Transcriptional activation of a geranylgeranyl diphosphate synthase gene, GGPPS2, isolated from Scoparia dulcis by treatment with methyl jasmonate and yeast extract.

A cDNA clone, designated SdGGPPS2, was isolated from young seedlings of Scoparia dulcis. The putative amino acid sequence of the translate of the gene showed high homology with geranylgeranyl diphosphate synthase (GGPPS) from various plant sources, and the N-terminal residues exhibited the characteristics of chloroplast targeting sequence. An appreciable increase in the transcriptional level of SdGGPPS2 was observed by exposure of the leaf tissues of S. dulcis to methyl jasmonate, yeast extract or Ca(2+) ionophore A23187. In contrast, SdGGPPS1, a homologous GGPPS gene of the plant, showed no or only negligible change in the expression level upon treatment with these stimuli. The truncated protein heterologously expressed in Escherichia coli in which the putative targeting domain was deleted catalyzed the condensation of farnesyl diphosphate and isopentenyl diphosphate to liberate geranylgeranyl diphosphate. These results suggested that SdGGPPS2 plays physiological roles in methyl jasmonate and yeast extract-induced metabolism in the chloroplast of S. dulcis cells.

Studies on tetrahydrocannabinolic acid synthase that produces the acidic precursor of tetrahydrocannabinol, the pharmacologically active cannabinoid in marijuana.

Tetrahydrocannabinol (THC), the psychoactive component of marijuana, is now regarded as a promising medicine because this cannabinoid has been shown to exert a variety of therapeutic activities. It has been demonstrated that THC is generated from the acidic precursor, tetrahydrocannabinolic acid (THCA) by nonenzymatic decarboxylation, and that THCA is biosynthesized by THCA synthase, which catalyzes a unique biosynthetic reaction, the stereospecific oxidative cyclization of the geranyl group of the substrate cannabigerolic acid. Molecular characterization of THCA synthase has revealed its structural characteristics and reaction mechanism. THCA synthase is the first cannabinoid synthase to be studied and is potentially attractive target for various biotechnological applications as it produces the direct precursor of THC. This review describes the research history of this enzyme, i.e., purification, molecular cloning, biochemical characterization, and possible biotechnological application of THCA synthase.

Anti-solasodine glycoside single-chain Fv antibody stimulates biosynthesis of solasodine glycoside in plants.

We constructed a recombinant antibody fragment--single chain fragment-variable (scFv) antibody--derived from hybridoma cell lines to control the concentration of solasodine glycosides in hairy root cultures of Solanum khasianum transformed by the anti-solamargine (As)-scFv gene. The properties of the As-scFv protein expressed in Escherichia coli were almost identical to those of the parent monoclonal antibody (MAb). Up to 220 ng recombinant As-scFv was expressed per milligram of soluble protein in transgenic hairy root cultures of S. khasianum. The concentration of solasodine glycosides was 2.3-fold higher in the transgenic than in the wild-type hairy root, as reflected by the soluble As-scFv level and antigen binding activities. These results suggested that the scFv antibody expressed in transgenic hairy roots controlled the antigen level, thus representing a novel plant breeding methodology that can produce secondary metabolites.

Morphine metabolism in the opium poppy and its possible physiological function. Biochemical characterization of the morphine metabolite, bismorphine.

We identified a novel metabolic system of morphine in the opium poppy (Papaver somniferum L.). In response to stress, morphine is quickly metabolized to bismorphine consisting of two morphine units, followed by accumulation in the cell wall. This bismorphine binds predominantly to pectins, which possess high galacturonic acid residue contents, through ionical bonds. Our newly developed method using artificial polysaccharides demonstrated that bismorphine bridges are formed between the two amino groups of bismorphine and the carboxyl groups of galacturonic acid residues, resulting in cross-linking of galacturonic acid-containing polysaccharides to each other. The ability of bismorphine to cross-link pectins is much higher than that of Ca2+, which also acts as a cross-linker of these polysaccharides. Furthermore, we confirmed that cross-linking of pectins through bismorphine bridges leads to resistance against hydrolysis by pectinases. These results indicated that production of bismorphine is a defense response of the opium poppy. Bismorphine formation is catalyzed by anionic peroxidase that pre-exists in the capsules and leaves of opium poppies. The constitutive presence of morphine, together with bismorphine-forming peroxidase, enables the opium poppy to rapidly induce the defense system.

Molecular characterization of a novel beta-glucuronidase from Scutellaria baicalensis georgi.

We cloned a gene encoding Scutellaria beta-glucuronidase (sGUS) that is involved in the initiation of H(2)O(2) metabolism in skullcap (Scutellaria baicalensis). This gene consists of a 1581-nucleotide open reading frame, the deduced amino acid sequence of which contains an ATP/GTP binding site and a leucine zipper motif. sGUS has apparent similarity to the heparan sulfate-metabolizing beta-glucuronidase heparanase but no homology to family 2 beta-glucuronidases. In addition, neither the family 2 glycosylhydrolase signature nor family 2 acid-base catalyst was found in this enzyme. These results suggested that sGUS does not belong to the family 2 beta-glucuronidases. We modified several residues predicted to act as the acid-base or nucleophilic residue of sGUS by site-directed mutagenesis. Mutations at Glu(212) or Glu(329) resulted in much lower k(cat)/K(m) values in the mutants as compared with the wild-type enzyme, indicating that these are the acid-base and nucleophilic residues of the active site, respectively. Moreover, similar site-directed mutagenesis confirmed that Tyr(281) is also involved in the beta-glucuronidase activity. The amino acid sequences of small regions containing these active site residues were conserved in heparanases. As sGUS has various structural characteristics in common with heparanase, we concluded that sGUS and heparanase belong to the same new family.

Histochemical investigation of ß-glucuronidase in culture cells and regenerated plants of Scutellaria baicalensis Georgi.

Strong activity of ß-glucuronidase first appeared in the epidermal and glandular hair cells of leaf primordia regenerated from callus of Scutellaria baicalensis Georgi. Leaf primordia matured rapidly in culture to form shoots within 1 month in which both the mesophyll cells and the glandular hairs were deeply stained. Leaves predominantly accumulated ß-glucuronidase in both glandular hair cells and mesophyll cells. ß-Glucronidase activity in leaves was higher in the summer and decreased in the winter. The stem section collected in the summer had a different ß-glucuronidase distribution pattern from that of the root in that in the former strong activity appeared in the periderm cells and collenchyma cells which was decreasingly dispersed into the phloem layer cells. In the winter, ß-glucronidase activity decreased compared to that in summer. It can be argued that the distribution of ß-glucuronidase in this plant is closely linked with the defense against pathogens: it is a starting key enzyme which may act together with the flavonoids, which play an important role as a proton donor for the detoxification metabolism of H2O2.

Identification and molecular characterization of novel peroxidase with structural protein-like properties.

Elicitor treatment or mechanical damage to Scutellaria baicalensis Georgi (skullcap plants) callus causes an immediate insolubilization of a 36-kDa protein into cell walls. The 36-kDa protein was identified as peroxidase 1 by analysis of its internal amino acid sequence and by immunoblotting using affinity-purified anti-peroxidase 1. Insolubilized peroxidase 1 is cross-linked to lignin through covalent bonds, and the cross-linking is catalyzed in the presence of H(2)O(2) by peroxidase 1 itself. The properties of insolubilized peroxidase 1 resemble those of defense-related structural proteins (extensins and proline-rich proteins) cross-linked to cell wall. Although the isozymes peroxidases 2 and 3 have enzyme activities similar to peroxidase 1, they are not insolubilized by stress treatment. Molecular characterization established that peroxidase 1 contains regions characteristic of structural proteins, but peroxidases 2 and 3 do not have such regions. These results suggest that among the three isozymes, only peroxidase 1 has a structural protein-like function as well as an enzymatic function.

Purification and characterization of cannabichromenic acid synthase from Cannabis sativa.

Cannabichromenic acid synthase was purified to apparent homogeneity by sequential column chromatography including DEAE-cellulose, phenyl-Sepharose CL-4B, and hydroxylapatite. The enzyme catalysed the oxidocyclization of cannabigerolic acid and cannabinerolic acid to cannabichromenic acid. The K(m) values for both substrates were in the same order of magnitude although the Vmax value for the former was higher than that for the latter. These results suggested that cannabichromenic acid is predominantly formed from cannabigerolic acid rather than cannabinerolic acid. The enzyme required neither molecular oxygen nor hydrogen peroxide, indicating that the cannabichromenic acid synthase reaction proceeds through direct dehydrogenation without hydroxylation.

Novel hydrogen peroxide metabolism in suspension cells of Scutellaria baicalensis Georgi.

We identified a rapid and novel system to effectively metabolize a large amount of H2O2 in the suspension cells of Scutellaria baicalensis Georgi. In response to an elicitor, the cells immediately initiate the hydrolysis of baicalein 7-O-beta-D-glucuronide by beta-glucuronidase, and the released baicalein is then quickly oxidized to 6,7-dehydrobaicalein by peroxidases. Hydrogen peroxide is effectively consumed during the peroxidase reaction. The beta-glucuronidase inhibitor, saccharic acid 1,4-lactone, significantly reduced the H2O2-metabolizing ability of the Scutellaria cells, indicating that beta-glucuronidase, which does not catalyze the H2O2 degradation, plays an important role in the H2O2 metabolism. As H2O2-metabolizing enzymes, we purified two peroxidases using ammonium sulfate precipitation followed by sequential chromatography on CM-cellulose and hydroxylapatite. Both peroxidases show high H2O2-metabolizing activity using baicalein, whereas other endogenous flavones are not substrates of the peroxidase reaction. Therefore, baicalein predominantly contributed to H2O2 metabolism. Because beta-glucuronidase, cell wall peroxidases, and baicalein pre-exist in Scutellaria cells, their constitutive presence enables the cells to rapidly induce the H2O2-metabolizing system.

Purification and characterization of cannabidiolic-acid synthase from Cannabis sativa L.. Biochemical analysis of a novel enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid.

We identified a unique enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid (CBDA) in Cannabis sativa L. (CBDA strain). The enzyme, named CBDA synthase, was purified to apparent homogeneity by a four-step procedure: ammonium sulfate precipitation followed by chromatography on DEAE-cellulose, phenyl-Sepharose CL-4B, and hydroxylapatite. The active enzyme consists of a single polypeptide with a molecular mass of 74 kDa and a pI of 6.1. The NH2-terminal amino acid sequence of CBDA synthase is similar to that of Delta1-tetrahydrocannabinolic-acid synthase. CBDA synthase does not require coenzymes, molecular oxygen, hydrogen peroxide, and metal ion cofactors for the oxidocyclization reaction. These results indicate that CBDA synthase is neither an oxygenase nor a peroxidase and that the enzymatic cyclization does not proceed via oxygenated intermediates. CBDA synthase catalyzes the formation of CBDA from cannabinerolic acid as well as cannabigerolic acid, although the kcat for the former (0.03 s-1) is lower than that for the latter (0.19 s-1). Therefore, we conclude that CBDA is predominantly biosynthesized from cannabigerolic acid rather than cannabinerolic acid.