Characterization of the Tautomycetin Biosynthetic Gene Cluster from Streptomyces griseochromogenes Provides New Insight into Dialkylmaleic Anhydride Biosynthesis

Tautomycetin (TTN) is a highly potent and specific protein phosphatase inhibitor isolated from Streptomyces griseochromogenes. The biological activity of TTN makes it an important lead for drug discovery, whereas its rare dialkylmaleic anhydride moiety and structural similarity to tautomycin (TTM), another potent phosphatase inhibitor with tremendous medicinal potential, draws attention to novel biosynthetic chemistries responsible for its production. To elucidate the biosynthetic machinery associated with TTN production, the ttn biosynthetic gene cluster from S. griseochromogenes was isolated and characterized, and its involvement in TTN biosynthesis confirmed by gene inactivation and complementation experiments. The ttn cluster was localized to a 79 kb DNA region, consisting of 19 open reading frames that encode two modular type I polyketide synthases (TtnAB), one type II thioesterase (TtnH), eight proteins for dialkylmaleic anhydride biosynthesis (TtnKLMNOPRS), four tailoring enzymes (TtnCDFI), two regulatory proteins (TtnGQ), and one resistance protein (TtnJ). A model for TTN biosynthesis is proposed on the basis of functional assignments from sequence analysis, which agrees well with previous feeding experiments, has been supported by in vivo gene inactivation experiments, and is supported by analogy to the recently reported ttm cluster. These findings set the stage to fully investigate TTN biosynthesis and to biosynthetically engineer new TTN analogues.