Hypericin Biosynthesis Research Articles

How Changes in Nitrogen Levels Impact Metabolites and Physiological Features of Hypericum androsaemum

Background: The manipulation of mineral nutrition may affect secondary metabolite production and thus determine the nutritional value of food/medicinal plants. Objectives: The present study investigated the impact of nitrogen supply on the production of secondary metabolites and physiological parameters of Hypericum androsaemum plants grown in sand culture. Methods: Four-week plants were irrigated by full-strength Hoagland solution (control), nitrate was reduced to 1/3, and no nitrate was provided for 14 days. Results: The growth of shoots was inhibited by nitrate limitation, but root growth was stimulated. Soluble proteins and water content were significantly affected by nitrate deficiency. Antioxidative enzyme activities (ascorbate peroxidase (APX) and superoxide dismutase (SOD)) were increased due to nitrate deficiency. Treatment of plants with NO3- deficiency caused an increase in total soluble phenols and phenylalanine ammonia-lyase (PAL) activity, while flavonoid content was mainly elevated by NO3- deficiency. At the level of specific metabolites, NO3- deficiency positively affected hypericin and pseudohypericin content but decreased hyperforin content. The expression of the putative gene for hypericin biosynthesis (hyp-1) was up-regulated in response to nitrate deficiency. Conclusions: The results demonstrated that the nitrogen deficiency in the H. androsaemum plant positively affected the antioxidant system, valuable phenols, and secondary metabolites.

Understanding the hypericin biosynthesis via reversible inhibition of dark gland development in Hypericum perforatum L.

Despite the pharmaceutical importance of hypericin as a drug lead molecule in various medical applications, the hypericin biosynthesis pathway is not known. Herein, we report on the ability to reversibly inhibit hypericin biosynthesis via impairing the dark glands that synthesize/accumulate hypericin, and reveal the correlation between important genes and hypericin biosynthesis. The number and size of dark glands were significantly reduced in shoots regenerated from St. John’s wort (Hypericum perforatum L.) root explants on medium containing sublethal level (5 µM) of glyphosate (N-(Phosphonomethyl)glycine). Ultra-Performance liquid chromatography (UPLC) system coupled with photodiode array (PDA) and fluorescence (FLR) analysis revealed that naphthodianthrones and their putative precursors i.e., emodin and bisanthrones were significantly inhibited in the presence of glyphosate, and these compounds could be fully recovered by withdrawing glyphosate, whereas phenolic compounds and phloroglucinols remain mostly unaffected. The expression of polyketide synthases (HpPKS2 and HpOKS) and phenolic oxidative coupling proteins (HpPOCP2, HpPOCP1 and HpPOCP3) were down-regulated upon glyphosate treatment and up-regulated after glyphosate withdrawal, highlighting the link between these genes and hypericin biosynthesis.

Physiological and Transcriptomic Analysis Provide Insight into Low Temperature Enhancing Hypericin Biosynthesis in Hypericum perforatum

Hypericin (Hyp), well-known as an antidepressant, is mainly extracted from Hypericum perforatum. Although Hyp accumulation and biomass are greater at lower compared to higher temperature, the regulation mechanism has not been reported. Here, the physiological characteristics and transcriptome of H. perforatum grown at 15 and 22 °C were determined and analyzed by HPLC and de novo sequencing. The results showed that the stomatal density and opening percentages were 1.1- and 1.4-fold more, and the Hyp content was 4.5-fold greater at 15 °C compared to 22 °C. A total of 1584 differentially expressed genes (DEGs) were observed at 15 versus 22 °C, with 749 characterized genes, 421 upregulated (UR) and 328 downregulated (DR). Based on biological functions, 150 genes were associated with Hyp biosynthesis, plant growth and the stress response, including photosynthesis, carbohydrate metabolism, fatty acids metabolism, cytochrome P450 (CYPs), morpho-physiological traits, heat shock proteins (HSPs), cold-responsive proteins (CRPs) and transcription factors (TFs). The differential expression levels of the master genes were confirmed by qRT-PCR and almost consistent with their Reads Per kb per Million (RPKM) values. This physiological and transcriptomic analyses provided insight into the regulation mechanisms of low temperature enhancing Hyp biosynthesis in H. perforatum.

RETRACTED ARTICLE: Homo and heterologous expression of the HpPKS2 gene in Hypericum perforatum and Bacopa monnieri

Hypericum perforatum has been known to produce hypericin and hyperforin that are used in treating mild to moderate depression. The HpPKS2 (H. perforatum polyketide synthase 2) gene is assumed to play a role in hypericin biosynthesis. The HpPKS2 gene was overexpressed in homologous H. perforatum in vitro grown plants through Agrobacterium tumefaciens-mediated genetic transformations. It leads to the establishment of seven glass house acclimatized transgenic lines. Among them, the HP12 transgenic plant showed 9.8 fold enhancement in hypericin content (379.4 ± 10.3 µg/g dry wt) followed by 3-fold in HP41 (117.1 ± 4.5 µg/g dry wt) as compared to control plants. This was further supported by the real-time PCR studies where it registered up to 5 fold enhancement of HpPKS2 gene expression. On the other hand, the heterologous expression of the HpPKS2 gene in Bacopa monnieri resulted in the establishment of five transgenic plant clones that were successfully acclimatized under glasshouse conditions. Among them, BT4 was found to be very slow-growing. The BT3 line showed maximum expression of the HpPKS2 gene which surprisingly also upregulates the expression of the other metabolic pathway genes of B. monierri namely isopentyl- diphosphate delta isomerase (IDDI), squaline synthase (SQS) and acetyl CoA C acetyltransferase (AA). The HPLC analysis in the heterologous system revealed the maximum production of bacopaside I (9.86 ± 1.0 mg/g dry wt), bacopaside II (5.89 ± 0.9 mg/g dry wt) and bacopasaponin C (3.59 ± 0.3 mg/g dry wt) by transgenic lines BT8, BT3 and BT4, respectively. This enhancement in bacopaside I, bacopaside II and bacopasaponin C production was more than 26-fold, 5-fold and 21-fold, respectively in comparison to the control non transformed plants. Overexpression of the HpPKS2 gene in H. perforatum led to higher hypericin content in the native system while its expression in the heterologous system i.e. B. monnieri also improves bacopaside I, bacopaside II and bacopasaponin C production.

Subject: UV-B radiation and low temperature promoted hypericin biosynthesis in adventitious root culture of Hypericum perforatum

ABSTRACT The hypericin is assumed as a highly demanded and key bioactive compound, which has antiviral, antimicrobial, antioxidant, and antitumor properties isolated from Hypericum perforatum. Nowadays, increasing bioactive molecules’ contents through generating novel compounds is one of the major research objectives of H. perforatum biotechnology; however, this plant remains recalcitrant and unmanageable to Agrobacterium mediated transformation and genetic improvement programs. In order to overcome these challenges, many researchers have focused on this unruly herb using biotic and abiotic eliciting strategies. Therefore, two experiments were separately designed for the evaluation of two types of abiotic elicitors, aiming at increasing the productivity of hypericin in the adventitious root suspension culture of H. perforatum. The first one was accomplished to evaluate the effect of UV-B light elicitors (the exposure time of 30, 60, and 90 min) and the recovery treatment (with or without) on hypericin content while the second one was assessed the effect of various temperatures (4°C, 8°C, 16°C, and 25°C) in three different exposure times (24 h, 72 h, and 7 d). Based on the results, UV-B (60 min) treatment followed by the recovery produced 0.430 µg/g DW hypericin and was distinguished as the most effective UV-B elicitation treatment. In addition, a temperature of 4°C for a period of 72 hours is required to get the highest amount of hypericin content. These findings indicate the fact that hypericin biosynthesis is notably affected by UV-B exposure time and Low-temperature. The data also clearly elucidate further mechanisms of hypericin production in H. perforatum adventitious root culture.

Simultaneous determination of naphtodianthrones, emodin, skyrin and new bisanthrones in Hypericum perforatum L. in vitro shoot cultures

Hypericum perforatum L. (St John's wort) extracts are top-selling herbal medicines for the treatment of various ailments including mild to moderate depression across the world. One of the major bioactive compounds of these extracts is hypericin that is also considered as a lead molecule for drug development. Here, we report on the development of a robust method for the simultaneous quantification of hypericins (hypericin, pseudohypericin, protohypericin and protopseudohypericin), their presumed precursors (emodin and skyrin) and new skyrin derivatives (oxyskyrin, iridoskyrin, rubroskyrin and luteoskyrin). Compounds extracted from the in vitro shoot cultures of H. perforatum L. in ethanol, acetone, 80 % methanol, ethylacetate and dichloromethane were separated by ultra-performance liquid chromatography (UPLC), quantified by photo diode array/ fluorescence (PDA-FLR) and annotated by Q- Exactive Orbitrap mass spectrometer (UPLC-QE-MS). Analyses of the UPLC data revealed that ethanol is the best extractant for the efficient quantification of all target compounds, although all of them could also be extracted in acetone and 80 % methanol. The extractants as well as the method of detection proved to be important for the efficient quantification of naphtodianthrones. Our results are expected to significantly contribute to the dissection of the hypericin biosynthesis pathway and the quality control of Hypericum extracts in the pharmaceutical industry.

Nitrogen nutrition modulates oxidative stress and metabolite production in Hypericum perforatum.

Impact of various nitrate concentrations (14.12 mM, 3.53 mM, no nitrate) or ammonium presence (14.12 mM) on physiological and metabolic changes in Hypericum perforatum after 14 days of cultivation was monitored. Nitrate deficiency suppressed growth of shoots but stimulated root growth while ammonium suppressed root growth: concomitant changes of ascorbic acid and glutathione supported these growth changes, e.g., unaltered level in roots under nitrate deficiency but depleted in ammonium treatment. Soluble proteins and water content were more suppressed by nitrate deficiency but total ROS, nitric oxide formation, and antioxidative enzyme activities (APX and SOD) indicate higher sensitivity of plants to ammonium. Though both extreme treatments (NO3- deficiency or ammonium) stimulated accumulation of total soluble phenols and affected PAL activity (in comparison with full or 1/4× nitrate dose), major phenols (chlorogenic acid and three flavonoids) were elevated mainly by NO3- deficiency. At the level of specific metabolites, NO3- deficiency had stimulatory impact on pseudohypericin (but not hypericin) content while hyperforin decreased. Expression of earlier putative gene of hypericin biosynthesis (hyp-1) showed rather partial correlation with pseudohypericin amount. Data indicate that depletion of NO3- is useful to obtain Hypericum plants with higher amount of health-positive secondary metabolites.

Discovery of key regulators of dark gland development and hypericin biosynthesis in St. John's Wort (Hypericum perforatum).

SummaryHypericin is a molecule of high pharmaceutical importance that is synthesized and stored in dark glands (DGs) of St. John's Wort (Hypericum perforatum). Understanding which genes are involved in dark gland development and hypericin biosynthesis is important for the development of new Hypericum extracts that are highly demanded for medical applications. We identified two transcription factors whose expression is strictly synchronized with the differentiation of DGs. We correlated the content of hypericin, pseudohypericin, endocrocin, skyrin glycosides and several flavonoids with gene expression and DG development to obtain a revised model for hypericin biosynthesis. Here, we report for the first time genotypes which are polymorphic for the presence/total absence (G+/G−) of DGs in their placental tissues (PTs). DG development was characterized in PTs using several microscopy techniques. Fourier transform infrared microscopy was established as a novel method to precisely locate polyaromatic compounds, such as hypericin, in plant tissues. In addition, we obtained transcriptome and metabolome profiles of unprecedented resolution in Hypericum. This study addresses for the first time the development of dark glands and identifies genes that constitute strong building blocks for the further elucidation of hypericin synthesis, its manipulation in plants, its engineering in microbial systems and its applications in medical research.

Temperature-dependent growth and hypericin biosynthesis in Hypericum perforatum

Hypericum perforatum is a perennial herb that produces the anti-depression metabolite hypericin (Hyp). While several efforts to increase Hyp production have been made, the effects of temperatures on growth and Hyp biosynthesis are still limited. In this study, the growth morphophysiological traits, Hyp biosynthesis and their related genes expression, as well as major bioactive compounds accumulation and antioxidant capacity were assessed by exposing H. perforatum seedlings to three different temperatures (15, 22 and 30 °C). The results showed that aerial parts biomass was greater at 15 °C with 1.3 and 1.6-fold increase compared to at 22 and 30 °C, in large part because of greater increase in chlorophyll content, stem number and leaf area on a per plant basis. Hyp content in the aerial parts was greater 1.9 and 5.6-fold on a per plant basis compared to 22 and 30 °C treatments, and the contents of other bioactive compounds (flavonoids and phenolics) as well as antioxidant capacity in the aerial parts, on dry weight and per plant basis, also exhibited significant increases with the temperatures decrease. The mRNA expressions of eight genes (psbA, psbB, psbC, psbD, ycf3, ycf4, ycf5 and matK) related to photosynthesis and two genes (Polyketide synthase, PKS; Phenolic oxidative coupling protein, Hyp-1) involved in Hyp biosynthesis were also up-regulated at 15 °C. The findings are useful in guiding cultivation and regulating Hyp biosynthesis in H. perforatum.

Phenotyping the genus Hypericum by secondary metabolite profiling: emodin vs. skyrin, two possible key intermediates in hypericin biosynthesis

A wide range of compounds that occur in the genus Hypericum are listed as effective drugs of natural origin. The main biological activities of several Hypericum representatives are due to the presence of naphthodianthrones, phloroglucinols, and other diverse groups of secondary metabolites that synergistically contribute to their therapeutic effects. The regulation of biosynthesis of hypericin as the key bioactive naphthodianthrone remains uncertain. Here, we present liquid chromatography mass spectrometry-based phenotyping of 17 Hypericum species, the results of which suggest an important role for skyrin and its derivatives in the polyketide pathway that leads to hypericin formation. Moreover, we report for the first time the presence of new metabolites in the genus Hypericum that are related to classes of anthraquinones, their derivatives, and phloroglucinols. As skyrin and other species of anthraquinones are rarely found in higher plants but frequently occur in fungal microorganisms, the obtained results suggest that further research on the synthesis pathways of hypericin and the role of anthraquinone derivatives in plant metabolism should be carried out. The fact that these compounds are commonly synthesized in endophytic fungi and perhaps there is some similarity in the metabolic pathways between these organisms should also be investigated.

Comparative Transcriptome Reconstruction of Four Hypericum Species Focused on Hypericin Biosynthesis.

Next generation sequencing technology rapidly developed research applications in the field of plant functional genomics. Several Hypericum spp. with an aim to generate and enhance gene annotations especially for genes coding the enzymes supposedly included in biosynthesis of valuable bioactive compounds were analyzed. The first de novo transcriptome profiling of Hypericum annulatum Moris, H. tomentosum L., H. kalmianum L., and H. androsaemum L. leaves cultivated in vitro was accomplished. All four species with only limited genomic information were selected on the basis of differences in ability to synthesize hypericins and presence of dark nodules accumulating these metabolites with purpose to enrich genomic background of Hypericum spp. H. annulatum was chosen because of high number of the dark nodules and high content of hypericin. H. tomentosum leaves are typical for the presence of only 1–2 dark nodules localized in the apical part. Both H. kalmianum and H. androsaemum lack hypericin and have no dark nodules. Four separated datasets of the pair-end reads were gathered and used for de novo assembly by Trinity program. Assembled transcriptomes were annotated to the public databases Swiss-Prot and non-redundant protein database (NCBI-nr). Gene ontology analysis was performed. Differences of expression levels in the marginal tissues with dark nodules and inner part of leaves lacking these nodules indicate a potential genetic background for hypericin formation as the presumed site of hypericin biosynthesis is in the cells adjacent to these structures. Altogether 165 contigs in H. annulatum and 100 contigs in H. tomentosum were detected as significantly differentially expressed (P < 0.05) and upregulated in the leaf rim tissues containing the dark nodules. The new sequences homologous to octaketide synthase and enzymes catalyzing phenolic oxidative coupling reactions indispensable for hypericin biosynthesis were discovered. The presented transcriptomic sequence data will improve current knowledge about the selected Hypericum spp. with proposed relation to hypericin biosynthesis and will provide a useful resource of genomic information for consequential studies in the field of functional genomics, proteomics and metabolomics.

Molecular Cloning and Expression Analysis of hyp-1 Type PR-10 Family Genes in Hypericum perforatum.

Hypericum perforatum L. is an important medicinal plant for the treatment of depression. The plant contains bioactive hypericins that accumulate in dark glands present especially in reproductive parts of the plant. In this study, pathogenesis-related class 10 (PR-10) family genes were identified in H. perforatum, including three previously unidentified members with sequence homology to hyp-1, a phenolic coupling protein that has earlier been suggested to participate in biosynthesis and binding/transportation of hypericin. The PR-10 genes showed constitutive but variable expression patterns in different H. perforatum tissues. They were all expressed at relatively high levels in leaves, variably in roots and low levels in stem and reproductive parts of the plant with no specific association with dark glands. The gene expression was up-regulated in leaves after salicylic acid, abscisic acid and wounding treatments but with variable levels. To study exact location of the gene expression, in situ hybridization of hyp-1 transcripts was performed and the accumulation of the Hyp-1 protein was examined in various tissues. The presence of Hyp-1 protein in H. perforatum tissues mostly paralleled with the mRNA levels. In situ RNA hybridization localized the hyp-1 transcripts predominantly in vascular tissues in root and stem, while in leaf the mRNA levels were high also in mesophyll cells in addition to vasculature. Our results indicate that the studied PR-10 genes are likely to contribute to the defense responses in H. perforatum. Furthermore, despite the location of the hyp-1 transcripts in vasculature, no support for the transportation of the Hyp-1 protein to dark glands was found in the current study. The present results together with earlier data question the role of the hyp-1 as a key gene responsible for the hypericin biosynthesis in dark glands of H. perforatum.

Differentially Expressed Genes in Hypericin-Containing Hypericum perforatum Leaf Tissues as Revealed by De Novo Assembly of RNA-Seq

Hypericum perforatum is a traditional medicinal plant used for various purposes since ancient times because of the valuable secondary metabolites. The genomic information for H. perforatum is limited and the regulatory networks of secondary metabolism are still unknown. The naphthodianthrone hypericin is the metabolite of our main interest. It is a red-colored photodynamic pigment localized in dark glands of some Hypericum species. High-throughput sequencing technology, especially RNA-Seq, followed by de novo assembly and analysis of differential gene expression provides an important tool for functional genomics of non-model organisms. It represents an opportunity of insight into dynamic biological processes including those of secondary metabolism. Transcriptome analysis followed by the analysis of differential gene expression of H. perforatum leaf tissues containing and lacking dark glands was performed to identify the genes involved in hypericin biosynthesis and to profile expression patterns in greater detail. A total of 18.53 G of cleaned read nucleotides were generated and assembled into 139,959 contigs with N50 of 1801 bp. Among them, 66,817 (47.74 %) contigs were annotated. Differentially expressed genes were discovered by comparison of dark glands with adjacent leaf tissue and contrasting inner part leaf tissue without dark glands. A total of 799 upregulated genes were found in the tissues containing dark glands and 263 enzymes were identified, including candidate genes of hypericin biosynthesis, especially the genes coding for polyketide synthases and those involved in defense reactions. This study determined candidate genes involved in hypericin biosynthesis providing a valuable source for perspective metabolic engineering of bioactive substances.

Construction of Hypericin Gland-Specific cDNA Library via Suppression Subtractive Hybridization.

Hypericin, an important determinant of the pharmacological properties of the genus Hypericum, is considered as a major molecule for drug development. However, biosynthesis and accumulation of hypericin is not well understood. Identification of genes differentially expressed in tissues with and without hypericin accumulation is a useful strategy to elucidate the mechanisms underlying the development of the dark glands and hypericin biosynthesis. Suppression Subtractive Hybridization (SSH) is a unique method for PCR-based amplification of specific cDNA fragments that differ between a control (driver) and experimental (tester) transcriptome. This technique relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs of similar abundance, and retaining differentially expressed or variable in sequence cDNAs. In our laboratory we applied this method to identify the genes involved in the development of dark glands and accumulation of hypericin in Hypericum perforatum. Here we describe the complete procedure for the construction of hypericin gland-specific subtracted cDNA library.

Spatial chemo-profiling of hypericin and related phytochemicals in Hypericum species using MALDI-HRMS imaging.

Advanced analytical imaging techniques, including matrix-assisted laser desorption/ionization high-resolution mass spectrometry (MALDI-HRMS) imaging, can be used to visualize the distribution, localization, and dynamics of target compounds and their precursors with limited sample preparation. Herein we report an application of MALDI-HRMS imaging to map, in high spatial resolution, the accumulation of the medicinally important naphthodianthrone hypericin, its structural analogues and proposed precursors, and other crucial phytochemical constituents in the leaves of two hypericin-containing species, Hypericum perforatum and Hypericum olympicum. We also investigated Hypericum patulum, which does not contain hypericin or its protoforms. We focused on both the secretory (dark glands, translucent glands, secretory canals, laminar glands, and ventral glands) and the surrounding non-secretory tissues to clarify the site of biosynthesis and localization of hypericin, its possible precursors, and patterns of localization of other related compounds concomitant to the presence or absence of hypericin. Hypericin, pseudohypericin, and protohypericin accumulate in the dark glands. However, the precursor emodin not only accumulates in the dark glands but is also present outside the glands in both hypericin-containing species. In hypericin-lacking H. patulum, however, emodin typically accumulates only in the glands, thereby providing evidence that hypericin is possibly biosynthesized outside the dark glands and thereafter stored in them. The distribution and localization of related compounds were also evaluated and are discussed concomitant to the occurrence of hypericin. Our study provides the basis for further detailed investigation of hypericin biosynthesis by gene discovery and expression studies.

Hypericin biosynthesis in Hypericum hookerianum Wight and Arn: Investigation on biochemical pathways using metabolite inhibitors and suppression subtractive hybridization

The biochemical pathway to hypericin biosynthesis is presumed to be polyketide synthase (PKS) mediated, but it has not been experimentally validated, and no alternate route (chorismate/o-succinylbenzoate pathway) has been analyzed. We report here our earlier developed auxin inducible culture systems of Hypericum hookerianum as a model, to study the metabolic pathway to hypericin synthesis. Inhibitors of the alternate pathway at varying concentrations showed steady synthesis of total hypericins with means of 2.80±0.22, 18.75±0.01; 16.39±3.75, 29.60±1.90 (mevinolin) 2.53±0.10, 18.12±0.56; 0.14±0.01, 14.28±1.11 (fosmidomycin) and 2.7±0.35, 18.75±0.61; 0.14±0.01, 12.80±1.09mgg−1 DW (glyphosate) in the control and auxin-induced shoot and shoot-forming callus cultures, respectively. SSH analysis classified the differentially expressed sequences into protein synthesis (38%), modification (20%), electron transport (9%) and remaining as unclassified (11%) and unknown proteins (22%). Functional annotation of sequences indicates the presence of additional protein components besides PKS activity. Our results demonstrate direct biochemical and molecular evidence of PKS hypothesis of hypericin biosynthesis for the first time.

Stress-induced expression and structure of the putative gene hyp-1 for hypericin biosynthesis

The phenolic oxidative coupling protein (Hyp-1) with proposed activity in the biosynthesis of hypericin in Hypericum perforatum shares about 50 % sequence similarity with Bet.v.1-like/PR-10 proteins. In our previous study, we showed that this protein is not a limiting factor in hypericin biosynthesis. To ascertain the role of Hyp-1 in defense mechanisms, we have analyzed some structural features of the hyp-1 gene in 14 Hypericum species with different abilities to synthesise hypericin. We show that the hyp-1 gene possesses characteristics typical for genes encoding plant PR-10 proteins. The coding sequence of the hyp-1 gene is interrupted by a single 86- to 125-bp intron localised strictly in codon 62, which is a typical feature of the dicot PR-10 subfamily. The localisation of the intron is conserved in all 14 tested Hypericum species indicating a common evolutionary history with genes encoding PR-10 proteins. In addition, we report that the hyp-1 gene exhibits a similar response to stress conditions as the PR-10 proteins encoding genes. Following either wounding or infection by Agrobacterium tumefaciens, all analysed Hypericum species exhibited rapid and significant upregulation of hyp-1 gene expression; this was particularly observed in hypericin-producing species. On the other hand, in the presence of high levels of abscisic acid, different levels of gene expression were observed.

Hyp-1 protein from St John’s wort as a PR-10 protein

PR-10 proteins form a large subclass of plant pathogenesis-related proteins that are expressed in response to harmful environmental factors in a wide range of species. Although their function is still not clear, structural data suggest that their characteristic internal hydrophobic cavity can bind relevant plant small-molecule mediators. Hyp-1 from St John's wort (Hypericum perforatum ), initially proposed as a catalyst for the biosynthesis of hypericin, was eventually shown to share sequence similarity and a folding pattern with PR-10 proteins. The crystal structure of Hyp-1 in complex with fluorescent probe ANS reveals three distinct and separated binding sites that are unique among PR-10 proteins. The structure can provide guidance in our quest for the true physiological ligands of Hyp-1.

Preparation of a polyclonal antibody against hypericin synthase and localization of the enzyme in red-pigmented Hypericum perforatum L. plantlets.

Hypericum perforatum is well known for its antidepressant and anti-inflammatory activities, for which hypericin and its derivatives are indicated to be the most active compounds. Hypericin synthase (Hyp-1) is the only protein proven to catalyze the synthesis of hypericin. In this study, the full-length cDNA of Hyp-1 was chemically synthesized according to the Hyp-1 sequence in GenBank (accession no. AY148090) and then cloned into the plasmid pET22b. Hyp-1 was expressed in Escherichia coli BL21 (DE3) and purified with a Ni-NTA column. The purified protein was used to immunize New Zealand white rabbits, from which an antiserum was purified by protein G affinity chromatography. The polyclonal antibody against Hyp-1 provides a valuable tool for the study of hypericin biosynthesis in H. perforatum. Expression of Hyp-1 and the cellular distribution of hypericin were analyzed in different organs of red-pigmented H. perforatum plantlets. The black glands were not the only site of hypericin accumulation and the results indicated that hypericin might be synthesized in mesophyll cells or in tissues of the root and/or stem and then transported to the glands. This work provides a foundation for further investigation of the regulatory mechanism of hypericin synthesis during the development of H. perforatum.

The hyp-1 gene is not a limiting factor for hypericin biosynthesis in the genus Hypericum.

Biosynthesis of the hypericins that accumulate in the dark glands of some members of the genus Hypericum is poorly understood. The gene named hyp-1, isolated from Hypericum perforatum L. has been proposed as playing an important role in the final steps of hypericin biosynthesis. To study the role of this candidate gene in relation to the production of hypericins, the expression of this gene was studied in 15 Hypericum species with varying ability to synthesise hypericin. While the accumulation of hypericins and emodin, an intermediate in the respective pathway, was associated with the dark glands in the hypericin-producing species, the hyp-1 gene was expressed in all studied species regardless of whether hypericins and emodin were detected in the plants. The coding sequences of hyp-1 cDNA were isolated from all species and showed more than 86% similarity to each other. Although, in general, an increased level of the hyp-1 gene transcript was detected in hypericin-producing species, several of the hypericin-lacking species expressed comparable levels as well. Our results question the role of the hyp-1 gene product as a key enzyme responsible for biosynthesis of hypericins in the genus Hypericum. The function of the hyp-1 gene may not be restricted to hypericin biosynthesis only, or some additional factors are necessary for completion of hypericin biosynthesis.