Abstract
The biological formation of methane (methanogenesis) is a globally important process, which is exploited in biogas technology, but also contributes to global warming through the release of a potent greenhouse gas into the atmosphere. The last and methane-releasing step of methanogenesis is catalysed by the enzyme methyl-coenzyme M reductase (MCR), which carries several exceptional posttranslational amino acid modifications. Among these, a 5-C-(S)-methylarginine is located close to the active site of the enzyme. Here, we show that a unique Radical S-adenosyl-L-methionine (SAM) methyltransferase is required for the methylation of the arginine residue. The gene encoding the methyltransferase is currently annotated as “methanogenesis marker 10” whose function was unknown until now. The deletion of the methyltransferase gene ma4551 in Methanosarcina acetivorans WWM1 leads to the production of an active MCR lacking the C-5-methylation of the respective arginine residue. The growth behaviour of the corresponding M. acetivorans mutant strain and the biophysical characterization of the isolated MCR indicate that the methylated arginine is important for MCR stability under stress conditions.
Highlights
The biological formation of methane represents an important branch of the global biogeochemical carbon cycle
Genotype of the M. acetivorans WWM1 and Mko4551 with the primer pairs used for PCR, their binding sites and the sequenced products
Pac-puromycin transacetylase gene and hpt-8-aza2,6-diaminopurine hypoxanthine phosphoribosyl transferase resistance gene flanked by two Flp recombinase recognition sites (FRT)
Summary
The biological formation of methane represents an important branch of the global biogeochemical carbon cycle. The methanogenic pathways differ for these substrates, they all share the last and methane-releasing step, which is catalysed by methyl-coenzyme M reductase (MCR)[3,4,5]. The reaction most likely proceeds via a methyl radical intermediate and relies on coenzyme F430 exclusively found in MCR4,13. It was speculated that in these cases Radical SAM methyltransferases could be responsible[21], since it is known that these enzymes are able to methylate electrophilic sp2- or sp3-carbon centres in a variety of different substrates[22,23]. The aim of this study was to look for candidate genes potentially encoding Radical SAM methyltransferases in the genomes of methanogenic archaea and to test the hypothesis that the corresponding enzymes are responsible for the C-methylation of either arginine or glutamine
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