The Na+-translocating methyltransferase complex from methanogenic archaea

Methanogenic archaea are dependent on sodium ions for methane formation. A sodium ion-dependent step has been shown to be methyl transfer from N-5-methyltetrahydromethanopterin to coenzyme M. This exergonic reaction (DeltaG degrees ' = -30 kJ/mol) is catalyzed by a Na+-translocating membrane-associated multienzyme complex composed of eight different subunits, MtrA-H. Subunit MtrA harbors a cob(I)amide prosthetic group which is methylated and demethylated in the catalytic cycle, demethylation being sodium ion-dependent. Based on the finding that in the cob(Il)amide oxidation state the corrinoid is bound in a base-off/His-on configuration it is proposed that methyl transfer from MtrA to coenzyme M is associated with a conformational change of the protein and that this change drives the electrogenic translocation of the sodium ions. (C) 2001 Elsevier Science B.V. All rights reserved.