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Methanosarcina barkeri
About: Methanosarcina barkeri is a research topic. Over the lifetime, 703 publications have been published within this topic receiving 32151 citations.
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01 May 1987
TL;DR: Cell suspensions of Methanosarcina barkeri convert the carboxyl and methyl group carbons of acetate to carbon dioxide and methane at pH 6 under an atmosphere of 100% CO/sub 2/ and CH/sub 4/.
Abstract: Cell suspensions of Methanosarcina barkeri convert the carboxyl and methyl group carbons of acetate to carbon dioxide and methane at pH 6 under an atmosphere of 100% CO/sub 2/. The rate of loss of radioactivity from (1-/sup 14/C)acetate was over three times greater than that from (2-/sup 14/C)acetate under these conditions. Control experiments with both labeled substrates present showed that the rates were additive. Addition of a high level of 2-bromoethanesulfonate to selectively inhibit methane formation largely inhibited release of /sup 14/C from methyl-labeled acetate but only marginally decreased the rate of loss from (1-/sup 14/C)acetate. Thus, in the absence of the inhibitor loss of /sup 14/C from (1-/sup 14/C)acetate likely reflects an isotopic exchange reaction with CO/sub 2/ superimposed on the overall conversion of acetate to CO/sub 2/ and CH/sub 4/. The exchange reaction was inhibited by uncouplers such as 2,4-dinitrophenol, CCCP, and FCCP. Cells permeabilized by treatment with nonionic detergents or disrupted by passage through a French pressure cell failed to catalyze the exchange reaction. Exchange activity was not restored by addition of ATP or by use of (1-/sup 14/C)acetyl CoA as substrate. No evidence for involvement of carbon monoxide dehydrogenase in the exchange was found in thesemore » experiments when CO/sub 2/ was replaced by CO. However, the soluble extracts retained the ability to convert acetate to methane in the presence of H/sub 2/ and ATP.« less
2 citations
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TL;DR: The authors performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚c and 0˚C with 10-20 mM calcium-, magnesium-, or sodium perchlorate.
Abstract: Observations of trace methane (CH4) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH4 on Earth. Previous studies have shown that methanogenic Archaea can generate CH4 when incubated with perchlorates, highly oxidizing chaotropic salts which have been found across the Martian surface. However, the regulatory mechanisms behind this remain completely unexplored. In this study we performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚C and 0˚C with 10-20 mM calcium-, magnesium-, or sodium perchlorate. Consistent with prior studies, we observed decreased CH4 production and apparent perchlorate reduction, with the latter process proceeding by heretofore essentially unknown mechanisms. Transcriptomic responses of M. barkeri to perchlorates include up-regulation of osmoprotectant transporters and selection against redox-sensitive amino acids. Increased expression of methylamine methanogenesis genes suggest competition for H2 with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H2 from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars' freezing temperatures alone pose greater constraints to CH4 production than perchlorates. These findings increase our understanding of methanogen survival in extreme environments and confers continued consideration of a potential biological contribution to Martian CH4.
1 citations
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TL;DR: It is proposed that MM1309 functions as either a guardian protein that protects the Cys moiety from oxidation or an alternative translation factor for Cys-tRNACys, and a hydrolysis protection assay revealed thatMM1309 binds cysteinyl (Cys)-t RNACys and protects the aminoacyl bond from non-enzymatic hydrolyism.
Abstract: The putative translation elongation factor Mbar_A0971 from the methanogenic archaeon Methanosarcina barkeri was proposed to be the pyrrolysine-specific paralogue of EF-Tu (“EF-Pyl”). In the present study, the crystal structures of its homologue from Methanosarcina mazei (MM1309) were determined in the GMPPNP-bound, GDP-bound, and apo forms, by the single-wavelength anomalous dispersion phasing method. The three MM1309 structures are quite similar (r.m.s.d. < 0.1 A). The three domains, corresponding to domains 1, 2, and 3 of EF-Tu/SelB/aIF2γ, are packed against one another to form a closed architecture. The MM1309 structures resemble those of bacterial/archaeal SelB, bacterial EF-Tu in the GTP-bound form, and archaeal initiation factor aIF2γ, in this order. The GMPPNP and GDP molecules are visible in their co-crystal structures. Isothermal titration calorimetry measurements of MM1309·GTP·Mg2+, MM1309·GDP·Mg2+, and MM1309·GMPPNP·Mg2+ provided dissociation constants of 0.43, 26.2, and 222.2 μM, respectively. Therefore, the affinities of MM1309 for GTP and GDP are similar to those of SelB rather than those of EF-Tu. Furthermore, the switch I and II regions of MM1309 are involved in domain–domain interactions, rather than nucleotide binding. The putative binding pocket for the aminoacyl moiety on MM1309 is too small to accommodate the pyrrolysyl moiety, based on a comparison of the present MM1309 structures with that of the EF-Tu·GMPPNP·aminoacyl-tRNA ternary complex. A hydrolysis protection assay revealed that MM1309 binds cysteinyl (Cys)-tRNACys and protects the aminoacyl bond from non-enzymatic hydrolysis. Therefore, we propose that MM1309 functions as either a guardian protein that protects the Cys moiety from oxidation or an alternative translation factor for Cys-tRNACys.
1 citations
17 Nov 1986
1 citations
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01 Sep 2014
TL;DR: This study focused on the AhbA and AhbB proteins from three sources and distinctly different properties were observed between the homologues including differences in oliogmeric state and haem/product binding capabilities.
Abstract: Haem, a cyclic tetrapyrrole, is found in organisms from all three domains of life. Haem is a prosthetic group for many proteins involved in essential biological processes such as respiration and oxygen transport. Synthesis of haem in eukaryotes and most bacteria follows a well defined route with highly conserved intermediates. However, an alternative haem biosynthesis pathway in Archaea and some bacteria was recently elucidated. This newly discovered pathway utilises sirohaem as a metabolic intermediate rather than a prosthetic group.
The alternative haem biosynthesis pathway is catalysed by the Ahb enzymes A, B, C and D. Initial decarboxylation of sirohaem occurs at the two acetic acid side-chains attached to carbons C12 and C18 to give didecarboxysirohaem, a process catalysed by AhbA and AhbB. Subsequently, the radical SAM enzyme AhbC converts didecarboxysirohaem to Fe-coproporphyrin III. Finally, AhbD catalyses the conversion of Fe-coproporphyrin III into haem in another SAM dependent reaction.
This study focused on the AhbA and AhbB proteins from three sources, Desulfovibrio desulfuricans, Desulfovibrio vulgaris and Methanosarcina barkeri. Purifications of individual recombinantly produced proteins revealed that both AhbA and AhbB are highly unstable. However, low concentrations of D. desulfuricans and D. vulgaris AhbA and AhbB proteins were isolated and were discovered to have decarboxylase activity. Simultaneous overproduction of AhbA and AhbB proteins facilitated the co-purification of stable heteromeric AhbA/B complexes from all three organisms. However, despite their sequence similarities, distinctly different properties were observed between the homologues including differences in oliogmeric state and haem/product binding capabilities. The D. desulfuricans enzyme has been crystallised and its structure has been elucidated in both apo- and product-bound forms. Mutagenesis of the D. desulfuricans complex has provided further information about active site residues and a mechanism of action has been proposed. Finally, novel functional chimeric complexes were produced using the Desulfovibrio proteins.
1 citations