title: Tetracenomycin F2 cyclase: intramolecular aldol condensation in the biosynthesis of tetracenomycin C in Streptomyces glaucescens.
abstract: Tetracenomycin (Tcm) F2 cyclase, which catalyzes the cyclization of the anthrone Tcm F2 to the naphthacenone Tcm F1 in the biosynthesis of the anthracycline antibiotic Tcm C in Streptomyces glaucescens, has been purified to homogeneity and characterized. The N-terminal sequence of the enzyme establishes that it is encoded by the tcmI gene, whose deduced product has a molecular weight of 12,728. SDS-PAGE analysis gave a single band with a molecular weight of 12,500, whereas gel-filtration chromatography yielded a molecular weight of 37,500, indicating that the Tcm F2 cyclase is a homotrimer in solution. Under pH > or = 8.0, the enzyme catalyzes the cyclization of Tcm F2 to Tcm F1 and has a Km of 121 +/- 18.2 microM and Vmax of 704 +/- 62.3 nmol.min-1.mg-1. In contrast, under pH < or = 6.5, it catalyzes the cyclization of Tcm F2 to 9-decarboxy Tcm F1, a known shunt metabolite of the Tcm C biosynthetic pathway. Tcm F2 cyclase represents the first discrete enzyme for carbon-carbon bond formation via an intramolecular aldol condensation-dehydration mechanism, a key biochemical operation proposed in the early steps of the biosynthesis of all aromatic polyketides.
authors.affiliation: School of Pharmacy, University of Wisconsin, Madison 53706.
authors.forename: B
authors.initials: B
authors.lastname: Shen
authors.forename: C R
authors.initials: CR
authors.lastname: Hutchinson
mesh_terms: D000446:Aldehyde-Lyases / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D001426:Bacterial Proteins; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009279:Naphthacenes / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D017421:Sequence Analysis; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046911:Macromolecular Substances; D009279:Naphthacenes; D010446:Peptide Fragments; C020938:tetracenomycin C; D000446:Aldehyde-Lyases; C083875:tetracenomycin F2 cyclase, Streptomyces