Antiplasmodial and Trypanocidal Activity of Violacein and Deoxyviolacein Produced from Synthetic Operons Elizabeth Bilsland1,2,3* , Tatyana A
Total Page:16
File Type:pdf, Size:1020Kb
Bilsland et al. BMC Biotechnology (2018) 18:22 https://doi.org/10.1186/s12896-018-0428-z RESEARCH ARTICLE Open Access Antiplasmodial and trypanocidal activity of violacein and deoxyviolacein produced from synthetic operons Elizabeth Bilsland1,2,3* , Tatyana A. Tavella3, Renata Krogh4, Jamie E. Stokes5, Annabelle Roberts1, James Ajioka6, David R. Spring5, Adriano D. Andricopulo4, Fabio T. M. Costa3 and Stephen G. Oliver1 Abstract Background: Violacein is a deep violet compound that is produced by a number of bacterial species. It is synthesized from tryptophan by a pathway that involves the sequential action of 5 different enzymes (encoded by genes vioAto vioE). Violacein has antibacterial, antiparasitic, and antiviral activities, and also has the potential of inducing apoptosis in certain cancer cells. Results: Here, we describe the construction of a series of plasmids harboring the complete or partial violacein biosynthesis operon and their use to enable production of violacein and deoxyviolacein in E.coli. We performed in vitro assays to determine the biological activity of these compounds against Plasmodium, Trypanosoma, and mammalian cells. We found that, while deoxyviolacein has a lower activity against parasites than violacein, its toxicity to mammalian cells is insignificant compared to that of violacein. Conclusions: We constructed E. coli strains capable of producing biologically active violacein and related compounds, and propose that deoxyviolacein might be a useful starting compound for the development of antiparasite drugs. Keywords: Violacein, Deoxyviolacein, Plasmodium falciparum, Trypanosoma cruzi, Synthetic operon, Antiparasitic, Escherichia coli Background potential and may represent a chemical scaffold for the Violacein is a violet indolocarbazole pigment that is pro- developemt of clinically useful drugs. duced by bacteria such as Chromobacterium violaceum, Commercially, violacein is usually isolated from Chro- which are commonly found in water and soil throughout mobacterium [20–22]orJanthinobacterium [23, 24]; the world [1–6]. Violacein has antipyretic [7, 8], ulcer- however, this process is costly and there are reports of protective [8], antibacterial [9–11], antifungal [3, 12], rare but deadly infections caused by these bacteria [25– trypanocidal [13, 14], antileishmanial [15], antinematode 28]. Hence, there has been considerable interest in the [16], and antiviral [17] activities. It also has the potential development of safe, and efficient routes to the biosyn- of inducing apoptosis in certain cancer cells [2, 18]. Vio- thesis of this compound [1, 29–34]. lacein kills wild-type and drug-resistant strains of the The violacein biosynthetic pathway from L-tryptophan malaria parasite, Plasmodium falciparum and is thera- (Fig. 1) requires the expression of five genes: vioA, vioB, peutically against malaria in mice [19]. These character- vioC, vioD, and vioE [35–39]. It should be noted that istics suggest that violacein has considerable research VioC enzyme is involved in both the production of deoxyviolacien from protodeoxyviolaceinic acid and in the generation of violacein from protoviolaceinic acid. * Correspondence: [email protected] Several studies have shown that transforming and ex- 1Cambridge Systems Biology Centre and Department of Biochemistry, pressing a complete metabolic pathway into a different University of Cambridge, Cambridge, UK bacterial host may lead to improved production of viola- 2Department of Structural and Functional Biology, Institute of Biology, UNICAMP, Campinas, SP, Brazil cein [40–43]. For example, Rodrigues and co-workers Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bilsland et al. BMC Biotechnology (2018) 18:22 Page 2 of 8 ab c d e Fig. 1 Violacein biosynthetic pathway (a) and plasmid maps of the complete (b) and partial (c, d and e) operons for violacein biosynthesis [32–34] have successfully engineered Escherichia coli to they fine-tuned the expression of violacein-producing en- produce high yields of violacein and the side-product zymes, leading to an improvement in the production of deoxyviolacein. This was accomplished by cloning the the compound by up to 30-fold when compared to previ- complete vioABCDE and the partial vioABCE operons (re- ously reported work. spectively) from C. violaceum into pBADMycHisB, which We have generated a synthetic operon containing the allows the induction of the operon by L-arabinose [32, coding sequences of each of the five genes required for vio- 34]. These authors also metabolically engineered the host’s lacein biosynthesis, with a codon-usage optimized for E. coli tryptophan production to maximize the yield of violacein (http://parts.igem.org/Part:BBa_K274002). We also con- and deoxyviolacein [32, 34, 42]. More recently Jones and structed strains lacking vioD, to promote the accumulation co-workers [44] and Xu and co-workers [45] utilized vio- of deoxyviolacein. A similar approach was employed by Ro- lacein biosynthesis as a model for metabolic pathway bal- drigues and co-workers for the production of high yields of ancing and optimization. Employing different approaches, violacein and deoxyviolacein [32–34]. We produced and Bilsland et al. BMC Biotechnology (2018) 18:22 Page 3 of 8 purified violacein and deoxyviolacein, and characterized Violacein and deoxyviolacein purification their toxicity and antiplasmodial activity in wild-type and Deoxyviolacein drug-resistant Plasmodium falciparum strains; we also de- The acetone cell extract was evaporated to dryness. The termined their activity against Trypanosoma cruzi. crude residue was suspended in acetone and dry-loaded onto silica gel (SiO2). Deoxyviolacein was purified by column chromatography on silica gel (SiO ), first wash- Methods 2 ing with petroleum ether (boiling point = 40–60 °C) and Bacterial strains and plasmids eluting with a 1:1 solution of ethyl acetate and petrol- We constructed plasmids expressing violacein and deoxy- eum ether. Deoxyviolacein was obtained as a purple violacein by sub-cloning the synthetic violacein operon solid and was analytically pure (100%). The identity and (Part: BBa_K274002) designed by Shuna Gould for the purity of deoxyviolacein were confirmed by 1H NMR iGEM09_Cambridge project (http://parts.igem.org/Part:B- (Additional file 1: Figure S1). We calculated the purity Ba_K274002).Thesyntheticviolaceinoperoniscomprised by integrating related peaks and comparing the areas. of the 5 coding sequences specifying violacein pathway en- No other analysis was run because the data is consistent zymes (vioA, vioB, vioC, vioD and vioE), each preceded by with that from the literature [46]. The apparent purity of a ribosome-binding site. The operon was designed with a deoxyviolacein allowed its quantitation and that of viola- BamHI site in the space between vioB and vioC open cein (see below). Minor contamination by inorganic reading-frames (ORFs), a BglII site between the vioC and compounds cannot be excluded but these would need to vioD ORFs, and a BclI site between the vioD and vioE be soluble in acetone. reading-frames. Since cleavage of the BamHI, BglII, and BclI sites generate compatible cohesive ends, this facili- tated the construction of three different operons: Violacein vioABCE; vioABDE; vioABE. The synthetic operons are The acetone cell extract was evaporated to dryness. The flanked by EcoRI and PstI restriction endonuclease crude residue was suspended in acetone with sonication sites, enabling the use of these two enzymes to readily and dry-loaded onto silica gel (SiO2). Violacein was puri- subclone the entire (vioABCDE) and partial operons fied by column chromatography on silica gel (SiO2), first (vioABCE, vioABDE, vioABE)intotheEcoRI and NsiI washing with petroleum ether (boiling point = 40–60 °C) sites of pBAT4 (Fig. 1). and eluting with 4:6, 1:1, and 6:4 solutions of ethyl acet- ate and petroleum ether (boiling point = 40–60 °C). Violacein was obtained as a crude mixture with approxi- Production and purification of violacein and deoxyviolacein mately 12% deoxyviolacein (estimated from 1H NMR). We transformed E. coli BL21(DE3) (New England Bio- The identity of violacein was confirmed by 1H NMR labs) cells with plasmids expressing the synthetic (Additional file 1: Figure S1) and was consistent with the vioABCDE (for production of both violacein and deoxy- literature [46]. violaein) or vioABCE (for production of deoxyviolacein alone) operons. The leaky expression from the T7 pro- moter in these plasmids was enough to allow sufficient Plasmodium falciparum drug sensitivity assays synthesis of the enzymes in the violacein biosynthetic We cultivated Plasmodium falciparum 3D7 and W2 pathway. strains in complete RPMI (RPMI 1640, Sigma, USA), − We picked individual colonies, inoculated 50 mL cul- supplemented with 10% plasma (AB ) and 2% Haemato- tures in 2× YT (16 g/L Tryptone, 10 g/L yeast extract, crit (O+). Plasmodium