Biosynthesis of the Sesquiterpene Antibiotic Albaflavenone
Lin, Xin (creator)
Cane, David (director)
Basu, Amit (reader)
Sello, Jason (reader)
Brown University. Chemistry (sponsor)
Streptomyces are Gram-positive, filamentous, soil-dwelling saprophytic bacteria that are the source of a vast array of bioactive secondary metabolites. The albaflavenone
biosynthetic gene cluster in S. coelicolor A3(2) contains two ORFs, sco5222 and sco5223. The 1086-bp sco5222 gene encodes a protein of 361 amino acids (aa), which has been expressed in E. coli
and characterized to catalyze the cyclization of farnesyl diphosphate (FPP) to epi-isozizaene. The sco5223 gene shares a four-nucleotide ATGA transcriptional overlap with sco5222 at its 5'-end,
and was demonstrated to catalyze the two-step allylic oxidation of epi-isozizaene to albaflavenone through the intermediacy of an epimeric mixture of albaflavenols. The incubation experiments of
labeled FPP and NPP with SCO5222 protein not only confirmed the intermediacy of (3R)-NPP in the cyclization mechanism, but also shed valuable new light on the stereochemistry of other reaction
intermediates. In addition, the site-directed mutagenesis gave rise to the affected distribution of aberrant products, providing strong support for the presence of proposed intermediates.
Recombinant SAV3032 in S. avermitilis has been expressed in E. coli and refolded from inclusion bodies, and the purified protein was characterized to catalyze the cyclization of FPP to
epi-isozizaene. This result therefore implied the presence of albaflavenone biosynthesis pathway in S. avermitilis.