The methanoreductosome: a high-molecular-weight enzyme complex in the methanogenic bacterium strain Gö1 that contains components of the methylreductase system

Abstract

The methanogenic bacterium strain G61 harbors a high-molecular-weight enzyme complex containing methyl coenzyme M methylreductase as revealed by immunoelectron microscopy. This Methanogenic bacteria utilize substrates such as H2-CO2, methanol, monomethylamine, dimethylamine, trimethylamine, and acetate (2,12,18,22) which are converted to a common intermediate, (2-methylthio)ethanesulfonic acid (methyl-CoM) (34). This compound is then reduced to methane and 2-mercaptoethanesulfonic acid in a reaction catalyzed by the enzyme methyl-CoM methylreductase (11,28,30). Studies of the effects of N,N'-dicyclohexylcarbodiimide and 3,5,4',5'-tetrachlorosalicylanilide [3,5-dichloro-N-(4,5-dichlorophenyl)-2-hydroxybenzamide] on methanogenesis, the transmembrane electrical gradient, and the cellular ATP level strongly indicate that ATP is synthesized by a chemiosmotic mechanism and that the methylreductase system is involved in proton translocation (3,4,6,7,22).Various models have been proposed for the generation of an electrochemical transmembrane gradient of protons in methanogenic bacteria (5, 10); one assumes that methylreductase might be membrane associated; one includes the view that a redox carrier might mediate between membrane and (cytoplasmic) methylreductase. Indications have accumulated that the methylreductase system is a multienzyme complex (3,17,23).

Identification of the mcrD gene product and its association with component C of methyl coenzyme M reductase in Methanococcus vannielii

“…We found both MR holoenzyme and gpmcrD almost exclusively in the S-120 supernatant fraction of M. vannielii, indicating that if MR is associated with the cell membrane in M. vannielii, this association does not survive, in a particulate form, cell lysis by freezing and thawing. Complex subcellular structures containing the ot,I, and yV subunit MR have been described (15,21), and a role for gpmcrD in the construction or as a component of these ".1methanoreductosomes" would S-till be consistent with the results reported here.…”

“…It is, however, also possible that most of the gpmcrD-MR complexes dissociate during cell lysis or that the coprecipitation results from nonspecific entrapment of small amounts of gpmcrD within the large amounts of MR present in, and precipitated from, M. vannielii S-120 supernatants by the anti-MR antibodies. In situ localizations (17) and in methanogen strain Gol (15) but that in Methanobacterium thermoautotrophicum the subcellular location of MR is growth r'ate dependent (1,17). We found both MR holoenzyme and gpmcrD almost exclusively in the S-120 supernatant fraction of M. vannielii, indicating that if MR is associated with the cell membrane in M. vannielii, this association does not survive, in a particulate form, cell lysis by freezing and thawing.…”

A hydrogenase-linked gene in Methanobacterium thermoautotrophicum strain delta H encodes a polyferredoxin.

“…The polymeric nature of the polypeptide suggests that it could act as an electron conduit, transferring electrons from one Fe4S4 center of the molecule to the next (Fig. 3), possibly passing electrons through a membrane or into the complex subcellular structures known to house the enzymes responsible for methanogenesis (22,23). An association of hydrogenase activities with membranes has been observed in M. thermoautotrophicum AH (1)(2)(3) (19).…”

Structure and comparative analysis of the genes encoding component C of methyl coenzyme M reductase in the extremely thermophilic archaebacterium Methanothermus fervidus

“…The discovery of the mcrD and mcrC genes was a complete surprise (4)(5)(6), and their conservation, now shown in four very different methanogenic species, argues strongly for important and conserved functions for the encoded gene products. These polypeptides probably play a role(s) in the construction or architecture of the subcellular structures which contain methyl reductase (17,31), but this remains to be determined. Their amino acid sequences are not closely related to those of any known polypeptides; however, the polypeptides encoded by mcrC do have features characteristic of membrane-bound proteins.…”