Methylthiol:coenzyme M methyltransferase from Methanosarcina barkeri, an enzyme of methanogenesis from dimethylsulfide and methylmercaptopropionate

Abstract

Dimethylsulfide (DMS) and related methylated thiols play significant roles in the ecosystem. DMS generated in the open ocean has been implicated as the major source of cloud condensation nuclei present in the marine atmosphere, with subsequent global effects on climate (9). A major source of DMS and other methylated thiols is dimethylsulfoniopropionate (DMSP), a compatible solute found in a diverse array of organisms including algae (29), reef corals, diatoms (21), and some plants (44). Concentrations of DMSP (56) and DMS (57) can be in the micromolar range in cyanobacterial mats and salt marsh sediments. DMSP can be directly metabolized by two major routes in the environment (56). It can be directly cleaved to DMS and acrylic acid by bacteria and algae, using DMSP lyase (11,12,35). DMSP can also be sequentially demethylated under aerobic or anaerobic conditions to yield 3-methylmercaptopropionate (MMPA) and 3-mercaptopropionic acid (MPA) (52, 56). Aerobic bacteria producing methanethiol (MSH) from either DMSP or MMPA have been described (52).DMS is also formed from several other processes. Methionine added to anaerobic sediments produces MSH and lesser amounts of DMS (28). DMS and MSH are also made from methoxylated aromatics and sulfide by some homoacetogens (1, 30). Dimethyl sulfoxide, an oxidation product of DMSP, is reduced to DMS by several marine sulfate-reducing bacteria (25). Phototrophic nonsulfur bacteria produce DMS during photosynthesis (38).Given the variety of reactions generating different methylated thiols from abundant environmental precursors, it is not surprising that methanogenic bacteria have been found to produce methane from these compounds. DMS and MSH are active methane precursors in freshwater sediments and sewage sludge (61), as well as in estuarine and alkaline or hypersaline sediments (27). Pure cultures of methanogens that grow on DMS and/or MSH include Methanolobus taylorii 42,43), Methanolobus bombayensis (26), Methanosarcina siciliae (40, 41), Methanosarcina sp. strain MTP4 (19), Methanosarcina acetivorans (41, 49), Methanohalophilus oregonense (36), and Methanohalophilus zhilinae (37). Recently, the three Methanosarcina spp. in this list were found to also grow on MMPA as well as DMS (53,54).Methanogens which can produce methane from methylated thiols typically consume other methylotrophic methanogenic substrates such as methylamines and methanol. Coenzyme M (CoM) is methylated by methylotrophic substrates as an intermediate step to both methane and carbon dioxide formation (17). Proteins mediating the methylation of CoM with trimethylamine (TMA) (15, 16), monomethylamine (MMA) (4, 6), and methanol (47, 55) have been isolated. In each pathway, a distinct corrinoid protein is methylated with the methylotrophic substrate by a substrate-specific polypeptide. The methylated corrinoid protein then serves as the substrate for one of two isoforms of methylcobamide:CoM methyltransferase (MT2) termed MT2-M and MT2-A. MT2-A is used for methylamine metabolism, while MT2-M is used for meth...

Regulation of putative methyl‐sulphide methyltransferases in Methanosarcina acetivorans C2A

“…One could imagine that this is simply a consequence of having the capacity to utilize methysulphides for methanogenesis. Transfer of methyl groups from methylsulphides to CoM is freely reversible (Tallant and Krzycki, 1997;Tallant et al, 2001). Thus, because CH 3-CoM is an intermediate in all known methanogenic pathways and because sulphide is ubiquitous in the anaerobic environments where these methanogens live, low levels of any of the Mts proteins could result in production of DMS, which in turn would trigger the positive feedback loop.…”

“…A methylthiol:CoM methyltransferase enzyme that allows M. barkeri MS to demethylate DMS has been characterized. It consists of a single methyltransferase (MtsA) and a corrinoid protein (MtsB) that catalyses the transfer of a methyl group from DMS to CoM (Tallant and Krzycki, 1997;Tallant et al, 2001). Although homologues for the MtsA/B system are present in M. barkeri Fusaro and Methanosarcina mazei Gö1, they are absent in M. acetivorans C2A.…”

The MtsA Subunit of the Methylthiol:Coenzyme M Methyltransferase of Methanosarcina barkeri Catalyses Both Half-reactions of Corrinoid-dependent Dimethylsulfide: Coenzyme M Methyl Transfer

“…In contrast, Methanosarcina barkeri was long thought not to utilize methylthiols as methane precursors (18). However, it was found that this species differentially expressed enzymes to produce methane from DMS or MMPA depending upon its growth substrate (19,20). During growth on acetate, but not methanol, cells of M. barkeri MS will convert either methylated thiol to methane.…”

“…A single enzyme was identified and purified from acetate grown cells of M. barkeri (21) that carries out CoM methylation with either DMS or MMPA (19). This methylthiol:CoM methyltransferase is a 480-kDa corrinoid protein that is comprised of equimolar amounts of 40-and 30-kDa subunits termed, respectively, MtsA and MtsB.…”

Metagenomics analysis of methane metabolisms in manure fertilized paddy soil

“…Our results show that PIG specific KO were found in various pathways towards production of methane. (Harms, 1996), and trimethylamine-corrinoid protein Co-methyltransferase (mttB) and dimethylamine/trimethylamine dehydrogenase (dmd-tmd) catalyze the synthesize of Methyl-CoM, a precursor of methane (Yang et al, 1995;Tallant and Krzycki, 1997;Jones et al, 2002;Pritchett and Metcalf, 2005 …”