Exploring 3-O-glycosylations of 20(R)-dammarane ginsenosides and the catalytic mechanism underlying the stereoselectivity with the combined assistance of AlphaFold 2 and molecular docking

Glycosylation at C3-OH is the favorable modification for pharmaceutical activities and diversity expansion of 20(R)-dammarane ginsenosides. The 3-O-glycosylation, exclusively occurring in 20(R)-PPD ginsenosides, has never been achieved in 20(R)-PPT ginsenosides. Herein, 3-O-glycosylation of 20(R)-PPT enabled by a glycosyltransferase (GT) OsSGT2 was achieved with the combined assistance of AlphaFold 2 and molecular docking. Firstly, we combined AlphaFold2 algorithm and molecular docking to predict interactions between 20(R)-PPT and candidate GTs. A catalytically favorable binding geometry was thus identified in the OsSGT2-20(R)-PPT complex, suggesting OsSGT2 might act on 20(R)-PPT. The enzymatic assays demonstrated that OsSGT2 reacted with varied sugar donors to form 20(R)-PPT 3-O-glycosides, exhibiting donor promiscuity. Additionally, OsSGT2 displayed acceptor promiscuity, catalyzing 3-O-glucosylation of 20(R/S)-PPT, 20(R/S)-PPD and 20(R/S)-Rh1, respectively. Protein engineering on OsSGT2 was thus performed to probe its catalytic mechanism underlying its stereoselectivity. The W207A mutant preferred 20(S)-dammarane aglycons, while F395Q/A396G(QG) displayed a conversion enhancement towards both 20(R/S)-dammarane aglycons. The QG mutant was then used to synthesize 20(R)-PPT 3-O-glucoside, which displayed a moderate angiotensin-converting enzyme inhibitory effect with an IC50 of 27.5 ± 4.7 μM, superior to that of its 20(S)-epimer, with the combined assistance of target fishing and reverse docking. The water solubility of 20(R)-PPT 3-O-glucoside increased as well.

Protein Engineering of PhUGT, a Donor Promiscuous Glycosyltransferase, for the Improved Enzymatic Synthesis of Antioxidant Quercetin 3-O-N-Acetylgalactosamine

Quercetin 3-O-N-acetylgalactosamine (Q3GalNAc), a derivative of dietary hyperoside, had never been enzymatically synthesized due to the lack of well-identified N-acetylgalactosamine-transferase (GalNAc-T). Herein, PhUGT, an identified flavonoid 3-O-galactosyltransferase from Petunia hybrida, was demonstrated to display quercetin GalNAc-T activity, transferring a N-acetylgalactosamine (GalNAc) from UDP-N-acetylgalactosamine (UDP-GalNAc) to the 3-OH of quercetin to form Q3GalNAc with a low conversion of 11.7% at 40 °C for 2 h. Protein engineering was thus performed, and the resultant PhUGT variant F368T got an enhanced conversion of 75.5% toward UDP-GalNAc. The enzymatically synthesized Q3GalNAc exhibited a comparable antioxidant activity with other quercetin 3-O-glycosides. Further studies revealed that PhUGT was a donor promiscuous glycosyltransferase (GT), recognizing seven sugar donors. This finding overturned a previous notion that PhUGT exclusively recognized UDP-galactose (UDP-Gal). The reason why PhUGT was mistaken for a UDP-Gal-specific GT was demonstrated to be a shorter reaction time, in which many quercetin 3-O-glycosides, except hyperoside, could not be effectively synthesized. The fact that the microbial cell factory expressing PhUGT could yield an array of Q3Gs further confirmed the donor promiscuity of PhUGT. This study laid a foundation for the scale production of Q3GalNAc and provided a potent biocatalyst capable of glycodiversifying quercetin as well.

Glycodiversifying Testosterone with a Promiscuous Glycosyltransferase OsSGT2 from Ornithogalum saundersiae

The diversity expansion of testosterone17-O-β-glycosides (TGs) will increase the probability of screening more active molecules from their acetylated derivatives with anticancer activities. Glycosyltransferases (GTs) responsible for the increased diversity of TGs, however, were seldom documented. Herein, a glycosyltransferase OsSGT2 with testosterone glycodiversification capacity was identified from Ornithogalum saundersiae through transcriptome-wide mining. Specifically, OsSGT2 was demonstrated to be reactive with testosterone and eight donors. OsSGT2 displayed both sugar-aglycon and sugar-sugar GT activities. OsSGT2-catalyzed testosterone glycodiversification could be achieved, generating testosterone monoglycosides and disglycosides with varied percentage conversions. Among the eight donors, the conversion of UDP-Glc was the highest, approaching 90%, while the percentage conversions of UDP-GlcNAc, UDP-Gal, helicin, and UDP-Rha were less than 10%. Protein engineering toward F395 was thus performed to improve the conversion of UDP-GlcNAc. Eight variants displayed increased conversions and the mutant F395C got the highest conversion of 72.11 ± 7.82%, eight times more than that of the wild-type. This study provides a promising alternative for diversity expansion of TGs, also significant insights into the molecular basis for the conversion improvement of sugar donors.

Diacerein as a Promising Acyl Donor in Biosynthetic Acetyl-CoA and Glycosyl Esters Mediated by a Multifunctional Maltose O-Acetyltransferase from Escherichia coli

Acetyl-coenzyme A (acetyl-CoA) is an important donor for acetylation modifications of nutritional supplements. The existing enzymatic methods for acetyl-CoA synthesis suffer from cofactor dependence, donor inaccessibility, and biocatalyst instability, leading to its high cost. Hence, a promising alternative is highly desired. Herein, a maltose O-acetyltransferase (MAT) with cofactor independence had been identified as a stable acetyl-CoA-synthesizing biocatalyst in a screen of the Escherichia coli genome. Under the action of MAT, an anthraquinone medicine containing two acetyl groups, diacerein, was screened as an acetyl donor. Saturation mutagenesis at Glu125 was performed to increase the acetyl-CoA-synthesizing capacity of MAT, while decreasing the accompanying hydrolase activities. A mutant MAT-E125F was thus generated and could convert diacerein and CoA into the highest yield of 3892.70 mg/L acetyl-CoA. Moreover, MAT could synthesize puerarin 6″-O-acetate and other glycosyl esters through acetyl-CoA-dependent acetylation or diacerein-based transesterification reaction. To most of the tested glycosides, the transesterification efficiency was higher than that of acetylation. The mutant MAT-E125V acquired the highest conversion of 94.0% to puerarin 6″-O-acetate through transesterification, while MAT-E125N yielded the highest conversion of 68.5% through acetylation. Taking together, the multifunctional MAT displayed a potent acetyl-CoA- and glycosyl ester-synthesizing capacity using diacerein as an acetyl donor.

Altering the Regioselectivity of Cytochrome P450 BM3 Variant M13 toward Genistein through Protein Engineering and Variation of Reaction Conditions

The biocatalysts responsible for the enzymatic synthesis of hydroxygenisteins, derivatives of genistein with multiple activities, usually show regioselective promiscuity, hydroxylating genistein to form a mixture of multiple products, which, in turn, results in a cumbersome separation and purification. Hence, it is highly desired to explore the underlying mechanism regulating the regioselectivity of hydroxylases. M13 is a variant of cytochrome P450 BM3 with oxidant activity toward genistein. Herein, genistein was demonstrated to be hydroxylated by M13 to form a mixture of 3'-hydroxygenistein (3'-OHG) and 8-hydroxygenistein (8-OHG), each giving 4% conversion with a ratio of 1:1. Protein engineering toward M13 was thus performed to improve its regioselectivity. When isoleucine at position 86 was mutated into cysteine, the resultant variant M13I86C displayed improved regioselectivity toward 3'-OHG with an increased conversion of 8.5%. The double mutation M13I86CP18W further boosted the conversion of 3'-OHG to 9.6%, and the ratio of 3'-OHG to 8-OHG increased to 12:1. Conversely, both CoCl₂ and glucose 6-phosphate (G6P) could lead to more 8-OHG. When Co²⁺ reached 37.5 mM, M13I86CP18W could give an 8-OHG conversion of 22.4%. The maximal ratio of 8-OHG to 3'-OHG reached 130 when 62.5 mM Co²⁺ was included in the reaction mixture. With the increase of G6P from 10 to 40 mM, the conversion of M13I86CP18W to 8-OHG gradually increased to 22.6%, while the conversion to 3'-OHG decreased to 6%. Thus, both intrinsic residues and external reaction conditions can affect the regiospecificity of M13, which laid the foundation for the selection of suitable biocatalysts for the hydroxylation of genistein.

Seven new 1-oxygenated cholestane glycosides from Ornithogalum saundersiae

As the continuous scientific research, seven new 1-oxygenated cholestane glycosides named osaundersiosides 1 A - 1 G were isolated from an EtOH extract of the bulbs of Ornithogalum saundersiae. Their structures were deduced by means of spectroscopic data, chemical evidence and the results of hydrolytic cleavage. The cytotoxicity and anti-inflammatory effects of osaundersiosides 1 A - 1 G were evaluated, but none of them displayed significant activities. [Formula: see text].

OcUGT1-Catalyzing Glycodiversification of Steroids through Glucosylation and Transglucosylation Actions

Steroidal glycosides are important sources of innovative drugs. The increased diversification of steroidal glycosides will expand the probability of discovering active molecules. It is an efficient approach to diversify steroidal glycosides by using steroidal glycosyltransferases. OcUGT1, a uridine diphosphate-d-glucose (UDP-Glc)-dependent glycosyltransferase from Ornithogalum caudatum, is a multifunctional enzyme, and its glycodiversification potential towards steroids has never been fully explored. Herein, the glycodiversification capability of OcUGT1 towards 25 steroids through glucosylation and transglucosylation reactions were explored. Firstly, each of 25 compounds was glucosylated with UDP-Glc. Under the action of OcUGT1, five steroids (testosterone, deoxycorticosterone, hydrocortisone, estradiol, and 4-androstenediol) were glucosylated to form corresponding mono-glucosides and biosides. Next, OcUGT1-mediated transglucosylation activity of these compounds with another sugar donor ortho-nitrophenyl-β-d-glucopyranoside (oNPGlc) was investigated. Results revealed that the same five steroids could be glucosylated to generate mono-glucosides and biosides by OcUGT1 through transglucosylation reactions. These data indicated that OcUGT1-assisted glycodiversification of steroids could be achieved through glucosylation and transglucosylation reactions. These results provide a way to diversify steroidal glycosides, which lays the foundation for the increase of the probability of obtaining active lead compounds.

Spectral data for cholestane glycosides from the bulbs of Ornithogalum saundersiae Baker

Herein, the spectral data, including nuclear magnetic resonance spectroscopy (NMR) and mass spectral data, and gas chromatography data of eight cholestane glycosides from Ornithogalum saundersiae Baker (Asparagaceae) bulbs are described. The data are linked with the article entitled “Structure and bioactivity of cholestane glycosides from the bulbs of Ornithogalum saundersiae Baker” (Chen et al., 2019).

Structure and bioactivity of cholestane glycosides from the bulbs of Ornithogalum saundersiae Baker

Eight undescribed cholestane glycosides named osaundersioside A-H, along with three previously known compounds named osaundersioside I-K were isolated from Ornithogalum saundersiae Baker bulbs (Asparagaceae). Their structures were elucidated by extensive spectroscopic analysis and chemical methods. All isolates were evaluated for their cytotoxic activity and inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production. Osaundersioside C was thus determined to exhibit specific cytotoxicity towards MCF-7 cell line with an IC₅₀ value of 0.20 μM, Osaundersioside H exhibited inhibitory effect on NO production in macrophages at the concentration of 10^-5 M, with inhibition rate of 56.81%.

Characterization of two flavonol synthases with iron-independent flavanone 3-hydroxylase activity from Ornithogalum caudatum Jacq

BACKGROUND

Flavonol synthase (FLS) is the key enzyme responsible for the biosynthesis of flavonols, the most abundant flavonoids, which have diverse pharmaceutical effects. Flavonol synthase has been previously found in other species, but not yet in Ornithogalum caudatum.

RESULTS

The transcriptome-wide mining and functional characterisation of a flavonol synthase gene family from O. caudatum were reported. Specifically, a small FLS gene family harbouring two members, OcFLS1 and OcFLS2, was isolated from O. caudatum based on transcriptome-wide mining. Phylogenetic analysis suggested that the two proteins showed the closest relationship with FLS proteins. In vitro enzymatic assays indicated OcFLS1 and OcFLS2 were flavonol synthases, catalysing the conversion of dihydroflavonols to flavonols in an iron-dependent fashion. In addition, the two proteins were found to display flavanone 3β-hydroxylase (F3H) activity, hydroxylating flavanones to form dihydroflavonols. Unlike single F3H enzymes, the F3H activity of OcFLS1 and OcFLS2 did not absolutely require iron. However, the presence of sufficient Fe²⁺ was demonstrated to be conducive to successive catalysis of flavanones to flavonols. The qRT-PCR analysis demonstrated that both genes were expressed in the leaves, bulbs, and flowers, with particularly high expression in the leaves. Moreover, their expression was regulated by developmental and environmental conditions.

CONCLUSIONS

OcFLS1 and OcFLS2 from O. caudatum were demonstrated to be flavonol synthases with iron-independent flavanone 3-hydroxylase activity.

The enzymatic biosynthesis of acylated steroidal glycosides and their cytotoxic activity

Herein we describe the discovery and functional characterization of a steroidal glycosyltransferase (SGT) from Ornithogalum saundersiae and a steroidal glycoside acyltransferase (SGA) from Escherichia coli and their application in the biosynthesis of acylated steroidal glycosides (ASGs). Initially, an SGT gene, designated as OsSGT1, was isolated from O. saundersiae. OsSGT1-containing cell free extract was then used as the biocatalyst to react with 49 structurally diverse drug-like compounds. The recombinant OsSGT1 was shown to be active against both 3β- and 17β-hydroxyl steroids. Unexpectedly, in an effort to identify OsSGT1, we found the bacteria lacA gene in lac operon actually encoded an SGA, specifically catalyzing the acetylations of sugar moieties of steroid 17β-glucosides. Finally, a novel enzymatic two-step synthesis of two ASGs, acetylated testosterone-17-O-β-glucosides (AT-17β-Gs) and acetylated estradiol-17-O-β-glucosides (AE-17β-Gs), from the abundantly available free steroids using OsSGT1 and EcSGA1 as the biocatalysts was developed. The two-step process is characterized by EcSGA1-catalyzed regioselective acylations of all hydroxyl groups on the sugar unit of unprotected steroidal glycosides (SGs) in the late stage, thereby significantly streamlining the synthetic route towards ASGs and thus forming four monoacylates. The improved cytotoxic activities of 3′-acetylated testosterone17-O-β-glucoside towards seven human tumor cell lines were thus observable.

Biosynthesis of 7,8-dihydroxyflavone glycosides via OcUGT1-catalyzed glycosylation and transglycosylation

Herein, a flavonoid glycosyltransferase (GT) OcUGT1 was determined to be able to attack C-8 position of 7,8-dihydroxyflavone (7,8-DHF) via both glycosylation and transglycosylation reactions. OcUGT1-catalyzed glycosylation of 7,8-DHF resulted in the formation of two monoglycosides 7-O-β-D-glucosyl-8-hydroxyflavone (1a), 7-hydroxy-8-O-β-D-glucosylflavone (1b), as well as one diglycoside 7,8-di-O-β-D-glucosylflavone (1c). Under the action of OcUGT1, inter-molecular trans-glycosylations from aryl β-glycosides to 7,8-DHF to form monoglycosides 1a and 1b were observable.

Transcriptome-Wide Identification of an Aurone Glycosyltransferase with Glycosidase Activity from Ornithogalum saundersiae

Aurone glycosides display a variety of biological activities. However, reports about glycosyltransferases (GTs) responsible for aurones glycosylation are limited. Here, the transcriptome-wide discovery and identification of an aurone glycosyltransferase with glycosidase activity is reported. Specifically, a complementary DNA (cDNA), designated as OsUGT1, was isolated from the plant Ornithogalum saundersiae based on transcriptome mining. Conserved domain (CD)-search speculated OsUGT1 as a flavonoid GT. Phylogenetically, OsUGT1 is clustered as the same phylogenetic group with a putative 5,6-dihydroxyindoline-2-carboxylic acid (cyclo-DOPA) 5-O-glucosyltransferase, suggesting OsUGT1 may be an aurone glycosyltransferase. The purified OsUGT1 was therefore used as a biocatalyst to incubate with the representative aurone sulfuretin. In vitro enzymatic analyses showed that OsUGT1 was able to catalyze sulfuretin to form corresponding monoglycosides, suggesting OsUGT1 was indeed an aurone glycosyltransferase. OsUGT1 was observed to be a flavonoid GT, specific for flavonoid substrates. Moreover, OsUGT1 was demonstrated to display transglucosylation activity, transferring glucosyl group to sulfuretin via o-Nitrophenyl-β-d-glucopyranoside (oNP-β-Glc)-dependent fashion. In addition, OsUGT1-catalyzed hydrolysis was observed. This multifunctionality of OcUGT1 will broaden the application of OcUGT1 in glycosylation of aurones and other flavonoids.

Isolation and characterization of a multifunctional flavonoid glycosyltransferase from Ornithogalum caudatum with glycosidase activity

Glycosyltransferases (GTs) are bidirectional biocatalysts catalyzing the glycosylation of diverse molecules. However, the extensive applications of GTs in glycosides formation are limited due to their requirements of expensive nucleotide diphosphate (NDP)-sugars or NDP as the substrates. Here, in an effort to characterize flexible GTs for glycodiversification of natural products, we isolated a cDNA, designated as OcUGT1 from Ornithogalum caudatum, which encoded a flavonoid GT that was able to catalyze the trans-glycosylation reactions, allowing the formation of glycosides without the additions of NDP-sugars or NDP. In addition, OcUGT1 was observed to exhibit additional five types of functions, including classical sugar transfer reaction and three reversible reactions namely NDP-sugar synthesis, sugars exchange and aglycons exchange reactions, as well as enzymatic hydrolysis reaction, suggesting OcUGT1 displays both glycosyltransferase and glycosidase activities. Expression profiles revealed that the expression of OcUGT1 was development-dependent and affected by environmental factors. The unusual multifunctionality of OcUGT1 broadens the applicability of OcUGT1, thereby generating diverse carbohydrate-containing structures.

Functional analyses of OcRhS1 and OcUER1 involved in UDP-L-rhamnose biosynthesis in Ornithogalum caudatum

UDP-L-rhamnose (UDP-Rha) is an important sugar donor for the synthesis of rhamnose-containing compounds in plants. However, only a few enzymes and their encoding genes involved in UDP-Rha biosynthesis are available in plants. Here, two genes encoding rhamnose synthase (RhS) and bi-functional UDP-4-keto-6-deoxy-D-glucose (UDP-4K6DG) 3, 5-epimerase/UDP-4-keto-L-rhamnose (UDP-4KR) 4-keto-reductase (UER) were isolated from Ornithogalum caudatum based on the RNA-Seq data. The OcRhS1 gene has an ORF (open reading frame) of 2019 bp encoding a tri-functional RhS enzyme. In vitro enzymatic assays revealed OcRhS1 can really convert UDP-D-glucose (UDP-Glc) into UDP-Rha via three consecutive reactions. Biochemical evidences indicated that the recombinant OcRhS1 was active in the pH range of 5-11 and over the temperature range of 0-60 °C. The K_m value of OcRhS1 for UDP-Glc was determined to be 1.52 × 10^-4 M. OcRhS1 is a multi-domain protein with two sets of cofactor-binding motifs. The cofactors dependent properties of OcRhS1 were thus characterized in this research. Moreover, the N-terminal portion of OcRhS1 (OcRhS1-N) was observed to metabolize UDP-Glc to form intermediate UDP-4K6DG. OcUER1 contains an ORF of 906 bp encoding a polypeptide of 301 aa. OcUER1 shared high similarity with the carboxy-terminal domain of OcRhS1 (OcRhS1-C), suggesting its intrinsic ability of converting UDP-4K6DG into UDP-Rha. It was thus reasonably inferred that UDP-Glc could be bio-transformed into UDP-Rha under the collaborating action of OcRhS1-N and OcUER1. The subsequently biochemical assay verified this notion. Importantly, expression profiles of OcRhS1 and OcUER1 revealed their possible involvement in the biosynthesis of rhamnose-containing polysaccharides in O. caudatum.

Transcriptome-guided gene isolation and functional characterization of UDP-xylose synthase and UDP-D-apiose/UDP-D-xylose synthase families from Ornithogalum caudatum Ait

The present study first identified the involvement of OcUAXS2 and OcUXS1-3 in anticancer polysaccharides biosynthesis in O. caudatum. UDP-xylose synthase (UXS) and UDP-D-apiose/UDP-D-xylose synthase (UAXS), both capable of converting UDP-D-glucuronic acid to UDP-D-xylose, are believed to transfer xylosyl residue to anticancer polysaccharides biosynthesis in Ornithogalum caudatum Ait. However, the cDNA isolation and functional characterization of genes encoding the two enzymes from O. caudatum has never been documented. Previously, the transcriptome sequencing of O. caudatum was performed in our laboratory. In this study, a total of six and two unigenes encoding UXS and UAXS were first retrieved based on RNA-Seq data. The eight putative genes were then successfully isolated from transcriptome of O. caudatum by reverse transcription polymerase chain reaction (RT-PCR). Phylogenetic analysis revealed the six putative UXS isoforms can be classified into three types, one soluble and two distinct putative membrane-bound. Moreover, the two UAXS isoenzymes were predicted to be soluble forms. Subsequently, these candidate cDNAs were characterized to be bona fide genes by functional expression in Escherichia coli individually. Although UXS and UAXS catalyzed the same reaction, their biochemical properties varied significantly. It is worth noting that a ratio switch of UDP-D-xylose/UDP-D-apiose for UAXS was established, which is assumed to be helpful for its biotechnological application. Furthermore, a series of mutants were generated to test the function of NAD⁺ binding motif GxxGxxG. Most importantly, the present study determined the involvement of OcUAXS2 and OcUXS1-3 in xylose-containing polysaccharides biosynthesis in O. caudatum. These data provide a comprehensive knowledge for UXS and UAXS families in plants.

Transcriptome-enabled discovery and functional characterization of enzymes related to (2S)-pinocembrin biosynthesis from Ornithogalum caudatum and their application for metabolic engineering

Background

(2S)-Pinocembrin is a chiral flavanone with versatile pharmacological and biological activities. Its health-promoting effects have spurred on research effects on the microbial production of (2S)-pinocembrin. However, an often-overlooked salient feature in the analysis of microbial (2S)-pinocembrin is its chirality.

Results

Here, we presented a full characterization of absolute configuration of microbial (2S)-pinocembrin from engineered Escherichia coli. Specifically, a transcriptome-wide search for genes related to (2S)-pinocembrin biosynthesis from Ornithogalum caudatum, a plant rich in flavonoids, was first performed in the present study. A total of 104,180 unigenes were finally generated with an average length of 520 bp. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway mapping assigned 26 unigenes, representing three enzyme families of 4-coumarate:coenzyme A ligase (4CL), chalcone synthase (CHS) and chalcone isomerase(CHI), onto (2S)-pinocembrin biosynthetic pathway. A total of seven, three and one full-length candidates encoding 4CL, CHS and CHI were then verified by reverse transcription polymerase chain reaction, respectively. These candidates were screened by functional expression in E. coli individual or coupled multienzyme reaction systems based on metabolic engineering processes. Oc4CL1, OcCHS2 and OcCHI were identified to be bona fide genes encoding respective pathway enzymes of (2S)-pinocembrin biosynthesis. Then Oc4CL1, OcCHS2 and MsCHI from Medicago sativa, assembled as artificial gene clusters in different organizations, were used for fermentation production of (2S)-pinocembrin in E. coli. The absolute configuration of the resulting microbial pinocembrin at C-2 was assigned to be 2S-configured by combination of retention time, UV spectrum, LC–MS, NMR, optical rotation and circular dichroism spectroscopy. Improvement of (2S)-pinocembrin titres was then achieved by optimization of gene organizations, using of codon-optimized pathway enzymes and addition of cerulenin for increasing intracellular malonyl CoA pools. Overall, the optimized strain can produce (2S)-pinocembrin of 36.92 ± 4.1 mg/L.

Conclusions

High titre of (2S)-pinocembrin can be obtained from engineered E. coli by an efficient method. The fermentative production of microbial (2S)-pinocembrin in E. coli paved the way for yield improvement and further pharmacological testing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0424-8) contains supplementary material, which is available to authorized users.

Transcriptome-guided discovery and functional characterization of two UDP-sugar 4-epimerase families involved in the biosynthesis of anti-tumor polysaccharides in Ornithogalum caudatum

A transcriptome-guided discovery and functional identification of UGE and UXE families were presented. Importantly, OcUGE1/2 and OcUXE1 were preliminarily revealed to be responsible for the biosynthesis of anticancer polysaccharides inO. caudatum.

Transcriptome-wide identification of sucrose synthase genes in Ornithogalum caudatum

A transcriptome-wide discovery and functional identification of a sucrose synthase family was presented. Importantly, OcSus1 and OcSus2 were first verified to be responsible for the biosynthesis of glucose-containing polysaccharides inO. caudatum.

Phenylalanine ammonia-lyase, a key component used for phenylpropanoids production by metabolic engineering

Phenylalanine ammonia-lyase, a versatile enzyme with industrial and medical applications.

cDNA cloning and expression analysis of farnesyl pyrophosphate synthase from Ornithogalum saundersiae

Farnesyl pyrophosphate synthase (FPPS, EC 2.5.1.10) catalyzes the consecutive head-to-tail condensations of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP) to form farnesyl pyrophosphate (FPP), a key precursor of sesquiterpenoids, triterpenoids, sterols, and farnesylated proteins. Here we report the molecular cloning and functional identification of a new full-length cDNA encoding FPPS from Ornithogalum saundersiae, a potential medicinal plant that produces a promising antitumour sterol glycoside, OSW-1. An 1327 bp long unigene with an open reading frame of 1044 bp was retrieved from the transcriptome sequencing of O. saundersiae. The full-length FPPS cDNA, designated OsaFPPS, was isolated from O. saundersiae with gene-specific primers. The resultant OsaFPPS encodes a 347-amino acids protein with a calculated molecular mass of 40,085.6 Da, and a theoretical isoelectric point of 5.01. Phylogenetic tree analysis indicated that OsaFPPS belongs to the plant FPPS super-family. Expression of soluble OsaFPPS in E. coli was verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis. Functional analysis of the purified OsaFPPS protein was carried out using IPP and DMAPP as substrates, and the product was unambiguously determined by gas chromatography-mass spectrometry (GC-MS) analyses.

[A cyclotide against influenza A H1N1 virus from Viola yedoensis]

Three cyclotides were isolated from the whole plant of Viola yedoensis in this study. The two, vary peptide E and cycloviolacin Y5, were previously reported, and a novel cycloviolacin VY1 was characterized according to the interpretation of MS/MS fragmentation of peptides which were produced from the reduced and alkylated parent peptide with the digestion of Endo Lys-C, trypsin and chymotrypsin, separately. The stability of remarkable resistance to proteolytic degradation by trypsin and chymotrypsin, and that of thermal denaturation was confirmed again. Besides, the IC50 value of cycloviolacin VY1 against influenza A H1N1 virus was (2.27 +/- 0.20) microg x mL(-1). It is the first cyclotide reported with anti-influenza A H1N1 virus activity in vitro assay.

Transcriptome-wide identification and characterization of Ornithogalum saundersiae phenylalanine ammonia lyase gene family

Transcriptome-wide identification and characterization ofOrnithogalum saundersiaephenylalanine ammonia lyase gene family.

[Research progresses in synthetic biology of artemisinin]

Abstract: The first-line drug artemisinin is widely used against malaria. Commercially available artemisinin is extracted from plants. However, the lack of sufficient raw material, artemisinin and the cost associated with the drug's manufacture have limited the supply of ACT to most malaria sufferers in the Developing World. As such, it is important to develop a low cost, fine to environment and high-quality method to supply sufficient and reliable quantities of artemisinin in the future. The field of synthetic biology, which utilizes cell factories to manipulate microbial metabolism to enhance the production of artemisinin and its intermediates, has a particularly strong impact by providing new platforms for chemical production. After a brief introduction of the artemisinin biosynthetic pathway, the present review focuses on the introduction of artemisinin biosynthetic genes, such as the genes encoding amorpha-4, 11-diene monooxygenase, NADPH: cytochrome P450 oxidoreductase, artemisinic aldehyde delta 11(13) reductase and aldehyde dehydrogenase. The review also addresses general considerations for potential contributions of synthetic biology to artemisinin production, with an emphasis on factors influencing interest compounds production in chassis cells.

[Construction and preliminary applications of a Saccharomyces cerevisiae detection plasmid using for screening promoter elements]

Synthetic biology of natural products is the design and construction of new biological systems by transferring a metabolic pathway of interest products into a chassis. Large-scale production of natural products is achieved by coordinate expression of multiple genes involved in genetic pathway of desired products. Promoters are cis-elements and play important roles in the balance of the metabolic pathways controlled by multiple genes by regulating gene expression. A detection plasmid of Saccharomyces cerevisiae was constructed based on DsRed-Monomer gene encoding for a red fluorescent protein. This plasmid was used for screening the efficient promoters applying for multiple gene-controlled pathways. First of all, eight pairs of primers specific to DsRed-Monomer gene were synthesized. The rapid cloning of DsRed-Monomer gene was performed based on step-by-step extension of a short region of the gene through a series of PCR reactions. All cloned sequences were confirmed by DNA sequencing. A vector named pEASYDs-M containing full-length DsRed-Monomer gene was constructed and was used as the template for the construction of S. cerevisiae expression vector named for pYeDP60-Ds-M. pYeDP60-Ds-M was then transformed into S. cerevisiae for heterologous expression of DsRed-Monomer gene. SDS-PAGE, Western blot and fluorescence microscopy results showed that the recombinant DsRed-Monomer protein was expressed successfully in S. cerevisiae. The well-characterized DsRed-Monomer gene was then cloned into a yeast expression vector pGBT9 to obtain a promoter detection plasmid pGBT9Red. For determination efficacy of pGBT9Red, six promoters (including four inducible promoters and two constitutive promoters) were cloned by PCR from the S. cerevisiae genome, and cloned into pGBT9Red by placing upstream of DsRed-Monomer gene, separately. The fluorescence microscopy results indicated that the six promoters (GAL1, GAL2, GAL7, GAL10, TEF2 and PGK1) can regulate the expression of DsRed-Monomer gene. The successful construction of pGBT9Red lays the foundation for further analysis of promoter activity and screening of promoter element libraries.

[The advance in synthetic biology: towards a microbe-derived paclitaxel intermediates]

The synthetic biology matures to promote the heterologous biosynthesis of the well-known drug paclitaxel that is one of the most important and active chemotherapeutic agents for the first-line clinical treatment of cancer. This review focuses on the construction and regulation of the biosynthetic pathway of paclitaxel intermediates in both Escherichia coli and Saccharomyces cerevisiae. In particular, the review also features the early efforts to design and overproduce taxadiene and the bottleneck of scale fermentation for producing the intermediates.

[Rapid cloning and functional characterization of hypericin synthase gene]

Hypericin, a red-colored naphtodianthrone, is a natural product synthesized in the medicinal plant Hypericum perforatum, commonly known as St. John's wort. Hypericin has attracted a growing attention of the pharmaceutical industry because of its potential application to various therapies, including the treatment of depression and remarkable antiviral and photodynamic activities, hyp-1 gene encodes for phenolic coupling protein which catalyzes in vitro direct and specific conversion of emodin to hypericin which, however, has not formed common opinion so far. Six pairs of primers specific to hyp-1 gene were synthesized. The rapid cloning of hyp-1 gene was performed based on step-by-step extension of a short region of the gene through a series of PCR reactions. All cloned sequences were confirmed by DNA sequencing. A vector named pET32ahyp containing hyp-1 gene was constructed and was transformed into E. coli to induce heterologous expression. SDS-PAGE and Western blot results showed the recombinant Hyp-1 protein was expressed successfully in E. coli. The soluble fraction was used to test the function of the recombinant Hyp-1. Hypericin was detected by LC-MS/MS with emodin as a substrate under in vitro conditions. The above results corroborated the Hyp-1 function, a confusing question, which lay a material foundation for the synthesis of hypericin by synthetic biotechnology.

A rapid approach to high-resolution fluorescence imaging in semi-thick brain slices

A fundamental goal to both basic and clinical neuroscience is to better understand the identities, molecular makeup, and patterns of connectivity that are characteristic to neurons in both normal and diseased brain. Towards this, a great deal of effort has been placed on building high-resolution neuroanatomical maps(1-3). With the expansion of molecular genetics and advances in light microscopy has come the ability to query not only neuronal morphologies, but also the molecular and cellular makeup of individual neurons and their associated networks(4). Major advances in the ability to mark and manipulate neurons through transgenic and gene targeting technologies in the rodent now allow investigators to 'program' neuronal subsets at will(5-6). Arguably, one of the most influential contributions to contemporary neuroscience has been the discovery and cloning of genes encoding fluorescent proteins (FPs) in marine invertebrates(7-8), alongside their subsequent engineering to yield an ever-expanding toolbox of vital reporters(9). Exploiting cell type-specific promoter activity to drive targeted FP expression in discrete neuronal populations now affords neuroanatomical investigation with genetic precision. Engineering FP expression in neurons has vastly improved our understanding of brain structure and function. However, imaging individual neurons and their associated networks in deep brain tissues, or in three dimensions, has remained a challenge. Due to high lipid content, nervous tissue is rather opaque and exhibits auto fluorescence. These inherent biophysical properties make it difficult to visualize and image fluorescently labelled neurons at high resolution using standard epifluorescent or confocal microscopy beyond depths of tens of microns. To circumvent this challenge investigators often employ serial thin-section imaging and reconstruction methods(10), or 2-photon laser scanning microscopy(11). Current drawbacks to these approaches are the associated labor-intensive tissue preparation, or cost-prohibitive instrumentation respectively. Here, we present a relatively rapid and simple method to visualize fluorescently labelled cells in fixed semi-thick mouse brain slices by optical clearing and imaging. In the attached protocol we describe the methods of: 1) fixing brain tissue in situ via intracardial perfusion, 2) dissection and removal of whole brain, 3) stationary brain embedding in agarose, 4) precision semi-thick slice preparation using new vibratome instrumentation, 5) clearing brain tissue through a glycerol gradient, and 6) mounting on glass slides for light microscopy and z-stack reconstruction (Figure 1). For preparing brain slices we implemented a relatively new piece of instrumentation called the 'Compresstome' VF-200 (http://www.precisionary.com/products_vf200.html). This instrument is a semi-automated microtome equipped with a motorized advance and blade vibration system with features similar in function to other vibratomes. Unlike other vibratomes, the tissue to be sliced is mounted in an agarose plug within a stainless steel cylinder. The tissue is extruded at desired thicknesses from the cylinder, and cut by the forward advancing vibrating blade. The agarose plug/cylinder system allows for reproducible tissue mounting, alignment, and precision cutting. In our hands, the 'Compresstome' yields high quality tissue slices for electrophysiology, immunohistochemistry, and direct fixed-tissue mounting and imaging. Combined with optical clearing, here we demonstrate the preparation of semi-thick fixed brain slices for high-resolution fluorescent imaging.

[Advances in functional studies of nonstructural proteins and development of antiviral agents for enterovirus 71]

Human enterovirus 71 (EV71) is one of the major etiological agents for the hand, foot, and month disease (HFMD) and is causing frequent, widespread occurrence in the mainland of China. The single positive-stranded RNA genome of EV71 is translated into a single polyprotein which is autocleavaged into structural and nonstructural proteins. The functions of many nonstructural proteins characterized in the life cycle of virus are potential targets for blocking viral replication. This article reviews the studies of the structures and functions of nonstructural proteins of EV71 and the anti-enterovirus 71 drugs targeting on these nonstructural proteins.

[Elucidating the structure of two cyclotides of Viola tianshanica maxim by MALDI TOF/TOF MS analysis]

The cyclotides are a family of cyclic "mini" proteins that occur in Violaceae, Rubiaceae and Cucurbitaceae plant families and contain a head-to-tail cyclic backbone and a cystine knot arranged by three disulfide bonds. To study the natural cyclotides of V tianshanica, dried herb was extracted with 50% ethanol, and the concentrated aqueous extract was subjected to a solvent-solvent partitioning between water and hexane, ethyl acetate and n-butanol, separately. The n-butanol extract containing cyclotides was subjected to column chromatography over Sephadex LH-20, eluted with 30% methanol. The subfractions were directly reduced by DTT and analyzed by reverse-phase HPLC. The peaks with different retention times were shown on the profile of RP-HPLC and collected. The cyclotides were speculated based on masses range from 3 000 to 3 500 Da. The purified cyclotides were reduced with DTT, alkylated with iodoacetamide, and then were cleaved with endoproteinase Glu-C, endoproteinase Lys-C and Trypsin, separately. The digested peptides were purified on RP-HPLC and analyzed on MALDI TOF/TOF analyzer. A new cyclotide, cycloviolacin T1 and a reported cyclotide varv E were systemically determined using MALDI TOF/TOF system. So the method for the isolation and characterization of cyclotides was quickly built up in succession.

[cDNA cloning, heterologous overexpression and activity analysis of cytochrome P450 reductase of Taxus chinensis]

NADPH-cytochrome P450 reductase (CPR), a partner for P450 monooxygenases, serves as the electron donor to almost all eukaryotic cytochrome P450s. One cDNA (TchCPR) encoding cytochrome P450 reductase of T. chinensis was isolated from callus cells. The cDNA contains an open reading frame of 2154 nucleotides which encodes a protein of 717 amino acid residues. The TchCPR has higher similarity to other CPRs of gumnosperms (>82%) than that of angiosperms (<74%). The recombinant full-length TchCPR and a series of N-terminal truncated constructs with N-terminal fusion of His Tag were obtained and induced to express in E. coli B121(DE3), and then purified using affinity chromatography. The truncated forms of N-terminal more than 61 amino acid residues could be efficiently expressed while the truncated mutant of N-terminal 48 amino acid residues and the wild-type TchCPR were not successfully expressed in E. coli cells. The activity of the truncated TchCPR was assayed by measuring the reduction of cytochrome C. The electron transfer activity of the recombinantly purified CPRT61 was 1.6057 nmol of cytochrome C reduced per min per microg TchCPR reductase, and it is higher than that of the other four truncated forms.

[Recent advances in the study of amorpha-4,11-diene synthase and its metabolic engineering]

Amorpha-4,11-diene synthase (ADS) can convert farnesyl pyrophosphate (FPP) to amorpha-4, 11-diene, a precursor of artemisinin. ADS plays an important role in the biosynthesis of artemisinin. This review summarizes the molecular biology and metabolic engineering study of ADS in recent years. The genomic DNA and its cDNA sequences of amorpha-4, 11-diene synthase were cloned from Artemisia annua L. The cDNA encoding amorpha-4, 11-diene synthase contains a 1 641 bp open reading frame coding for 546 amino acids. ADS shows a broad pH optimum and an absolute requirement for divalent metal ions as cofactors. The specificity of ADS to the substrates and products is not high and the formation of amorpha-4, 11-diene by ADS from FPP is achieved by an initial 1, 6-closure with subsequent 1, 10-closure. The ADS cDNA cloned from Artemisia annua L, or totally synthesized by PCR, was introduced into different hosts including E. coli, S. cerevisiae, Nicotiana tabacum L. Arabidopsis thaliana and A. nidulans resulting in varied engineering microorganisms and cells producing amorpha-4, 11-diene. The way to improve the production of amorpha-4, 11-diene was investigated by two strategies such as improving the supply of substrate and directing FPP flux to amorpha-4, 11-diene production from competing pathways.

[Expression, purification and antibody preparation of recombinat SARS-CoV X5 protein]

X5 protein is one of the putative unknown proteins of SARS-CoV. The recombinant protein has been successfully expressed in E. coli in the form of insoluble inclusion body. The inclusion body was dissolved in high concentration of urea. Affinity Chromatography was preformed to purify the denatured protein, and then the product was refolded in a series of gradient solutions of urea. The purified protein was obtained with the purity of > 95% and the yield of 93.3 mg x L(-1). Polyclonal antibody of this protein was obtained, and Western blotting assay indicated that the X5 protein has the strong property of antigen. Sixty-eight percent of the recombinant protein sequence was confirmed by LC-ESI-MS/MS analysis.

[Cloning and bioinformatics analysis of P450 cDNA in Artemisia annua]

OBJECTIVE

Cloning and bioinformatics analysis of P450 cDNA in Artemisia annua.

METHOD

A P450 cDNA gene was cloned from A. annua by RT-PCR. The bioinformatics analysis of the P450 gene was performed.

RESULT

The complete ORF of this P450 cDNA is 1 464 bp and encodes 488 aa. The sequence was reported to GenBank and coded as DQ667171. Bioinformatics analysis of the P450 cDNA showed it encoded an A-type P450 protein with 54. 992 kDa, it's isoelectric point was 8.83 and the possibility of export to mitochondria was 0.893 2.

CONCLUSION

The comparable analysis of the P450 with CYP71AV1 revealed that the two proteins probably performed the same function because of the similar character.

[Optimization of expression condition of SARS-CoV PUPs genes in E. coli]

According to previous studies of SARS-CoV (Severe acute respiratory syndrome coronavirus), a variety of novel accessory genes have been identified in SARS-CoV genome, which were interspersed the structural genes of SARS-CoV and considered to be unique to the SARS-CoV genome. The predicted unknown proteins (PUPs) encoded by the accessory genes might play important roles in the SARS-CoV infection. Three of those genes, called X4, X5 and ORF10, were synthesized and introduced into E. coli to induce expression. SDS-PAGE and Western blotting revealed that the three genes have been expressed in E. coli. The induction of SARS PUPs genes expression in different temperatures, induction times, IPTG concentrations and A values of E. coli cells were performed. The optimal induction condition of SARS-CoV PUPs genes was characterized according to the orthorgonal analysis. The ratio of recombinant proteins of PUPs to total proteins is as follows: X4, 20%; X5, 27.8%; ORF10, 68.5% under the optimum conditions.

Patch-clamp studies in the CNS illustrate a simple new method for obtaining viable neurons in rat brain slices: glycerol replacement of NaCl protects CNS neurons

Viable neurons in brain slices are crucial for electrophysiological studies. The present study describes a new method for obtaining viable cells in several regions of the central nervous system including the ventral tegmental area, the hypothalamus, the periaqueductal grey matter and the spinal cord. The essence of the method was to use a modified artificial cerebrospinal fluid (ACSF) in which all NaCl was replaced initially by equi-osmotic glycerol. This modified glycerol-based ACSF was used during slice preparation. The underlying principle for the modification is to prevent the possible acute neurotoxic effects of passive chloride entry, subsequent cell swelling and lysis. This method significantly increased the live/dead ratio in morphology compared to the normal ACSF or sucrose-base ACSF, in which NaCl was replaced by sucrose. An examination of some electrophysiological and pharmacological properties of the neurons in these preparations, by means of current-clamp and voltage-clamp recordings, revealed similar properties of those neurons obtained with the traditional ACSF method. Due to the increase in the number of viable neurons, the new ACSF increases the productivity of experiments. Based on our data, we propose that this glycerol-based solution may protect CNS neurons.

[Sweet protein thaumatin and it's genetic engineering]

Thaumatin is one of the sweetest substances known to date,it is important to study the thaumatin. The biochemical properties of thaumatin have been clarified clearly. Thaumatin had been isolated and sequenced. The mechanism of the sweetness of thaumatin may be due to the combination of some special groups and the receptors. The exact function of thaumatin is still not clear. Although gene engineering of thaumatin has been carried out for 20 years, there are still some difficulties to be solved for using in the market.

Cellular depolarization of neurons in the locus ceruleus region of the guinea pig associated with the development of tolerance to opioids

These experiments were designed to test two hypotheses: 1) the tolerance induced by morphine pellet implantation in guinea pigs will result in subsensitivity of cells in the locus ceruleus (LC), not only to morphine, but to another agonist acting on a different receptor and transduction system, namely the gamma-aminobutyric acid(A) receptor agonist, muscimol; and 2) The nonspecific (heterologous) tolerance would be associated with a partial depolarization of the tolerant cells and a decrease in the contribution of electrogenic Na(+)/K(+) pumping. Extracellular recording from LC neurons in brain slices from animals implanted with either morphine or placebo pellets established that the tolerant preparations were subsensitive to both morphine and muscimol. Immunocytochemical analysis identified the alpha(3)-subunit as the primary isoform of the Na(+)/K(+) pump in the cells under investigation. Whole-cell patch clamp recording of neurons in brain slices demonstrated that, with electrodes containing 20 mM Na(+) (approximating [Na](i)), tolerant cells were significantly depolarized by a mean of 6.7 mV. Dialysis with antibody specific for the alpha(3)-isoform from patch pipettes produced depolarization of both control and tolerant cells. However, the depolarizing effect of the antibody was less in tolerant cells, suggesting a lesser degree of electrogenic Na(+) pumping. Furthermore, the presence of antibody reduced the membrane potentials of tolerant and placebo cells to equal values, suggesting that the diffusion potentials were not different. In contrast, antibody specific for the alpha(1)-subunit isoform in the pipettes had no effect on membrane potential in either control or tolerant cells. In conclusion, both hypotheses were supported.

Quantification of the alpha(3) subunit of the Na(+)/K(+)-ATPase in developing rat cerebellum

Cerebellar Purkinje neurons of rats have been shown to exhibit a progressive increase in resting membrane potential as the animals develop postnatally. The magnitude of this increase was equivalent in magnitude to the increase in the depolarizing action of ouabain, consistent with a role for the Na(+)/K(+)-pump in the hyperpolarization. Ouabain binding sites in whole cerebellum also increased with age. The present study was undertaken to confirm that the increases in ouabain binding and the electrophysiological responses to ouabain were a consequence of increases in the sodium pump and to determine whether the changes seen at the whole organ level were reflective of changes taking place at the cellular level. Using antibodies directed against the alpha(1), alpha(2), and alpha(3) subunits of the Na(+)/K(+)-ATPase, rats between 13 and 19 days of age exhibited a statistically significant increase in the relative amount of the alpha(3) subunit at the level of the whole organ, as determined by Western and slot blot analyses, with no change in the levels of either the alpha(1) or the alpha(2) subunit. Using immunohistochemistry, the alpha(3) subunit was shown to increase in both the Purkinje cell layer and the white matter during this postnatal time period, while the alpha(1) subunit increased in the granular layer. These results support and extend previous work, which pointed to a role for the electrogenic sodium pump in the developmental increase in Purkinje cell membrane potential. Furthermore, the data provide a cellular mechanism underlying the increase in resting membrane potential, that is, by the specific modulation of the alpha(3) subunit isoform.

Renal cortical Na+-K+-ATPase activity and abundance is decreased in normal pregnant rats

During late pregnancy, the rat undergoes massive plasma volume expansion due to cumulative renal sodium retention. In the present study, conducted in virgin, mid- (days 11-13), and late-pregnant (days 18-20) rats, we measured both Na+-K+-ATPase activity (by coupled enzyme assay) and abundance of the alpha-subunits of the Na+-K+-ATPase (by Western and slot blot analyses) in renal cortex, medulla, and brain stem. Unexpectedly, Na+-K+-ATPase in renal cortex, in both stages of pregnancy, is reduced versus the virgin, consistent with our finding of a reduced quantity of the alpha1-subunit. In renal medulla, there is a small rise in activity at midterm, but there is no difference in either activity or abundance of the alpha1-subunit in late pregnancy, when renal Na retention is maximal. In brain stem, where only alpha2- and alpha3-subunits are evident, pregnancy has no impact on enzyme activity or abundance of either isoform. In conclusion, the outcome of these experiments was unexpected in that we did not observe increased renal Na+-K+-ATPase activity in late pregnancy in the rat. In fact, in renal cortex, Na+-K+-ATPase activity and abundance are reduced. Whatever promotes net sodium retention in pregnancy must be capable of overwhelming this and several other strong natriuretic signals.

Hyperpolarizing effects of morphine, clonidine and 2-chloroadenosine in myenteric neurons associated with tolerance to morphine

Chronic treatment of guinea pigs with morphine produces non-specific subsensitivity (tolerance) of the longitudinal smooth muscle myenteric plexus (LM/MP) preparation of the guinea pig ileum to morphine, clonidine and 2-chloroadenosine correlated with a partial depolarization of myenteric S neurons. The purpose of our investigation was to gain further evidence regarding the cellular mechanism of tolerance. Either morphine or placebo pellets were implanted s.c. in guinea pigs 7 days before the experiment. Subsensitivity was confirmed by a marked decrease of the inhibitory effect of 0.1 microM morphine and 0.3 microM clonidine on neurogenically induced twitches in longitudinal smooth muscle myenteric plexus preparations from the morphine-pretreated guinea pigs. Intracellular microelectrode recording established that only myenteric S neurons that were hyperpolarized by morphine exhibited the depolarized state (difference of 7.2 mV), which occurred without a change in the threshold for initiation of action potentials. S neurons that were hyperpolarized by superfusion with solution containing morphine, 0.1 microM, were acutely hyperpolarized an equivalent amount (6-8 mV) by clonidine, 0.3 microM, or 2-chloroadenosine, 0.1 microM. Morphine and clonidine, but not 2-chloroadenosine, reduced input resistance. The hyperpolarizations and changes in conductance were not different between tolerant and control preparations for any agonist. It is concluded that 1) the receptors for the three agonists are colocalized on selected S neurons, 2) the transduction process for the hyperpolarizing effect of 2-chloroadenosine is different than that for morphine and clonidine, 3) cross-tolerance among the agonists is not a function of altered receptors or signal transduction processes and 4) the depolarized state is associated with tolerance of myenteric S neurons.

Evidence that tolerance and dependence of guinea pig myenteric neurons to opioids is a function of altered electrogenic sodium-potassium pumping

Ouabain acutely depolarizes most types of cells through inhibition of electrogenic Na+,K+ pumping and is a useful tool with which to study conditions that affect electrogenic pumping. Intracellular recording techniques were used with neurons of the guinea pig myenteric plexus/longitudinal muscle preparation exposed to ouabain. Of 35 S neurons exposed to ouabain (1 microM), 15 were hyperpolarized by 10 +/- 2 mV, 11 were depolarized by 8 +/- 2 mV and the remaining neurons had no change in membrane potential. The nonselective potassium channel antagonist tetraethylammonium chloride (TEA; 0.5 mM) alone evoked modest (<5 mV) and inconsistent changes in the resting membrane potential of S neurons. However, in the presence of TEA, the hyperpolarizing response to 1 microM ouabain was eliminated, and the proportion of cells depolarized by ouabain increased from 31% to 83%. Glibenclamide (10 microM) and 100 nM iberiotoxin did not change the pattern of membrane potential changes induced by 1 microM ouabain. Calcium-free buffer eliminated the hyperpolarization and potentiated the depolarization induced by 1 microM ouabain. Ouabain (5 microM), in either the presence or absence of TEA, induced depolarization in all neurons tested (mean, 15-16 mV), indicating a predominant effect of inhibition of electrogenic pumping. These data suggest that ouabain may directly or indirectly activate myenteric S neuron calcium-sensitive potassium channels as well as inhibit the Na+,K+ pump and that TEA will antagonize the former effect. Chronic exposure (morphine pellets) of guinea pigs to morphine resulted in a partial depolarized state of myenteric neurons, as previously reported. Ouabain (5 microM), either with or without TEA, depolarized neurons from chronically morphine-treated guinea pigs very little (5-6 mV) in comparison with naive neurons (15-16 mV). This supports the conclusion that the depolarized state of morphine-tolerant neurons is associated with a reduction in electrogenic Na+,K+ pumping.

Sustained hypertension in Dahl rats. Negative correlation of agonist response to blood pressure

The perfused mesenteric vasculature of Dahl salt-sensitive rats on a high salt diet for 5 days (prehypertensive or early hypertensive) is selectively supersensitive to norepinephrine. The present goal was to determine whether that supersensitivity was maintained as hypertension developed. Littermates of salt-sensitive and salt-resistant rats (Dahl Brookhaven strain) were followed on low or high salt for up to 6 weeks. Systolic blood pressure was elevated in the salt-sensitive, high salt rats after 3 or 6 weeks but not after 5 days of the diet. The perfused mesenteric vascular beds from salt-sensitive rats were supersensitive to norepinephrine and nerve stimulation but not to potassium chloride when the rats had been maintained for 5 days or 3 weeks on the high salt diet. However, responses to norepinephrine declined after 6 weeks of the high salt diet. To determine whether sustained high blood pressure has a negative effect on mesenteric vascular responses, we conducted additional experiments with perfused mesenteric vascular beds from salt-sensitive Brookhaven (high salt, 5 weeks) and Rapp (high salt, 6 weeks) animals. Both groups exhibited significant negative correlations between in vivo systolic pressure and maximal responses of mesenteric vessels to norepinephrine and potassium chloride. We suggest that sustained hypertension in Dahl rats has a negative effect on the contractility of the mesenteric arterial system that, by 5 to 6 weeks, masks the initial supersensitivity to norepinephrine. No effects of any diet on the dilating responses of the mesenteric vessels to acetylcholine were observed in any group.

Functional distribution and role of alpha-1 adrenoceptor subtypes in the mesenteric vasculature of the rat

Because alpha-1 adrenoceptor subtypes are distributed differentially in different arteries, experiments were conducted to determine the functional contribution of these subtypes in conduit vs. resistance vessels. Concentration- or dose-response curves for norepinephrine were obtained from aortic rings, superior mesenteric artery rings or the isolated perfused mesenteric vasculature from male Sprague-Dawley rats. Frequency-response curves to transmural electrical stimulation were obtained from the latter two preparations. The effects of 5-methylurapidil (5-MU), an alpha-1a adrenoceptor antagonist, and chloroethyl-clonidine (CEC), an alpha-1b adrenoceptor antagonist, on contractile responses were determined. In artery rings, 5-MU (30 nM) had no effect on the EC50 of norepinephrine but reduced the maximum response of the mesenteric artery rings by nearly 25%. In the perfused mesenteric vasculature, however, 5-MU (30 nM) shifted the ED50 for norepinephrine about 40-fold while reducing the maximum response by 30%. 5-MU depressed the frequency-response curve in the perfused mesenteric vasculature by nearly 80%, but did not alter the response of artery rings. In aorta, pretreatment with CEC (10 microM) shifted the concentration-response curve of norepinephrine by 800-fold without effecting the maximum. In mesenteric artery rings and perfused mesenteric vasculature, CEC reduced the slope and maximum response of both frequency-response and norepinephrine dose-response curves. Responses to norepinephrine (10 microM) in the perfused mesentery were abolished by 5-MU and reduced only 25% by nifedipine. These data suggest that the density or role of alpha-1a adrenoceptors may be greater in resistance vessels than in conduit vessels.

Dietary fish oil administration retards blood pressure development and influences vascular properties in the spontaneously hypertensive rat (SHR) but not in the stroke prone-spontaneously hypertensive rat (SHR-SP)

In the present study, we compared the blood pressure in the SHR-SP and in the spontaneously hypertensive rat (SHR) after dietary administration of fish oil from 4 to 17 weeks of age. The retarding influence of dietary fish oils on the development of hypertension was prominent in the SHR (26 mmHg) and not evident in the SHR-SP (8 mmHg). The enhanced development of blood pressure in both the SHR and the SHR-SP is characterised by an elevated maximum contraction in the mesenteric vascular bed to sympathetic nerve stimulation and to injected noradrenaline. In SHR, but not SHR-SP, this maximum contraction was significantly attenuated by dietary fish oil. Likewise, acetylcholine mediated relaxation of the isolated aorta was enhanced in preparations from the SHR but not the SHR-SP. These physiological changes were also associated with a change in the total n-3 polyunsaturated fatty acids (PUFAs) content in vascular tissue, which were inversely proportional to the prevailing blood pressure values seen in all three strains of rat receiving dietary fish oils. Platelet activated thromboxane production was equally depressed in WKY (Wistar Kyoto), SHR and SHR-SP rats. The results indicate that the blood pressure lowering effect of fish oil when administered during the period of development of hypertension is much greater in the SHR than it is in the SHR-SP. Furthermore the lowering of blood pressure by fish oil administration is related to a restoration of normal vascular contraction and normal vascular relaxation, but not related to a suppression of serum thromboxane production.

Membrane potential in myenteric neurons associated with tolerance and dependence to morphine

Chronic treatment of guinea pigs with morphine produces subsensitivity (tolerance) of the longitudinal smooth muscle-myenteric plexus preparation to a variety of inhibitory agonists (e.g., mu opioid, alpha adrenoceptor and adenosine receptor agonists) and supersensitivity (dependence) to a variety of excitatory agonists (e.g., nicotine, 5-hydroxytryptamine and potassium ions). The present investigation was to determine if these changes in sensitivity could be related to changes in electrical properties of the S and AH neurons in the myenteric plexus. S neurons from morphine-implanted animals were significantly depolarized (7 mV) relative to those from placebo-implanted animals, whereas the membrane potential of AH neurons was unchanged. Approximately 60% of S neurons were hyperpolarized by morphine. In this subset of neurons, membranes were significantly depolarized but the threshold was unchanged in morphine-implanted animals. This means that resting potentials of S neurons from tolerant preparations are closer to threshold. The hyperpolarization produced by morphine (0.1 microM) was similar in preparations from morphine- and placebo-implanted animals. Thus, the partially depolarized state of S neurons in the myenteric plexus is the cause of the subsensitivity and supersensitivity to agonists and can explain both tolerance and dependence. Changes in opioid receptors or their coupling to potassium channels do not appear to contribute to tolerance in the longitudinal smooth muscle-myenteric plexus.

Age-related changes in pulmonary venous epinephrine concentration, and pulmonary vascular response after intratracheal epinephrine

Using an isolated salt-perfused lung model in rabbits from 1 to 21 d of age, we measured the concentration of epinephrine in the pulmonary venous drainage and the pulmonary vascular response after a single dose of intratracheal epinephrine (0.1 microgram/g body weight). Lungs from 30 rabbits were isolated, ventilated, and perfused at one of four age groups (n = 7-8 per group). After ventilation/perfusion was judged to be stable, saline control was injected into the trachea, changes in pulmonary pressure were recorded, and perfusate was collected for 45 s. After restabilization, epinephrine was injected into the trachea, changes in pulmonary vascular pressure were recorded, and perfusate was collected for 45 s x two aliquots. Perfusate epinephrine concentrations were determined by HPLC. Little epinephrine was detected in the perfusate after control over all age groups, and little vascular response was noted. There was a significant age-related increase in perfusate epinephrine concentration as well as an age-related increase in vascular response (increased PAP), with the maximum epinephrine concentration and change in PAP noted at 14-21 d [group 4 = (1.72 +/- 0.42) x 10(4) pmol/L]. Also, in rabbits less than 6 d of age, deposition of epinephrine into the pulmonary venous drainage was delayed. In the rabbit model, the concentration of epinephrine reaching the heart via pulmonary circulation after intratracheal injection is, at birth, very low, and the pulmonary vascular response is diminished. Both increase as a function of age until 14-21 d of age. These findings may have clinical importance in human neonatal resuscitation endeavors.

Antagonism of norepinephrine by clonidine in the isolated rat mesenteric vascular bed

Experiments were done in isolated, perfused mesenteric vascular beds from Sprague-Dawley rats. Bolus injections of norepinephrine (3-100 nmol) induced dose-dependent increases in perfusion pressure with a maximum increase greater than 100 mm Hg. In the same dose range, clonidine had no effect on perfusion pressure. In the presence of an elevated pressure caused by constant infusions of norepinephrine (6-20 microM), bolus injections of clonidine (0.1-10 nmol) or acetylcholine (0.007-7 nmol) caused dose-related decreases in perfusion pressure. Procedures which damage endothelium (brief exposure to methylene blue or reactive oxygen radicals) abolished the depressor action of acetylcholine but only moderately reduced the depressor action of clonidine. The depressor action of clonidine was not antagonized by the alpha-2 adrenoceptor antagonist, idazoxan. Acetylcholine produced depressor responses in the presence of 5-hydroxy-tryptamine or vasopressin, but clonidine did not. Dose-response curves to bolus doses of norepinephrine were shifted markedly to the right by an alpha-1 selective concentration of prazosin (1 nM) and were shifted to the right with depression of maximum by infusions of clonidine (0.3 and 1.0 microM). It is concluded that, in the mesenteric vasculature of the rat: 1) the role of alpha-2 adrenoceptors, in responses to clonidine, is minimal; 2) endothelial factors play little role, if any, in the depressor effects of clonidine and 3) clonidine has a potent ability to interfere with the alpha-1 adrenoceptor-mediated vasoconstriction induced by norepinephrine. This antagonistic action may be at the level of the receptor but could involve postreceptor steps.

Mesenteric vascular responses of young spontaneously hypertensive rats

Frequency-responses curves for nerve stimulation and dose-response curve for norepinephrine, 5-hydroxytryptamine potassium chloride, vasopressin and acetylcholine (ACh) were determined in isolated, perfused mesenteric vascular beds from young (approximately 5 weeks) spontanelouly hypertensive (SHR) and Wistar Kyoto rats. Although mean systolic blood pressure (measured by tail cuff plethysmography) was slightly higher in the SHR, this difference was not significant. Slopes and maximum responses were increased significantly for nerve stimulation and all agonists. The basal perfusion pressure was also significantly elevated in the SHR. These differences are consistent with existing evidence that structural changes occur in blood vessels of SHR at an early stage and probably precede development of hypertension. Such structural changes could therefore contribute to development of the hypertension. Cocaine (1 microM) markedly increased responses to nerve stimulation and bolus injections of norepinephrine in preparations from SHR with little or no effect on such responses in Wistar Kyoto preparations, a result consistent with the known greater density of noradrenergic nerves in SHR vasculature. In the presence of cocaine, there was unmasked a selective super-sensitivity (significantly lower ED50) to norepinephrine in the SHR. Thus SHR mesenteric vessels may possess an alteration in adrenoreceptors or their coupling to other cellular mechanisms. Responses to ACh revealed no indication of a deficient endothelial mediated relaxation. An altered media:lumen ratio of small arteries, hypernoradrenergic innervation and supersensitivity to the transmitter may contribute to development of hypertension.