Establishing Modular Cell-Free Expression System for the Biosynthesis of Bicyclomycin from a Chemically Synthesized Cyclodipeptide

Cell-free expression systems have emerged as a versatile and powerful platform for metabolic engineering,biosynthesis and synthetic biology studies.Nevertheless,successful examples of the synthesis of complex natural products using this system are still limited.Bicyclomycin,a structurally unique and complex diketopiperazine alkaloid,is a clinically promising antibiotic that selectively inhibits the transcription termination factor Rho.Here,we established a modular cell-free expression system with cascade catalysis for the biosynthesis of bicyclomycin from a chemically synthesized cyclodipeptide.The six cell-free expressed biosynthetic enzymes,including five iron-andα-ketoglutarate-dependent dioxygenases and one cytochrome P450 monooxygenase,were active in converting their substrates to the corresponding products.The co-expressed enzymes in the cell-free module were able to complete the related partial pathway.In vitro biosynthesis of bicyclomycin was also achieved by reconstituting the entire biosynthetic pathways(i.e.,six enzymes)using the modular cell-free expression system.This study demonstrates that the modular cell-free expression system can be used as a robust and promising platformforthe biosynthesis of complex antibiotics.

Metabolites Identification of Curcumin,Demethoxycurcumin and Bisdemethoxycurcumin in Rats After Oral Administration of Nanoparticle Formulations by Liquid Chromatography Coupled with Mass Spectrometry

Background: Curcuminoids are promising cancer chemopreventive agents. Curcumin, demethoxycurcumin(DMC) and bisdemethoxycurcumin(BDMC) are the major bioactive curcuminoids in turmeric. However, comprehensive metabolic studies of these three curcuminoids are still limited.Objective: To identify the metabolites of curcumin, DMC and BDMC in rats after oral administration of solid lipid nanoparticles(SLNs).Methods: Male Sprague-Dawley rats(250 ± 20 g, body weight) were randomly divided into 4 groups(n=3), and were orally administered with curcumin-SLN, DMC-SLN, BDMC-SLN, or blank-SLN, respectively. Plasma samples(500 μL) via the angular vein were collected at 1, 2 and 4 h post dosing, and the urine and feces samples were collected at 0–12 h and 12–24 h post-intake. An HPLC-DAD-ESI-MSnmethod was developed to identify the metabolites. The structures of phase II metabolites were further confirmed by enzyme hydrolysis.Results: A total of 34 metabolites were identified in rats plasma, urine, and feces. Most of them were phase II metabolites, including glucuronide conjugates and sulfate conjugates. Among them, the glucuronide conjugates were the major metabolites in rats plasma. In the meanwhile, the three parent curcuminoids were detected in high amounts in the urine and feces samples.Conclusion: The possible metabolic pathways of curcuminoids in rats were proposed.