The iron guanylylpyridinol (FeGP) cofactor biosynthesis enzymes are encoded in a cluster of at least seven conserved genes (hcgA-G). This family represents the (SAM)-dependent methyltransferase HgcC [1,2], which covalently attaches the methyl group at the 3-position of the pyridinol ring. It is predominantly found as a monomer in solution, composed of a Rossmann-like coenzyme-binding-domain consisting of six parallel and one peripheral antiparallel strand flanked by six alpha-helices and a smaller alpha/beta domain [1].

1: Identification of HcgC as a SAM-Dependent Pyridinol Methyltransferase in [Fe]-Hydrogenase Cofactor Biosynthesis. Fujishiro T, Bai L, Xu T, Xie X, Schick M, Kahnt J, Rother M, Hu X, Ermler U, Shima S; Angew Chem Int Ed Engl. 2016;55:9648-9651. PMID:27391308

2: A Water-Bridged H-Bonding Network Contributes to the Catalysis of the SAM-Dependent C-Methyltransferase HcgC. Bai L, Wagner T, Xu T, Hu X, Ermler U, Shima S; Angew Chem Int Ed Engl. 2017;56:10806-10809. PMID:28682478