title: Characterization of streptonigrin biosynthesis reveals a cryptic carboxyl methylation and an unusual oxidative cleavage of a N-C bond.
abstract: Streptonigrin (STN, 1) is a highly functionalized aminoquinone alkaloid with broad and potent antitumor activity. Here, we reported the biosynthetic gene cluster of STN identified by genome scanning of a STN producer  Streptomyces flocculus  CGMCC4.1223. This cluster consists of 48 genes determined by a series of gene inactivations. On the basis of the structures of intermediates and shunt products accumulated from five specific gene inactivation mutants and feeding experiments, the biosynthetic pathway was proposed, and the sequence of tailoring steps was preliminarily determined. In this pathway, a cryptic methylation of lavendamycin was genetically and biochemically characterized to be catalyzed by a leucine carboxyl methyltransferase StnF2. A [2Fe-2S](2+) cluster-containing aromatic ring dioxygenase StnB1/B2 system was biochemically characterized to catalyze a regiospecific cleavage of the N-C8' bond of the indole ring of the methyl ester of lavendamycin. This work provides opportunities to illuminate the enzymology of novel reactions involved in this pathway and to create, using genetic and chemo-enzymatic methods, new streptonigrinoid analogues as potential therapeutic agents.
authors.affiliation: State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Xu
authors.forename: Dekun
authors.initials: D
authors.lastname: Kong
authors.forename: Xinyi
authors.initials: X
authors.lastname: He
authors.forename: Zhang
authors.initials: Z
authors.lastname: Zhang
authors.forename: Mo
authors.initials: M
authors.lastname: Han
authors.forename: Xinqiang
authors.initials: X
authors.lastname: Xie
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.forename: Hairong
authors.initials: H
authors.lastname: Cheng
authors.forename: Meifeng
authors.initials: M
authors.lastname: Tao
authors.forename: Liping
authors.initials: L
authors.lastname: Zhang
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
authors.forename: Shuangjun
authors.initials: S
authors.lastname: Lin
mesh_terms: D055162:Biocatalysis; D008745:Methylation; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011497:Protein O-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D013302:Streptomyces / Q000201:enzymology; D013308:Streptonigrin / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D013308:Streptonigrin; C085457:C-terminal leucine protein methyltransferase; D011497:Protein O-Methyltransferase