Fig. 5: Proposed \({\mathbf{SO}}_{\mathbf{4}}^{{\mathbf{2-}}}\) assimilation pathway in a methanogen.
From: Assimilatory sulfate reduction in the marine methanogen Methanothermococcus thermolithotrophicus
a, Sulfite-reductase activity in cell extract from M. thermolithotrophicus grown on different sulfur sources. Data are presented as mean ± s.d. and individual values are shown as grey spheres (n = 3 biologically independent replicates). b, hrCN gel with M. thermolithotrophicus cell extract grown on different sulfur sources (15 µg protein loaded per sample, n = 2 biologically independent duplicates). c, Proposed \({{\rm{SO}}}_{4}^{2-}\) assimilation pathway in M. thermolithotrophicus. Yellow and grey backgrounds highlight the \({{\rm{SO}}}_{4}^{2-}\) reduction and methanogenesis pathways, respectively. Thick arrows indicate high metabolic fluxes. The structures of the enzymes operating the \({{\rm{SO}}}_{4}^{2-}\)-assimilation pathway are shown in surface representation, with ligands as balls and sticks. Enzymes are abbreviated as follows: Fwd/Fmd, formylmethanofuran dehydrogenases; Ftr, tetrahydromethanopterin (H4MPT) formyltransferase; Mch, methenyl-H4MPT cyclohydrolase; Mtd, methylene-H4MPT dehydrogenase; Mer, 5,10-methylene-H4MPT reductase; Mtr, N5-CH3-H4MPT: coenzyme M methyl-transferase; Mcr, methyl-coenzyme M reductase; Adk, adenylate kinase; Frh, F420-reducing [NiFe]-hydrogenase; Eha/Ehb, energy-converting hydrogenase. The putative \({{\rm{SO}}}_{4}^{2-}\) transporters belonging to the class DASS/SUIP are proposed to be WP_018154444/WP_018154062 and the pyrophosphatase WP_018154121.
