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Homology modeling and molecular interaction field studies of alpha-glucosidases as a guide to structure-based design of novel proposed anti-HIV inhibitors.

For AIDS therapy, there are currently a number of compounds available for multiple targets already approved by the FDA and in clinic, e.g. protease inhibitors, reverse transcriptase inhibitors (NRTI, NNRTI), fusion inhibitors, CCR4, CCR5 among others. Some pharmaceuticals act against the virus before the entrance of HIV into the host cells. One of these targets is the glucosidase protein. This novel fusion target has been recently explored because the synthesis of viral glycoproteins depends on the activity of enzymes, such as glucosidase and transferase, for the elaboration of the polysaccharides. In this work we have built an homology model of Saccharomyces cerevisiae glucosidase and superimposed all relevant glucosidase-like enzymes in complex with carbohydrates, and calculated as well molecular interaction fields in our S. cerevisiae active site model. Our results suggest that there are two saccharide binding sites which are the most important for the binding of inhibitors with this family of enzymes which supports the possibility of inhibitors containing only two sugar units. Based on these results, we have proposed a novel pseudo-dissacharide which is a potential pharmaceutical for AIDS treatment.

Anti-HIV Agents↗

Miglustat (NB-DNJ) works as a chaperone for mutated acid beta-glucosidase in cells transfected with several Gaucher disease mutations.

Gaucher disease (GD) is a disorder of glycosphinglipid metabolism caused by deficiency of lysosomal acid beta-glucosidase (GC), resulting in progressive deposition of glucosylceramide in macrophages. The glucose analogue, N-butyl-deoxynojirimycin (NB-DNJ, Miglustat), is an inhibitor of the ceramide-specific glucosyltransferase (CSG) which catalyzes the first step of glycosphingolipids biosynthesis and is currently approved for the oral treatment of type 1 GD. Using site-directed mutagenesis, we constructed plasmids containing wild-type and several mutations in glucocerebrosidase (GBA) gene. The plasmids were transfected into COS-7 cells and stable transfected cell lines were obtained by geneticin (G418) selection. Cells were cultured during 6 days with medium with or without 10 microM NB-DNJ. The addition of NB-DNJ to COS-7 cell medium leads to 1.3-, 2.1-, 2.3-, 3.6-, and 9.9-fold increase in the activity of S364R, wild-type, N370S, V15M, and M123T GC, respectively. However, no significant changes were observed in the activity of the L444P, L336P, and S465del mutated proteins, but a small decrease in the rare P266L variant was observed. These results suggest that NB-DNJ, in addition to the inhibitory effect on CSG, also works as a "chemical chaperone", increasing the activity of acid beta-glucosidase of wild-type and several GC mutated proteins, including the most frequent N370S mutation. The specific location of the Miglustat binding site in GC is unknown. Potential binding sites in the enzyme have been searched for using computational molecular docking. The searching strategy identified three potential GC binding sites for Miglustat, one being the substrate-binding site of the enzyme, which was the best-ranked site by AutoDock program. Therefore, it is possible that Miglustat exerts its chaperoning activity on acid beta-glucosidase by acting as an inhibitor bound at the active site. This increase on the activity of the acid beta-glucosidase would imply that Miglustat is not only a substrate reducer but also an inhibitor of the GC degradation, with very promising clinical implications for the treatment of GD patients.

1-Deoxynojirimycin↗

Structure-activity relationships of trans-cinnamic acid derivatives on alpha-glucosidase inhibition.

trans-Cinnamic acid and its derivatives were investigated for the alpha-glucosidase inhibitory activity. 4-Methoxy-trans-cinnamic acid and 4-methoxy-trans-cinnamic acid ethyl ester showed the highest potent inhibitory activity among those of trans-cinnamic acid derivatives. The presence of substituents at 4-position in trans-cinnamic acid altered the alpha-glucosidase inhibitory activity. Increasing of bulkiness and the chain length of 4-alkoxy substituents as well as the increasing of the electron withdrawing group have been shown to decrease the inhibitory activity. 4-Methoxy-trans-cinnamic acid was a noncompetitive inhibitor for alpha-glucosidase, whereas, 4-methoxy-trans-cinnamic acid ethyl ester was a competitive inhibitor. These results indicated that trans-cinnamic acid derivatives could be classified as a new group of alpha-glucosidase inhibitors.

Cinnamates↗

Aglycon specificity profiling of alpha-glucosidases using synthetic probes.

We designed and synthesized hydrogen bond based probes 1-8 with the exception of known glycosidase inhibition mechanisms, and aglycon specificity of 11 different sources of alpha-glucosidases were investigated using their probes. Probe 4 (2,6-anhydro-1-deoxy-1-[(1-oxopentyl-5-hydroxy)amino]-D-glycero-D-ido-heptitol) showed a potent inhibition of S. cerevisiae alpha-glucosidase among all alpha-glucosidases. Probe 4 was found to be a competitive inhibitor for S. cerevisiae alpha-glucosidase with Ki 0.13 mM.

1-Deoxynojirimycin↗

Crystal structure at 1.1 Angstroms resolution of an insect myrosinase from Brevicoryne brassicae shows its close relationship to beta-glucosidases.

The aphid Brevicoryne brassicae is a specialist feeding on Brassicaceae plants. The insect has an intricate defence system involving a beta-D-thioglucosidase (myrosinase) that hydrolyses glucosinolates sequestered from the host plant into volatile isothiocyanates. These isothiocyanates act synergistically with the pheromone E-beta-farnesene to form an alarm system when the aphid is predated. In order to investigate the enzymatic characteristics of the aphid myrosinase and its three-dimensional structure, milligram amounts of pure recombinant aphid myrosinase were obtained from Echerichia coli. The recombinant enzyme had similar physiochemical properties to the native enzyme. The global structure is very similar to Sinapis alba myrosinase and plant beta-O-glucosidases. Aphid myrosinase has two catalytic glutamic acid residues positioned as in plant beta-O-glucosidases, and it is not obvious why this unusual enzyme hydrolyses glucosinolates, the common substrates of plant myrosinases which are normally not hydrolyzed by plant beta-O-glucosidases. The only residue specific for aphid myrosinase in proximity of the glycosidic linkage is Tyr180 which may have a catalytic role. The aglycon binding site differs strongly from plant myrosinase, whereas due to the presence of Trp424 in the glucose binding site, this part of the active site is more similar to plant beta-O-glucosidases, as plant myrosinases carry a phenylalanine residue at this position.

Amino Acid Sequence↗

Alpha-glucosidase inhibitors as potential broad based anti-viral agents.

N-Linked oligosaccharides play many roles in the fate and functions of glycoproteins. One function is to assist in the folding of proteins by mediating interactions of the lectin-like chaperone proteins calnexin and calreticulin with nascent glycoproteins. These interactions can be prevented by inhibitors of the alpha-glucosidases and this causes some proteins to be misfolded and retained within the endoplasmic reticulum. In human immunodeficiency virus (HIV) and hepatitis B virus (HBV) the misfolding of key viral envelope glycoproteins interferes with the viral life cycle. It has been demonstrated in an animal model of chronic HBV that glucosidase inhibitors can alter glycosylation and have anti-viral activity. As the mechanism of action of alpha-glucosidase inhibitors is the induction of misfolded or otherwise defective viral glycoproteins, such inhibitors may be useful therapeutics for many viruses, especially those which bud from the endoplasmic reticulum (where protein folding takes place). For example bovine viral diarrhea virus, a pestivirus akin to hepatitis C virus, is also extremely sensitive to glucosidase inhibition.

Animals↗

Purification and characterisation of a beta-glucosidase abundantly expressed in ripe sweet cherry (Prunus avium L.) fruit.

A beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) was purified to homogeneity from ripe fruits of sweet cherry (Prunus avium L.) by ammonium sulphate precipitation, ion exchange and size exclusion chromatography. The enzyme is a monomer with a molecular mass of approximately 68 kDa and an acidic isoelectric point. N-terminal sequence analysis indicated that sweet cherry beta-glucosidase is related to other plant cyanogenic beta-glucosidases. Substrate specificity studies revealed that the enzyme is able to attack and hydrolyse several synthetic substrates and total cell walls purified from ripe fruit. Biochemical and immunolocalisation studies showed that sweet cherry beta-glucosidases are mainly localised in the cytosol and in the apoplast, at the unripe stage of ripening; in ripe fruit it is also associated with cell wall.

Journal Article↗

Frameshift mutation events in beta-glucosidases.

Compensated frameshift mutation is a modification of the reading frame of a gene that takes place by way of various molecular events. It appears to be a widespread event that is only observed when homologous amino acid and nucleodotide sequences are compared. To identify these mutation events, the sequence analysis rationale was based on the search for short regions that would have much lower degrees of conservation in protein, but not in DNA, in well-conserved beta-glucosidase families. We have restricted our study to a seed set of sequences of O-glycoside hydrolase families 1 and 3. We found compensated frameshift mutation in the family of 1 beta-glucosidases for the Erwinia herbicola, Cellulomonas fimi, and (non-cyanogenic) Trifolium repens gene sequences, and in the family of 3 beta-glucosidases for the Clostridium thermocellum and Clostridium stercorarium gene sequences. By computational treatment, the observed mutation events in the gene frameshifting sub-sequence have been neutralised. Each nucleotide insertion must be eliminated and each nucleotide deletion must be substituted by the symbol N (any nucleotide). When the frameshifting fragments of the amino acid sequences were substituted by the computationally neutralised subsequences, the beta-glucosidase alignments were improved. We also discuss the structural implications of the compensated frameshift mutations events.

Amino Acid Sequence↗

Gaucher disease: expression and characterization of mild and severe acid beta-glucosidase mutations in Portuguese type 1 patients.

Type 1 Gaucher disease (GD), the most prevalent lysosomal storage disease, results from the deficient activity of acid beta-glucosidase. Molecular analysis of 12 unrelated Portuguese patients with type 1 GD identified three novel acid beta-glucosidase mutations (F109V, W184R and R395P), as well as three previously reported, but uncharacterized, lesions (R359Q, G377S and N396T). The type 1 probands were either heteroallelic for the well-characterized common lesion, N370S, and the F109V, W184R, R359Q or N396T lesions or homoallelic for the G377S or N396T mutations. Expression of the W184R, R359Q and R395P mutations revealed very low specific activities based on cross-reacting immunologic material (CRIM SAs of 0.0004, 0.016 and 0.045, respectively), consistent with their being found only in type 1 patients who had a neuroprotective N370S allele. In contrast, the F109V, G377S and N396T alleles had significant acid beta-glucosidase activity (CRIM specific activities of 0.15, 0.17, 0.14, respectively), in agreement with their being mild type 1 alleles. Thus, these studies identified additional acid beta-glucosidase mutations in the Portuguese population and demonstrated that the G377S and N396T mutations were neuroprotective, consistent with the mild clinical phenotypes of the type 1 patients who were homoallelic for the G377S and N396T lesions.

Adolescent↗

Clinical evaluation of pioglitazone in patients with type 2 diabetes using alpha-glucosidase inhibitor and examination of its efficacy profile.

AIM: Pioglitazone is considered to reduce insulin resistance. This study was conducted to evaluate the efficacy, safety and clinical profile of pioglitazone in patients whose type 2 diabetes were poorly controlled with alpha-glucosidase inhibitor alone or alpha-glucosidase in combination with sulfonylurea. METHODS: Twenty patients with type 2 diabetes were treated with pioglitazone (30 mg q.d.) orally for 16 weeks. RESULTS: There were significant reductions in HbA1C, FPG and postprandial plasma glucose at week 16. As adverse events, oedema, hypoglycaemia-like reaction, increases in LDH, CPK, etc. were noted. There was no significant change in TNF-alpha. Leptin levels increased significantly at week 16 and were still increasing 4 weeks after the treatment. Per cent body fat was almost constant throughout the study period. When efficacy was classified by demographic variables, pioglitazone was found to be more effective in the subjects who had a higher postprandial 2-h plasma glucose level, leptin level or per cent body fat value. CONCLUSION: Pioglitazone was considered to be effective when used in patients whose type 2 diabetes were poorly controlled with alpha-glucosidase inhibitor alone or alpha-glucosidase in combination with sulfonylurea.

Adult↗

Alpha-glucosidase inhibition from a Chinese medical herb (Ramulus mori) in normal and diabetic rats and mice.

Alpha-glucosidase inhibitors are oral antidiabetic drugs. A traditional Chinese medical herb, Sangzhi (Ramulus mori), appears to have properties similar to those of alpha-glucosidase inhibitors. The effects of an aqueous extract of Shangzhi (SZ) were studied in normal and alloxan diabetic rats and mice, and these results compared with those for acarbose, an alpha-glucosidase inhibitor. In our grade-dose studies, SZ was found to lower and prolong the zenith of blood glucose concentration (ZBG) after sucrose or starch loading and stabilize blood glucose levels in fasting normal and alloxan diabetic mice. After 2 weeks of SZ administration with high-calorie chow or a normal diet, the fasting and non-fasting blood glucose concentrations in alloxan diabetic mice and rats were decreased. In alloxan rats, the blood fructosamine concentration was lowered. Results for acarbose and SZ were similar. These indicate that SZ has alpha-glucosidase inhibitory effects.

Alloxan↗

Glucosylceramide and glucosylsphingosine metabolism in cultured fibroblasts deficient in acid beta-glucosidase activity.

The metabolism of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph) was studied using cultured fibroblasts deficient in acid beta-glucosidase activity. In fibroblasts from patients with Gaucher's disease, in vitro beta-glucosidase activities were 2.7-11.7% and 4.8-13.6% of control values when 4-methylumbelliferyl beta-D-glucoside and GlcSph were used as substrates, respectively. In spite of the enzyme deficiency, GlcCer and GlcSph, the natural substrates of the deficient enzyme, did not accumulate in the cells. When normal fibroblasts were incubated with conduritol B epoxide (CBE), a specific inhibitor of acid beta-glucosidase, the in vitro enzyme activities decreased dose-dependently (2.2-2.4% of control values at 50 microM CBE), and GlcCer and GlcSph accumulated in the cells at concentrations of CBE higher than 50 microM. To investigate the intracellular metabolism of GlcCer and GlcSph, either radioactive GlcCer or GlcSph was loaded onto cultured fibroblasts. In fibroblasts treated with a high dose of CBE (1 mM), the degradation of GlcCer and GlcSph was retarded (5-21% on day 7; normal range, 81-99%), while in fibroblasts from patients with Gaucher's disease, both the pattern and rate of the degradation of the lipids (83-97% on day 7) were almost the same as those seen in the control cells. These results indicate that in Gaucher's disease fibroblasts the intracellular metabolism of GlcCer and GlcSph is normal in spite of the deficiency in beta-glucosidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cells, Cultured↗

The Role of Pea Chloroplast [alpha]-Glucosidase in Transitory Starch Degradation.

Pea chloroplastic [alpha]-glucosidase (EC 3.2.1.20) involved in transitory starch degradation was purified to apparent homogeneity by ion exchange, reactive dye, hydroxylapatite, hydrophobic interaction, and gel filtration column chromatography. The native molecular mass and the subunit molecular mass were about 49.1 and 24.4 kD, respectively, suggesting that the enzyme is a homodimer. The enzyme had a Km of 7.18 mM for maltose. The enzyme's maximal activity at pH 7.0 and stability at pH 6.5 are compatible with the diurnal oscillations of the chloroplastic stromal pH and transitory starch accumulation. This pH modulation of the [alpha]-glucosidase's activity and stability is the only mechanism known to regulate starch degradative enzymes in leaves. Although the enzyme was specific for the [alpha]-D-glucose in the nonreducing end as the glycon, the aglycon moieties could be composed of a variety of groups. However, the hydrolysis rate was greatly influenced by the aglycon residues. Also, the enzyme could hydrolyze glucans in which carbon 1 of the glycon was linked to different carbon positions of the penultimate glucose residue. The ability of the [alpha]-glucosidase to hydrolyze [alpha]-1,2- and [alpha]-1,3-glucosidic bonds may be vital if these bonds exist in starch granules because they would be barriers to other starch degradative enzymes. This purified pea chloroplastic [alpha]-glucosidase was demonstrated to initiate attacks on native transitory chloroplastic starch granules.

Journal Article↗

Partial Characterization and Subcellular Localization of Three alpha-Glucosidase Isoforms in Pea (Pisum sativum L.) Seedlings.

Three isoforms of alpha-glucosidase (EC 3.2.1.20) have been extracted from pea (Pisum sativum L.) seedlings and separated by DEAE-cellulose and CM-Sepharose chromatography. Two alpha-glucosidase isoforms (alphaG1 and alphaG2) were most active under acid conditions, and appeared to be apoplastic. A neutral form (alphaG3) was most active near pH 7, and was identified as a chloroplastic enzyme. Together, the activity of alphaG1 and alphaG2 in apoplastic preparations accounted for 21% of the total acid alpha-glucosidase activity recovered from pea stems. The vast majority (86%) of the apoplastic acid alpha-glucosidase activity was due to alphaG1. The apparent K(m) values for maltose of alphaG1 and alphaG2 were 0.3 and 1.3 millimolar, respectively. The apparent K(m) for maltose of alphaG3 was 33 millimolar. The respective native molecular weights of alphaG1, alphaG2, and alphaG3 were 125,000, 150,000, and 110,000.

Journal Article↗

Manipulating volatile emission in tobacco leaves by expressing Aspergillus nigerbeta-glucosidase in different subcellular compartments.

Expression of the Aspergillus nigerbeta-glucosidase gene, BGL1, in Nicotiana tabacum plants (cv. Xanthi) had a profound effect on the volatile emissions of intact and crushed leaves. BGL1 was expressed under the control of the cauliflower mosaic virus (CaMV) 35S promoter and targeted to the cytoplasm, cell wall, lytic vacuole (LV), chloroplast or endoplasmic reticulum (ER). Subcellular localization was confirmed by gold immunolabelling, followed by transmission electron microscopy (TEM). Significant beta-glucosidase activity was observed in transgenic plants expressing BGL1 in the cell wall, LV and ER. Compared with controls, all intact transgenic leaves were found to emit increased levels of 2-ethylhexanol, as determined by gas chromatography-mass spectrometry (GC-MS) analysis of the headspace volatiles. Plants expressing BGL1 in the cell wall (Tcw) emitted more trans-caryophyllene than did non-transgenic controls, whereas plants expressing BGL1 in the ER (Ter) and LV (Tvc) emitted more cembrene than did non-transgenic controls. Volatiles released from crushed transgenic leaves and collected with solid-phase microextraction (SPME) polydimethylsiloxane fibre were distinctly enhanced. Significant increases in linalool, nerol, furanoid cis-linalool oxide, 4-methyl-1-pentanol, 6-methyl-hept-5-en-2-ol and 2-ethylhexanol were detected in transgenic plants when compared with wild-type controls. 3-Hydroxyl-beta-ionone levels were increased in crushed Tcw and Ter leaves, but were undetectable in Tvc leaves. The addition of glucoimidazole, a beta-glucosidase inhibitor, abolished the increased emission of these volatiles. These results indicate that the expression of a fungal beta-glucosidase gene in different subcellular compartments has the potential to affect the emission of plant volatiles, and thereby to modify plant-environment communication and aroma of agricultural products.

Journal Article↗

beta-Glucosidase catalyzing specific hydrolysis of an iridoid beta-glucoside from Plumeria obtusa.

An iridoid beta-glucoside, namely plumieride coumarate glucoside, was isolated from the Plumeria obtusa (white frangipani) flower. A beta-glucosidase, purified to homogeneity from P. obtusa, could hydrolyze plumieride coumarate glucoside to its corresponding 13-O-coumarylplumieride. Plumeria beta-glucosidase is a monomeric glycoprotein with a molecular weight of 60.6 kDa and an isoelectric point of 4.90. The purified beta-glucosidase had an optimum pH of 5.5 for p-nitrophenol (pNP)-beta-D-glucoside and for its natural substrate. The Km values for pNP-beta-D-glucoside and Plumeria beta-glucoside were 5.04+/-0.36 mM and 1.02+/-0.06 mM, respectively. The enzyme had higher hydrolytic activity towards pNP-beta-D-fucoside than pNP-beta-D-glucoside. No activity was found for other pNP-glycosides. Interestingly, the enzyme showed a high specificity for the glucosyl group attached to the C-7' position of the coumaryl moiety of plumieride coumarate glucoside. The enzyme showed poor hydrolysis of 4-methylumbelliferyl-beta-glucoside and esculin, and did not hydrolyze alkyl-beta-glucosides, glucobioses, cyanogenic-beta-glucosides, steroid beta-glucosides, nor other iridoid beta-glucosides. In conclusion, the Plumeria beta-glucosidase shows high specificity for its natural substrate, plumieride coumarate glucoside.

Apocynaceae↗

Formation, Location, and Regulation of Endo-1,4-beta-Glucanases and beta-Glucosidases from Cellulomonas uda.

The formation and location of endo-1,4-beta-glucanases and beta-glucosidases were studied in cultures of Cellulomonas uda grown on microcrystalline cellulose, carboxymethyl cellulose, printed newspaper, and some mono- or disaccharides. Endo-1,4-Glucanases were found to be extracellular, but a very small amount of cell-bound endo-1,4-beta-glucanase was considered to be the basal endoglucanase level of the cells. The formation of extracellular endo-1,4-beta-glucanases was induced by cellobiose and repressed by glucose. Extracellular endoglucanase activity was inhibited by cellobiose but not by glucose. beta-Glucosidases, on the other hand, were formed constitutively and found to be cell bound. beta-Glucosidase activity was inhibited noncompetitively by glucose. Some characteristics such as the optimal pH for and the thermostability of the endoglucanases and beta-glucosidases and the end products of cellulose degradation were determined.

Journal Article↗

Regulation of beta-1, 4-Glucosidase Expression by Candida wickerhamii.

Candida wickerhamii NRRL Y-2563 expressed beta-glucosidase activity (3 to 8 U/ml) constitutively when grown aerobically in complex medium containing either glycerol, succinate, xylose, galactose, or cellobiose as the carbon source. The addition of a high concentration of glucose (>75 g/liter) repressed beta-glucosidase expression (<0.3 U/ml); however, this yeast did produce beta-glucosidase when the initial glucose concentration was </=50 g/liter. When grown aerobically in medium containing glucose plus the above-listed carbon sources, diauxic utilization of the carbon source was observed and the expression of beta-glucosidase was glucose repressed. Surprisingly, glucose repression did not occur when the cells were grown anaerobically. When grown anaerobically in medium containing 100 g of glucose per liter, C. wickerhamii produced 6 to 9 U of enzyme per ml and did not demonstrate diauxic utilization of glucose-cellobiose mixtures. To our knowledge, this is the first report of apparent derepression of a glucose-repressed enzyme by anaerobiosis.

Journal Article↗