Screening method for inhibitors against formosan subterranean termite beta-glucosidases in vivo

Cellulose, a main structural constituent of plants, is the major nutritional component for wood-feeding termites. Enzymatic hydrolysis of cellulose to glucose occurs by the action of cellulases, a mixture of the three major classes of enzymes including endo-1,4-beta-glucanases, exo-1,4-beta-glucanases, and beta-glucosidase. Lower termites, such as the Formosan subterranean termite, Coptotermes formosanus Shiraki, require cellulolytic protozoa to efficiently digest cellulose for survival. Inhibitors developed against any of these cellulase system enzymes would be a potential termite treatment avenue. Our effort was to develop a screening system to determine whether termites could be controlled by administration of cellulase system inhibitors. Some reported compounds such as gluconolactone, conduritol B epoxide, and 1-deoxynojirimycin are potential beta-glucosidase inhibitors, but they have only been tested in vitro. We describe an in vivo method to test the inhibitory ability of the designated chemicals to act on beta-1,4-glucosidases, one member of the cellulase system that is the key step that releases glucose for use as an energy and carbon source for termites. Inhibition in releasing glucose from cellooligosaccharides might be sufficient to starve termites. Fluorescein di-beta-D-glucopyranoside was used as the artificial enzyme substrate and the fluorescent intensity of the reaction product (fluorescein) quantified with an automated fluorescence plate reader. Several known in vitro beta-1,4-glucosidase inhibitors were tested in vivo, and their inhibitory potential was determined. Endogenous and protozoan cellulase activities are both assumed to play a role.

Synthesis and glycosidase inhibitory activity of some N-substituted 5a-carba-β-fuco- and β-galactopyranosylamines, and selected derivatives

In the course of chemical modification of alpha-fucosidase inhibitors of 5a-carba-fucopyranosylamine type, an N-dodecyl derivative of the enantiomer 6-deoxy-5a-carba-beta-D-galactopyranosylamine demonstrated very strong inhibition of beta-galactosidase and beta-glucosidase. This finding led us to synthesize corresponding 6-hydroxy compounds, in order to elucidate structure-activity relationships for inhibitors of this type. Among four N-alkyl-5a-carba-beta-D-galactopyranosylamines prepared, the N-octyl derivative could be demonstrated to possess moderate activity toward alpha- and beta-galactosidases, and beta-glucosidase.

Biological Properties of d- and l-1-Deoxyazasugars

L-Enantiomers of 1-deoxynojirimycin (DNJ), 1-deoxymannojirimycin (manno-DNJ), 1-deoxyallonojirimycin (allo-DNJ), 1-deoxyaltronojirimycin (altro-DNJ), 1-deoxygalactonojirimycin (galacto-DNJ), 1-deoxygulonojirimycin (gulo-DNJ), and 1-deoxyidonojirimycin (ido-DNJ) were prepared according to prior methods for the d-enantiomers. These enantiospecific syntheses established unambiguously the absolute configuration of naturally occurring DNJ, manno-DNJ, allo-DNJ, altro-DNJ, and gulo-DNJ. Although d-DNJ and d-galacto-DNJ are known to be powerful competitive inhibitors of alpha-glucosidase and alpha-galactosidase, respectively, with K(i) values in the nM range, l-DNJ and l-galacto-DNJ were noncompetitive inhibitors of alpha-glucosidase and alpha-galactosidase, respectively, with K(i) values in the muM range. However, the azasugar mimicking the structure of the terminal sugar moiety of the natural substrate is not always an inhibitor of the glycosidase responsible for the hydrolysis. d-manno-DNJ is known as a much better inhibitor of alpha-l-fucosidase than alpha-mannosidase, while l-allo-DNJ was a better inhibitor than d-manno-DNJ of alpha-mannosidase. l-galacto-DNJ can be regarded as the 6-hydroxylated derivative of deoxyfuconojirimycin (DFJ), which is a powerful inhibitor of alpha-l-fucosidase with a K(i) value in the nM range. However, this replacement of the methyl group in DFJ by a hydroxymethyl group reduced its affinity by about 50-fold. This suggests that there is a hydrophobic region in or around the active site of alpha-l-fucosidase. It has been found that inhibitors of human lysosomal glycosidases have therapeutic potential for the corresponding lysosomal storage diseases (Nat. Med. 1999, 5, 112; Proc. Natl. Acad. Sci. USA, 2002, 99, 15428). Inhibition of human lysosomal glycosidases by the 1-deoxyazasugars synthesized was investigated. d-galacto-DNJ is a potent inhibitor of lysosomal alpha-galactosidase (IC(50) = 90 nM) and is now being evaluated preclinically for its potential use in Fabry disease, while d-DNJ inhibiting alpha-glucosidase (IC(50) = 40 nM) potently does not appear to become a potential therapeutic agent because of additional inhibitory activity toward glycoprotein processing alpha-glucosidases. On the other hand, although l-allo-DNJ is a moderate inhibitor of alpha-mannosidase (IC(50) = 64 microM), it may become a key compound for the drug design of potential therapeutic agents for alpha-mannosidosis.

Structural Determinants of Substrate Specificity in Family 1 β-Glucosidases

Plant beta-glucosidases play a crucial role in defense against pests. They cleave, with variable specificity, beta-glucosides to release toxic aglycone moieties. The Sorghum bicolor beta-glucosidase isoenzyme Dhr1 has a strict specificity for its natural substrate dhurrin (p-hydroxy-(S)-mandelonitrile-beta-D-glucoside), whereas its close homolog, the maize beta-glucosidase isoenzyme Glu1, which shares 72% sequence identity, hydrolyzes a broad spectrum of substrates in addition to its natural substrate 2-O-beta-D-glucopyranosyl-4-hydroxy-7-methoxy-1,4-benzoxaxin-3-one. Structural data from enzyme.substrate complexes of Dhr1 show that the mode of aglycone binding differs from that previously observed in the homologous maize enzyme. Specifically, the data suggest that Asn(259), Phe(261), and Ser(462), located in the aglycone-binding site of S. bicolor Dhr1, are crucial for aglycone recognition and binding. The tight binding of the aglycone moiety of dhurrin promotes the stabilization of the reaction intermediate in which the glycone moiety is in a deformed (1)S(3) conformation within the glycone-binding site, ready for nucleophilic attack to occur. Compared with the broad specificity maize beta-glucosidase, this different binding mode explains the narrow specificity of sorghum dhurrinase-1.

Iminosugar Glycosidase Inhibitors: Structural and Thermodynamic Dissection of the Binding of Isofagomine and 1-Deoxynojirimycin to β-Glucosidases

The design and synthesis of transition-state mimics reflects the growing need both to understand enzymatic catalysis and to influence strategies for therapeutic intervention. Iminosugars are among the most potent inhibitors of glycosidases. Here, the binding of 1-deoxynojirimycin and (+)-isofagomine to the "family GH-1" beta-glucosidase of Thermotoga maritima is investigated by kinetic analysis, isothermal titration calorimetry, and X-ray crystallography. The binding of both of these iminosugar inhibitors is driven by a large and favorable enthalpy. The greater inhibitory power of isofagomine, relative to 1-deoxynojirimycin, however, resides in its significantly more favorable entropy; indeed the differing thermodynamic signatures of these inhibitors are further highlighted by the markedly different heat capacity values for binding. The pH dependence of catalysis and of inhibition suggests that the inhibitory species are protonated inhibitors bound to enzymes whose acid/base and nucleophile are ionized, while calorimetry indicates that one proton is released from the enzyme upon binding at the pH optimum of catalysis (pH 5.8). Given that these results contradict earlier proposals that the binding of racemic isofagomine to sweet almond beta-glucosidase was entropically driven (Bülow, A. et al. J. Am. Chem. Soc. 2000, 122, 8567-8568), we reinvestigated the binding of 1-deoxynojirimycin and isofagomine to the sweet almond enzyme. Calorimetry confirms that the binding of isofagomine to sweet almond beta-glucosidases is, as observed for the T. maritima enzyme, driven by a large favorable enthalpy. The crystallographic structures of the native T. maritima beta-glucosidase, and its complexes with isofagomine and 1-deoxynojirimycin, all at approximately 2.1 A resolution, reveal that additional ordering of bound solvent may present an entropic penalty to 1-deoxynojirimycin binding that does not penalize isofagomine.

Bioassay screening of Amazonian plants

OBJECTIVE

The purpose of this study was to evaluate several biological activities of thirty plant extracts collected in the North West Amazon (Ecuador). Some of these plants are being used for their reputed medicinal properties by the natives of this region.

METHODS

Five in vitro bioassays were used to screen the plant material. 1. The brine shrimp lethality examination (BSLT) in microplate is a general test that seems capable of detecting a broad spectrum of bioactivity present in crude plant extracts. 2. Free radical scavenging properties were studied in a colorimetric assay using 2,2-diphenyl-1-picrylhydrazyl (DPPH). 3. The beta-glucosidase inhibition test is thought to be a method for the evaluation of anti-AIDS, anti-diabetic or anti-obesity compounds. 4. The xanthine oxidase inhibition assay is used to identify potential anti-gout agents. 5. The antibacterial activity that is being used to isolate and identify antibiotic drugs.

RESULTS

In the BSLT, we found that Piscidia carthagenensis demonstrated very good activity with a LC50: 21.81 micrograms/mL. It is considered that plant extracts with low LC50 values may contain metabolites with cytotoxic, antifungal, insecticidal or pesticide activities. In the antioxidant activity bioassay, several plant extracts were confirmed to have excellent free radical scavenging properties. Rhus juglandifolia and Clusia venusta leaves exhibited an ED50: 3.12 micrograms/mL and 3.61 micrograms/mL, respectively. Piper reticulatum (84%), Inga heteroptera (77%), Clusia venusta (70.9%), and Rhus juglandifolia (70.5%) showed fairly good inhibition activity for beta-glucosidase. On the other hand, none of the plant extracts was capable of inhibiting xanthine oxidase. Finally, the Gram-positive microorganisms Staphylococcus aureus and Corynebacterium diphteriae were found to be sensitive to the majority of the plant extracts, whereas the Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, and Salmonella typhi were proved to be resistant toward the plant extracts.

CONCLUSIONS

It is important to continue investigating our plant kingdom, especially the world tropical reserves as an alternative for finding new or better drugs. It should be essential to follow-up this type of investigation to isolate and elucidate the active principles of the bio-positive plants.

Alkaloidal components in the poisonous plant, Ipomoea carnea (Convolvulaceae)

Natural intoxication of livestock by the ingestion of Ipomoea carnea (Convolvulaceae) sometimes occurs in tropical regions of the world. Polyhydroxylated alkaloids were isolated from the leaves, flowers, and seeds of the poisonous plant and characterized. Chromatographic separation of the leaf extract resulted in the isolation of swainsonine (1), 2-epi-lentiginosine (2), calystegines B(1) (3), B(2) (4), B(3) (5), and C(1) (6), and N-methyl-trans-4-hydroxy-l-proline (7). The contents of 1 in the fresh leaves and flowers were 0.0029 and 0.0028%, respectively, whereas the contents of 1, 3, and 4 in the seeds were approximately 10 times higher than those in the leaves and flowers. Alkaloids 3, 4, and 6 showed a potent inhibitory activity toward rat lysosomal beta-glucosidase, with IC(50) values of 2.1, 0.75, and 0.84 microM, respectively, and alkaloid 5 was a moderate inhibitor of alpha- and beta-mannosidases. Although alkaloid 1 is known as a powerful inhibitor of lysosomal alpha-mannosidase (IC(50) = 0.02 microM), alkaloid 2, which has been thought to be an intermediate in the biosynthesis of 1, was also a potent inhibitor of alpha-mannosidase with an IC(50) value of 4.6 microM.

Interaction between acidic polysaccharides and proteins

There was an ionic interaction between acidic polysaccharides (APS) and proteins at the pH range in which APS were negatively charged and proteins were positively charged, and in enzymes the interaction was detected as a change in the enzyme activity. At pH 4.7, acid phosphatase (pI, 5.4), alpha-glucosidase (pI, 5.7), and beta-glucosidase (pI, 7.3) were inhibited by APS to various extents. On the other hand, alpha-glucosidase and alkaline phosphatase (pI, 4.5) were not inhibited by APS at pH 6.8 and 9.8, respectively, most of these two enzymes being negatively charged at the respective pHs. Sulfated polysaccharides combined with hemoglobin (pI, 6.8 to approximately 7.0) by an ionic bond at pH 2 to make hemoglobin unsusceptible to proteolysis by pepsin, but polyuronides which were not charged at this pH did not affect hydrolysis of hemoglobin.

Unfolding and inactivation of Ampullarium crossean beta-glucosidase during denaturation by guanidine hydrochloride

Changes of activity and conformation of Ampullarium crossean beta-glucosidase in different concentrations of guanidine hydrochloride (GuHCl) have been studied by measuring the fluorescence spectra and its relative activity after denaturation. The fluorescence intensity of the enzyme decreased distinctly with increasing guanidine concentrations, the emission peaks appeared red shifted (from 338.4 to 350.8 nm), whereas a new fluorescence emission peak appeared near 310 nm. Changes in the conformation and catalytic activity of the enzyme were compared. A corresponding rapid decrease in catalytic activity of the enzyme was also observed. The extent of inactivation was greater than that of conformational changes, indicating that the active site of the enzyme is more flexible than the whole enzyme molecule. k(+0)>k(+0)' also showed that the enzyme was protected by substrate to a certain extent during guanidine denaturation.

Synthesis and partial biological evaluation of a small library of differentially-linked beta-C-disaccharides

The synthesis of a small library of differentially-linked beta-C-disaccharides has been carried out through the use of a radical allylation-RCM strategy. Acids 6 were prepared by Keck allylation of a suitable carbohydrate-based radical precursor, followed by oxidative cleavage of the formed alkene. Dehydrative coupling of these acids with the known olefin alcohol 5 then gave the precursor esters 7 in excellent yield. Methylenation of the esters 7 was followed by RCM and in situ hydroboration-oxidation of the formed glycals to furnish the protected beta-C-disaccharides 10 in good overall yield. Five examples were then deprotected and screened for their efficacy as enzyme inhibitors of beta-glycosidase and against several solid-tumor cell lines for in vitro differential cytotoxicity.

Aziridines as a structural motif to conformational restriction of azasugars

In order to investigate the hypothesis that the glycosidase inhibitor isofagomine was bound to alpha- or beta-glucosidase in a 1,4B conformation, a number of bicyclic aziridines that adopt the 1,4B or B1,4 conformations were synthesised and investigated. (1R)-2-endo,3-exo-2,3-Dihydroxy-4-endo-4-hydroxymethyl-6- azabicyclo[3.1.0]hexane (5) and its N-methyl and N-benzyl analogues and (1S)-2-exo-3-endo-2,3-dihydroxy-4- endo-4-hydroxymethyl-6-azabicyclo-[3.1.0]hexane (6) were synthesised. The aziridines 5 and 6 were found to be weak or not inhibitors of alpha-glucosidase, beta-glucosidase and alpha-fucosidase.

Chemical chaperones increase the cellular activity of N370S beta -glucosidase: a therapeutic strategy for Gaucher disease

Gaucher disease is a lysosomal storage disorder caused by deficient lysosomal beta-glucosidase (beta-Glu) activity. A marked decrease in enzyme activity results in progressive accumulation of the substrate (glucosylceramide) in macrophages, leading to hepatosplenomegaly, anemia, skeletal lesions, and sometimes CNS involvement. Enzyme replacement therapy for Gaucher disease is costly and relatively ineffective for CNS involvement. Chemical chaperones have been shown to stabilize various proteins against misfolding, increasing proper trafficking from the endoplasmic reticulum. We report herein that the addition of subinhibitory concentrations (10 microM) of N-(n-nonyl)deoxynojirimycin (NN-DNJ) to a fibroblast culture medium for 9 days leads to a 2-fold increase in the activity of N370S beta-Glu, the most common mutation causing Gaucher disease. Moreover, the increased activity persists for at least 6 days after the withdrawal of the putative chaperone. The NN-DNJ chaperone also increases WT beta-Glu activity, but not that of L444P, a less prevalent Gaucher disease variant. Incubation of isolated soluble WT enzyme with NN-DNJ reveals that beta-Glu is stabilized against heat denaturation in a dose-dependent fashion. We propose that NN-DNJ chaperones beta-Glu folding at neutral pH, thus allowing the stabilized enzyme to transit from the endoplasmic reticulum to the Golgi, enabling proper trafficking to the lysosome. Clinical data suggest that a modest increase in beta-Glu activity may be sufficient to achieve a therapeutic effect.

Involvement of [beta]-glucans in the wide-spectrum antimicrobial activity of Williopsis saturnus var. mrakii MUCL 41968 killer toxin

BACKGROUND

Williopsis saturnus var. mrakii MUCL 41968 secretes a 85-kDa glycoprotein killer toxin (WmKT) that displays a cytocidal activity against a wide range of microorganisms, making WmKT a promising candidate for the development of new antimicrobial molecules. Although the killing mechanism of WmKT is still unknown, the toxin was recently proposed to bind to the surface of sensitive microorganisms through the recognition of beta-glucans. Indeed, Saccharomyces cerevisiae strains sensitive to the toxin become resistant when mutated in their beta-glucan synthesis pathway.

MATERIALS AND METHODS

To investigate the interaction of WmKT with beta-glucans, we examined in agar diffusion assays the WmKT activity in the presence of enzymes displaying beta-glucanase activity. The toxin activity was also investigated using spheroplasts derived from sensitive yeast cells. The hydrolytic activity of WmKT was studied using specific glucosidase inhibitors as well as various sugar molecules covalently linked to p-nitrophenyl as potential substrates. Finally, the ultrastructural modifications induced by WmKT activity on sensitive yeasts were assessed by scanning electron microscopy.

RESULTS

The data reported here support the hypothesis that WmKT binds to sensitive cells using surface-exposed beta-glucans. Indeed beta-glucanase exerts an antagonistic effect on WmKT activity and spheroplasts derived from WmKT-sensitive yeast cells are shown to be resistant to WmKT, suggesting that cell wall beta-glucans are required for WmKT lethal effect. Because WmKT exhibits amino acid sequence similarities with proteins suspected to be glucanase, we also investigated the effect of castanospermine, a potent glucosidase inhibitor, on WmKT activity. Castanospermine completely abolished WmKT killer activity as well as its hydrolytic enzymatic activity against p-nitrophenyl beta-D-glucopyranoside. The scanning electron microscopy analysis of sensitive yeast cells treated with the toxin reveals that WmKT causes cell wall modifications similar to those observed with zymolyase.

CONCLUSION

The results reported in this study show that WmKT activity requires an interaction between the mycocin and the cell wall beta-glucans. Moreover, they indicate that WmKT acts on sensitive yeast cells through a hydrolytic activity directed against cell wall beta-glucans that disrupts the yeast cell wall integrity leading to death.

Inhibition of some hepatic glycosidases by the diseco nucleoside, 4-amino-3-(D-glucopentitol-1-yl)-5-mercapto-1,2,4-triazole and its 3-methyl analog

The in vivo and in vitro effects of 4-amino-3-(D-glucopentitol-1-yl)-5-mercapto-1,2,4-triazole and its 3-methyl analogue on alpha- and beta-glucosidases, beta-glucuronidase as well as alpha-amylase have been investigated. alpha-Glucosidase is the enzyme that is markedly affected in vivo and in vitro in a dose-dependent manner. The compounds showed a reversible inhibition of a competitive type for alpha-glucosidase. Moreover, they exert a relatively potent inhibition on alpha-glucosidase with a Ki magnitude of 3.6 x 10(-4), 9.5 x 10(-5) M.

Castanospermine-trehazolin hybrids: a new family of glycomimetics with tuneable glycosidase inhibitory properties

Bicyclic azasugar glycomimetics related to castanospermine and trehazolin have been prepared from sugar carbodiimides via aminooxazoline intermediates; preliminary enzyme inhibition tests showed a marked dependence of the selectivity and potency towards alpha and beta-glucosidases upon the nature of the exocyclic substituent.

Functional expression of human liver cytosolic beta-glucosidase in Pichia pastoris. Insights into its role in the metabolism of dietary glucosides

Human tissues such as liver, small intestine, spleen and kidney contain a cytosolic beta-glucosidase (CBG) that hydrolyses various beta-d-glycosides, but whose physiological function is not known. Here, we describe the first heterologous expression of human CBG, a system that facilitated a detailed assessment of the enzyme specificity towards dietary glycosides. A full-length CBG cDNA (cbg-1) was cloned from a human liver cDNA library and expressed in the methylotrophic yeast Pichia pastoris at a secretion yield of approximately 10 mg x L-1. The recombinant CBG (reCBG) was purified from the supernatant using a single chromatography step and was shown to be similar to the native enzyme isolated from human liver in terms of physical properties and specific activity towards 4-nitrophenyl-beta-D-glucoside. Furthermore, the reCBG displayed a broad specificity with respect to the glycone moiety of various aryl-glycosides (beta-D-fucosides, alpha-L-arabinosides, beta-D-glucosides, beta-D-galactosides, beta-L-xylosides, beta-D-arabinosides), similar to the native enzyme. For the first time, we show that the human enzyme has significant activity towards many common dietary xenobiotics including glycosides of phytoestrogens, flavonoids, simple phenolics and cyanogens with higher apparent affinities (K(m)) and specificities (k(cat)/K(m)) for dietary xenobiotics than for other aryl-glycosides. These data indicate that human CBG hydrolyses a broad range of dietary glucosides and may play a critical role in xenobiotic metabolism.

Purification and characterization of two beta-glucosidases from the thermophilic fungus Thermoascus aurantiacus

beta-Glucosidase from the fungus Thermoascus aurantiacus grown on semi-solid fermentation medium (using ground corncob as substrate) was partially purified in 5 steps--ultrafiltration, ethanol precipitation, gel filtration and 2 anion exchange chromatography runs, and characterized. After the first anion exchange chromatography, beta-glucosidase activity was eluted in 3 peaks (Gl-1, Gl-2, Gl-3). Only the Gl-2 and Gl-3 fractions were adsorbed on the gel matrix. Gl-2 and Gl-3 exhibited optimum pH at 4.5 and 4.0, respectively. The temperature optimum of both glucosidases was at 75-80 degrees C. The pH stability of Gl-2 (4.0-9.0) was higher than Gl-3 (5.5-8.5); both enzyme activities showed similar patterns of thermostability. Under conditions of denaturing gel chromatography the molar mass of Gl-2 and Gl-3 was 175 and 157 kDa, respectively. Using 4-nitrophenyl beta-D-glucopyranoside as substrate, Km values of 1.17 +/- 0.35 and 1.38 +/- 0.86 mmol/L were determined for Gl-2 and Gl-3, respectively. Both enzymes were inhibited by Ag+ and stimulated by Ca2+.

Synthesis and evaluation of calystegine B2 analogues as glycosidase inhibitors

A practical synthesis of polyhydroxylated 6-oxa-nor-tropanes incorporating the essential structural features of calystegine B(2) from 5-deoxy-5-thioureido and 5-ureido-L-idofuranose precursors is presented. The methodology relies on the ability of pseudoamide-type nitrogen atoms (thiourea, urea, and carbamate) to undergo nucleophilic addition to the masked aldehyde group of the monosaccharide. The generated hemiaminal functionality may further undergo in situ intramolecular glycosidation to give the bicyclic aminoacetal compounds, the whole process being favored by the anomeric effect. A series of derivatives bearing different substituents at nitrogen has been prepared and screened against several glycosidases in comparison with xylonojirimycin-type piperidine analogues. Interestingly, strong and highly specific inhibition of bovine liver beta-glucosidase was observed for 6-oxacalystegine B(2) analogues incorporating aromatic pseudoaglyconic groups. On the basis of these data, a 1-azasugar inhibition mode is proposed for this family of glycomimetics.

[Isolation and properties of cellobiase from Penicillium verruculosum]

Cellobiase (beta-D-glucosidase) with a molecular weight of 100 kDa and pI 5.2 was isolated from the cellulolytic system of Penicillium verruculosum. Kinetic parameters of enzymatic hydrolysis of cellobiose, gentiobiose, sophorose, and synthetic substrates, i.e. methylumbelliferyl and p-nitrophenyl sugar derivatives were determined. Glucose and D-glucose-delta-lactone competitively inhibited cellobiase (Ki = 0.19 mM and 17 microM, respectively). Glucosyl transfer reactions were studied with cellobiose as a single substrate and in the mixture of cellobiose and methylumbelliferyl cellobioside. The product composition was determined in these systems. The ratio of hydrolysis and transfer reaction rates for cellobiose conversion was calculated.

AAA in KAT/DYKAT processes: first- and second-generation asymmetric syntheses of (+)- and (-)-cyclophellitol

Kinetic resolutions and kinetic asymmetric transformations (KAT) as well as dynamic kinetic resolutions and dynamic kinetic asymmetric transformations (DYKAT) are important synthetic protocols. The feasibility of KAT and DYKAT processes for asymmetric allylic alkylations (AAA) is explored utilizing a single substrate--conduritol B tetraesters. Both processes can be performed resulting in excellent enantioselectivity. The impact of nucleophile and leaving group on the effectiveness of each is outlined. The ability to differentiate the various hydroxyl groups is also described. For this purpose, 4-tert-butyldimethylsiloxy-2,2-dimethylbutyric acid was developed as a nucleophile. The utility of effecting KAT/DYKAT processes through the Pd-catalyzed AAA reaction is demonstrated by efficient syntheses of both enantiomers of the potent glycosidase inhibitor cyclophellitol.

Purification and some properties of a beta-glucosidase from Trichoderma harzianum type C-4

Type C-4 strain of Trichoderma harzianum was isolated as a microorganism with high cellulolytic activity. Beta-glucosidase is involved in the last step of cellulose saccharification by degrading cellobiose to glucose, and plays an important role in the cellulase enzyme system with a synergic action with endoglucanase and cellobiohydrolase for cellulose degradation. Beta-glucosidase from T. harzianum type C-4 was purified to homogeneity through Sephacryl S-300, DEAE-Sephadex A-50, and Mono P column chromatographies. It was a single polypeptide with the molecular mass of 75,000 by SDS-PAGE. The enzyme was very active at pH 5.0 and 45 degrees C. No significant inhibition was observed in the presence of metal ions, thiol reagents, or EDTA. The enzyme was stable in the presence of 5% ox gall and digestive enzymes. p-Nitrophenyl-beta-D-cellobioside worked as a substrate for the enzyme as much as p-nitrophenyl-beta-glucopyranoside. Glucose and gluconolactone showed competitive inhibition with a Ki of 1 mM and 1.8 microM, respectively, while galactose, mannose, and xylose did not inhibit the enzyme significantly.

Cloning and characterization of human liver cytosolic beta-glycosidase

Cytosolic beta-glucosidase (EC 3.2.1.21) from mammalian liver is a member of the family 1 glycoside hydrolases and is known for its ability to hydrolyse a range of beta-D-glycosides, including beta-D-glucoside and beta-D-galactoside. We therefore refer to this enzyme as cytosolic beta-glycosidase. We cloned the cDNA encoding the human cytosolic beta-glycosidase by performing PCR on cDNA prepared from total human liver RNA. Specific primers were based on human expressed sequence tags found in the expressed sequence tag database. The cloned cDNA contained 1407 nt with an open reading frame encoding 469 amino acid residues. Amino acid sequence analysis indicates that human cytosolic beta-glycosidase is most closely related to lactase phlorizin hydrolase and klotho protein. The enzyme was characterized by using cell lysates of COS-7 cells transfected with a eukaryotic expression vector containing the cDNA. The biochemical, kinetic and inhibition properties of the cloned enzyme were found to be identical with those reported for the enzyme purified from human liver.

Catalytic mechanism of a family 3 beta-glucosidase and mutagenesis study on residue Asp-247

A family 3 beta-glucosidase (EC 3.2.1.21) from Flavobacterium meningosepticum has been cloned and overexpressed. The mechanistic action of the enzyme was probed by NMR spectroscopy and kinetic investigations, including substrate reactivity, secondary kinetic isotope effects and inhibition studies. The stereochemistry of enzymic hydrolysis was identified as occurring with the retention of an anomeric configuration, indicating a double-displacement reaction. Based on the k(cat) values with a series of aryl glucosides, a Bronsted plot with a concave-downward shape was constructed. This biphasic behaviour is consistent with a two-step mechanism involving the formation and breakdown of a glucosyl-enzyme intermediate. The large Bronsted constant (beta=-0.85) for the leaving-group-dependent portion (pK(a) of leaving phenols >7) indicates substantial bond cleavage at the transition state. Secondary deuterium kinetic isotope effects with 2,4-dinitrophenyl beta-D-glucopyanoside, o-nitrophenyl beta-D-glucopyanoside and p-cyanophenyl beta-D-glucopyanoside as substrates were 1.17+/-0.02, 1.19+/-0.02 and 1.04+/-0.02 respectively. These results support an S(N)1-like mechanism for the deglucosylation step and an S(N)2-like mechanism for the glucosylation step. Site-directed mutagenesis was also performed to study essential amino acid residues. The activities (k(cat)/K(m)) of the D247G and D247N mutants were 30000- and 200000-fold lower respectively than that of the wild-type enzyme, whereas the D247E mutant retained 20% of wild-type activity. These results indicate that Asp-247 is an essential amino acid. It is likely that this residue functions as a nucleophile in the reaction. This conclusion is supported by the kinetics of the irreversible inactivation of the wild-type enzyme by conduritol-B-epoxide, compared with the much slower inhibition of the D247E mutant and the lack of irreversible inhibition of the D247G mutant.

Novel, lipophilic derivatives of 2,5-dideoxy-2,5-imino-D-mannitol (DMDP) are powerful beta-glucosidase inhibitors

Novel derivatives of the D-glucosidase inhibitor 2,5-dideoxy-2,5-imino-D-mannitol bearing lipophilic aliphatic or aromatic amides attached to C-1 have been found to inhibit beta-glucosidase from Agrobacterium sp. in the nanomolar range. One of them, a coumarin derivative, ranks amongst the most active compounds in the class of reversible glycosidase inhibitors of the iminoalditol type.