Identification and characterization of a l-tyrosine decarboxylase in Methanocaldococcus jannaschii

Methanofuran is the first coenzyme in the methanogenic pathway used by the archaeon Methanocaldococcus jannaschii, as well as other methanogens, to reduce CO2 to methane. The details of the pathway for the biosynthesis of methanofuran and the responsible genes have yet to be established. A clear structural element in all known methanofurans is tyramine, likely produced by the decarboxylation of l-tyrosine. We show here that the mfnA gene at M. jannaschii locus MJ0050 encodes a thermostable pyridoxal phosphate-dependent l-tyrosine decarboxylase that specifically produces tyramine. Homologs of this gene are widely distributed among euryarchaea but are not specifically related to known bacterial or plant tyrosine decarboxylases.