the reduction of methylene-H4MPT to methyl-H4MPT is catalyzed by a different enzyme, the F420-dependent methylene-H4MPT reductase (Mer) using reduced F420 (F420H2) as electron donor. Despite the very similar structure of the three H4MPT derivatives and the fact that Hmd can bind methylene-H4MPT and generates H2 by oxidation of the methylene-group, Hmd is not capable of reducing methylene-H4MPT. The question arises what the structural features are that let Hmd specifically reduce only methenyl-H4MPT+. To this end, we aim to compare the active site structures of Hmd and Mer. We heterologously expressed Mer originating from Methanocaldococcus jannaschii in E. coli. Subsequently, we purified and crystalized highly active Mer in presence of the substrates. So far, we obtained the crystal structure of the Mer apoenzyme and Mer in complex with F420. From this structure we could derive informations about the catalytic mechanism of Mer and could target interesting amino acid residues for future mutation experiments.

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