title: A novel 4-methylideneimidazole-5-one-containing tyrosine aminomutase in enediyne antitumor antibiotic C-1027 biosynthesis.
abstract: The C-1027 enediyne antibiotic contains an unusual 3-chloro-4,5-dihydroxy-beta-phenylalanine moiety that is thought to be derived from tyrosine by an aminomutase reaction. However, none of the genes identified within the C-1027 gene cluster encode proteins with strong homology to known aminomutases. The sgcC4 gene encodes a protein with strong homology to dehydroalanine-dependent histidine/phenylalanine ammonia lyases. The sgcC4 gene was expressed in E. coli, and overproduced SgcC4 was purified as a His6-tagged fusion protein. Biochemical characterization of the purified SgcC4 establishes that SgcC4 is an aminomutase that catalyzes the conversion of l-tyrosine to (S)-beta-tyrosine and employs 4-methylideneimidazole-5-one (MIO) at its active site. The latter was supported by borohydride and cyanide inhibition studies and confirmed by site-directed mutagenesis. The S153A mutant exhibited a 340-fold decrease in kcat/KM. SgcC4 represents a novel type of aminomutase, extending the known MIO chemistry from ammonia lyases into aminomutases.
authors.affiliation: Department of Chemistry, University of California-Davis, 95616, USA.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Christenson
authors.forename: Wen
authors.initials: W
authors.lastname: Liu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Toney
authors.forename: Ben
authors.initials: B
authors.lastname: Shen
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives* / Q000378:metabolism; D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000096:biosynthesis*; D000903:Antibiotics, Antineoplastic / Q000096:biosynthesis*; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D053281:Enediynes; D007093:Imidazoles / Q000378:metabolism*; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D013302:Streptomyces / Q000201:enzymology / Q000235:genetics / Q000378:metabolism
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D000903:Antibiotics, Antineoplastic; D053281:Enediynes; D007093:Imidazoles; C447541:methylidene-imidazolone; C058024:C 1027; C015102:dehydroalanine; D019751:Intramolecular Transferases; C023206:tyrosine 2,3-aminomutase; D000409:Alanine