title: In vitro characterization of echinomycin biosynthesis: formation and hydroxylation of L-tryptophanyl-S-enzyme and oxidation of (2S,3S) β-hydroxytryptophan.
abstract: Quinoxaline-2-carboxylic acid (QXC) and 3-hydroxyquinaldic acid (HQA) feature in quinomycin family and confer anticancer activity. In light of the significant potency against cancer, the biosynthetic gene clusters have been reported from many different Streptomyces strains, and the biosynthetic pathway were proposed mainly based on the in vivo feeding experiment with isotope labeled putative intermediates. Herein we report another gene cluster from Streptomyces griseovariabilis subsp. bandungensis subsp. nov responsible for the biosynthesis of echinomycin (a member of quinomycin family, also named quinomycin A) and presented in vitro evidence to corroborate the previous hypothesis on QXC biosynthesis, showing that only with the assistance of a MbtH-like protein Qui5, did the didomain NRPS protein (Qui18) perform the loading of a L-tryptophan onto its own PCP domain. Particularly, it was found that Qui5 and Qui18 subunits form a functional tetramer through size exclusion chromatography. The subsequent hydroxylation on β-carbon of the loaded L-tryptophan proved in vitro to be completed by cytochrome P450-dependent hydroxylase Qui15. Importantly, only the Qui18 loaded L-tryptophan can be hydroxylated by Qui15 and the enzyme was inactive on free L-tryptophan. Additionally, the chemically synthesized (2S,3S) β-hydroxytryptophan was detected to be converted by the tryptophan 2,3-dioxygenase Qui17 through LC-MS, which enriched our previous knowledge that tryptophan 2,3-dioxygenase nearly exclusively acted on L-tryptophan and 6-fluoro-tryptophan.
authors: State Key Laboratory of Microbial Metabolism and School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
authors: Chen
authors: C
authors: Zhang
authors: Lingxin
authors: L
authors: Kong
authors: Qian
authors: Q
authors: Liu
authors: Xuan
authors: X
authors: Lei
authors: Tao
authors: T
authors: Zhu
authors: Jun
authors: J
authors: Yin
authors: Birun
authors: B
authors: Lin
authors: Zixin
authors: Z
authors: Deng
authors: Delin
authors: D
authors: You
mesh_terms: D006916:5-Hydroxytryptophan / Q000378:metabolism; D053898:Biosynthetic Pathways; D003001:Cloning, Molecular; D004448:Echinomycin / Q000096:biosynthesis*; D004789:Enzyme Activation; D005798:Genes, Bacterial; D006900:Hydroxylation; D005810:Multigene Family; D009154:Mutation; D016366:Open Reading Frames; D010453:Peptide Synthases / Q000378:metabolism; D010802:Phylogeny; D011810:Quinoxalines / Q000378:metabolism; D013302:Streptomyces / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D014366:Tryptophan Oxygenase / Q000145:classification / Q000235:genetics / Q000378:metabolism
chemical_list: D011810:Quinoxalines; C031945:triostin A; D004448:Echinomycin; D006916:5-Hydroxytryptophan; D014366:Tryptophan Oxygenase; D010453:Peptide Synthases; C104385:non-ribosomal peptide synthase; C042218:quinoxaline-2-carboxylic acid