Structures of the sMMO proteins. (a) Overall structure of MMOH highlighting one protomer of the α2β2γ2 dimer (PDB ID: 1MTY). The α subunit is shown in light purple, the β subunit is shown in dark purple, and the γ subunit is shown in wheat. (b) Structure of MMOB (green, PDB ID: 4GAM). (c) Structure of the MMOR ferredoxin domain (light pink, PDB ID: 1JQ4) and the MMOR FAD domain (salmon, PDB ID: 1TVC).