Cytosolic Β-glucosidase Research Articles

Engineering of a new Escherichia coli strain efficiently metabolizing cellobiose with promising perspectives for plant biomass-based application design

The necessity to decrease our fossil energy dependence requests bioprocesses based on biomass degradation. Cellobiose is the main product released by cellulases when acting on the major plant cell wall polysaccharide constituent, the cellulose. Escherichia coli, one of the most common model organisms for the academy and the industry, is unable to metabolize this disaccharide. In this context, the remodeling of E. coli to catabolize cellobiose should thus constitute an important progress for the design of such applications. Here, we developed a robust E. coli strain able to metabolize cellobiose by integration of a small set of modifications in its genome. Contrary to previous studies that use adaptative evolution to achieve some growth on this sugar by reactivating E. coli cryptic operons coding for cellobiose metabolism, we identified easily insertable modifications impacting the cellobiose import (expression of a gene coding a truncated variant of the maltoporin LamB, modification of the expression of lacY encoding the lactose permease) and its intracellular degradation (genomic insertion of a gene encoding either a cytosolic β-glucosidase or a cellobiose phosphorylase). Taken together, our results provide an easily transferable set of mutations that confers to E. coli an efficient growth phenotype on cellobiose (doubling time of 2.2 ​h in aerobiosis) without any prior adaptation.

Decreased expression of GBA3 correlates with a poor prognosis in hepatocellular carcinoma patients.

Beta-glucosidase (GBA), also known as acid β-glucosidase, exhibits an activity of glucosylceramidase (EC 3.2.1.45). Three main isoforms of β-glucosidases have been identified in mammals: GBA1, GBA2, and GBA3. The deficiency of these enzymes leads to glucosylceramide accumulation, resulting in Gaucher's disease. The present study is focused on the cytosolic β-glucosidase, GBA3, and its relationship with hepatocellular carcinoma (HCC). The expression of GBA3 mRNA in HCC was evaluated first using the TCGA database, and then by immunohistochemistry using tissue microarrays of 328 clinically characterized HCC samples and 151 non-tumor liver controls. Moreover, the presence of a correlation between GBA3 expression and clinicopathological characteristics of patients was examined. The obtained results indicated that the expression of GBA3 mRNA was significantly lower in HCC than in the adjacent non-tumor liver tissues. The expression of GBA3 was inversely related to the number of tumors (p=0.041), tumor size (p<0.001), Edmondson grade (p=0.007), microvascular invasion (p=0.049), patient status (p<0.001), and α-fetoprotein level (p<0.001). Patients exhibiting low GBA3 expression had a shorter survival time than those with high expression (p<0.001). In conclusion, the decreased GBA3 expression is strongly associated with a poor prognosis in HCC patients, and GBA3 may be a potential therapeutic target for HCC.

Distinguishing the differences in β-glycosylceramidase folds, dynamics, and actions informs therapeutic uses

Glycosyl hydrolases (GHs) are carbohydrate-active enzymes that hydrolyze a specific β-glycosidic bond in glycoconjugate substrates; β-glucosidases degrade glucosylceramide, a ubiquitous glycosphingolipid. GHs are grouped into structurally similar families that themselves can be grouped into clans. GH1, GH5, and GH30 glycosidases belong to clan A hydrolases with a catalytic (β/α)8 TIM barrel domain, whereas GH116 belongs to clan O with a catalytic (α/α)6 domain. In humans, GH abnormalities underlie metabolic diseases. The lysosomal enzyme glucocerebrosidase (family GH30), deficient in Gaucher disease and implicated in Parkinson disease etiology, and the cytosol-facing membrane-bound glucosylceramidase (family GH116) remove the terminal glucose from the ceramide lipid moiety. Here, we compare enzyme differences in fold, action, dynamics, and catalytic domain stabilization by binding site occupancy. We also explore other glycosidases with reported glycosylceramidase activity, including human cytosolic β-glucosidase, intestinal lactase-phlorizin hydrolase, and lysosomal galactosylceramidase. Last, we describe the successful translation of research to practice: recombinant glycosidases and glucosylceramide metabolism modulators are approved drug products (enzyme replacement therapies). Activity-based probes now facilitate the diagnosis of enzyme deficiency and screening for compounds that interact with the catalytic pocket of glycosidases. Future research may deepen the understanding of the functional variety of these enzymes and their therapeutic potential.

Gluco-1 H-imidazole: A New Class of Azole-Type β-Glucosidase Inhibitor.

Gluco-azoles competitively inhibit glucosidases by transition-state mimicry and their ability to interact with catalytic acid residues in glucosidase active sites. We noted that no azole-type inhibitors described, to date, possess a protic nitrogen characteristic for 1H-imidazoles. Here, we present gluco-1H-imidazole, a gluco-azole bearing a 1H-imidazole fused to a glucopyranose-configured cyclitol core, and three close analogues as new glucosidase inhibitors. All compounds inhibit human retaining β-glucosidase, GBA1, with the most potent ones inhibiting this enzyme (deficient in Gaucher disease) on a par with glucoimidazole. None inhibit glucosylceramide synthase, cytosolic β-glucosidase GBA2 or α-glucosidase GAA. Structural, physical and computational studies provide first insights into the binding mode of this conceptually new class of retaining β-glucosidase inhibitors.

Cytosolic β-glucosidase inhibition and renal blood flow suppression are leading causes for the enhanced systemic exposure of salidroside in hypoxic rats.

The promising benefits of salidroside (SAL) in alleviating high altitude sickness boost investigations on its pharmacokinetics and biological activity. However, the transportation and disposition process of SAL under hypoxic conditions has never been explored. The current study was proposed to investigate the pharmacokinetics of SAL in hypoxic rats and to explore the underlying mechanisms for the distinct metabolic fate of SAL under hypoxia. Pharmacokinetic studies on SAL was conducted in both hypoxic and normoxic rats. The transport properties of SAL were investigated on both hypoxic and normoxic Caco-2 monolayer models. Enzymes involved in SAL metabolism were identified and the effects of hypoxia on these enzymes were assessed by real-time PCR, western blotting analyses, and rat liver homogenate incubation. The renal clearance (CLr) of SAL, effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) in both hypoxic and normoxic rats were also determined for renal function assessment. It was found that the systemic exposure of SAL in hypoxic rats was remarkably higher than that in normoxic rats. The barrier function of Caco-2 monolayer was weakened under hypoxia due to the impaired brush border microvilli and decreased expression of tight junction protein. Hepatic metabolism of SAL in hypoxic rats was attenuated due to the reduced activity of cytosolic β-glucosidase (CBG). Moreover, CLr of SAL was reduced in hypoxic rats due to the suppressed ERPF. Our findings suggest the potential need for dose-adjustment of SAL or its structural analogs under hypoxic conditions.

Cytosolic β-glucosidase inhibition and renal blood flow suppression are leading causes for the enhanced systemic exposure of salidroside in hypoxic rats

Cytosolic β-glucosidase inhibition and renal blood flow suppression are leading causes for the enhanced systemic exposure of salidroside in hypoxic rats

The Effect of Genistein Supplementation on Vitamin D Levels and Bone Turnover Markers during the Summer in Healthy Postmenopausal Women: Role of Genotypes of Isoflavone Metabolism

Aims: The objective of this study was to determine whether vitamin D and genistein supplementation had an additive beneficial effect on levels of vitamin D and bone markers and whether this effect was mediated by genes regulating isoflavone metabolism. Materials and Methods: We carried out a prospective study in postmenopausal women randomized to calcium and vitamin D supplementation or calcium, vitamin D, and genistein supplementation. Vitamin D, parathyroid hormone (PTH), cross-linked C-telopeptide (CTX), and procollagen 1 N-terminal (P1NP) were determined by electrochemiluminescence. Three SNPs - rs2231142 (ABCG2), rs358231 (cytosolic β-glucosidase [CBG]), and rs2273697 (ABCC2) - were determined. Results: We included 102 women. The effects on bone remodeling were similar: rises in vitamin D were significantly associated with reductions in PTH, CTX, and P1NP. Pharmacogenomic analysis of the genotypes showed that, in AT heterozygotes of the CBG1368T>A polymorphism, CTX and P1NP were not reduced. Conclusion: Genistein added to calcium and vitamin D supplementation had no additional effect. The supplementation of individual AT heterozygotes of the CBG1368T>A polymorphism had no effect on markers of bone remodeling.

Study on the uptake and deglycosylation of the masked forms of zearalenone in human intestinal Caco-2 cells

This study investigated for the first time the intestinal transfer of two modified forms of zearalenone (ZEN), zearalenone-14-glucoside (ZEN14Glc) and zearalenone-16-glucoside (ZEN16Glc), using polarized monolayers of Caco-2 cells. The cells were apically exposed to 40 μM of ZEN14Glc, ZEN16Glc and ZEN, separately. Results showed that, after apical administration, ZEN14Glc and ZEN16Glc can be detected in cellular extracts indicating uptake by intestinal cells. Moreover, the glucosylated forms were cleaved to release ZEN, with a different cleavage ability for the two conjugated isomers. In particular, ZEN16Glc seems to be less prone to deglycosylation compared to ZEN14Glc, probably on account of an increased steric hindrance. We could show that human cytosolic β-glucosidase is able to cleave ZEN14Glc liberating ZEN, but is unable to cleave ZEN16Glc.All metabolites could cross the cell membrane and be detected in the apical compartment, while ZEN was also found in the basolateral compartment together with the modified mycotoxin form.

In vivo effects of curcumin on the paraoxonase, carbonic anhydrase, glucose-6-phosphate dehydrogenase and β-glucosidase enzyme activities in dextran sulphate sodium-induced ulcerative colitis mice

Increases in the risk of infections and malignancy due to immune suppressive therapies of inflammatory bowel diseases (IBDs) have led the researchers to focus on more nontoxic and acceptable natural products like curcumin. Here we investigate whether prophylactic and therapeutic application of the curcumin alters the enzyme activities of paraoxonase (PON), carbonic anhydrase (CA), glucose-6-phosphate dehydrogenase (G6PD) and cytosolic β-glucosidase in dextran sulphate sodium (DSS)-induced ulcerative colitis mice. Prophylactic application of curcumin resulted in higher MPO activity, less body weight loss and longer colon lengths compared to therapeutic group indicating preventive role of curcumin in IBDs. DSS-induced decrease in liver and serum PON activities were completely recovered by prophylactic administration of curcumin. DSS-induced reduction in liver cytosolic β-glucosidase activity was not affected by curcumin neither in the prophylactic group nor in the therapeutic group. Erythrocyte CA activity was significantly increased in curcumin groups, however no remarkable change in G6PD activity was observed.

Glucosylceramidases and malignancies in mammals.

Sphingolipids represent a major class of lipids that are essential constituents of eukaryotic cells. They are predominantly located in plasma membrane microdomains, and play an important structural role in regulating membrane fluidity. They are also bioactive effectors involved in diverse key cellular functions such as apoptosis and proliferation. The implication of some sphingolipids in cancer is well established whereas that of some others is still a matter of intense investigation. Glucosylceramide is the backbone of more than 300 structurally different glycosphingolipids including gangliosides and sulfatides, and is essential for mammalian development. Therefore, glucosylceramidases (also named GBA1, GBA2 and GBA3 β-glucosidases), the enzymes that hydrolyse β-glucosylceramide, play important functions. GBA1 is a lysosomal hydrolase whose deficiency causes Gaucher disease, the most prevalent inherited lysosomal storage disorder. GBA2 is a ubiquitous non-lysosomal glucosylceramidase whose mutations have been associated with some forms of hereditary spastic paraplegia. GBA3 is a cytosolic β-glucosidase, mostly present in the kidney, liver, spleen, intestine and lymphocytes of mammals, the function of which is still unclear. Whereas glucosylceramide synthase is implicated in multidrug resistance, the role of glucosylceramide breakdown in cancer is not yet fully appreciated. Defective GBA1 enzyme activity in humans, i.e., Gaucher disease, is associated with an increased risk of multiple myeloma and other malignancies. Putative molecular links between Gaucher disease and cancer, which might implicate the malignant cell and/or its microenvironment, are reviewed. The functions of GBA2 and GBA3 in cancer progression are also discussed.

High β-glucosidase (GBA) activity not attributable to GBA1 and GBA2 in live normal and enzyme-deficient fibroblasts may emphasise the role of additional GBAs

Beta-glucosidases (GBA) include GBA1, GBA2 and other β-glucosidases (non-GBA1-2). GBA1 is a lysosomal and GBA2 an extra-lysosomal enzyme. GBA1- and GBA2-deficient genetic conditions, with different phenotypes, are glucosylceramide (GC; the main GBA substrate) accumulating diseases. To study the activity profile of GBA, live fibroblasts were loaded with radioactive GC. The GC metabolism was measured in wild-type, GBA1-deficient (Gaucher disease) and GBA2-deficient (Gba2(-/- )mouse) cells. The differences found allowed the prediction of marked proportions of GBA1, GBA2, and particularly non-GBA1-2 (probably including GBA3, a cytosolic β-glucosidase) activity for wild-type cells. The high proportion of non-GBA1-2 suggests an important role of these enzymes.

Hydrolytic fate of deoxynivalenol-3-glucoside during digestion

Deoxynivalenol-3-β-d-glucoside (D3G), a plant phase II metabolite of the Fusarium mycotoxin deoxynivalenol (DON), occurs in naturally contaminated wheat, maize, oat, barley and products thereof. Although considered as a detoxification product in plants, the toxicity of this substance in mammals is currently unknown. A major concern is the possible hydrolysis of the D3G conjugate back to its toxic precursor mycotoxin DON during mammalian digestion. We used in vitro model systems to investigate the stability of D3G to acidic conditions, hydrolytic enzymes and intestinal bacteria, mimicking different stages of digestion. D3G was found resistant to 0.2M hydrochloric acid for at least 24h at 37°C, suggesting that it will not be hydrolyzed in the stomach of mammals. While human cytosolic β-glucosidase also had no effect, fungal cellulase and cellobiase preparations could cleave a significant portion of D3G. Most importantly, several lactic acid bacteria such as Enterococcus durans, Enterococcus mundtii or Lactobacillus plantarum showed a high capability to hydrolyze D3G. Taken together these data indicate that D3G is of toxicological relevance and should be regarded as a masked mycotoxin.

Value of serum cytosolic β-glucosidase in diagnosis of neonatal necrotizing enterocolitis

This study was conducted to compare serum cytosolic β-glucosidase (CBG) levels of age-matched control patients with those of infants with necrotizing enterocolitis (NEC) thereby to determine the eventual association between serum CBG levels with extensive disease in infants with NEC. A total of 96 premature infants were divided into the early NEC group (n = 25), confirmed NEC group (n = 23) and the control group (n = 48). Serum CBG concentration, C-reactive protein (CRP) and peripheral blood white blood cells (WBC) were measured at the onset of the disease in patients in early NEC or confirmed NEC groups and at weeks 2-3 in control infants. Data were analyzed using descriptive statistics, non-parametric tests, Student's t-test, linear correlation, Spearman correlation analysis, receiver operating characteristic (ROC) curve were used for statistical analysis. The median birth weights (mean ± SE) in the three groups were not statistically significant (P > 0.05). Serum CBG concentration in the 3 groups were (112.369 ± 108.539) nmol/L, (693.013 ± 211.614) nmol/L and (36.478 ± 28.31) nmol/L, respectively. The infants in the confirmed NEC group had highest CBG levels, compared with the other 2 groups (P < 0.05). When the levels of CBG ≥ 65 ng/ml, CRP ≥ 2 mg/L and WBC < 5 × 10(9)/L within 3 days after birth or > 20 × 10(9)/L 3 days after birth were considered as positive parameters, the sensitivity of CBG and CRP was higher than that of WBC (P < 0.05). Among these indices, CBG had the highest specificity (87.4%), positive predictive (95.6%) and Youden's index (81.3%). CBG is correlated with CRP (the Spearman correlation coefficient was 0.379, P < 0.01). Serum CBG concentration increases early in NEC. Serum CBG level was associated with extensive disease in infants with NEC. Therefore CBG can be used as a marker in the early diagnosis of NEC.

The cytosolic β-glucosidase GBA3 does not influence type 1 Gaucher disease manifestation

GBA3, also known as cytosolic β-glucosidase, is thought to hydrolyze xenobiotic glycosides in man. Deficiency of glucocerebrosidase (GBA), a β-glucosidase degrading glucosylceramide, underlies Gaucher disease. We examined GBA3, which recently was proposed to degrade glucosylceramide and influence the clinical manifestation of Gaucher disease. Recombinant GBA3 was found to hydrolyze artificial substrates such as 4-methylumbelliferyl-β-D-glucoside and C6-NBD-glucosylceramide, but hydrolysis of naturally occurring lipids like glucosylceramide and glucosylsphingosine was hardly detected. Consistent with this, inhibition of GBA3 in cultured cells using a novel inhibitor (alpha-1-C-nonyl-DIX) did not result in an additional increase in glucosylceramide as compared to GBA inhibition alone. Examination of the GBA3 gene led to the identification of a common substitution in its open reading frame (1368T→A), resulting in a truncated GBA3 protein missing the last α-helix of its (β/α) 8 barrel. Both recombinant 1368A GBA3 and 1368A enzyme from spleen of a homozygous individual were found to be inactive. Amongst non-neuronopathic (type 1) Gaucher disease patients, we subsequently identified individuals being wild-type, heterozygous, or homozygous for the GBA3 1368T→A mutation. No correlation was observed between GBA3 1368A/T haplotypes and severity of type 1 Gaucher disease manifestation. In conclusion, GBA3 does not seem to modify type 1 Gaucher disease manifestation.

Crystal structure of the covalent intermediate of human cytosolic β-glucosidase

Human cytosolic beta-glucosidase, also known as klotho-related protein (KLrP, GBA3), is an enzyme that hydrolyzes various beta-D-glucosides, including glucosylceramide. We recently reported the crystal structure of KLrP in complex with glucose [Y. Hayashi, N. Okino, Y. Kakuta, T. Shikanai, M. Tani, H. Narimatsu, M. Ito, Klotho-related protein is a novel cytosolic neutral beta-glycosylceramidase, J. Biol. Chem. 282 (2007) 30889-30900]. Here, we report the crystal structure of a covalent intermediate of the KLrP mutant E165Q, in which glucose was covalently bound to a nucleophile, Glu(373). The structure confirms the double displacement mechanism of the retaining beta-glucosidase. In addition, the structure suggests that a water molecule could be involved in the stabilization of transition states through a sugar, 2-hydroxyl.

Crystal structure of the covalent intermediate of human cytosolic β-glucosidase

Human cytosolic β-glucosidase, also known as klotho-related protein (KLrP, GBA3), is an enzyme that hydrolyzes various β- d-glucosides, including glucosylceramide. We recently reported the crystal structure of KLrP in complex with glucose [Y. Hayashi, N. Okino, Y. Kakuta, T. Shikanai, M. Tani, H. Narimatsu, M. Ito, Klotho-related protein is a novel cytosolic neutral beta-glycosylceramidase, J. Biol. Chem. 282 (2007) 30889–30900]. Here, we report the crystal structure of a covalent intermediate of the KLrP mutant E165Q, in which glucose was covalently bound to a nucleophile, Glu 373. The structure confirms the double displacement mechanism of the retaining β-glucosidase. In addition, the structure suggests that a water molecule could be involved in the stabilization of transition states through a sugar, 2-hydroxyl.

The Crystal Structure of Human Cytosolic β-Glucosidase Unravels the Substrate Aglycone Specificity of a Family 1 Glycoside Hydrolase

Human cytosolic β-glucosidase (hCBG) is a xenobiotic-metabolizing enzyme that hydrolyses certain flavonoid glucosides, with specificity depending on the aglycone moiety, the type of sugar and the linkage between them. In this study, the substrate preference of this enzyme was investigated by mutational analysis, X-ray crystallography and homology modelling. The crystal structure of hCBG was solved by the molecular replacement method and refined at 2.7 Å resolution. The main-chain fold of the enzyme belongs to the (β/α) 8 barrel structure, which is common to family 1 glycoside hydrolases. The active site is located at the bottom of a pocket (about 16 Å deep) formed by large surface loops, surrounding the C termini of the barrel of β-strands. As for all the clan of GH-A enzymes, the two catalytic glutamate residues are located on strand 4 (the acid/base Glu165) and on strand 7 (the nucleophile Glu373). Although many features of hCBG were shown to be very similar to previously described enzymes from this family, crucial differences were observed in the surface loops surrounding the aglycone binding site, and these are likely to strongly influence the substrate specificity. The positioning of a substrate molecule (quercetin-4′-glucoside) by homology modelling revealed that hydrophobic interactions dominate the binding of the aglycone moiety. In particular, Val168, Trp345, Phe225, Phe179, Phe334 and Phe433 were identified as likely to be important in determining substrate specificity in hCBG, and site-directed mutagenesis supported a key role for some of these residues.

Identification of the Non-lysosomal Glucosylceramidase as β-Glucosidase 2

The primary catabolic pathway for glucosylceramide is catalyzed by the lysosomal enzyme glucocerebrosidase that is defective in Gaucher disease patients. A distinct non-lysosomal glucosylceramidase has been described but its identity remained enigmatic for years. We here report that the non-lysosomal glucosylceramidase is identical to the earlier described bile acid beta-glucosidase, being beta-glucosidase 2 (GBA2). Expressed GBA2 is identical to the native non-lysosomal glucosylceramidase in various enzymatic features such as substrate specificity and inhibitor sensitivity. Expression of GBA2 coincides with increased non-lysosomal glucosylceramidase activity, and GBA2-targeted RNA interference reduces endogenous non-lysosomal glucosylceramidase activity in cells. GBA2 is found to be located at or close to the cell surface, and its activity is linked to sphingomyelin generation. Hydrophobic deoxynojirimycins are extremely potent inhibitors for GBA2. In mice pharmacological inhibition of GBA2 activity is associated with impaired spermatogenesis, a phenomenon also very recently reported for GBA2 knock-out mice (Yildiz, Y., Matern, H., Thompson, B., Allegood, J. C., Warren, R. L., Ramirez, D. M., Hammer, R. E., Hamra, F. K., Matern, S., and Russell, D. W. (2006) J. Clin. Invest. 116, 2985-2994). In conclusion, GBA2 plays a role in cellular glucosylceramide metabolism.

Expression, purification, characterization and crystallization of a recombinant human cytosolic β-glucosidase produced in insect cells

Human cytosolic β-glucosidase is a monomeric enzyme that hydrolyzes various β- d-glycosides and its real physiological role remains unclear. Here, we describe the production of this enzyme in Sf9 cells with a N-terminal 6× His tag. The production yield of the recombinant protein was in the 10 to 30 mg/l range. The protein was purified to homogeneity using two chromatographic steps, taking advantage of the 6× His tag in the first step, then using the physical and chemical properties of the protein for ionic exchange. Gel filtration analysis revealed that the protein is monomeric as expected. The kinetic parameters for 4-methylumbelliferyl β- l-glucopyranoside, V M and K M, were measured ( K M = 32 μM and V M = 157 μmol/h/mg at pH 7.0) and found similar to those reported for either the natural isolated enzyme or the recombinant protein expressed in COS7 cells ( K M of 60–70 μM and 40 μM, respectively). Protein crystals were obtained and are now under structural investigations. In summary, we set up a heterologous expression system in Sf9 insect cells allowing the expression and production of large amounts of a pure active human protein, suitable for crystallographic studies.

Mutations in the gene encoding cytosolic β-glucosidase in Gaucher disease

Patients with Gaucher disease have a deficiency of the lysosomal acid β-glucosidase. The phenotypes of genotypically identical patients with Gaucher disease may differ markedly. We have examined the possibility that polymorphisms in another β-glucosidase are responsible for this variability in the phenotype. Sequence analysis of the gene encoding cytosolic β-glucosidase (GBA3) from 4 chromosomes revealed the presence of 4 single-nucleotide substitutions: c.316 G →A (D106N), c.1353A→G (Y451Y), c.1368T→A (Y456X), and c.1540 to 1541AG →T in the 3′ untranslated region. We examined the DNA from 62 patients with Gaucher disease who were homozygous for the 1226A→G (N370S) mutation and from 542 control subjects from various populations for these polymorphisms. Six of the possible 16 haplotypes were found, and none was over- or underrepresented among patients with the severe Gaucher disease phenotypes compared with those from patients with mild phenotypes.