The violacein biosynthetic enzyme VioE shares a fold with lipoprotein transporter proteins

Recent Advances in Synthetic, Industrial and Biological Applications of Violacein and Its Heterologous Production

Violacein, a purple pigment first isolated from a gram-negative coccobacillus Chromobacterium violaceum, has gained extensive research interest in recent years due to its huge potential in the pharmaceutic area and industry. In this review, we summarize the latest research advances concerning this pigment, which include (1) fundamental studies of its biosynthetic pathway, (2) production of violacein by native producers, apart from C. violaceum, (3) metabolic engineering for improved production in heterologous hosts such as Escherichia coli, Citrobacter freundii, Corynebacterium glutamicum, and Yarrowia lipolytica, (4) biological/pharmaceutical and industrial properties, (5) and applications in synthetic biology. Due to the intrinsic properties of violacein and the intermediates during its biosynthesis, the prospective research has huge potential to move this pigment into real clinical and industrial applications.

Microbial synthesis of violacein pigment and its potential applications

Violacein is a pigment synthesized by Gram-negative bacteria such as Chromobacterium violaceum. It has garnered significant interest owing to its unique physiological and biological activities along with its synergistic effects with various antibiotics. In addition to C. violaceum, several microorganisms, including: Duganella sp., Pseudoalteromonas sp., Iodobacter sp., and Massilia sp., are known to produce violacein. Along with the identification of violacein-producing strains, the genetic regulation, quorum sensing mechanism, and sequence of the vio-operon involved in the biosynthesis of violacein have been elucidated. From an engineering perspective, the heterologous production of violacein using the genetically engineered Escherichia coli or Citrobacter freundii host has also been attempted. Genetic engineering of host cells involves the heterologous expression of genes involved in the vio operon and the optimization of metabolic pathways and gene regulation. Further, the crystallography of VioD and VioE was revealed, and mass production by enzyme engineering has been accelerated. In this review, we highlight the biologically assisted end-use applications of violacein (such as functional fabric development, nanoparticles, functional polymer composites, and sunscreen ingredients) and violacein activation mechanisms, production strains, and the results of mass production with engineered methods. The prospects for violacein research and engineering applications have also been discussed.

Direct RBS Engineering of the biosynthetic gene cluster for efficient productivity of violaceins in E. coli

Background

Violaceins have attracted much attention as potential targets used in medicines, food additives, insecticides, cosmetics and textiles, but low productivity was the key factor to limit their large-scale applications. This work put forward a direct RBS engineering strategy to engineer the violacein biosynthetic gene cluster cloned from Chromobacterium violaceum ATCC 12,472 to efficiently improve the fermentation titers.

Results

Through four-rounds of engineering of the native RBSs within the violaceins biosynthetic operon vioABCDE, this work apparently broke through the rate-limiting steps of intermediates conversion, resulting in 2.41-fold improvement of violaceins production compared to the titers of the starting strain Escherichia coli BL21(DE3) (Vio12472). Furthermore, by optimizing the batch-fermentation parameters including temperature, concentration of IPTG inducer and fermentation time, the maximum yield of violaceins from (BCDE)m (tnaA⁻) reached 3269.7 µM at 2 mM tryptophan in the medium. Interestingly, rather than previous reported low temperature (20 ℃), we for the first time found the RBS engineered Escherichia coli strain (BCDE)m worked better at higher temperature (30 ℃ and 37 ℃), leading to a higher-level production of violaceins.

Conclusions

To our knowledge, this is the first time that a direct RBS engineering strategy is used for the biosynthesis of natural products, having the potential for a greater improvement of the product yields within tryptophan hyperproducers and simultaneously avoiding the costly low temperature cultivation for large-scale industrial production of violaciens. This direct RBS engineering strategy could also be easily and helpfully used in engineering the native RBSs of other larger and value-added natural product biosynthetic gene clusters by widely used site-specific mutagenesis methods represented by inverse PCR or CRISPR-Cas9 techniques to increase their fermentation titers in the future.

Okanin in Coreopsis tinctoria Nutt is a major quorum-sensing inhibitor against Chromobacterium violaceum

ETHNOPHARMACOLOGICAL RELEVANCE

Coreopsis tinctoria Nutt has various medical and functional properties and its flower is widely used as health-care tea to decrease blood glucose and to lower blood lipids. However, the quorum sensing (QS) inhibition activity of Coreopsis tinctoria Nutt flower remains unclear.

AIM OF THE STUDY

To assess inhibitory activity against quorum sensing by Chromobacterium violaceum, to identify the chemical composition of the extracts and to disclose the action mechanism of separated compound.

MATERIAL AND METHODS

Violacein inhibition assays were performed in 96-wells microplates. The compounds extracted from Coreopsis tinctoria Nutt flower were separated and purified by various chromatography techniques. Respectively, thin layer chromatography (TLC, GF254), mass spectrometer (Agilent 1100 Series LC/MSD Trap SL), Medium-pressure automatic purification system (Buscisepacore C 620, Switzerland), High performance liquid chromatography (HPLC, Shimadzu LC-20AD, Japan), Liquid preparation Chromatography (Waters2545, USA). The chemical structures were identified by nuclear magnetic resonance (NMR, Bruker AV-500, Germany) technique. The inhibitory mechanism of okanin against C. violaceum quorum sensing was detected by quantitative real-time PCR (qRT-PCR).

RESULTS

Quorum sensing regulates production of bacterial virulence factors, thereby making it an intriguing target for attenuating bacterial pathogenicity. In this study, anti-QS activity of Coreopsis tinctoria Nutt methanol fraction (CTM) was investigated against C. violaceum ATCC12472. CTM showed an inhibitory effect on the QS-mediated virulence factors production such as violacein in C. violaceum without effect on growth rate. Also, okanin was isolated from CTM and its potential of anti-QS was confirmed after observing a significant reduction of violacein production in C. violaceum. An attempt was made to assess the effect of okanin on vioABCDE expression in C. violaceum to disclose acting mechanisms.

CONCLUSIONS

The results of this study contribute to validate an inhibitory effect of Coreopsis tinctoria Nutt flower on quorum sensing by Chromobacterium violaceum and to determine the compound responsible for inhibition. Also, the inhibitory effect was achieved in tandem with the down-regulation of vio operon.

Structures of three ependymin-related proteins suggest their function as a hydrophobic molecule binder

Ependymin was first discovered as a predominant protein in brain extracellular fluid in fish and was suggested to be involved in functions mostly related to learning and memory. Orthologous proteins to ependymin called ependymin-related proteins (EPDRs) have been found to exist in various tissues from sea urchins to humans, yet their functional role remains to be revealed. In this study, the structures of EPDR1 from frog, mouse and human were determined and analyzed. All of the EPDR1s fold into a dimer using a monomeric subunit that is mostly made up of two stacking antiparallel β-sheets with a curvature on one side, resulting in the formation of a deep hydrophobic pocket. All six of the cysteine residues in the monomeric subunit participate in the formation of three intramolecular disulfide bonds. Other interesting features of EPDR1 include two asparagine residues with glycosylation and a Ca2+-binding site. The EPDR1 fold is very similar to the folds of bacterial VioE and LolA/LolB, which also use a similar hydrophobic pocket for their respective functions as a hydrophobic substrate-binding enzyme and a lipoprotein carrier, respectively. A further fatty-acid binding assay using EPDR1 suggests that it indeed binds to fatty acids, presumably via this pocket. Additional interactome analysis of EPDR1 showed that EPDR1 interacts with insulin-like growth factor 2 receptor and flotillin proteins, which are known to be involved in protein and vesicle translocation.

Light-based control of metabolic flux through assembly of synthetic organelles

To maximize a desired product, metabolic engineers typically express enzymes to high, constant levels. Yet permanent pathway activation can have undesirable consequences including competition with essential pathways and accumulation of toxic intermediates. Faced with similar challenges, natural metabolic systems compartmentalize enzymes into organelles or post-translationally induce activity under certain conditions. Here, we report that optogenetic control can be used to extend compartmentalization and dynamic control to engineered metabolisms in yeast. We describe a suite of optogenetic tools to trigger assembly and disassembly of metabolically-active enzyme clusters. Using the deoxyviolacein biosynthesis pathway as a model system, we find that light-switchable clustering can enhance product formation by six-fold and product specificity by 18-fold by decreasing the concentration of intermediate metabolites and reducing flux through competing pathways. Inducible compartmentalization of enzymes into synthetic organelles can thus be used to control engineered metabolic pathways, limit intermediates and favor the formation of desired products.

Crystal structures of human lysosomal EPDR1 reveal homology with the superfamily of bacterial lipoprotein transporters

EPDR1, a member of the ependymin-related protein family, is a relatively uncharacterized protein found in the lysosomes and secretomes of most vertebrates. Despite having roles in human disease and health, the molecular functions of EPDR1 remain unknown. Here, we present crystal structures of human EPDR1 and reveal that the protein adopts a fold previously seen only in bacterial proteins related to the LolA lipoprotein transporter. EPDR1 forms a homodimer with an overall shape resembling a half-shell with two non-overlapping hydrophobic grooves on the flat side of the hemisphere. EPDR1 can interact with membranes that contain negatively charged lipids, including BMP and GM1, and we suggest that EPDR1 may function as a lysosomal activator protein or a lipid transporter. A phylogenetic analysis reveals that the fold is more widely distributed than previously suspected, with representatives identified in all branches of cellular life.

Investigating the Biosynthesis of Natural Products from Marine Proteobacteria: A Survey of Molecules and Strategies

The phylum proteobacteria contains a wide array of Gram-negative marine bacteria. With recent advances in genomic sequencing, genome analysis, and analytical chemistry techniques, a whole host of information is being revealed about the primary and secondary metabolism of marine proteobacteria. This has led to the discovery of a growing number of medically relevant natural products, including novel leads for the treatment of multidrug-resistant Staphylococcus aureus (MRSA) and cancer. Of equal interest, marine proteobacteria produce natural products whose structure and biosynthetic mechanisms differ from those of their terrestrial and actinobacterial counterparts. Notable features of secondary metabolites produced by marine proteobacteria include halogenation, sulfur-containing heterocycles, non-ribosomal peptides, and polyketides with unusual biosynthetic logic. As advances are made in the technology associated with functional genomics, such as computational sequence analysis, targeted DNA manipulation, and heterologous expression, it has become easier to probe the mechanisms for natural product biosynthesis. This review will focus on genomics driven approaches to understanding the biosynthetic mechanisms for natural products produced by marine proteobacteria.

Biosynthesis of nitrogen-containing natural products, C7N aminocyclitols and bis-indoles, from actinomycetes

Actinomycetes are a major source of bioactive natural products with important pharmaceutical properties. Understanding the natural enzymatic assembly of complex small molecules is important for rational metabolic pathway design to produce “artificial” natural products in bacterial cells. This review will highlight current research on the biosynthetic mechanisms of two classes of nitrogen-containing natural products, C7N aminocyclitols and bis-indoles. Validamycin A is a member of C7N aminocyclitol natural products from Streptomyces hygroscopicus. Here, two important biosynthetic steps, pseudoglycosyltranferase-catalyzed C–N bond formation, and C7-sugar phosphate cyclase-catalyzed divergent carbasugar formation, will be reviewed. In addition, the bis-indolic natural products indolocarbazole, staurosporine from Streptomyces sp. TP-A0274, and rearranged bis-indole violacein from Chromobacterium violaceum are reviewed including the oxidative course of the assembly pathway for the bis-indolic scaffold. The identified biosynthesis mechanisms will be useful to generating new biocatalytic tools and bioactive compounds.

A scalable metabolite supplementation strategy against antibiotic resistant pathogen Chromobacterium violaceum induced by NAD+/NADH+ imbalance

BACKGROUND

The leading edge of the global problem of antibiotic resistance necessitates novel therapeutic strategies. This study develops a novel systems biology driven approach for killing antibiotic resistant pathogens using benign metabolites.

RESULTS

Controlled laboratory evolutions established chloramphenicol and streptomycin resistant pathogens of Chromobacterium. These resistant pathogens showed higher growth rates and required higher lethal doses of antibiotic. Growth and viability testing identified malate, maleate, succinate, pyruvate and oxoadipate as resensitising agents for antibiotic therapy. Resistant genes were catalogued through whole genome sequencing. Intracellular metabolomic profiling identified violacein as a potential biomarker for resistance. The temporal variance of metabolites captured the linearized dynamics around the steady state and correlated to growth rate. A constraints-based flux balance model of the core metabolism was used to predict the metabolic basis of antibiotic susceptibility and resistance.

CONCLUSIONS

The model predicts electron imbalance and skewed NAD/NADH ratios as a result of antibiotics - chloramphenicol and streptomycin. The resistant pathogen rewired its metabolic networks to compensate for disruption of redox homeostasis. We foresee the utility of such scalable workflows in identifying metabolites for clinical isolates as inevitable solutions to mitigate antibiotic resistance.

Advances in Chromobacterium violaceum and properties of violacein-Its main secondary metabolite: A review

Chromobacterium violaceum is important in the production of violacein, like other bacteria, such as Alteromonas, Janthinobacterium, Pseudoalteromonas, Duganella, Collimonas and Escherichia. Violacein is a versatile pigment, where it exhibits several biological activities, and every year, it shows increasing commercially interesting uses, especially for industrial applications in cosmetics, medicines and fabrics. This review on violacein focuses mainly on the last five years of research regarding this target compound and describes production and importance of quorum sensing in C. violaceum, mechanistic aspects of its biosynthesis, monitoring processes, genetic perspectives, pathogenic effects, antiparasitic and antimicrobial activities, immunomodulatory potential and uses, antitumor potential and industrial applications.

Isoprenyl caffeate, a major compound in manuka propolis, is a quorum-sensing inhibitor in Chromobacterium violaceum

The emergence of antibiotic-resistant bacterial pathogens, especially Gram-negative bacteria, has driven investigations into suppressing bacterial virulence via quorum sensing (QS) inhibition strategies instead of bactericidal and bacteriostatic approaches. Here, we investigated several bee products for potential compound(s) that exhibit significant QS inhibitory (QSI) properties at the phenotypic and molecular levels in Chromobacterium violaceum ATCC 12472 as a model organism. Manuka propolis produced the strongest violacein inhibition on C. violaceum lawn agar, while bee pollen had no detectable QSI activity and honey had bactericidal activity. Fractionated manuka propolis (pooled fraction 5 or PF5) exhibited the largest violacein inhibition zone (24.5 ± 2.5 mm) at 1 mg dry weight per disc. In C. violaceum liquid cultures, at least 450 µg/ml of manuka propolis PF5 completely inhibited violacein production. Gene expression studies of the vioABCDE operon, involved in violacein biosynthesis, showed significant (≥two-fold) down-regulation of vioA, vioD and vioE in response to manuka propolis PF5. A potential QSI compound identified in manuka propolis PF5 is a hydroxycinnamic acid-derivative, isoprenyl caffeate, with a [M-H] of 247. Complete violacein inhibition in C. violaceum liquid cultures was achieved with at least 50 µg/ml of commercial isoprenyl caffeate. In silico docking experiments suggest that isoprenyl caffeate may act as an inhibitor of the violacein biosynthetic pathway by acting as a competitor for the FAD-binding pockets of VioD and VioA. Further studies on these compounds are warranted toward the development of anti-pathogenic drugs as adjuvants to conventional antibiotic treatments, especially in antibiotic-resistant bacterial infections.

Characterization of an environmental DNA-derived gene cluster that encodes the bisindolylmaleimide methylarcyriarubin

Bisindolylmaleimides represent a naturally occurring class of metabolites that are of interest because of their protein kinase inhibition activity. From a metagenomic library constructed with soil DNA, we identified the four gene mar cluster, a bisindolylmaleimide gene cluster that encodes for methylarcyriarubin (1) production. Heterologous expression of the mar gene cluster in E. coli revealed that the Rieske dioxygenase MarC facilitates the oxidative decarboxylation of a chromopyrrolic acid (CPA) intermediate to yield the bisindolylmaleimide core. The characterization of the mar cluster defines a new role for CPA in the biosynthesis of structurally diverse bacterial tryptophan dimers.

The Janthinobacterium sp. HH01 genome encodes a homologue of the V. cholerae CqsA and L. pneumophila LqsA autoinducer synthases

Janthinobacteria commonly form biofilms on eukaryotic hosts and are known to synthesize antibacterial and antifungal compounds. Janthinobacterium sp. HH01 was recently isolated from an aquatic environment and its genome sequence was established. The genome consists of a single chromosome and reveals a size of 7.10 Mb, being the largest janthinobacterial genome so far known. Approximately 80% of the 5,980 coding sequences (CDSs) present in the HH01 genome could be assigned putative functions. The genome encodes a wealth of secretory functions and several large clusters for polyketide biosynthesis. HH01 also encodes a remarkable number of proteins involved in resistance to drugs or heavy metals. Interestingly, the genome of HH01 apparently lacks the N-acylhomoserine lactone (AHL)-dependent signaling system and the AI-2-dependent quorum sensing regulatory circuit. Instead it encodes a homologue of the Legionella- and Vibrio-like autoinducer (lqsA/cqsA) synthase gene which we designated jqsA. The jqsA gene is linked to a cognate sensor kinase (jqsS) which is flanked by the response regulator jqsR. Here we show that a jqsA deletion has strong impact on the violacein biosynthesis in Janthinobacterium sp. HH01 and that a jqsA deletion mutant can be functionally complemented with the V. cholerae cqsA and the L. pneumophila lqsA genes.

Dioxins: diagnostic and prognostic challenges arising from complex mechanisms

Dioxins are ubiquitous environmental challenges to humans, with a pervasiveness that arises from 200 years of rapid industrialization and mechanization of Western societies and which is now extending into the developing world. In spite of their penetrance of the human biota, these compounds are poorly understood in terms of their true physiological potential for harm, and the mechanisms by which they impact cellular and organ level function are only recently becoming clear. Emerging awareness that chronic exposures to toxins may have generational and subtle effects on the outcomes of diseases such as cancer and diabetes, which are already multifactorial and highly complex, creates the context for the current review paper. Here, we summarize dioxin exposure paradigms and the resulting physiological effects that have been documented in animals and humans. Novel insights into potential endogenous end exogenous ligands, as well as the mechanisms by which these ligands impact acute and chronic cellular processes, are discussed. We develop the idea that the diagnosis of dioxin exposure, the subtleties of the cellular effects of the compounds and prognosis of the long-term effects of exposure are problems requiring that researchers leverage the power of genomics and epigenetics. However, the continuation of longitudinal epidemiological studies and the development of a firmer basis from which to extrapolate animal studies will be critical in ensuring optimal insight from these resource-intensive techniques.

Pathway redesign for deoxyviolacein biosynthesis in Citrobacter freundii and characterization of this pigment

Violacein (Vio) is an important purple pigment with many potential bioactivities. Deoxyviolacein, a structural analog of Vio, is always synthesized in low concentrations with Vio in wild-type bacteria. Due to deoxyviolacein's low production and difficulties in isolation and purification, little has been learned regarding its function and potential applications. This study was the first effort in developing a stable and efficient biosynthetic system for producing pure deoxyviolacein. A recombinant plasmid with vioabce genes was constructed by splicing using an overlapping extension-polymerase chain reaction, based on the Vio-synthesizing gene cluster of vioabcde, originating from Duganella sp. B2, and was introduced into Citrobacter freundii. With the viod gene disrupted in the Vio synthetic pathway, Vio production was completely abolished and the recombinant C. freundii synthesized only deoxyviolacein. Interestingly, vioe gene expression was strongly stimulated in the viod-deleted recombinant strain, indicating that viod disruptions could potentially induce polar effects upon the downstream vioe gene within this small operon. Deoxyviolacein production by this strain reached 1.9 g/L in shaker flasks. The product exhibited significant acid/alkali and UV resistance as well as significant inhibition of hepatocellular carcinoma cell proliferation at low concentrations of 0.1-1 μM. These physical characteristics and antitumor activities of deoxyviolacein contribute to illuminating its potential applications.

Bioactive pigments from marine bacteria: applications and physiological roles

Research into natural products from the marine environment, including microorganisms, has rapidly increased over the past two decades. Despite the enormous difficulty in isolating and harvesting marine bacteria, microbial metabolites are increasingly attractive to science because of their broad-ranging pharmacological activities, especially those with unique color pigments. This current review paper gives an overview of the pigmented natural compounds isolated from bacteria of marine origin, based on accumulated data in the literature. We review the biological activities of marine compounds, including recent advances in the study of pharmacological effects and other commercial applications, in addition to the biosynthesis and physiological roles of associated pigments. Chemical structures of the bioactive compounds discussed are also presented.

Plasmid encoded antibiotics inhibit protozoan predation of Escherichia coli K12

Bacterial plasmids and phages encode the synthesis of toxic molecules that inhibit protozoan predation. One such toxic molecule is violacein, a purple pigmented, anti-tumour antibiotic produced by the Gram-negative soil bacterium Chromobacterium violaceum. In the current experiments a range of Escherichia coli K12 strains were genetically engineered to produce violacein and a number of its coloured, biosynthetic intermediates. A bactivorous predatory protozoan isolate, Colpoda sp.A4, was isolated from soil and tested for its ability to 'graze' on various violacein producing strains of E. coli K12. A grazing assay was developed based on protozoan "plaque" formation. Using this assay, E. coli K12 strains producing violacein were highly resistant to protozoan predation. However E. coli K12 strains producing violacein intermediates, showed low or no resistance to predation. In separate experiments, when either erythromycin or pentachlorophenol were added to the plaque assay medium, protozoan predation of E. coli K12 was markedly reduced. The inhibitory effects of these two molecules were removed if E. coli K12 strains were genetically engineered to inactivate the toxic molecules. In the case of erythromycin, the E. coli K12 assay strain was engineered to produce an erythromycin inactivating esterase, PlpA. For pentachlorophenol, the E. coli K12 assay strain was engineered to produce a PCP inactivating enzyme pentachlorophenol-4-monooxygenase (PcpB). This study indicates that in environments containing large numbers of protozoa, bacteria which use efflux pumps to remove toxins unchanged from the cell may have an evolutionary advantage over bacteria which enzymatically inactivate toxins.

Violacein and related tryptophan metabolites produced by Chromobacterium violaceum: biosynthetic mechanism and pathway for construction of violacein core

Violacein is a natural violet pigment produced by several gram-negative bacteria, including Chromobacterium violaceum, Janthinobacterium lividum, and Pseudoalteromonas tunicata D2, among others. This pigment has potential medical applications as antibacterial, anti-trypanocidal, anti-ulcerogenic, and anticancer drugs. The structure of violacein consists of three units: a 5-hydroxyindole, an oxindole, and a 2-pyrrolidone. The biosynthetic origins of hydrogen, nitrogen, and carbon in the pyrrolidone nucleus were established by feeding experiments using various stable isotopically labeled tryptophans (Trps). Pro-S hydrogen of CH(2) at the 3-position of Trp is retained during biosynthesis. The nitrogen atom is exclusively from the α-amino group, and the skeletal carbon atoms originate from the side chains of the two Trp molecules. All three oxygen atoms in the violacein core are derived from molecular oxygen. The most interesting biosynthetic mechanism is the 1,2-shift of the indole nucleus on the left side of the violacein scaffold. The alternative Trp molecule is directly incorporated into the right side of the violacein core. This indole shift has been observed only in violacein biosynthesis, despite the large number of natural products having been isolated. There were remarkable advances in biosynthetic studies in 2006-2008. During the 3 years, most of the intermediates and the complete pathway were established. Two independent processes are involved: the enzymatic process catalyzed by the five proteins VioABCDE or the alternative nonenzymatic oxidative decarboxylation reactions. The X-ray crystallographic structure of VioE that mediates the indole rearrangement reaction was recently identified, and the mechanism of the indole shift is discussed here.

Characterization of a gene cluster and its putative promoter region for violacein biosynthesis in Pseudoalteromonas sp. 520P1

Violacein, a purple pigment produced by some Gram-negative bacteria, has various physiological properties, such as antitrypanosomal and antitumoral activities. A gene cluster that encodes five enzymes, VioA-VioE, is responsible for synthesizing violacein. The expression of these enzymes is known to be regulated by a quorum sensing mechanism in Chromobacterium violaceum and Pseudoalteromonas sp. 520P1. To clarify the molecular mechanism of regulation of violacein synthesis, we cloned and characterized the gene cluster from Pseudoalteromonas sp. 520P1. A fosmid library of strain 520P1 was constructed and clones containing the gene cluster were isolated. The gene cluster was 7383 bp in length and encoded five enzyme genes, vioA-vioE. A putative promoter sequence was predicted in the upstream region of the cluster. In the promoter region, two contiguous palindromic sequences, a possible quorum sensing regulatory site, were found. However, the isolated Escherichia coli clones harboring the gene cluster and its upstream region were unable to produce violacein probably due to the lack of quorum sensing machinery for expression. To further examine the ability of vioA-vioE genes to synthesize violacein in vivo, the upstream promoter region was removed from the cluster and heterologous expression of the treated cluster was performed in E. coli using a recombinant pET vector with T7 promoter. Purple pigment was expressed, and the pigment was identified to be violacein using ultraviolet and visible light and HPLC analysis. These results will contribute to further studies regarding violacein biosynthesis and its mass production.

Chromobacterium violaceum and its important metabolites--review

C. violaceum appeared as important bacterium in different applications and mainly these aspects are related to the production of violacein. This review discusses the last reports on biosynthetic pathways, production, genetic aspects, biological activities, pathological effects, antipathogenic screening through quorum sensing, environmental effects and the products of C. violaceum with industrial interest. An important discussion is on biological applications in medicine and as industrial products such as textile and in cosmetics.

Divergent pathways in the biosynthesis of bisindole natural products

Two molecules of the amino acid L-tryptophan are the biosynthetic precursors to a class of natural products named the "bisindoles." Hundreds of these bisindole molecules have been isolated from natural sources, and many of these molecules have potent medicinal properties. Recent studies have clarified the biosynthetic construction of six bisindole molecules, revealing novel enzymatic mechanisms and leading to combinatorial synthesis of new bisindole compounds. Collectively, these results provide a vantage point for understanding how much of the diversity of the bisindole class is generated from a small number of diverging pathways from L-tryptophan, as well as enabling identification of bisindoles that are likely derived via completely distinct biosynthetic pathways.

Opening and closing of the hydrophobic cavity of LolA coupled to lipoprotein binding and release

Outer membrane-specific lipoproteins of Escherichia coli are released from the inner membrane through the action of Lol-CDE, which leads to the formation of a complex between the lipoprotein and LolA, a periplasmic chaperone. LolA then transfers lipoproteins to LolB, a receptor in the outer membrane. The structures of LolA and LolB are very similar, having an incomplete beta-barrel covered with an alpha-helical lid forming a hydrophobic cavity inside. The cavity of LolA, but not that of LolB, is closed and thus inaccessible to the bulk solvent. Previous studies suggested that Arg at position 43 of LolA is critical for maintaining this closed structure. We show here, through a crystallographic study, that the cavity of the LolA(R43L) mutant, in which Leu replaces Arg-43, is indeed open to the external milieu. We then found that the binding of a fluorescence probe distinguishes the open/close state of the cavity. Furthermore, it was revealed that the hydrophobic cavity of LolA opens upon the binding of lipoproteins. Such a liganded LolA was found to be inactive in the release of lipoproteins from the inner membrane. On the other hand, the liganded LolA became fully functional when lipoproteins were removed from LolA by detergent treatment or transferred to LolB. Free LolA thus formed was inaccessible to a fluorescence probe. These results, taken together, reveal the LolA cycle, in which the hydrophobic cavity undergoes opening and closing upon the binding and release of lipoproteins, respectively.

A short helix in the C-terminal region of LolA is important for the specific membrane localization of lipoproteins

The structures of a lipoprotein carrier, LolA, and a lipoprotein receptor, LolB, are similar except for an extra C-terminal loop containing a 3(10) helix and beta-strand 12 in LolA. Lipoprotein release was significantly reduced when beta-12 was deleted. Deletion of the 3(10) helix also inhibited the lipoprotein release. Furthermore, lipoproteins were non-specifically localized to membranes when LolA lacked the 3(10) helix. Thus, the membrane localization of lipoproteins with the LolA derivative lacking the 3(10) helix was independent of LolB whereas LolB was essential for the outer membrane localization of lipoproteins with the wild-type LolA.