Synthesis and glycogen phosphorylase inhibitory activity of N-(β-d-glucopyranosyl)amides possessing 1,4-benzodioxane moiety

A series of N-(β-d-glucopyranosyl)amides 5d–i were synthesized by PMe₃ mediated Staudinger reaction of O-peracetylated β-d-glucopyranosyl azide (1) followed by acylation with carboxylic acids 3d–i and subsequent Zemplén deacetylation. The new compounds were tested for their inhibitory activity against rabbit muscle glycogen phosphorylase and the structure–activity relationships of these compounds are also discussed in this paper.     

Growth inhibition of unicellular and colonial Microcystis strains (Cyanophyceae) by compounds isolated from rice (Oryza sativa) hulls

The algicidal effects of crude and pure rice hull extracts on the growth of Microcystis aeruginosa were investigated using cultured unicellular and colonial strains. Upon treatment with rice hull crude extract (RHE), growth inhibition of unicellular M. aeruginosa was much higher than that of colonial M. aeruginosa. However, purified compounds from the crude extract, β-sitosterol-β-d-glucoside and dicyclohexanyl orizane, powerfully inhibited the growth of colonial M. aeruginosa cells. At the same concentrations, the two compounds were almost equipotent (66% and 80% growth inhibition for colonial M. aeruginosa, respectively; P < 0.05). As rice hulls are readily obtainable, and as extracts show high algicidal activity (targeting colonial algae rather than unicellular organisms) at low concentrations, the results suggest that some pure compounds extracted from rice hulls, such as β-sitosterol-β-d-glucoside and dicyclohexanyl orizane, may serve as environmentally friendly agents for controlling the growth of toxic colonial M. aeruginosa in eutrophic waters.     

Expression, purification and characterization of the chitinolytic β-N-acetyl-d-hexosaminidase from the insect Ostrinia furnacalis

Insect β-N-acetyl-d-hexosaminidases are of particular interest due to their multiple physiological roles in many life processes. Chitinolytic β-N-acetyl-d-hexosaminidases, which function only in chitin degradation in insects, have long been regarded as species-specific target potentials in developing environmental friendly pesticides. Here the chitinolytic β-N-acetyl-d-hexosaminidase from the insect Ostrinia furnacalis was cloned and expressed in the yeast strain, Pichia pastoris, to meet the demands of biochemical studies and drug development. Enzymatic assay as well as Western blot confirmed that the high-level expression could be achieved after the induction of methanol for 120 h. Through the sequential combination of ammonium sulfate precipitation, metal chelating chromatography as well as anion exchange chromatography, 7.7 mg of the recombinant OfHex1 with high purity was obtained from 1 liter of culture supernatant. The recombinant OfHex1, characterized as a homodimer with molecular weight of 130 kDa, exhibited the same enzymatic activities as its native form, which could efficiently degrade the chitooligosaccharide substrate (GlcNAc)₂ and release 4-methylumbelliferone (4MU) from substrates, 4MU-β-GlcNAc and 4MU-β-GalNAc. This work provides a low-costing and high-efficient purification procedure for the preparation of insect β-N-acetyl-d-hexosaminidases.     

Using native hydantoinase promoter to induce d-carbamoylase soluble expression in Escherichia coli

By use of PCR, the genes encoding d-carbamoylase from A. radiobacter TH572 were cloned in plasmid pET30a and transformed into Escherichia coli BL21 (DE3) to overexpress d-carbamoylase. However, almost all of the protein remained trapped in inclusion bodies. To improve the expression of the properly folded active enzyme, a constitutive plasmid of pGEMT-DCB was constructed using the native hydantoinase promoter (P_Hase) whose optimal length was confirmed to 209 bp. Furthermore, the RBS region in the downstream of P_Hase was optimized to increase the expression level, so the plasmid pGEMT-R-DCB was constructed and transformed into E. coli strain Top10F′. The enzyme activity of Top10F′/pGEMT-R-DCB grown at 37 °C was found to be 0.603 U/mg (dry cell weight, DCW) and increase 58-fold over cells of BL21 (DE3) harboring the plasmid pET-DCB grown at 28 °C.     

Unique transglycosylation potential of extracellular α-d-galactosidase from Talaromyces flavus

The transglycosylation potential of the extracellular α-d-galactosidase from the filamentous fungus Talaromyces flavus CCF 2686, chosen as the best enzyme from the screening, was investigated using a series of sterically hindered alcohols (primary, secondary and tertiary) as galactosyl acceptors. Nine alkyl α-d-galactopyranosides derived from the following alcohols – tert-butyl alcohol, 2-methyl-2-butyl alcohol, 2-methyl-1-propyl alcohol, 2,2,2-trifluoroethyl alcohol, 2-propyn-1-ol, n-pentyl alcohol, 3,5-dihydroxybenzyl alcohol, 1-phenylethyl alcohol and 1,4-dithio-dl-threitol – were prepared on a semi-preparative scale. This demonstrates a broad synthetic potential of the T. flavus α-d-galactosidase that has not been observed with another enzyme tested. Moreover, this enzyme exhibits good transglycosylation yields (6–34%). The enzymatic synthesis of tert-butyl α-d-galactopyranoside by transglycosylation was studied in detail.     

Steroidal saponins from the rhizomes of Paris delavayi

Two new steroidal saponins, padelaosides A (1) and B (2), along with two other known steroidal saponins (3 and 4) were isolated from the rhizomes of Paris delavayi. Their structures were elucidated by 1D and 2D NMR techniques, HRFTMS, physical data and chemical methods. The two different absolute configurations of fucose, assigned as l and d that were found on compounds 1 and 2, respectively, were simultaneously reported in a natural medicine for the first time.     

Purification and characterization of a thermostable intracellular β-xylosidase from the thermophilic fungus Sporotrichum thermophile

An intracellular β-xylosidase from the thermophilic fungus Sporotricum thermophile strain ATCC 34628 was purified to homogeneity by Q-Sepharose and Mono-Q column chromatographies. The protein properties correspond to molecular mass and pI values of 45 kDa and 4.2, respectively. The enzyme is optimally active at pH 7.0 and 50 °C. The purified β-xylosidase is fully stable at pH 6.0–8.0 and temperatures up to 50 °C and retained over 58% of its activity after 1 h at 60 °C. The enzyme hydrolyzes β-1,4-linked xylo-oligosaccharides with chain lengths from 2 to 6, releasing xylose from the non-reducing end, but is inactive against xylan substrates. The apparent K_m and V_max values from p-nitrophenyl β-d-xylopyranoside are 1.1 mM and 114 μmol p-nitrophenol min⁻¹ mg⁻¹, respectively. Alcohols inactivate the enzyme, ethanol at 10% (v/v) yields a 30% decrease of its activity. The enzyme is irreversibly inhibited by 2,3-epoxypropyl β-d-xylobioside while alkyl epoxides derived from d-xylose were not inhibitors of the enzyme. The enzyme catalyses the condensation reaction using high donor concentration, up to 60% (w/v) xylose.     

Construction and co-expression of polycistronic plasmid encoding d-hydantoinase and d-carbamoylase for the production of d-amino acids

d-Hydantoinase and d-carbamoylase genes from Agrobacterium radiobacter TH572 were cloned by polymerase chain reaction (PCR). The plasmid pUCCH3 with a polycistronic structure that is controlled by the native hydantoinase promoter was constructed to co-express the two genes and transformed into Escherichia coli strain JM105. To obtain the highest level of expression of the d-carbamoylase and avoid intermediate accumulation, the d-carbamoylase gene was cloned closer to the promoter and the RBS region in the upstream of it was optimized. This resulted in high active expression of soluble d-hydantoinase and d-carbamoylase that is obtained without any inducer. Thus, by the constitutive recombinant JM105/pUCCH3, d-p-hydroxyphenylglycine (d-HPG) was obtained directly with 95.2% production yield and 96.3% conversion yield.     

Synthesis of monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside for epitope mapping of anti-Candida albicans antibodies

A panel of six complementary monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside (1) were synthesized by stereoselective glycosylation of monodeoxy and mono-O-methyl monosaccharide acceptors with a 2-O-acetyl-glucosyl trichloroacetimidate donor, followed by a two-step oxidation–reduction sequence at C-2′. The β-manno configurations of the final deprotected congeners 2–7 were confirmed by measurement of ¹J_C1,H1 heteronuclear and ³J_1′,2′ homonuclear coupling constants. These disaccharide derivatives will be used to map the protective epitope recognized by a protective anti-Candida albicans monoclonal antibody C3.1 (IgG3) and to determine its key polar contacts with the binding site.     

Enzymatic resolution of methyl dl-β-acetylthioisobutyrate and dl-β-acetylthioisobutyramide using a stereoselective esterase from Pseudomonas putida IFO12996

Esterase (PpEST) from Pseudomonas putida IFO12996 catalyzes the stereoselective hydrolysis of methyl dl-β-acetylthioisobutyrate (DL-MATI) and dl-β-acetylthioisobutyramide (DL-ATIA) to give d-β-acetylthioisobutyric acid (DAT). DAT is a key intermediate for the synthesis of a series of angiotensin converting enzyme inhibitors. To use enzyme for the DAT production, the PpEST gene of P. putida IFO12996 was cloned and expressed in Escherichia coli. PpEST with a molecular weight of 33 kDa could hydrolyze DL-MATI and DL-ATIA to give DAT with enantiometric excess value (e.e. value) about 97% and enantioselectivity value (E-value) >150, respectively. The kinetic constants of PpEST for DL-MATI and DL-ATIA were examined and they showed that DL-ATIA was a poorer substrate than DL-MATI for PpEST. However, DL-ATIA was 20-fold more soluble in water than DL-MATI, it was more stable than DL-MATI and it did not show substrate inhibition of the PpEST up to 780 mM. This result suggested that PpEST is an esterase but with amidase activity, which can kinetically resolve DL-ATIA to yield DAT and DL-ATIA is a better choice than DL-MATI for industrial production of DAT by the enzymatic resolution method.     

Structural characterization of an active polysaccharide from Phellinus ribis

A water-soluble polysaccharide named as PRP was isolated from the fruiting bodies of Phellinus ribis by hot water extraction, DEAE-cellulose and Superdex 30 column chromatography. Its structural characteristics were investigated by FT-IR, NMR spectroscopy, GLC-MS, methylation analysis, periodate oxidation and Smith degradation. Based on the data obtained, PRP was found to be a β-d-glucan containing a (1 → 4), (1 → 6)-linked backbone, with a single β-d-glucose at the C-3 position of (1 → 6)-linked glucosyl residue every eight residues, along the main chain. The glucan has a weight-average molecular weight of about 8.59 kDa by HPGPC determination using dextran samples as the standards. Preliminary activity tests in vitro revealed that PRP could stimulate the proliferation of spleen lymphocyte.     

Neural cell protective compounds isolated from Phoenix hanceana var. formosana

A platform for screening drugs for their ability to protect neuronal cells against cytotoxicity was developed. Nerve growth factor (NGF) differentiates PC12 cells into nerves, and these differentiated PC12 cells enter apoptosis when challenged with 6-hydroxydopamine (6-OHDA). A screening spectrophotometer was used to assay cytotoxicity in these cells; pretreatment with test samples allowed identification of compounds that protected against this neuronal cytotoxicity. The 95% ethanol extract of Phoenix hanceana Naudin var. formosana Beccari. (PH) showed potential neuroprotective activity in these assays. The PH ethanol extract was further fractionated by sequential partitioning with n-hexane, ethyl acetate (EtOAc), n-butanol (n-BuOH), and water. Subsequent rounds of assaying resulted in the isolation of ten constituents, and their structures were characterized by various spectroscopic techniques and identified by comparison with previous data as: isoorientin (1), isovitexin (2), veronicastroside (3), luteolin-7-O-β-d-glucopyranoside (4), isoquercitrin (5), tricin-7-neohesperidoside (6), tricin-7-O-β-d-gluco-pyranoside (7), (+)-catechin (8), (−)-epicatechin (9), and orientin 7-O-β-d-glucopyranoside (10). Among these compounds, isovitexin (2), luteolin-7-O-β-d-glucopyranoside (4) and (+)-catechin (8) showed significant neuroprotective activity in cell viability (WST-8 reduction), anti-apoptosis (Annexin V-FITC/propidium iodide double-labeled flow cytometry), and cellular ROS scavenging assays (besides isovitexin (2)), as well as a decreased caspase-8 activity in 6-OHDA-induced PC12 cells. Hence, isovitexin (2), luteolin-7-O-β-d-glucopyranoside (4), and (+)-catechin (8) protected PC12 cells from 6-OHDA-induced apoptotic neurotoxicity.     

Inhibitors of bacterial N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) and demonstration of in vitro antimicrobial activity

The dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) is a critical bacterial enzyme for the construction of the bacterial cell wall. A screen biased toward compounds containing zinc-binding groups (ZBG’s) including thiols, carboxylic acids, boronic acids, phosphonates and hydroxamates has delivered a number of micromolar inhibitors of DapE from Haemophilus influenzae, including the low micromolar inhibitor l-captopril (IC₅₀ = 3.3 μM, K_i = 1.8 μM). In vitro antimicrobial activity was demonstrated for l-captopril against Escherichia coli.     

Gene cloning, purification, and characterization of α-methylserine aldolase from Bosea sp. AJ110407 and its applicability for the enzymatic synthesis of α-methyl-l-serine and α-ethyl-l-serine

The gene encoding α-methylserine aldolase was isolated from Bosea sp. AJ110407. Sequence analysis revealed that the predicted amino acid sequence encoded by the 1320-bp open reading frame was 65.0% similar to the corresponding sequence of the enzyme isolated from Ralstonia sp. AJ110405. The gene was expressed in Escherichia coli, and the recombinant enzyme was purified. Gel filtration revealed the molecular mass of the purified enzyme to be approximately 78 kDa, suggesting that the enzyme is a homodimer. The enzyme exhibited a specific peak at 429 nm in the spectrum and contained 1 mol pyridoxal 5′-phosphate per mole of the subunit. The V_max value was 1.40 μmol min⁻¹ mg⁻¹, and the K_m value was 1.5 mM for the reaction wherein formaldehyde was released from α-methyl-l-serine. This enzyme could also catalyze the reverse reaction, i.e., the synthesis of α-methyl-l-serine from l-alanine and formaldehyde. This activity was inhibited in the excess of formaldehyde; however, α-methyl-l-serine was efficiently produced from l-alanine in the presence of formaldehyde. This method was also applicable for producing α-ethyl-l-serine from l-2-aminobutyric acid.     

Screening strains for directed biosynthesis of β-d-mono-glucuronide-glycyrrhizin and kinetics of enzyme production

One fungus, tentatively named Penicillium sp. Li-3, was screened to biosynthesize β-d-mono-glucuronide-glycyrrhizin (GAMG), directly. Using glycyrrhizin as elicitor and the sole carbon source, this strain was capable of expressing β-d-glucuronidase, one intracellular enzyme with high substrate specificity. And glycyrrhizin was hydrolyzed directly into GAMG by enzyme from Penicillium sp. Li-3 with high production. It was found that the mol conversion ratio of this reaction was up to 88.45%. Research about kinetics of β-d-glucuronidase production showed that the cell growth and enzyme production of this strain was partial coupled. During the expressing of target enzyme, carbon catabolite repression existed, so only glycyrrhizin was the best carbon source as well as the elicitor. It was found that the surfactant (Tween 80 0.12%) could improve the ability of enzyme production markedly. Under the condition of initial pH 4.8 of the medium and 32 °C of the culture temperature, the maximum enzyme activity of 181.53 U ml⁻¹ was obtained.     

Chain conformation and anti-tumor activities of phosphorylated (1→3)-β-d-glucan from Poria cocos

(1→3)-β-d-Glucan isolated from Poria cocos was phosphorylated to obtain a series of phosphorylated derivatives. Their structures, weight-average molecular weights (M_w), and chain conformation were studied by ¹³C NMR, ³¹P NMR, static laser light scattering and viscometry. The experimental results revealed that the phosphorylated glucan existed as relatively extended flexible chain in 0.15 M NaCl aqueous solution, and exhibited relatively strong inhibition against S-180 tumor cell in vitro and in vivo. In vivo, the fractions with relatively high molecular weight at low dosage exhibited stronger anti-tumor activities. The results revealed that the molecular weights and molecular conformation could influence the anti-tumor activities. The molecular weight ranging from 2.6 × 10⁴ to 26.8 × 10⁴ and the extended chain conformation were beneficial to enhance the anti-tumor activity, as a result of the increasing of the interaction between polysaccharide and immune system.     

Chain conformation of carboxymethylated derivatives of (1 → 3)-β-d-glucan from Poria cocos sclerotium

A water-insoluble (1 → 3)-β-d-glucan (PCSG) isolated from the fresh sclerotium of Poria cocos was carboxymethylated to afford a water-soluble derivative coded as C-PCSG. The carboxymethylated (1 → 3)-β-d-glucan was fractionated to obtain eight fractions according to the nonsolvent addition method. The weight-average molecular mass (M_w), radius of gyration and intrinsic viscosity ([η]) of the fractions were determined by size-exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry in 0.2 M NaCl aqueous solution at 25 °C. The dependences of [η] and on M_w for C-PCSG were found to be , and (nm), respectively. Analysis of M_w and [η] in terms of the known theories for wormlike chain model yielded 633 nm⁻¹ for molar mass per unit contour length (M_L), 5.5 nm for persistence length (q), and 20.2 for characteristic ratio (C_∞). These results indicated that C-PCSG exists as a relatively extended flexible chain in 0.2 M NaCl aqueous solution. Therefore, the introduction of the carboxymethyl groups into the β-glucan improved significantly the water solubility and enhanced the stiffness of the chains.     

Hepatoprotective potential of Fumaria indica Pugsley whole plant extracts, fractions and an isolated alkaloid protopine

The present investigation demonstrates the hepatoprotective potential of 50% ethanolic water extract of whole plant of Fumaria indica and its three fractions viz., hexane, chloroform and butanol against d-galactosamine induced hepatotoxicity in rats. The hepatoprotection was assessed in terms reduction in histological damage, changes in serum enzymes (SGOT, SGPT, ALP) and metabolites bilirubin, reduced glutathione (GSH) and lipid peroxidation (MDA content). Among fractions more than 90% protection was found with butanol fraction in which alkaloid protopine was quantified as highest i.e. about 0.2 mg/g by HPTLC. The isolated protopine in doses of 10–20 mg p.o. also proved equally effective hepatoprotectants as standard drug silymarine (single dose 25 mg p.o.). In general all treatments excluding hexane fraction proved hepatoprotective at par with silymarine (p0.01).     

[+]-Huperzine A treatment protects against N-methyl-d-aspartate-induced seizure/status epilepticus in rats

The toxicity of organophosphorous (OP) nerve agents is attributed to their irreversible inhibition of acetylcholinesterase (AChE), which leads to excessive accumulation of acetylcholine (ACh) and is followed by the release of excitatory amino acids (EAA). EAAs sustain seizure activity and induce neuropathology due to over-stimulation of N-methyl-d-aspartate (NMDA) receptors. Huperzine A (Hup A), a blood–brain barrier permeable selective reversible inhibitor of AChE, has been shown to reduce EAA-induced cell death by interfering with glutamate receptor-gated ion channels in primary neuronal cultures. Although [−]-Hup A, the natural isomer, inhibits AChE approximately 38-fold more potently than [+]-Hup A, both [−]- and [+]-Hup A block the NMDA channel similarly. Here, we evaluated the protective efficacy of [+]-Hup A for NMDA-induced seizure in a rat model. Rats implanted with radiotelemetry probes to record electroencephalography (EEG), electrocardiography (ECG), body temperature, and physical activity were administered various doses of [+]-Hup A (intramuscularly) and treated with 20 μg/kg NMDA (intracerebroventricular) 20–30 min later. For post-exposure, rats were treated with [+]-Hup A (3 mg/kg, intramuscularly) 1 min after NMDA (20 μg/kg). Our data showed that pre- and post-exposure, [+]-Hup A (3 mg/kg) protects animals against NMDA-induced seizures. Also, NMDA-administered animals showed increased survival following [+]-Hup A treatment. [+]-Hup A has no visible effect on EEG, heart-rate, body temperature, or physical activity, indicating a reduced risk of side effects, toxicity, or associated pathology. Our results suggest that [+]-Hup A protects against seizure and status epilepticus (SE) by blocking NMDA-induced excitotoxicity in vivo. We propose that [+]-Hup A, or a unique combination of [+]- and [−]-Hup A, may prove to be effective for pre- and post-exposure treatment of lethal doses of OP-induced neurotoxicity.     

Mechanisms of catalysis and inhibition operative in the arginine deiminase from the human pathogen Giardia lamblia

Giardia lamblia arginine deiminase (GlAD), the topic of this paper, belongs to the hydrolase branch of the guanidine-modifying enzyme superfamily, whose members employ Cys-mediated nucleophilic catalysis to promote deimination of l-arginine and its naturally occurring derivatives. G. lamblia is the causative agent in the human disease giardiasis. The results of RNAi/antisense RNA gene-silencing studies reported herein indicate that GlAD is essential for G. lamblia trophozoite survival and thus, a potential target for the development of therapeutic agents for the treatment of giardiasis. The homodimeric recombinant protein was prepared in Escherichia coli for in-depth biochemical characterization. The 2-domain GlAD monomer consists of a N-terminal domain that shares an active site structure (depicted by an in silico model) and kinetic properties (determined by steady-state and transient state kinetic analysis) with its bacterial AD counterparts, and a C-terminal domain of unknown fold and function. GlAD was found to be active over a wide pH range and to accept l-arginine, l-arginine ethyl ester, N^α-benzoyl-l-arginine, and N^ω-amino-l-arginine as substrates but not agmatine, l-homoarginine, N^α-benzoyl-l-arginine ethyl ester or a variety of arginine-containing peptides. The intermediacy of a Cys424–alkylthiouronium ion covalent enzyme adduct was demonstrated and the rate constants for formation (k₁ = 80 s⁻¹) and hydrolysis (k₂ = 35 s⁻¹) of the intermediate were determined. The comparatively lower value of the steady-state rate constant (k_cat = 2.6 s⁻¹), suggests that a step following citrulline formation is rate-limiting. Inhibition of GlAD using Cys directed agents was briefly explored. S-Nitroso-l-homocysteine was shown to be an active site directed, irreversible inhibitor whereas N^ω-cyano-l-arginine did not inhibit GlAD but instead proved to be an active site directed, irreversible inhibitor of the Bacillus cereus AD.