Diverse chalcone synthase superfamily enzymes from the most primitive vascular plant, Psilotum nudum

Psilotum nudum Griseb is a pteridophyte and belongs to the single family (Psilotaceae) of the division, Psilophyta. Being the only living species of a once populated division, P. nudum is the most primitive vascular plant. Chalcone synthase (CHS; EC 2.3.1.74) superfamily enzymes are responsible for biosyntheses of diverse secondary metabolites, including flavonoids and stilbenes. Using a reverse transcription-polymerase chain reaction strategy, four CHS-superfamily enzymes (PnJ, PnI, PnL and PnP) were cloned from P. nudum, and heterologously expressed in Escherichia coli. These four enzymes of 396-406 amino acids showed sequence identity of > 50% among themselves and to other higher-plant CHS-superfamily enzymes. PnJ and PnP preferred p-coumaroyl-CoA and isovaleryl-CoA respectively, as starter CoA and catalyzed CHS-type ring formation, indicating that they are CHS and phlorisovalerophenone synthase, respectively. On the other hand, PnI and PnL preferred cinnamoyl-CoA as starter CoA and catalyzed stilbene synthase-type cyclization and thus were determined to be pinosylvin synthases (EC 2.3.1.146). In addition, PnE, which uniquely contains a glutamine in place of otherwise strictly conserved histidine, had no apparent in vitro catalytic activity. Phylogenetic analysis indicated that these P. nudum clones form a separate cluster together with Equisetum arvense CHS. This cluster of pteridophytes is located next to the cluster formed by pine (gymnosperm) enzymes, in agreement with their evolutionary relationships. Psilotum nudum represents a plant with the most diverse CHS-superfamily enzymes and this ability to diverge may have provided a survival edge during evolution.

A novel antivirally active fucan sulfate derived from an edible brown alga, Sargassum horneri

A novel fucan sulfate (Hor-1) was isolated from the hot water extract of an edible brown alga, Sargassum horneri (Turner) C. Agardh. The fucan sulfate was revealed to have sugar linkage types, sulfate content and uronic acid content different from those of sodium hornan (Na-HOR), another fucan sulfate isolated from this alga. However, it exhibited inhibitory activity against replication of herpes simplex virus type 1 with similar potency to Na-HOR.

Identification of Claisen cyclase domain in fungal polyketide synthase WA, a naphthopyrone synthase of Aspergillus nidulans

BACKGROUND

Based on the homology with fatty acid synthases and bacterial polyketide synthases (PKSs), thioesterase domains have been assigned at the C-terminus regions of fungal iterative type I PKSs. We previously overexpressed Aspergillus nidulans wA PKS gene in a heterologous fungal host and identified it to encode a heptaketide naphthopyrone synthase. In addition, expression of C-terminus-modified WA PKS gave heptaketide isocoumarins suggesting that the C-terminus region of WA PKS is involved in the cyclization of the second aromatic ring of naphthopyrone. To unravel the actual function of the C-terminus region, we carried out functional analysis of WA PKS mutants by C-terminus deletion and site-directed mutagenesis.

RESULTS

Only the 32 amino acid deletion from the C-terminus of WA PKS caused product change to heptaketide isocoumarins from heptaketide naphthopyrone, YWA1 1, a product of intact WA PKS. Further C-terminus deletion mutant of WA PKS up to Ser(1967), an active site residue of so far called thioesterase, still produced isocoumarins. Site-directed mutagenesis of amino acid residues in this C-terminus region showed that even a single mutation of S1967A or H2129Q caused production of isocoumarin instead of naphthopyrone. Furthermore, the role of tandem acyl carrier proteins (ACPs), a typical feature of fungal aromatic PKSs, was examined by site-directed mutagenesis and the results indicated that both ACPs can function as ACP independently.

CONCLUSIONS

Claisen-type cyclization is assumed to be involved in formation of aromatic compounds by some fungal type I PKSs. These PKSs have a quite identical architecture of active site domain organization, beta-ketoacyl synthase, acyltransferase, tandem ACPs and thioesterase (TE) domains. Since the C-terminus region of WA PKS of this type was determined to be involved in Claisen-type cyclization of the second ring of naphthopyrone, we propose that the so far called TE of these PKSs work not just as TE but as Claisen cyclase.

Mechanistic studies on the biomimetic reduction of tetrahydroxynaphthalene, a key intermediate in melanin biosynthesis

1,3,6,8-Tetrahydroxynaphthalene (T4HN) is an aromatic polyketide, serving as a general precursor of fungal melanin. Melanin biosynthesis involves two consecutive deoxygenations of T4HN, consisting of the reduction of a phenolic carbon followed by dehydration. The first reduction to produce scytalone was studied in a biomimetic reduction with sodium borohydride. The reduction required a strong alkaline condition, leading to the tautomerization of T4HN to a reactive species whose structure was clarified by NMR spectroscopy.

Geranylgeranyl diphosphate synthase from Scoparia dulcis and Croton sublyratus. Plastid localization and conversion to a farnesyl diphosphate synthase by mutagenesis

cDNAs encoding geranylgeranyl diphosphate synthase (GGPPS) of two diterpene-producing plants, Scoparia dulcis and Croton sublyratus, have been isolated using the homology-based polymerase chain reaction (PCR) method. Both clones contained highly conserved aspartate-rich motifs (DDXX(XX)D) and their N-terminal residues exhibited the characteristics of chloroplast targeting sequence. When expressed in Escherichia coli, both the full-length and truncated proteins in which the putative targeting sequence was deleted catalyzed the condensation of farnesyl diphosphate and isopentenyl diphosphate to produce geranylgeranyl diphosphate (GGPP). The structural factors determining the product length in plant GGPPSs were investigated by constructing S. dulcis GGPPS mutants on the basis of sequence comparison with the first aspartate-rich motif (FARM) of plant farnesyl diphosphate synthase. The result indicated that in plant GGPPSs small amino acids, Met and Ser, at the fourth and fifth positions before FARM and Pro and Cys insertion in FARM play essential roles in determination of product length. Further, when a chimeric gene comprised of the putative transit peptide of the S. dulcis GGPPS gene and a green fluorescent protein was introduced into Arabidopsis leaves by particle gun bombardment, the chimeric protein was localized in chloroplasts, indicating that the cloned S. dulcis GGPPS is a chloroplast protein.

Characterization of inhibitory action of concanamycins against herpes simplex virus

Concanamycins A (Conmy A) and B (Conmy B), well-known inhibitors of the vacuolar proton-ATPase, were isolated from the culture broth of Streptomyces sp. strain FK51 as antiherpetic agents. These compounds showed potent inhibition of herpes simplex virus type 1 (HSV-1) replication in an in vitro assay system, having antiviral activities with 50% inhibitory concentrations of 0.072 and 0.51 ng/ml for Conmy A and Conmy B, respectively. While the attachment of HSV-1 to Vero cells was not inhibited, both of the compounds blocked the penetration of virus into host cells. When added to the late stages of virus replication, the concanamycins also exerted marked inhibitory effects on the production of viruses. Release of progeny viruses was found to be suppressed by the agents. SDS-PAGE analysis of isotope-labelled HSV-specific proteins revealed that the synthesis of beta proteins was moderately inhibited and some of the glycoproteins were synthesized with reduced molecular weights. Western blot analysis using antibodies against two HSV-specific glycoproteins (gC and gD) showed differences in their syntheses between untreated and Conmy A-treated cells. Syncytium formation by HSV-1 strain HF was inhibited, and small plaques with rounded cells were formed in Conmy A-treated cell cultures. When wild-type HSV-1 was serially propagated under the selective pressure of Conmy A, and the resulting progeny viruses were grown in drug-free medium, their plaque morphology of syncytium and sensitivity to Conmy A were the same as those of parent virus. From these findings, antiherpetic activities of Conmy A and B might be mainly dependent on their activities as vacuolar proton-ATPase inhibitors with intracellular translocation of glycoproteins and the inhibition of the maturation of virus glycoproteins.

Effects of structural modification of calcium spirulan, a sulfated polysaccharide from Spirulina platensis, on antiviral activity

Calcium ion binding with the anionic part of a molecule was replaced with various metal cations and their inhibitory effects on the replication of herpes simplex virus type 1 were evaluated. Replacement of calcium ion with sodium and potassium ions maintained the antiviral activity while divalent and trivalent metal cations reduced the activity. Depolymerization of sodium spirulan with hydrogen peroxide decreased in antiviral activity as its molecular weight decreased.

Evidence for catalytic cysteine-histidine dyad in chalcone synthase

Chalcone and stilbene synthases (CHS and STS) catalyze condensation reactions of p-coumaroyl-CoA and three C(2)-units from malonyl-CoA, but catalyze different cyclization reactions to produce naringenin chalcone and resveratrol, respectively. Condensing activities of wild-type CHS and STS as well as STS-C60S mutant were inhibited by iodoacetamide (Idm) and diethyl pyrophosphate (DPC). DPC also inhibited malonyl-CoA decarboxylation activity of wild-type and C164S mutants of CHS and STS. Meanwhile, Idm treatment enhanced (two- to fourfold) malonyl decarboxylase activity of wild-type enzymes and STS-C60S, whereas this priming effect was not observed with C164S mutants of CHS and STS, indicating that the cysteine residue being modified by Idm is the catalytic Cys164 of CHS and STS. DPC inhibition of decarboxylation activity of wild-type CHS was pH-independent in the range of pH 5.8 to 7.8; however, its inhibitory effect on CHS-C164S increased as pH increased from 6.2 to 7.4 with a midpoint of 6.4. Based on the 3-D structure of CHS and the observed shift in microscopic pK(a), it was concluded that the histidine residue being modified by DPC in CHS is likely the catalytic His303 and that His303 forms an ionic pair (catalytic dyad) with Cys164 in wild-type CHS. In addition, our results showed that Cys60 in STS is not essential for the activity and only a single cysteine (Cys164) participates in the catalysis as in CHS.

Identification of amino acid residues important in the cyclization reactions of chalcone and stilbene synthases

Chalcone synthase (CHS) and stilbene synthase (STS) catalyse condensation reactions of p-coumaroyl-CoA and three C(2) units from malonyl-CoA up to a common tetraketide intermediate but then catalyse different cyclization reactions to produce naringenin chalcone and resveratrol respectively. On the basis of sequence alignment with other condensing enzymes including 3-ketoacyl-(acyl carrier protein) synthases of polyketide and fatty-acid synthases, site-directed mutagenesis was performed on the active-site G(372)FGPG loops in CHS and STS. The CHS-P375G mutant showed a 6-fold decrease in overall condensing activity with selectively increased production of p-coumaroyltriacetic acid lactone (CTAL, the derailment product of the tetraketide intermediate). Meanwhile, resveratrol production by STS-P(375)G strongly decreased to give various products in the order CTAL> resveratrol approximately bisnoryangonin>naringenin. As a result, naringenin production (cross-reaction) by STS-P(375)G was close to 30% of resveratrol production. Both G(374)L mutants of CHS and STS showed no condensing activity with residual malonyl-CoA decarboxylase activity. These results suggested that the G(372)FGPG loop in CHS and STS contribute to a determination of the outcome during cyclization reactions by serving as a part of the active-site scaffold on which the stereochemistry of cyclization is performed. These observations provide the first biochemical indication that cyclization reactions are modulated by active-site geometry. The implications for the evolutionary relationship of these enzymes are also discussed.

Evaluation of (1R,2R)-1-(5'-methylfur-3'-yl)propane-1,2,3-triol, a sphydrofuran derivative isolated from a Streptomyces species, as an anti-herpesvirus drug

(1R,2R)-1-(5'-Methylfur-3'-yl)propane-1,2,3-triol (MFPT), a stable anhydro derivative of sphydrofuran, was obtained from the culture broth of STREPTOMYCES: sp. strain FV60 as an inhibitor of herpes simplex virus type 1 (HSV-1). The compound showed antiherpetic activity with a 50% inhibitory concentration of 1.2 IM in an in vitro assay system. Although the binding of virus to host cells was not inhibited, the penetration of virus into cells was moderately blocked by MFPT. Some of the viruses, once they had penetrated cells, failed to form plaques in the presence of MFPT. When added to the late stages of HSV-1 replication, MFPT also inhibited virus production. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of isotope-labelled HSV-specific proteins revealed that a protein or proteins with reduced molecular weight (about 120 kDa) was clearly detected in cells treated with MFPT. Western blot analysis with antibodies against three HSV-specific glycoproteins (gB, gC and gD) showed a significant difference in gC synthesis between untreated and MFPT-treated cells. Release of progeny viruses was suppressed by MFPT. Syncytium formation by HSV-1 strain HF was inhibited and small plaques with rounded cells were formed in MFPT-treated cell cultures. When wild-type HSV-1 was serially propagated under the selective pressure of MFPT, resistant virus emerged. MFPT-resistant progeny were accompanied by the formation of plaques with rounded cells. These results, taken together, suggest that MFPT might act by limiting the maturation of HSV-specific glycoproteins, particularly of HSV-1 gC.

Chalcone and stilbene synthases expressed in eucaryotes exhibit reduced cross-reactivity in vitro

Chalcone synthase (CHS) and stilbene synthase (STS) catalyze different cyclization reactions of the common tetraketide to give different products, naringenin chalcone and resveratrol, respectively. We have previously observed in vitro cross-reaction of CHS and STS overexpressed in Escherichia coli, resveratrol production by CHS and chalcone production by STS. When expressed in eucaryotic cells, or in E. coli as thioredoxin-fusion proteins, CHS and STS exhibited reduced cross-reaction. STS refolded from inclusion bodies also showed reduced cross-reaction. While addition of bovine serum albumin and pH in the reaction were without noticeable effect, addition of glycerol decreased the cross-reaction of CHS likely due to its stabilizing effect on enzyme conformation. These results were interpreted to provide supporting evidence to our earlier proposition (Yamaguchi T. et al., FEBS Lett., 460, 457-4 61 (1999)) that the in vitro cross-reaction of CHS and STS is due to intrinsic capability of these enzymes to catalyze different types of cyclization, which, in turn, is endowed by conformational flexibility of their active sites.

Structural analysis of calcium spirulan (Ca-SP)-derived oligosaccharides using electrospray ionization mass spectrometry

Detailed structural analyses of calcium spirulan (Ca-SP)-derived oligosaccharides were performed by ESI-MS and collision-induced dissociation tandem mass spectrometry. This study indicates that Ca-SP is composed of two types of disaccharide repeating units, O-rhamnosyl-acofriose and O-hexuronosyl-rhamnose (aldobiuronic acid).

Cross-reaction of chalcone synthase and stilbene synthase overexpressed in Escherichia coli

Chalcone synthase (CHS) and stilbene synthase (STS) are related plant polyketide synthases belonging to the CHS superfamily. CHS and STS catalyze common condensation reactions of p-coumaroyl-CoA and three C(2)-units from malonyl-CoA but different cyclization reactions to produce naringenin chalcone and resveratrol, respectively. Using purified Pueraria lobata CHS and Arachis hypogaea STS overexpressed in Escherichia coli, bisnoryangonin (BNY, the derailed lactone after two condensations) and p-coumaroyltriacetic acid lactone (the derailed lactone after three condensations) were detected from the reaction products. More importantly, we found a cross-reaction between CHS and STS, i.e. resveratrol production by CHS (2.7-4.2% of naringenin) and naringenin production by STS (1.4-2.3% of resveratrol), possibly due to the conformational flexibility of their active sites.

Antiviral activities against HSV-1, HCMV, and HIV-1 of rhamnan sulfate from Monostroma latissimum

Rhamnan sulfate (RS), a natural sulfated polysaccharide isolated from Monostroma latissimum, showed potent inhibitory effects on the virus replication of herpes simplex virus type 1 (HSV-1), human cytomegalovirus (HCMV), and human immunodeficiency virus type 1 (HIV-1) in vitro. The antiviral action of RS was not only due to the inhibition of virus adsorption, but also might involve the later steps of viral replication in host cells on the basis of the results of time-of-addition experiments. Furthermore, RS and 3'-azido-3'-deoxythymidine (AZT) were synergistic in their anti-HIV-1 activities. These data indicate that RS is a potent antiviral substance against HSV-1, HCMV, and HIV-1.

Inhibition effects of 5-S-glutathionyl-N-beta-alanyl-L-dopa analogues against Src protein tyrosine kinase

Twelve analogues of the antibacterial phenolic peptide 5-S-glutathionyl-N-beta-alanyl-L-dopa (5-S-GA-L-D, 1) were synthesized via orthoquinone using tyrosinase. Several synthesized compounds inhibited the v-Src autophosphorylation tyrosine kinase reaction with an IC50 value comparable to that of herbimycin A. The inhibition of c-Src substrate phosphorylation was much less active than v-Src autophosphorylation inhibition. 5-S-GA-L-D (1) and its analogous competed with peptide substrate and non-compared with ATP. The analogues showed no effects on substrate phosphorylation by epidermal growth factor receptor (EGFR), and this selectivity is the most characteristic feature of the 5-S-GA-L-D and its analogues (1-12).

Different inhibitory effects of 5-S-glutathionyl-beta-alanyl-L-dopa (5-S-GA-L-D) analogues on autophosphorylation and substrate phosphorylation of Src protein tyrosine kinase

Starting with 5-S-glutathionyl-beta-alanyl-L-dopa (1) and 5-S-glutathionyl-beta-alanyl-dopamine (2), a series of analogues with truncated glutathionyl and beta-alanyl-dopa moieties were synthesized, and their inhibitory effects on autophosphorylation and substrate phosphorylation reaction by c-Src and by epidermal growth factor receptor (EGFR) were evaluated. When the glutamyl residue was removed, the inhibitory effects on v-Src autophosphorylation decreased about 4- to 5-fold, and concomitant removal of the glutamyl and beta-alanyl residues resulted in a 40- to 60-fold decrease in the inhibition of v-Src autophosphorylation. On the other hand, these modifications had little effect on the inhibitory activity of substrate (Raytide) phosphorylation by c-Src. Interestingly, 5-S-cysteinyl dopamine inhibited the Src substrate phosphorylation reaction with comparable potency to that of genistein. Nonpeptide lipophilic derivatives had a similar inhibition on v-Src autophosphorylation but decreased inhibitory effects on substrate phosphorylation when compared to the lead compounds. Most compounds showed little effect on substrate phosphorylation by EGFR.

Selective inhibition of Src protein tyrosine kinase by analogues of 5-S-glutathionyl-beta-alanyl-L-dopa

Twelve analogues of the antibacterial phenolic peptide 5-S-glutathionyl-beta-alanyl-L-dopa (5-S-GA-L-D: 1) were synthesized via orthoquinones using tyrosinase. Several synthesized compounds inhibited the v-Src autophosphorylation tyrosine kinase reaction with an IC50 value comparable to that of herbimycin. The inhibition of c-Src substrate phosphorylation was much less active than v-Src autophosphorylation inhibition. The analogues showed no effects on substrate phosphorylation by epidermal growth factor receptor (EGFR), and this selectivity is the most characteristic feature of the analogues (1-12).

Further purification and structural analysis of calcium spirulan from Spirulina platensis

An antiviral sulfated polysaccharide, calcium spirulan (Ca-SP), isolated from Spirulina platensis, was subjected to further purification. Ca-SP was found to be composed of rhamnose, 3-O-methylrhamnose (acofriose), 2,3-di-O-methylrhamnose, 3-O-methylxylose, uronic acids, and sulfate. The backbone of Ca-SP consisted of 1,3-linked rhamnose and 1,2-linked 3-O-methylrhamnose units with some sulfate substitution at the 4-position. The polymer was terminated at the nonreducing end by 2,3-di-O-methylrhamnose and 3-O-methylxylose residues.

An antivirally active sulfated polysaccharide from Sargassum horneri (TURNER) C. AGARDH

A sulfated polysaccharide was isolated from the hot water extract of a brown alga, Sargassum horneri (TURNER) C. AGARDH. Fucose was detected as the main component sugar of this polysaccharide. This compound showed potent antiviral activity against herpes simplex virus type 1, human cytomegalovirus and human immunodeficiency virus type 1. Time-of-addition experiments suggested that it inhibited not only the initial stages of viral infection, such as attachment to and penetration into host cells, but also later replication stages after virus penetration.

Molecular cloning of pea cDNA encoding cycloartenol synthase and its functional expression in yeast

The cDNA encoding cycloartenol synthase [EC 5.4.99.8] has been isolated from pea seedling by an efficient PCR using sets of degenerate primers based on the highly conserved sequences of the known 2,3-oxidosqualene cyclase cDNAs. The obtained cDNA contains a 2271-bp open reading frame and is encoding a predicted protein of 757 amino acids with high homology (81%) to Arabidopsis thaliana cycloartenol synthase. The PCR-amplified open reading frame (ORF) has been inserted into pYES2, an expression vector in yeast, under the control of galactose-inducible promoter. Significant cycloartenol synthase activity has been found in the homogenate of the yeast transformed with the plasmid containing PCR-amplified ORF.

Cloning of the polyketide synthase gene atX from Aspergillus terreus and its identification as the 6-methylsalicylic acid synthase gene by heterologous expression

Southern blot analysis of genomic DNAs of several fungi that produce polyketide compounds with the 6-methylsalicylic acid synthase (MSAS) gene of Penicillium patulum as a probe indicated the presence of an MSAS-homologous gene in the (+)-geodin-producing strain IMI 16,043 of Aspergillus terreus. The gene, designated atX was cloned from an A. terreus genomic DNA library and 7588 bp of the gene together with its flanking regions were sequenced to reveal the presence of a 5.5 kb open reading frame coding for a protein of 1800 amino acids with 190 kDa molecular mass. The presence of a short (70 bp) intron near the N-terminus of the atX gene was predicted that contains the canonical GT and AG dinucleotides at its 5'- and 3'-splicing junctions. The predicted ATX polypeptide showed high homology with P. patulum MSAS along the whole sequence. On the other hand, slight homology was detected only around the beta-ketoacyl synthase regions of Aspergillus nidulans wA, PKSST and Colletotrichum lagenarium PKS1. No transcription of atX was observed throughout the culture period by Northern blotting analysis. To identify the function of the polypeptide encoded by the atX gene, its coding region was introduced into the fungal expression vector pTAex3 under the control of the amyB promoter. The constructed expression plasmid was introduced into A. nidulans. The transformant produced significant amounts of 6-methylsalicylic acid, the structure of which was identified by physicochemical analysis. This result unambiguously demonstrated that the atX gene codes for MSAS of A. terreus.

Cloning of chalcone-flavanone isomerase cDNA from Pueraria lobata and its overexpression in Escherichia coli

Chalcone-flavanone isomerase (CHI) cDNA was isolated from Pueraria lobata by combination of cDNA library screening using Phaseolus vulgaris CHI cDNA as a probe and polymerase chain reaction techniques. Analysis of nucleotide sequence of the cloned cDNA revealed a 675-bp open reading frame encoding a 225-amino-acid polypeptide with a molecular weight of 23,803 Da. The CHI cDNA coding region was cloned into pET-3d expression vector and successfully overexpressed in Escherichia coli cells as active CHI enzyme. The recombinant CHI was then purified to apparent homogeneity by DEAE-cellulose column chromatography. Replacement of Cys-119 with Ala was carried out by site-directed mutagenesis and the result that the mutant CHI showed CHI enzyme activity confirmed that Cys-119 is not involved in the CHI catalytic active site.

cDNA and genomic DNA clonings of chalcone synthase from Pueraria lobata

Four cDNAs encoding chalcone synthase (CHS), the key enzyme in flavonoid biosynthesis, were isolated from Pueraria lobata cells challenged with yeast extract elicitor using bean CHS cDNA as a probe. The longest clone contained a complete open reading frame of 1170 bp which would predict a protein of about 43 kDa. The others were not full-length clones. Using isolated cDNA as a probe, Southern blot hybridization of genomic DNA fragments revealed the presence of multiple CHS genes in the P. lobata genome. We cloned and sequenced one CHS genomic clone, gCHS14, whose 5' untranslated region showed homology with the bean CHS gene CHS15 and included the several reported sequences characteristic of stress response.

Purification and characterization of sulochrin oxidase from Penicillium frequentans

Sulochrin oxidase, an enzyme catalyzing regio- and stereospecific phenol oxidative coupling reaction to form (+)-bisdechlorogeodin from sulochrin, was isolated from Penicillium frequentans CMI 96659. By chromatographies on DEAE-cellulose, hydroxyapatite, Phenyl-Sepharose, Mono P, Mono Q, and HPLC gel filtration columns, sulochrin oxidase was purified to apparent homogeneity. The purified enzyme had a molecular weight of 230 K as estimated by gel filtration and 110 K as estimated by sodium dodecylsulfate-polyacrylamide gel electrophoresis under denaturing conditions, suggesting that the active enzyme was a homodimer. The enzyme showed pI 4.0 and an optimum pH of 6. The enzyme activity was strongly inhibited by the copper-chelating reagent, diethyldithiocarbamate, and did not recover its full activity even after removing the inhibitor by dialysis. However, enzyme activity was fully restored by the addition of Cu2+. Thus, sulochrin oxidase is considered to be a copper protein. The enzyme showed high substrate specificity for benzophenone compounds such as sulochrin and dihydrogeodin.

Transformations of Penicillium islandicum and Penicillium frequentans that produce anthraquinone-related compounds

Wild-type strains of Penicillium islandicum and Penicillium frequentans, which produce anthraquinone and related compounds, were transformed to benomyl and hygromycin B resistance. Plasmids pSV50 and pBT6, with benomyl-resistant beta-tublin genes, and plasmids pAN7-1 and pDH25, with a bacterial hygromycin phosphotransferase gene under the control of Aspergillus nidulans sequences, were used respectively. Transformation frequencies with these plasmids were 10-20 transformants per micrograms of DNA per 4-8 x 10(7) viable protoplasts. Integration of plasmid DNAs into chromosomal DNAs was confirmed by Southern-blot analysis. Copy numbers and sites of integration varied among transformants. The integrated plasmid DNAs conferring a drug-resistant phenotype were mitotically stable with or without selection. The demonstration of such transformation systems in the essential first step in the application of recombinant DNA technology to study the biosynthetic genes of anthraquinone and related compounds in P. islandicum and P. frequentans.

Molecular cloning of cDNA encoding human lanosterol synthase

A cDNA encoding human lanosterol synthase, the enzyme responsible for the backbone formation step in sterol biosynthesis, was cloned by extensive application of PCRs. Five degenerate oligonucleotide primers (139S, 440S, 528A, 575A and 712A) corresponding to the homologous amino acid sequences among the known 2,3-oxidosqualene cyclase(OSC) were designed. PCR with one pair(440S and 528A) of five primers yielded a 285-bp fragment. PCRs with the primers based on the obtained fragment and the degenerate primers (139S and 712A) gave longer fragments. Finally, full nucleotide sequence of cDNA was obtained by a "rapid amplification of cDNA ends" (RACE) method.

Molecular cloning and heterologous expression of the gene encoding dihydrogeodin oxidase, a multicopper blue enzyme from Aspergillus terreus

Aspergillus terreus dihydrogeodin oxidase (DHGO) is an enzyme catalyzing the stereospecific phenol oxidative coupling reaction converting dihydrogeodin to (+)- geodin. We previously reported the purification of DHGO from A. terreus and raised polyclonal antibody against DHGO. From the first cDNA library constructed in lambda gt11 using mRNA from 3-day-old mycelium of A. terreus, four clones were identified using anti-DHGO antibody, but all contained partial cDNA inserts around 280 base pairs. This cDNA fragment was used as a probe to clone the genomic DNA and cDNA for dihydrogeodin oxidase from A. terreus. The sequence of the cloned DHGO genomic DNA and cDNA predicted that the DHGO polypeptide consists of 605 amino acids showing significant homology with multicopper blue proteins such as laccase and ascorbate oxidase. Four potential copper binding domains exist in DHGO polypeptide. The DHGO gene consists of seven exons separated by six short introns. Expression of the DHGO gene in Aspergillus nidulans under the starch or maltose-inducible Taka-amylase A promoter as an active enzyme established the functional identity of the gene. Also, introduction of the genomic DNA for DHGO into Penicillium frequentans led to the production of DHGO polypeptide as judged by Western blot analysis.

Molecular cloning of cDNA encoding rat 2,3-oxidosqualene: lanosterol cyclase

A cDNA encoding rat 2,3-oxidosqualene: lanosterol cyclase, the enzyme responsible for the complex cyclization/rearrangement step in sterol biosynthesis, was cloned by extensive application of PCRs. Oligonucleotide primers were designed in sense and anti-sense directions corresponding to internal peptide sequences of purified enzyme. Successive PCRs with all possible combinations of these primers yielded a 178-bp fragment, and based on its sequence full nucleotide sequence of cDNA was obtained by a "rapid amplification of cDNA ends" (RACE) method.

Nucleotide sequence of the aknA region of the aklavinone biosynthetic gene cluster of Streptomyces galilaeus

A 3.4-kb BamHI fragment that is assumed to be a part of the aklavinone biosynthetic gene cluster of Streptomyces galilaeus 3AR-33 and contains the genes required for the early stage of polyketide biosynthesis was sequenced. The nucleotide sequence of the region that hybridizes to the actIII probe reveals the presence of a gene, aknA, whose deduced protein product is very similar to the ActIII protein and other known oxidoreductases. The predicted AknA protein is believed to be responsible for catalyzing the reduction of the keto group at the ninth carbon from the carboxyl terminus of the assembled polyketide to the corresponding secondary alcohol. The predicted AknA protein has a calculated molecular mass of 27,197 Da (261 amino acids) and the highly conserved sequence Gly-Xaa-Gly-Xaa-Xaa-Ala commonly seen in oxidoreductases. Cloning and sequence analysis of the aknA region of the 2-hydroxyaklavinone-producing strain S. galilaeus ANR-58 identified an alteration in the gene, confirming that the aknA gene is essential for aklavinone biosynthesis.

Post-aromatic deoxygenation in polyketide biosynthesis: reduction of aromatic rings in the biosyntheses of fungal melanin and anthraquinone

Two enzyme reactions involved in the post-aromatic deoxygenation process of fungal melanin and pigments were studied from the viewpoint of enzymic reduction of aromatic rings. Hydroxynaphthalene reductase that catalyzes reduction of the aromatic rings of 1,3,6,8-tetrahydroxynaphthalene and 1,3,8-trihydroxynapthalene was partially purified from Phialophora lagerbergii and characterized. Emodin deoxygenase of Pyrenochaeta terrestris that catalyzes deoxygenation of emodin to afford chrysophanol was found to be resolved into two protein fractions with DEAE-cellulose column. The two protein fractions acted synergistically in regard to emodin deoxygenase activity.

Inhibitors of prostaglandin biosynthesis from Dalbergia odorifera

The root heartwood of Dalbergia odorifera T. Chen (Leguminosae) is a Chinese medicinal drug (Japanese name koshinko) used for a stagnant blood syndrome (stagnation of disordered blood; Japanese, oketsu). In addition to 10 known compounds, five new phenolic compounds, isomucronustyrene and hydroxyobtustyrene (cinnamylphenols), (+)-isoduartin (isoflavan), odoriflavene (isoflav-3-ene) and (-)-odoricarpan (pterocarpan) were isolated and their structures were elucidated on the basis of chemical and spectroscopic methods. Of the fifteen compounds isolated, cinnamylphenols, isoflavans, isoflavene and benzoic acid derivative significantly inhibited prostaglandin biosynthesis as well as platelet aggregation induced by arachidonic acid.

Cloning of aklavinone biosynthesis genes from Streptomyces galilaeus

Aklavinone is an aglycone of aclacinomycin A which is an important antitumor drug. Genes for the biosynthesis of aklavinone were cloned from Streptomyces galilaeus 3AR-33, an aklavinone-producing mutant, by use of the actI and actIII polyketide synthase gene probes. Restriction mapping and Southern analysis of the DNA cloned in a lambda phage vector established that the DNA represented three different regions of the S. galilaeus 3AR-33 genome that contained 3.4, 2.5, and 4.1 kb BamHI fragments which hybridized with actIII. Of those, only the 3.4 kb fragment also hybridized with actI. Complementation experiments with specifically blocked mutants confirmed that the cloned 3.4 kb BamHI fragment contains the genes required for the early stage of polyketide synthesis in aklavinone biosynthesis.

Emodin O-methyltransferase from Aspergillus terreus

Emodin O-methyltransferase, an enzyme catalyzing methylation of the 8-hydroxy group of emodin, was identified in the mould Aspergillus terreus IMI 16043, a (+)-geodin producing strain. The enzyme catalyzed the formation of questin from emodin and S-adenosyl-L-methionine. By chromatography on DEAE-cellulose, Phenyl Sepharose, Q-Sepharose, Hydroxyapatite, and CM-cellulose, emodin O-methyltransferase was purified to apparent homogeneity. The purified protein had a molecular weight of 322 kDa as estimated by gel filtration and 53.6 kDa as estimated by gel electrophoresis under denaturing conditions, suggesting that the active enzyme was a homohexamer. The enzyme showed pI 4.4 and optimum pH 7-8. Magnesium ion or manganese ion was not an absolute requirement, nor increased the enzyme activity. The enzyme had strict substrate specificity and very low Km values for both emodin (3.4 x 10(-7) M) and S-adenosyl-L-methionine (4.1 x 10(-6) M).

Platelet activating factor (PAF) antagonists contained in medicinal plants: lignans and sesquiterpenes

Hot aqueous extracts of medicinal plants were tested for their inhibitory effect on the binding of platelet activating factor (PAF) to rabbit platelets. The extracts of Forsythia suspensa VAHL. (Oleaceae), Arctium lappa L. (Compositae) and Centipeda minima (L.) A. BRAUN et ASCHERS (Compositae) showed significant activities. Since the main constituents of F. suspensa and A. lappa are lignans, 30 lignans were tested for their inhibitory effects on PAF binding to platelets and 9 lignans were found active. Four sesquiterpenes were isolated as active compounds from C. minima. In particular 6-O-angeloylplenolin and 6-O-senecioyplenolin are the most potent and specific PAF antagonists found in this study.

Inhibition of in vitro prostaglandin and leukotriene biosyntheses by cinnamoyl-beta-phenethylamine and N-acyldopamine derivatives

N-trans- and N-cis-Feruloyltyramines were isolated as the inhibitors of in vitro prostaglandin (PG) synthesis from an Indonesian medicinal plant, Ipomoea aquatica (Convolvulaceae). In order to clarify structure activity relationships, cinnamoyl-beta-phenethylamines with possible combinations of naturally occurring cinnamic acids and beta-phenethylamines were synthesized and tested for their inhibitory activities against PG synthetase and arachidonate 5-lipoxygenase. The compounds containing catechol groups such as N-caffeoyl-beta-phenethylamine (CaP) showed higher inhibitory effects on PG synthetase. The catechol group was found to be essential for the inhibition of arachidonate 5-lipoxygenase. The investigation of concentration dependent effects on PG biosynthesis revealed that CaP enhanced PG biosynthesis at a lower concentration range, whereas it inhibited the reaction at a higher concentration. The effects of CaP on each reaction step were investigated with purified PG endoperoxide synthase and microsomal PG synthetase. CaP inhibited the cyclooxygenase reaction, while it enhanced the hydroperoxidase reaction. N-Acyldopamines which contain catechol and lipophylic group were synthesized from dopamine and fatty acids to test their inhibitory effects on arachidonate 5-lipoxygenase. N-Linoleoyldopamine was the most active compound and its IC50 value was 2.3 nM in our assay system, in which an IC50 value of AA 861, a specific inhibitor of 5-lipoxygenase, was 8 nM.

Inhibition of prostaglandin and leukotriene biosynthesis by gingerols and diarylheptanoids

The rhizomes of Zingiber officinale (ginger) and Alpinia officinarum contain potent inhibitors against prostaglandin biosynthesizing enzyme (PG synthetase). Gingerols and diarylhepatanoids were identified as active compounds. Their possible mechanism of action which was deduced from the structures of active compounds indicated that the inhibitors would also be active against arachidonate 5-lipoxygenase, an enzyme of leukotriene (LT) biosynthesis. This was verified by testing their inhibitory effects on 5-lipoxygenase prepared from RBL-1 cells. A diarylheptanoid with catechol group was the most active compound against 5-lipoxygenase, while yakuchinone A was the most active against PG synthetase.

Biologically active constituents of Magnolia salicifolia: inhibitors of induced histamine release from rat mast cells

The extracts of the flower buds of Magnolia salicifolia showed remarkable anti-allergy effects in passive cutaneous anaphylaxis (PCA) test. The bioactive constituents of this medicinal drug were isolated by monitoring their activities with an in vitro bioassay system measuring inhibitory effects on induced histamine release from rat mast cells. Of the ten isolated compounds magnosalicin is a new compound of neolignan structure. In addition to the isolated compounds samples of coumarins and lignans were evaluated their biological activities with the in vitro bioassay.

Biologically active constituents of Centipeda minima: sesquiterpenes of potential anti-allergy activity

Ether, methanol and aqueous extracts of Centipeda minima (Compositae) herbs were found to have significant anti-allergy activities in passive cutaneous anaphylaxis (PCA) test. Three flavonoids, two sesquiterpene lactones and an amide were isolated from this plant material as inhibitors to induced histamine release from mast cells. The sesquiterpenes were identified as isobutyroylplenolin and senecioylplenolin by spectral investigations. The flavonoids and sesquiterpenes exhibited significant anti-allergy activity in PCA test with p.o. administration.

Biologically active constituents of Melaleuca leucadendron: inhibitors of induced histamine release from rat mast cells

Chloroform and methanol extracts of the fruits of Melaleuca leucadendron strongly inhibited histamine release from rat mast cells induced by compound 48/80 or concanavalin A. Ursolic acid, a triterpene, was the most active compound contained in the chloroform extract and two stilbenes, piceatannol and oxyresveratrol, were isolated as active compounds from the methanol extract. Several other stilbenes and related compounds were examined to obtain information on the structure activity relationships of stilbenes.

Identification of emodinanthrone oxygenase in fungus Aspergillus terreus

Emodinanthrone oxygenase, which catalyzes the oxidation of emodinanthrone to emodin, has been identified in fungus, Aspergillus terreus. The fixation of an oxygen atom at the C-10 position of emodinanthrone from molecular oxygen catalyzed by the enzyme was proved by the 18O2 incubation experiment and analyses of the product emodin by mass spectrometry and nuclear magnetic resonance. The fact that the reaction did not require any foreign electron donor suggested the involvement of internal monooxygenase. Emodinanthrone oxygenase activities were found in other microbes which produce anthraquinone related metabolites.

Biologically active constituents of Arnebia euchroma: structures of new monoterpenylbenzoquinones: arnebinone and arnebifuranone

Two quinonic compounds, arnebinone and arnebifuranone, were isolated from the roots of Arnebia euchroma and their structures were elucidated on the basis of spectral evidence. Arnebionone is a monoterpenyl-benzoquinone in which the monoterpene moiety forms a fused ring to the benzoquinone. Arnebifuranone is another monoterpenylbenzoquinone with a furan ring containing side chain which is bonded to the benzoquinone at the head carbon of C10 moiety originating from the geranyl moiety of geranylhydroquinone.

Biologically active constituents of Arnebia euchroma: structure of arnebinol, an ansa-type monoterpenylbenzenoid with inhibitory activity on prostaglandin biosynthesis

Three phenolic compounds were isolated from the roots of Arnebia euchroma as inhibitors of in vitro prostaglandin biosynthesis. Two known compounds were identified as shikonofurans and des-O-methyllasiodiplodin. The other new compound was named arnebinol and its structure was elucidated as a novel ansa-type monoterpenylbenzenoid derivative.

Synergistic action of phenolic signal compounds and carbohydrates in the induction of virulence gene expression of Agrobacterium tumefaciens

Virulence (vir) gene expression of Agrobacterium tumefaciens is activated by plant phenolic compounds such as alpha-hydroxyacetosyringone (HOAS), acetosyringone (AS), methyl syringate, coniferyl alcohol and sinapyl alcohol. Inositol was found to be a potentiating factor of vir-inducing activity, which enhanced the vir-inducing activity of AS and HOAS in a synergistic manner, in particular at a low concentrations of AS and HOAS. Of the other sugars tested D-glucose, L-rhamnose, D-xylose and D-galacturonic acid, the main components of plant cell wall polysaccharides, remarkedly potentiated the vir-inducing activity of AS, indicating the cooperative action of the signal compounds and sugars in Agrobacterium infection to plants.

Isolation, sequence and bacterial expression of a cDNA for chalcone synthase from the cultured cells of Pueraria lobata

cDNA clones for chalcone synthase (CHS) of Pueraria lobata cultured cells were isolated by screening the cDNA library using CHS cDNA of Phaseolus vulgaris as a probe. Analysis of nucleotide sequences of the cloned cDNA revealed a 1170-bp open reading frame that encoded a 390-amino acid polypeptide with an Mr of 43,000. The full-length cDNA was cloned into the expression vector pT7-7. CHS activity was found in the crude extracts of transformed E. coli after induction and two protein bands of ca. 43 and 34 kd were hybridized with anti-persley CHS antiserum.

Purification and some properties of squalene-2,3-epoxide: lanosterol cyclase from rat liver

Squalene-2,3-epoxide: lanosterol cyclase was purified from rat liver in five steps as a soluble and homogeneous protein. The purified enzyme showed a single band on SDS-polyacrylamide gel electrophoresis with a molecular weight of 75 kD. In its native state it behaved as a homo-dimer. The isoelectric point of 5.5 and the apparent Km value for (3S)-squalene-epoxide of 55 microM were estimated for the cyclase.

Reaction mechanism of oxidative rearrangement of flavanone in isoflavone biosynthesis

Microsomes that were prepared from elicitor-treated Pueraria lobata cell cultures catalyzed the conversion of liquiritigenin, a flavanone, into daidzein, an isoflavone. The reaction was resolved into two steps. 2, 7, 4'-Trihydroxyisoflavonone was formed as a major product when liquiritigenin was incubated with carefully washed microsomes in the presence of NADPH. The structure of 2, 7, 4'-trihydroxyisoflavanone was confirmed by mass and 1H NMR spectroscopies. The enzyme responsible for this rearrangement reaction is a cytochrome P-450-dependent monooxygenase. Upon treatment with a soluble enzyme fraction 2, 7, 4'-trihydroxyisoflavone yielded daidzein quantitatively. The incorporation of 18O from 18O2 into the 2-hydroxy group of 2, 7, 4'-trihydroxyisoflavanone was demonstrated by the shift of molecular ion in its mass spectrum. Based on these observations a new reaction mechanism, hydroxylation associated with 1,2-migration, is proposed for the oxidative rearrangement reaction catalyzed by the cytochrome P-450 enzyme of Pueraria lobata.

Inhibition of adenosine 3',5'-cyclic monophosphate phosphodiesterase by flavonoids. III

Sixty-one flavanones, twenty-six isoflavones and eight other flavonoids, obtained from Sophora tomentosa, S. flavescens, Scutellaria baicalensis and other medicinal plants or synthesized, were tested for their inhibitory activity against adenosine 3',5'-cyclic monophosphate (cAMP) phosphodiesterase from beef heart. The structure-activity relationships were investigated.

The screening of Chinese crude drugs for Ca2+ antagonist activity: identification of active principles from the aerial part of Pogostemon cablin and the fruits of Prunus mume

Hot aqueous extracts of 134 Chinese crude drugs were subjected to screening for inhibitory activity on K+ contracture of guinea pig taenia coli, and significant activity was observed in 17 crude drugs. Chemical investigations of two crude drugs, Kakko and Ubai, which originate from Pogostemon cablin and Prunus mume, respectively, were undertaken, and patchouli alcohol (I) and 5-(hydroxymethyl)-2-furaldehyde (II) were identified as their active principles, respectively.

Inhibitory effect of disodium cromproxate on superoxide anion (O2-) generation and membrane potential changes in stimulated neutrophils

Disodium cromproxate is an antiallergic agent. This drug (0.5-2 mmol/L) inhibited O2- production by neutrophils induced by FMLP and PMA. However, the inhibition of FMLP-induced O2- generation was more pronounced than that induced by PMA. Disodium cromproxate also counteracted the changes in membrane potential in neutrophils induced by either FMLP or PMA. The actions of disodium cromproxate differed from those of propranolol, as propranolol had no antagonistic action on membrane potential changes induced by FMLP and PMA.