Fig. 2. Unusual FDHs. (A) Trimer of VirX1, the first FDH with a preference for iodination, and the first halogenase from a virus showing the large and accessible active site, with a bulky substrate 16 modelled in the active site. (B) View of a subunit of VirX1, again with substrate 16 modelled into the active site, and embedded in a hydrophobic cleft. (C) Key hydrogen bonds between VirX1 and 16 as predicted by structural modelling. (D) Regiospecific iodination of 16 by VirX1.⁴⁷ (E) Model of compound 16 in the active site of VirX1. (F) Decarboxylative bromination of 18 observed for Bmp5.⁴⁸ (G) Iterative dihalogenation in malbrancheamides 21 and 22 biosynthesis, by an unusual zinc-containing FDH.⁴⁶.