title: Molecular cloning, sequence analysis and functional characterization of the gene cluster for biosynthesis of K-252a and its analogs.
abstract: Among the indolocarbazole alkaloids of antitumor antibiotics, K-252a represents a structurally unique indolocarbazole glycoside and exhibits potent neuroprotective and broad anticancer activities. K-252a consists of K-252c and the unusual dihydrostreptose moiety, linked together with oxidative and glycosidic C-N bonds. Herein, we reported a complete sequence of an approximately 45 kb genomic fragment harboring the gene cluster for the biosynthesis of indolocarbazole alkaloids in Nocardiopsis sp. K-252 (NRRL15532). The sequence of 35 open reading frames discovered several new, critical genes, hence shedding new light on biosynthesis, resistance and regulation of K-252a and its analogs. To functionally characterize the gene cluster in vitro and in enzyme level, a multigene expression cassette containing the K-252c biosynthetic genes was constructed and successfully overexpressed in Escherichia coli to yield soluble proteins for cell-free tandem enzymatic assays. Consequently, the heterologous expression with soluble NokA and NokB led to in vitro production of chromopyrrolic acid (CPA), thereby providing functional evidence for K-252c biosynthesis. Moreover, a facile production of CPA in culture broth was successfully accomplished by using an in vivo biotransformation of L-tryptophan with E. coli harboring the gene cassette. Importantly, by sequence analysis and the functional characterization here and in the companion paper, biosynthetic pathways leading to formation of K-252a and its analogs were hence proposed. Together, the results provide critical information and materials useful for combinatorial biosynthesis of K-252a and its analogs for therapeutic applications.
authors.affiliation: Department of Biological Science and Technology, National Chiao Tung University, 75 Po-Ai Street, Hsinchu 300, Taiwan. Chiu@mail.nctu.edu.tw
authors.forename: Hsien-Tai
authors.initials: HT
authors.lastname: Chiu
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Chen
authors.forename: Chien-Yu
authors.initials: CY
authors.lastname: Chen
authors.forename: Chyn
authors.initials: C
authors.lastname: Jin
authors.forename: Meng-Na
authors.initials: MN
authors.lastname: Lee
authors.forename: Yu-Chin
authors.initials: YC
authors.lastname: Lin
mesh_terms: D000192:Actinomycetales / Q000235:genetics*; D020029:Base Pairing / Q000235:genetics; D002227:Carbazoles / Q000737:chemistry* / Q000378:metabolism*; D003001:Cloning, Molecular; D004926:Escherichia coli; D015723:Gene Library; D016680:Genome, Bacterial / Q000235:genetics; D026121:Indole Alkaloids / Q000737:chemistry* / Q000378:metabolism*; D007211:Indoles / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D017422:Sequence Analysis, DNA; D019311:Staurosporine / Q000096:biosynthesis
chemical_list: D002227:Carbazoles; D026121:Indole Alkaloids; D007211:Indoles; C053339:rebeccamycin; C049985:staurosporine aglycone; D019311:Staurosporine; C063155:violacein