The ether-cleaving methyltransferase of the strict anaerobe Acetobacterium dehalogenans: analysis of the zinc-binding site.

The anaerobic phenyl methyl ether cleavage in acetogenic bacteria is mediated by multicomponent enzyme systems designated O-demethylases. Depending on the growth substrate, different O-demethylases are induced in Acetobacterium dehalogenans. A vanillate- and a veratrol-O-demethylase of this organism have been described earlier. The methyltransferase I (MT I), a component of this enzyme system, catalyzes the ether cleavage and the transfer of the methyl group to a super-reduced corrinoid bound to a protein. The MT I of the vanillate- and veratrol-O-demethylase (MT I(van) and MT I(ver)) were found to be zinc-containing enzymes. By site-directed mutagenesis, putative zinc ligands were identified, from which the following unique zinc-binding motifs were derived: E-X(14)-E-X(20)-H for MT I(van) and D-X(27)-C-X(39)-C for MT I(ver).