Coenzyme M

Methyl-coenzyme M reductase participates in the conversion of CO2 to CH4 and contains 6-coordinate nickel(II) in a highly hydrogenated and highly flexible porphyrin system. This flexibility is believed to allow sufficient distortion of the octahedral ligand field to produce low-spin Ni" (Fig. 27.7) which facilitates the formation of a Ni -CHs intermediate. 

Coleman NV, JC Spain (2003) Epoxyalkane coenzyme M transferase in the ethene and vinyl chloride biodegradation pathways of Mycobacterium strain JS60. J Bacterial 185 5536-5546. 

FIGURE 3.4 Mechanism for carboxylation of acetone involving FAD, NADP, and coenzyme M. 

Allen JR, DD Clark, JG Krumn, SA Ensign (1999) A role for coenzyme M (2-mercaptoethanesulfonic acid) in a bacterial pathway of aliphatic epoxide carboxylation. Proc Natl Acad Sci USA 96 8432-8437. 

Methyl coenzyme M reductase plays a key role in the production of methane in archaea. It catalyzes the reduction of methyl-coenzyme M with coenzyme B to produce methane and the heterodisulfide (Figure 3.35). The enzyme is an a2P2Y2 hexamer, embedded between two molecules of the nickel-porphinoid F jg and the reaction sequence has been delineated (Ermler et al. 1997). The heterodisulfide is reduced to the sulfides HS-CoB and HS-CoM by a reductase that has been characterized in Methanosarcina thermoph-ila, and involves low-potential hemes, [Fe4S4] clusters, and a membrane-bound metha-nophenazine that contains an isoprenoid chain linked by an ether bond to phenazine (Murakami et al. 2001). 

The methyl gronp is snbseqnently transferred to a tetrahydropterin and coenzyme M. The p-snbnnit contains Ni and an Fe/S center, and an NijKFe-dS] arrangement at the active site has been proposed (Gencic and Grahame 2003). 

Ermler U, W Grabarse, S Shima, M Goubeaud, RK Thauer (1997) Crystal structure of methyl-coenzyme M reductase the key enzyme of biological methane formation. Science 278 1457-1462. 

Xanthobacter sp. strain Py2 may be grown with propene or propene oxide. On the basis of amino acid sequences, the monooxygenase that produces the epoxide was related to those that catalyzes the monooxygenation of benzene and toluene (Zhou et al. 1999). The metabolism of the epoxide is initiated by nucleophilic reaction with coenzyme M followed by dehydrogenation (Eigure 7.13a). There are alternative reactions, both of which are dependent on a pyridine nucleotide-disulfide oxidoreductase (Swaving et al. 1996 Nocek et al. 2002) ... 

The degradation of vinyl chloride and ethene has been examined in Mycobacterium sp. strain JS 60 (Coleman and Spain 2003) and in Nocardioides sp. strain JS614 (Mattes et al. 2005). For both substrates, the initially formed epoxides underwent reaction with reduced coenzyme M and, after dehydrogenation and formation of the coenzyme A esters, reductive loss of coenzyme M acetate resulted in the production of 5-acetyl-coenzyme A. The reductive fission is formally analogous to that in the glutathione-mediated reaction. 

Acetate may also be converted into methane by a few methanogens belonging to the genus Meth-anosarcina. The methyl group is initially converted into methyltetrahydromethanopterin (corresponding to methyltetrahydrofolate in the acetate oxidations discussed above) before reduction to methane via methyl-coenzyme M the carbonyl group of acetate is oxidized via bound CO to CO2. 

Boyd JM, A Ellsworth, SA Ensign (2006) Characterization of 2-bromoethanesulfonate as a selective inhibitor of the coenzyme M-dependent pathway and enzymes of bacterial aliphatic epoxide metabolism. J Bacteriol 188 8062-8069. 

Clark DD, JR Allen, SA Ensign (2000) Characterization of five catalytic activities associated with the NADPH 2-ketopropyl-coenzyme M [2-(2-ketopropylthio)ethanesulfonate] oxidoreductase/carboxylase of the Xanthobacter strain Py2 epoxide carboxylase system. Biochemistry 39 1294-1304. 

Krum JG, SA Ensign (2001) Evidence that a linear megaplasmid encodes enzymes of aliphatic alkene and epoxide metabolism and coenzyme M (2-mercaptoethanesulfonate) biosynthesis in Xanthobacter strain Py2. J Bacterial 183 2172-2177. 

Nocek B, SB Jang, MS Jeong, DD Clark, SA Ensign, JW Peters (2002) Structural basis for COj fixation by a novel member of the disulfide oxidoreductase family of enzymes, 2-ketopropyl-coenzyme M oxidore-ductase/carboxylase. Biochemistry Al 12907-12913. 

Danko AS, CA Saski, JP Tomkins, DL Freedman (2006) Involvement of coenzyme M during aerobic degradation of vinyl chloride and ethene by Pseudomonas putida strain AJ and Ochrobactrum sp. stain TD. Appl Environ Microbiol 72 3756-3758. 

Hallam SJ, PR Girguis, CM Preston, PM Richardson, EF DeLong (2003) Identification of methyl coenzyme M reductase A (merA) genes associated with methane-oxidizing archaea. Appl Environ Microbiol 69 5483-5491. 

A handbook on inorganic and coordination chemistry of porphyrins has been published.1765 Factor F430 is the nickel-hydrocorphinoid group of the enzyme methyl coenzyme M reductase.47,48 The mystery of this particular metalloprotein is one of the major reasons for the development of Ni11-porhyrin coordination chemistry, although not the only one. 

Each catalytic center of methyl coenzyme M reductase, (MCR), contains a yellow chromophore factor F430.4 The structure of Ni-F430 determined by the crystallographic analysis and the proposed mechanism of MCR is shown in Scheme 10.47... 

Similar to porphyrin systems, Ni1 complexes with macrocyclic N4 ligands (in particular of the cyclam type) have been considered particularly instructive with respect to the chemistry of the active site of methyl coenzyme M reductase. In most cases, Ni1 species are produced by... 

As part of a study into the activation of metal catalysts in thiol or thiolate-rich environments, X-substituted coenzyme M and thioglycolate derivatives were investigated in a Ni-catalyzed crosscoupling reaction with a zinc co-factor the role of zinc was shown to be in a transmetallation process.571... 

C. Finazzo, J. Harmer, B. Jaun, E.C. Duin, F. Mahlert, R.K. Thauer, S. Van Doorslaer and A. Schweiger, Characterization of the MCRred2 form of methyl-coenzyme M reductase A pulse EPR and ENDOR study, J. Biol. Inorg. Chem., 2003, 8, 586. 

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