Assay of methylotrophic methyltransferases from methanogenic archaea.

The family Methanosarcinaceae has an expanded repertoire of growth substrates relative to most other methanogenic archaea. Various methylamines, methylated thiols, and methanol can serve as precursors to both methane and carbon dioxide. These compounds are mobilized into metabolism by methyltransferases that use the growth substrate to methylate a cognate corrinoid protein, which in turn is used as a substrate by a second methyltransferase to methylate Coenzyme M (CoM), forming methyl-SCoM, the precursor to both methane and carbon dioxide. Orthologs of the methyltransferases, as well as the small corrinoid proteins, are found in many archaeal and bacterial genomes. Some of these are homologs of the methylamine methyltransferases predicted to require pyrrolysine, an atypical genetically encoded amino acid, for synthesis. As a resource for the study of these sizable families of proteins, we describe here techniques our laboratories have used for the study of methanogen corrinoid-dependent methyltransferases, focusing especially on isolation and assay techniques useful for various activities of components of the methylamine- and methylthiol-dependent CoM methyltransferase systems.