C-terminal catalytic domain of plant choline monooxygenase (CMO) and related aromatic ring hydroxylating dioxygenases
C-terminal catalytic domain of plant choline monooxygenase and related Rieske-type non-heme iron aromatic ring-hydroxylating oxygenases (RHOs, also known as aromatic ring hydroxylating dioxygenases). RHOs utilize non-heme Fe(II) to catalyze the addition of hydroxyl groups to the aromatic ring, an initial step in the oxidative degradation of aromatic compounds. RHOs are composed of either two or three protein components, and are comprised of an electron transport chain (ETC) and an oxygenase. The ETC transfers reducing equivalents from the electron donor to the oxygenase component, which in turn transfers electrons to the oxygen molecules. The oxygenase components are oligomers, either (alpha)n or (alpha)n(beta)n. The alpha subunits are the catalytic components and have an N-terminal domain, which binds a Rieske-like 2Fe-2S cluster, and a C-terminal domain which binds the non-heme Fe(II). The Fe(II) is co-ordinated by conserved His and Asp residues. Plant choline monooxygenase catalyzes the first step in a two-step oxidation of choline to the osmoprotectant glycine betaine. This subfamily belongs to the SRPBCC (START/RHO_alpha_C/PITP/Bet_v1/CoxG/CalC) domain superfamily of proteins that bind hydrophobic ligands. SRPBCC domains have a deep hydrophobic ligand-binding pocket.