Letter Cite This: Org. Lett. 2017, 19, 5617-5620
pubs.acs.org/OrgLett
Elucidating the Sugar Tailoring Steps in the Cytorhodin Biosynthetic Pathway Chun Gui,†,‡ Xuhua Mo,§ Yu-Cheng Gu,⊥ and Jianhua Ju*,†,‡ †
CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Key Laboratory of Marine Materia Medica, RNAM Center for Marine Microbiology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China ‡ University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 110039, China § Shandong Key Laboratory of Applied Mycology, School of Life Sciences, Qingdao Agricultural University, Qingdao, 266109, China ⊥ Syngenta Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY, U.K. S Supporting Information *
ABSTRACT: Anthracycline antitumor cytorhodins X and Y feature a rare 9α-glycoside and 7-dexoy-aglycone. Characterization of the cytorhodin gene cluster from Streptomyces sp. SCSIO 1666 through gene inactivations and metabolite analyses reveals three glycosyltransferases (GTs) involved in the sugar tailoring steps. The duo of CytG1 and CytL effects C-7 glycosylation with L-rhodosamine whereas the iterative GT CytG3 and CytW similarly modifies both C-9 and C-10 positions. CytG2 also acts iteratively by incorporating the second and third sugar moiety into the trisaccharide chains at the C-7 or C-10 position.
A
Tirandamycins A and B5 (Figure 2, i) are hybrid type I polyketide synthase (PKS)-nonribosomal peptide synthetase (NRPS) assembled metabolites produced by Streptomyces sp. SCSIO 1666. Inactivation of a site-directed mutagenesis strain Streptomyces sp. SCSIO 1666/ΔtrdA1DH, from Streptomyces sp. SCSIO 1666 in which the conserved DH domain motif in trdA1 from the tirandamycin BGC was point mutated (SI, Figure S2), resulted in the abolishment of tirandamycins which otherwise diverted the metabolic flux to the type II PKS pathway (Figure 2, ii). A series of new peaks with UV absorptions characteristic of daunorubicin in the extract of strain Streptomyces sp. SCSIO 1666/ΔtrdA1DH were observed. Accordingly, large scale fermentation of the Streptomyces sp. SCSIO 1666/ΔtrdA1DH mutant strain enabled the isolation and elucidation of five anthracycline compounds, namely cytorhodins X (1)3 and Y (2),4 cosmomycins A (3) and B (4),6−8 and iremycin (5) (Figure 1A).9 All of these compounds were elucidated by HRESIMS, 1H, and 13C NMR spectroscopic methods and comparisons with previously reported literatures. Based on the chemical structures of cytorhodins, cosmomycins A and B, and iremycin, we hypothesize that they are assembled by the same BGC and that the ultimate products of the assembly line are 1 and 2. Next, the complete genomic data for Streptomyces sp. SCSIO 1666 were acquired. AntiSMASH analysis revealed that at least 32 BGCs were involved in
nthracyclines represent a large family of type II polyketidederived metabolites with diverse bioactivities.1 Especially characteristic of the anthracyclines is their cytotoxicity as is reflected by the success of the clinically employed drugs daunorubicin, doxorubicin, epirubicin, idarubicin, and aclacinomycin (Supporting Information (SI), Figure S1). Notably, minor modifications of the pendant glycosyl moieties often alter anthracycline cytotoxicity.2 Cytorhodins X (1) and Y (2) (Figure 1A) consist of a linear tetracyclic polyketide backbone and feature a 7-dexoy-aglycone; 1 and 2 were originally isolated from Streptomyces sp. HPLY-11472 (DSM 2658) and DSM 11149, respectively.3,4 Both agents project a C-10 linked trisaccharide and a rhodosamine sugar moiety at the C-9 of γ-rhodomycinone. This glycosylation pattern is rare among the anthracyclines. Additionally, 1 is cytotoxic to L1210 murine leukemia cells and 2 exhibits cytotoxic activity against HT29 and LXFL 529L cells with IC50 values of
