N-terminal aromatase/cyclase domain of the multifunctional protein tetracenomycin (TcmN) and related domains
This family includes the N-terminal aromatase/cyclase (ARO/CYC) domain of Streptomyces glaucescens TcmN, and related domains. It 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. ARO/CYC domains participate in the diversification of aromatic polyketides by promoting polyketide cyclization. They occur in two architectural forms, monodomain and didomain. Monodomain aromatase/cyclases have a single ARO/CYC domain. For some, such as TcmN, this single domain is linked to a second domain of unrelated function. TcmN is a multifunctional cyclase-dehydratase-O-methyl transferase. Its N-terminal ARO/CYC domain participates in polyketide binding and catalysis; it promotes C9-C14 first-ring (and C7-C16 second-ring) cyclizations. Its C-terminal domain has O-methyltransferase activity. Didomain aromatase/cyclases contain two ARO/CYC domains, and they biosynthesize C7-C12 first ring cyclized polyketides. These latter domains belong to a different subfamily in the SRPBCC superfamily.