Methyl-coenzyme M formation in methanogenic archaea. Involvement of zinc in coenzyme M activation.
Methyl-coenzyme M (2-methylthioethane sulfonate) is the key intermediate of methane formation in methanogenic archaea. It is generated from coenzyme M (2-mercaptoethane sulfonate) in methyl transfer reactions catalyzed by proteins containing zinc. Here, we report that, for methyltransferase MtaA from Methanosarcina barkeri, the zinc is involved in coenzyme M activation. For the experiments an inactive MtaA apoprotein was obtained by heterologous overproduction in Escherichia coli grown in the presence of 2 mM EDTA. The apoprotein was found to react with zinc or cobalt to the fully active holoenzyme. Appoximately 1 mol of transition metal was bound per mol of protein. Upon incubation of the holoenzyme with coenzyme M approximately 1 mol of proton was released per mol of zinc or cobalt. Protons were not released upon incubation of the apoprotein with coenzyme M or of the holoprotein with other thiol compounds or with methyl-coenzyme M. The findings are interpreted as indicating that the role of the transition metal in MtaA is to lower the microscopic pKa of the thiol group of coenzyme M by coordination to the zinc, and thus to increase its nucleophilicity for methyl group attack. The pKZn2+ of MtaA was re-determined and found to be > 15 and not 9.6 as previously reported by us.
Sauer
K
K
Max-Planck-Institut für terrestrische Mikrobiologie and Laboratorium für Mikrobiologie des Fachbereichs Biologie der Philipps-Universität, Marburg, Germany.
Thauer
R K
RK
D004789:Enzyme Activation; D015080:Mesna / Q000031:analogs & derivatives* / Q000378:metabolism; D017021:Methanosarcina barkeri / Q000201:enzymology*; D008780:Methyltransferases / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D011994:Recombinant Proteins; C023349:methyl coenzyme M; D008780:Methyltransferases; D015032:Zinc; D015080:Mesna