The URO-D_CIMS_like protein superfamily includes bacterial and eukaryotic uroporphyrinogen decarboxylases (URO-D), coenzyme M methyltransferases and other putative bacterial methyltransferases, as well as cobalamine (B12) independent methionine synthases. Despite their sequence similarities, members of this family have clearly different functions. Uroporphyrinogen decarboxylase (URO-D) decarboxylates the four acetate side chains of uroporphyrinogen III (uro-III) to create coproporphyrinogen III, an important branching point of the tetrapyrrole biosynthetic pathway. The methyltransferases represented here are important for ability of methanogenic organisms to use other compounds than carbon dioxide for reduction to methane, and methionine synthases transfer a methyl group from a folate cofactor to L-homocysteine in a reaction requiring zinc.
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