The occurrence of two immunologically distinguishable beta-glucocerebrosidases in human spleen

GCase and LIMP2 Abnormalities in the Liver of Niemann Pick Type C Mice

The lysosomal storage disease Niemann-Pick type C (NPC) is caused by impaired cholesterol efflux from lysosomes, which is accompanied by secondary lysosomal accumulation of sphingomyelin and glucosylceramide (GlcCer). Similar to Gaucher disease (GD), patients deficient in glucocerebrosidase (GCase) degrading GlcCer, NPC patients show an elevated glucosylsphingosine and glucosylated cholesterol. In livers of mice lacking the lysosomal cholesterol efflux transporter NPC1, we investigated the expression of established biomarkers of lipid-laden macrophages of GD patients, their GCase status, and content on the cytosol facing glucosylceramidase GBA2 and lysosomal integral membrane protein type B (LIMP2), a transporter of newly formed GCase to lysosomes. Livers of 80-week-old Npc1-/- mice showed a partially reduced GCase protein and enzymatic activity. In contrast, GBA2 levels tended to be reciprocally increased with the GCase deficiency. In Npc1-/- liver, increased expression of lysosomal enzymes (cathepsin D, acid ceramidase) was observed as well as increased markers of lipid-stressed macrophages (GPNMB and galectin-3). Immunohistochemistry showed that the latter markers are expressed by lipid laden Kupffer cells. Earlier reported increase of LIMP2 in Npc1-/- liver was confirmed. Unexpectedly, immunohistochemistry showed that LIMP2 is particularly overexpressed in the hepatocytes of the Npc1-/- liver. LIMP2 in these hepatocytes seems not to only localize to (endo)lysosomes. The recent recognition that LIMP2 harbors a cholesterol channel prompts the speculation that LIMP2 in Npc1-/- hepatocytes might mediate export of cholesterol into the bile and thus protects the hepatocytes.

Human glucocerebrosidase mediates formation of xylosyl-cholesterol by β-xylosidase and transxylosidase reactions

Deficiency of glucocerebrosidase (GBA), a lysosomal β-glucosidase, causes Gaucher disease. The enzyme hydrolyzes β-glucosidic substrates and transglucosylates cholesterol to cholesterol-β-glucoside. Here we show that recombinant human GBA also cleaves β-xylosides and transxylosylates cholesterol. The xylosyl-cholesterol formed acts as an acceptor for the subsequent formation of di-xylosyl-cholesterol. Common mutant forms of GBA from patients with Gaucher disease with reduced β-glucosidase activity were similarly impaired in β-xylosidase, transglucosidase, and transxylosidase activities, except for a slightly reduced xylosidase/glucosidase activity ratio of N370S GBA and a slightly reduced transglucosylation/glucosidase activity ratio of D409H GBA. XylChol was found to be reduced in spleen from patients with Gaucher disease. The origin of newly identified XylChol in mouse and human tissues was investigated. Cultured human cells exposed to exogenous β-xylosides generated XylChol in a manner dependent on active lysosomal GBA but not the cytosol-facing β-glucosidase GBA2. We later sought an endogenous β-xyloside acting as donor in transxylosylation reactions, identifying xylosylated ceramide (XylCer) in cells and tissues that serve as donor in the formation of XylChol. UDP-glucosylceramide synthase (GCS) was unable to synthesize XylChol but could catalyze the formation of XylCer. Thus, food-derived β-D-xyloside and XylCer are potential donors for the GBA-mediated formation of XylChol in cells. The enzyme GCS produces XylCer at a low rate. Our findings point to further catalytic versatility of GBA and prompt a systematic exploration of the distribution and role of xylosylated lipids.

Activity-Based Probes for Glycosidases: Profiling and Other Applications

Glycosidases mediate the fragmentation of glycoconjugates in the body, including the vital recycling of endogenous molecules. Several inherited diseases in man concern deficiencies in lysosomal glycosidases degrading glycosphingolipids. Prominent is Gaucher disease caused by an impaired lysosomal β-glucosidase (glucocerebrosidase, GBA) and resulting in pathological lysosomal storage of glucosylceramide (glucocerebroside) in tissue macrophages. GBA is a retaining glucosidase with a characteristic glycosyl-enzyme intermediate formed during catalysis. Using the natural suicide inhibitor cyclophellitol as a lead, we developed mechanism-based irreversible inhibitors of GBA equipped with a fluorescent reporter. These reagents covalently link to the catalytic nucleophile residue of GBA and permit specific and sensitive visualization of active enzyme molecules. The amphiphilic activity-based probes (ABPs) allow in situ detection of active GBA in cells and organisms. Furthermore, they may be used to biochemically confirm the diagnosis of Gaucher disease and they might assist in screening for small compounds interacting with the catalytic pocket. While the focus of this chapter is ABPs for β-glucosidases and Gaucher disease, the described concept has meanwhile been extended to other retaining glycosidases and related disease conditions as well.

Stabilization of Glucocerebrosidase by Active Site Occupancy

Glucocerebrosidase (GBA) is a lysosomal β-glucosidase that degrades glucosylceramide. Its deficiency results in Gaucher disease (GD). We examined the effects of active site occupancy of GBA on its structural stability. For this, we made use of cyclophellitol-derived activity-based probes (ABPs) that bind irreversibly to the catalytic nucleophile (E340), and for comparison, we used the potent reversible inhibitor isofagomine. We demonstrate that cyclophellitol ABPs improve the stability of GBA in vitro, as revealed by thermodynamic measurements (T_m increase by 21 °C), and introduce resistance to tryptic digestion. The stabilizing effect of cell-permeable cyclophellitol ABPs is also observed in intact cultured cells containing wild-type GBA, N370S GBA (labile in lysosomes), and L444P GBA (exhibits impaired ER folding): all show marked increases in lysosomal forms of GBA molecules upon exposure to ABPs. The same stabilization effect is observed for endogenous GBA in the liver of wild-type mice injected with cyclophellitol ABPs. Stabilization effects similar to those observed with ABPs were also noted at high concentrations of the reversible inhibitor isofagomine. In conclusion, we provide evidence that the increase in cellular levels of GBA by ABPs and by the reversible inhibitor is in part caused by their ability to stabilize GBA folding, which increases the resistance of GBA against breakdown by lysosomal proteases. These effects are more pronounced in the case of the amphiphilic ABPs, presumably due to their high lipophilic potential, which may promote further structural compactness of GBA through hydrophobic interactions. Our study provides further rationale for the design of chaperones for GBA to ameliorate Gaucher disease.

Visualization of Active Glucocerebrosidase in Rodent Brain with High Spatial Resolution following In Situ Labeling with Fluorescent Activity Based Probes

Gaucher disease is characterized by lysosomal accumulation of glucosylceramide due to deficient activity of lysosomal glucocerebrosidase (GBA). In cells, glucosylceramide is also degraded outside lysosomes by the enzyme glucosylceramidase 2 (GBA2) of which inherited deficiency is associated with ataxias. The interest in GBA and glucosylceramide metabolism in the brain has grown following the notion that mutations in the GBA gene impose a risk factor for motor disorders such as α-synucleinopathies. We earlier developed a β-glucopyranosyl-configured cyclophellitol-epoxide type activity based probe (ABP) allowing in vivo and in vitro visualization of active molecules of GBA with high spatial resolution. Labeling occurs through covalent linkage of the ABP to the catalytic nucleophile residue in the enzyme pocket. Here, we describe a method to visualize active GBA molecules in rat brain slices using in vivo labeling. Brain areas related to motor control, like the basal ganglia and motor related structures in the brainstem, show a high content of active GBA. We also developed a β-glucopyranosyl cyclophellitol-aziridine ABP allowing in situ labeling of GBA2. Labeled GBA2 in brain areas can be identified and quantified upon gel electrophoresis. The distribution of active GBA2 markedly differs from that of GBA, being highest in the cerebellar cortex. The histological findings with ABP labeling were confirmed by biochemical analysis of isolated brain areas. In conclusion, ABPs offer sensitive tools to visualize active GBA and to study the distribution of GBA2 in the brain and thus may find application to establish the role of these enzymes in neurodegenerative disease conditions such as α-synucleinopathies and cerebellar ataxia.

Eliglustat tartrate for the treatment of adults with type 1 Gaucher disease

The purpose of this article is to review eliglustat tartrate, a substrate reduction therapy, for the treatment of Gaucher disease type 1 (GD1). GD is an rare inborn error of metabolism caused by accumulation of lipid substrates such as glucosylceramide within the monocyte-macrophage system that affects the body by causing enlargement of the spleen and liver, destruction of bone, and abnormalities of the lungs and blood, such as anemia, thrombocytopenia, and leukopenia. GD is classified into three types: GD1, a chronic and non-neuronopathic disease accounting for 95% of GD cases; and types 2 and 3 (GD2 GD3) which are more progressive diseases with no approved drugs available at this time. Treatment options for GD1 include enzyme replacement therapy and substrate reduction therapy. Eliglustat works by inhibiting UDP-glucosylceramide synthase, the first enzyme that catalyzes the biosynthesis of glycosphingolipids, thus reducing the load of glucosylceramide influx into the lysosome. Eliglustat was approved by the US Food and Drug Administration after three Phase I, two Phase II, and two Phase III clinical trials. The dose of eliglustat is 84 mg twice a day or once daily depending on the cytochrome P450 2D6 genotype of the patient.

Gaucher disease and its treatment options

OBJECTIVE

To review the epidemiology, pathophysiology, and treatments of Gaucher disease (GD), focusing on the role of enzyme replacement therapy (ERT), andsubstrate reduction therapy (SRT).

DATA SOURCES

A literature search through PubMed (1984-May 2013) of English language articles was performed with terms: Gaucher's disease, lysosomal storage disease. Secondary and tertiary references were obtained by reviewing related articles.

STUDY SELECTION AND DATA EXTRACTION

All articles in English identified from the data sources, clinical studies using ERT, SRT and articles containing other interesting aspects were included.

DATA SYNTHESIS

GD is the most common inherited LSD, characterized by a deficiency in the activity of the enzyme acid β-glucosidase, which leads to accumulation of glucocerebroside within lysosomes of macrophages, leading to hepatosplenomegaly, bone marrow suppression, and bone lesions. GD is classified into 3 types: type 1 GD (GD1) is chronic and non-neuronopathic, accounting for 95% of GDs, and types 2 and 3 (GD2, GD3) cause nerve cell destruction. Regular monitoring of enzyme chitotriosidase and pulmonary and activation-regulated chemokines are useful to confirm the diagnosis and effectiveness of GD treatment.

CONCLUSIONS

There are 4 treatments available for GD1: 3 ERTs and 1 SRT. Miglustat, an SRT, is approved for mild to moderate GD1. ERTs are available for moderate to severe GD1 and can improve quality of life within the first year of treatment. The newest ERT, taliglucerase alfa, is plant-cell derived that can be produced on a large scale at lower cost. Eliglustat tartrate, another SRT, is under phase 3 clinical trials. No drugs have been approved for GD2 or GD3.

Action myoclonus-renal failure syndrome: diagnostic applications of activity-based probes and lipid analysis

Lysosomal integral membrane protein-2 (LIMP2) mediates trafficking of glucocerebrosidase (GBA) to lysosomes. Deficiency of LIMP2 causes action myoclonus-renal failure syndrome (AMRF). LIMP2-deficient fibroblasts virtually lack GBA like the cells of patients with Gaucher disease (GD), a lysosomal storage disorder caused by mutations in the GBA gene. While GD is characterized by the presence of glucosylceramide-laden macrophages, AMRF patients do not show these. We studied the fate of GBA in relation to LIMP2 deficiency by employing recently designed activity-based probes labeling active GBA molecules. We demonstrate that GBA is almost absent in lysosomes of AMRF fibroblasts. However, white blood cells contain considerable amounts of residual enzyme. Consequently, AMRF patients do not acquire lipid-laden macrophages and do not show increased plasma levels of macrophage markers, such as chitotriosidase, in contrast to GD patients. We next investigated the consequences of LIMP2 deficiency with respect to plasma glycosphingolipid levels. Plasma glucosylceramide concentration was normal in the AMRF patients investigated as well as in LIMP2-deficient mice. However, a marked increase in the sphingoid base, glucosylsphingosine, was observed in AMRF patients and LIMP2-deficient mice. Our results suggest that combined measurements of chitotriosidase and glucosylsphingosine can be used for convenient differential laboratory diagnosis of GD and AMRF.

Glycomimetic affinity-enrichment proteomics identifies partners for a clinically-utilized iminosugar

Widescale evaluation of interacting partners for carbohydrates is an underexploited area. Probing of the 'glyco-interactome' has particular relevance given the lack of direct genetic control of glycoconjugate biosynthesis. Here we design, create and utilize a natural product-derived glycomimetic iminosugar probe in a Glycomimetic Affinity-enrichment Proteomics (glyco-AeP) strategy to elucidate key interactions directly from mammalian tissue. The binding partners discovered here and the associated genomic analysis implicate a subset of chaperone and junctional proteins as important in male fertility. Such repurposing of existing therapeutics thus creates direct routes to probing in vivo function. The success of this strategy suggests a general approach to discovering 'carbohydrate-active' partners in biology.

Assessment of partially deoxygenated deoxynojirimycin derivatives as glucosylceramide synthase inhibitors

Glucosylceramide synthase (GCS) is an approved drug target for the treatment of Gaucher disease and is considered as a valid target for combating other human pathologies, including type 2 diabetes. The clinical drug N-butyldeoxynojirimycin (Zavesca) is thought to inhibit through mimicry of its substrate, ceramide. In this work we demonstrate that, in contrast to what is proposed in this model, the C2-hydroxyl of the deoxynojirimycin core is important for GCS inhibition. Here we show that C6-OH appears of less important, which may set guidelines for the development of GCS inhibitors that have less affinity (in comparison with Zavesca) for other glycoprocessing enzymes, in particular those hydrolases that act on glucosylceramide.

Biomarkers in the diagnosis of lysosomal storage disorders: proteins, lipids, and inhibodies

A biomarker is an analyte indicating the presence of a biological process linked to the clinical manifestations and outcome of a particular disease. In the case of lysosomal storage disorders (LSDs), primary and secondary accumulating metabolites or proteins specifically secreted by storage cells are good candidates for biomarkers. Clinical applications of biomarkers are found in improved diagnosis, monitoring disease progression, and assessing therapeutic correction. These are illustrated by reviewing the discovery and use of biomarkers for Gaucher disease and Fabry disease. In addition, recently developed chemical tools allowing specific visualization of enzymatically active lysosomal glucocerebrosidase are described. Such probes, coined inhibodies, offer entirely new possibilities for more sophisticated molecular diagnosis, enzyme replacement therapy monitoring, and fundamental research.

Identification of potent and selective glucosylceramide synthase inhibitors from a library of N-alkylated iminosugars

Glucosylceramide synthase (GCS) is an important target for clinical drug development for the treatment of lysosomal storage disorders and a promising target for combating type 2 diabetes. Iminosugars are useful leads for the development of GCS inhibitors; however, the effective iminosugar type GCS inhibitors reported have some unwanted cross-reactivity toward other glyco-processing enzymes. In particular, iminosugar type GCS inhibitors often also inhibit to some extent human acid glucosylceramidase (GBA1) and the nonlysosomal glucosylceramidase (GBA2), the two enzymes known to process glucosylceramide. Of these, GBA1 itself is a potential drug target for the treatment of the lysosomal storage disorder, Gaucher disease, and selective GBA1 inhibitors are sought after as potential chemical chaperones. The physiological importance of GBA2 in glucosylceramide processing in relation to disease states is less clear, and here, selective inhibitors can be of use as chemical knockout entities. In this communication, we report our identification of a highly potent and selective N-alkylated l-ido-configured iminosugar. In particular, the selectivity of 27 for GCS over GBA1 is striking.

Generation of polyclonal antibodies against recombinant human glucocerebrosidase produced in Escherichia coli

Deficiency of the lysosomal glucocerebrosidase (GCR) enzyme results in Gaucher's disease, the most common inherited storage disorder. Treatment consists of enzyme replacement therapy by the administration of recombinant GCR produced in Chinese hamster ovary cells. The production of anti-GCR antibodies has already been described with placenta-derived human GCR that requires successive chromatographic procedures. Here, we report a practical and efficient method to obtain anti-GCR polyclonal antibodies against recombinant GCR produced in Escherichia coli and further purified by a single step through nickel affinity chromatography. The purified GCR was used to immunize BALB/c mice and the induction of anti-GCR antibodies was evaluated by enzyme-linked immunosorbent assay. The specificity of the antiserum was also evaluated by western blot analysis against recombinant GCR produced by COS-7 cells or against endogenous GCR of human cell lines. GCR was strongly recognized by the produced antibodies, either as cell-associated or as secreted forms. The detected molecular masses of 59-66 kDa are in accordance to the expected size for glycosylated GCR. The GCR produced in E. coli would facilitate the production of polyclonal (shown here) and monoclonal antibodies and their use in the characterization of new biosimilar recombinant GCRs coming in the near future.

Glycosphingolipids and insulin resistance

Glycosphingolipids are structural membrane components, residing largely in the plasma membrane with their sugar-moieties exposed at the cell's surface. In recent times a crucial role for glycosphingolipids in insulin resistance has been proposed. A chronic state of insulin resistance is a rapidly increasing disease condition in Western and developing countries. It is considered to be the major underlying cause of the metabolic syndrome, a combination of metabolic abnormalities that increases the risk for an individual to develop Type 2 diabetes, obesity, cardiovascular disease, polycystic ovary syndrome and nonalcoholic fatty liver disease. As discussed in this chapter, the evidence for a direct regulatory interaction of glycosphingolipids with insulin signaling is still largely indirect. However, the recent finding in animal models that pharmacological reduction of glycosphingolipid biosynthesis ameliorates insulin resistance and prevents some manifestations of metabolic syndrome, supports the view that somehow glycosphingolipids act as critical regulators, Importantly, since reductions in glycosphingolipid biosynthesis have been found to be well tolerated, such approaches may have a therapeutic potential.

Dual-action lipophilic iminosugar improves glycemic control in obese rodents by reduction of visceral glycosphingolipids and buffering of carbohydrate assimilation

The lipophilic iminosugar N-[5-(adamantan-1-ylmethoxy)pentyl]-1-deoxynojirimycin (2, AMP-DNM) potently controls hyperglycemia in obese rodent models of insulin resistance. The reduction of visceral glycosphingolipids by 2 is thought to underlie its beneficial action. It cannot, however, be excluded that concomitant inhibition of intestinal glycosidases and associated buffering of carbohydrate assimilation add to this. To firmly establish the mode of action of 2, we developed a panel of lipophilic iminosugars varying in configuration at C-4/C-5 and N-substitution of the iminosugar. From these we identified the l-ido derivative of 2, l-ido-AMP-DNM (4), as a selective inhibitor of glycosphingolipid synthesis. Compound 4 lowered visceral glycosphingolipids in ob/ob mice and ZDF rats on a par with 2. In contrast to 2, 4 did not inhibit sucrase activity or sucrose assimilation. Treatment with 4 was significantly less effective in reducing blood glucose and HbA1c. We conclude that the combination of reduction of glycosphingolipids in tissue and buffering of carbohydrate assimilation by 2 produces a superior glucose homeostasis.

Glycosphingolipids--nature, function, and pharmacological modulation

The discovery of the glycosphingolipids is generally attributed to Johan L. W. Thudichum, who in 1884 published on the chemical composition of the brain. In his studies he isolated several compounds from ethanolic brain extracts which he coined cerebrosides. He subjected one of these, phrenosin (now known as galactosylceramide), to acid hydrolysis, and this produced three distinct components. One he identified as a fatty acid and another proved to be an isomer of D-glucose, which is now known as D-galactose. The third component, with an "alkaloidal nature", presented "many enigmas" to Thudichum, and therefore he named it sphingosine, after the mythological riddle of the Sphinx. Today, sphingolipids and their glycosidated derivatives are the subjects of intense study aimed at elucidating their role in the structural integrity of the cell membrane, their participation in recognition and signaling events, and in particular their involvement in pathological processes that are at the basis of human disease (for example, sphingolipidoses and diabetes type 2). This Review details some of the recent findings on the biosynthesis, function, and degradation of glycosphingolipids in man, with a focus on the glycosphingolipid glucosylceramide. Special attention is paid to the clinical relevance of compounds directed at interfering with the factors responsible for glycosphingolipid metabolism.

Synthesis and evaluation of D-gluco-pyranocyclopropyl amines as potential glucosidase inhibitors

In the recent past sugar-derived cyclopropylamines were proposed as structurally new glycosidase inhibitors. In this Letter we report our efforts in the synthesis of a set of alpha-glucose configured oxabicyclo[4.1.0] heptanes, based on this hypothesis, bearing an amine substituent on the propyl ring and reveal that their inhibitory potential towards a range of mammalian glucosidases is modest.

Oral maintenance clinical trial with miglustat for type I Gaucher disease: switch from or combination with intravenous enzyme replacement

Enzyme replacement therapy (ERT) with imiglucerase reduces hepatosplenomegaly and improves hematologic parameters in Gaucher disease type 1 within 6-24 months. Miglustat reduces organomegaly, improves hematologic parameters, and reverses bone marrow infiltration. This trial evaluates miglustat in patients clinically stable on ERT. Tolerability of miglustat and imiglucerase, alone and in combination, pharmacokinetic profile, organ reduction, and chitotriosidase activity were assessed. Thirty-six patients stable on imiglucerase were randomized into this phase II, open-label trial. Statistically significant changes from baseline were assessed (paired t test) on primary objectives with secondary analyses on biochemical and safety parameters. Liver and spleen volume were unchanged in switched patients. No significant differences were seen between groups regarding mean change in hemoglobin. Mean change in platelet counts was only significant between miglustat and imiglucerase groups (P = .035). Chitotriosidase activity remained stable. In trial extension, clinical endpoints were generally maintained. Miglustat was well tolerated alone or in combination. Miglustat's safety profile was consistent with previous trials; moreover, no new cases of peripheral neuropathy were observed. Gaucher disease type 1 (GD1) parameters were stable in most switched patients. Combination therapy did not show benefit. Findings suggest miglustat could be an effective maintenance therapy in stabilized patients with GD1.

In vivo methotrexate selection of murine hemopoietic cells transduced with a retroviral vector for Gaucher disease

The studies described were performed to investigate whether in vivo selection of retrovirus-transduced hemopoietic cells is feasible starting from a low percentage of transduced hemopoietic stem cells (PHSCs). The vector used is an amphotropic bicistronic retroviral vector carrying a cDNA for human lysosomal glucocerebrosidase (hGC) for treatment of Gaucher disease and a methotrexate (MTX) resistant mutant cDNA encoding human dihydrofolate reductase (DHFR). We tested the effect of MTX selection in mice that were either myeloablated or not before infusion of transduced cells. In addition, we determined whether repeated administration of transduced bone marrow cells has an additional effect on the percentage of hGC expressing cells. The results obtained have shown that, in myeloablated mice transplanted once with transduced bone marrow and treated twice weekly with 10 mg/kg of MTX for a total of 6 months, a two- to three-fold increased numbers of hGC expressing cells could be detected in both peripheral blood and bone marrow as compared with non-MTX treated mice. In mice transplanted with transduced bone marrow once every 2 weeks for a total of four times, percentages of hGC expressing cells were not significantly increased as compared with mice transplanted once. In non-ablated mice neither MTX selection nor multiple infusions of transduced bone marrow resulted in detection of hGC expressing cells 6 months after transplantation, indicating that the success of in vivo selection using MTX is highly dependent on the ratio of transduced hemopoietic stem cells transplanted versus residing and untransduced stem cells.

A flow cytometric assay enabling specific detection of the human lysosomal enzyme, beta-glucocerebrosidase

We have developed a flow cytometric assay specific for human lysosomal beta-glucocerebrosidase (hGC) which is the enzyme deficient in Gaucher disease, a lysosomal storage disorder. The assay is based on the primate-specific monoclonal antibody 8E4 and thus allows detection of endogenous hGC and primate GC protein at a single cell level. We demonstrate that detection of endogenous hGC is possible in rhesus and human cells. Since antibody 8E4 does not bind to rodent GC, hGC detection in murine cell lines and primary cells upon transduction with a retrovirus carrying the hGC cDNA is possible. Comparison of this assay to a flow cytometric method which detects enzymatic GC activity shows that the 8E4-based assay is significantly more sensitive. We also show that multiparameter analyses in combination with hGC detection are feasible. This enables hGC detection in different lineages of complex cell populations. The increased sensitivity in combination with the specificity for hGC makes the 8E4-based flow cytometric assay ideally suited to monitor hGC expression. This assay is therefore of significant value to monitor the success of therapeutic strategies for Gaucher disease such as enzyme supplementation therapy, allogeneic bone marrow transplantation, and gene therapy.

Cytosolic pyridoxine-beta-D-glucoside hydrolase from porcine jejunal mucosa. Purification, properties, and comparison with broad specificity beta-glucosidase

During studies of the nutritional utilization of pyridoxine 5'-beta-D-glucoside, a major form of vitamin B6 in plants, we detected two cytosolic beta-glucosidases in jejunal mucosa. As expected, one was broad specificity beta-glucosidase that hydrolyzed aryl beta-D-glycosides but not pyridoxine beta-D-glucoside. We also found a previously unknown enzyme, designated pyridoxine-beta-D-glucoside hydrolase, that efficiently hydrolyzed pyridoxine beta-D-glucoside. These were separated and purified as follows: broad specificity beta-glucosidase 1460-fold and pyridoxine-beta-D-glucoside hydrolase 36,500-fold. Purified pyridoxine-beta-D-glucoside hydrolase did not hydrolyze any of the aryl glycosides tested but did hydrolyze cellobiose and lactose. Pyridoxine-beta-D-glucoside hydrolase exhibited a pH optimum of 5.5 and apparent molecular mass of 130 kDa by SDS-polyacrylamide gel electrophoresis and 160 kDa by nondenaturing gel filtration, in contrast to 60 kDa for native and denatured broad specificity beta-glucosidase. Glucono-delta-lactone was a strong inhibitor of both enzymes. Ionic and nonionic detergents were inhibitory for each enzyme. Conduritol B epoxide, a potent inhibitor of lysosomal acid beta-glucosidase, inhibited pyridoxine-beta-D-glucoside hydrolase but not broad specificity beta-glucosidase, but both were inhibited by the mechanism-based inhibitor 2-deoxy-2-fluoro-beta-D-glucosyl fluoride. Our findings indicate major differences between these two cytosolic beta-glucosidases. Studies addressing the role of vitamin B6 nutrition in regulating the activity and its consequences regarding pyridoxine glucoside bioavailability are in progress.

Quantitative analysis of the targeting of mannose-terminal glucocerebrosidase. Predominant uptake by liver endothelial cells

Gaucher's disease is an inherited lysosomal storage disorder that is caused by a deficiency of glucocerebrosidase. The resulting accumulation of the substrate glucosylceramide in macrophages of liver, spleen, and bone marrow causes severe clinical symptoms. Gaucher's disease is treated by intravenous administration of a modified glucocerebrosidase (Alglucerase), which has exposed mannose residues to promote uptake by target macrophages. To evaluate the effectiveness of the targeting of Alglucerase, we studied the fate of the enzyme in the rat. Intravenously injected Alglucerase was rapidly cleared from the circulation (half-life 2.0 +/- 0.5 min). The liver was the main site of uptake, with 65.6 +/- 1.2% of the dose present at 10 min after injection. Smaller amounts ( < 3% of the dose) were taken up by spleen and bone marrow. Previous injection with mannan substantially increased the plasma half-life of the enzyme (14.8 +/- 3.2 min versus 1.7 +/- 0.3 min in solvent-preinjected controls) and uptake of the enzyme by liver, spleen and bone marrow was reduced by > 90%. These findings indicate that the enzyme is taken up by these organs via mannose-specific receptors. Subcellular fractionation of the liver indicated that the enzyme is internalized and transported to the lysosomes. By isolating various liver cell types after injection of the Alglucerase, it was found that endothelial cells are the main site of uptake of the enzyme: 60.8 +/- 3.4% of the total liver uptake. Parenchymal and Kupffer cells were responsible for 31.0 +/- 3.1% and 8.2 +/- 0.7% of the hepatic uptake, respectively. We conclude that Alglucerase is rapidly cleared from the circulation by mannose-specific receptors in liver, spleen, and bone marrow. However, less than 10% of the enzyme taken up by the liver is accounted for by Kupffer cells, the hepatic target cells for therapeutic intervention. It is suggested that alterations of the formulation of the therapeutic enzyme may lead to a higher uptake by Kupffer cells and other macrophages, and thus to a more (cost)effective therapy of Gaucher's disease.

Demonstration of direct glycosylation of nondegradable glucosylceramide analogs in cultured cells

After uptake by various cells (human skin fibroblasts, rat neuroblastoma B 104, human neuroblastoma SHSY5Y, murine cerebellar cells), a radioactive and a fluorescent analog of a nondegradable glucosylceramide with sulfur in the glycosidic link were glycosylated to a cell-specific pattern of glycolipid analogs. These results, for the first time, show that a glucosylceramide analog can be conveyed from the plasma membrane of cultured cells to those Golgi compartments that function in the early glycosylation steps of glycolipids. This observation is further confirmed by the fact that the cationic ionophore monensin, known to impede membrane flow from proximal to distal Golgi cisternae, inhibited the formation of complex ganglioside analogs but not those of lactosylceramide, sialyl lactosylceramide (GM3), and disialyl lactosylceramide (GD3).

Characterization of glucocerebrosidase in Greek Gaucher disease patients: mutation analysis and biochemical studies

Gaucher disease is the most frequent lysosomal storage disease in Greece, accounting for 24% of all lysosomal disorders diagnosed during the last 13 years at the Institute of Child Health in Athens. The nature of the defects in glucocerebrosidase in Greek Gaucher patients with non-neuronopathic (type 1) and neuronopathic (types 2 and 3) phenotypes was investigated at the level of the glucocerebrosidase gene and enzyme activity. Mutation analysis performed in 10/23 Gaucher patients with different types of the disorder led to the identification of four mutations, N370S, L444P, R463C and D409H, comprising 75% of the investigated alleles. N370S was only found in association with type 1 disease. The genotype D409H/R463C was identified for the first time and was associated with the severe type 2 disorder. There was no correlation between residual in vitro enzyme activity and either phenotype or genotype. However, in cultured fibroblast of the neuronopathic cases, glucocerebrosidase protein concentration was reduced and the capacity to degrade exogenous C6NBD-glucosylceramide was more severely impaired.

Subcellular fractionation of cultured normal human melanocytes: new insights into the relationship of melanosomes with lysosomes and peroxisomes

In order to obtain information on the disputed nature of melanosomes a comparison was made between the localization of melanosomal markers with those of other well-defined subcellular organelles such as lysosomes and peroxisomes. The distribution of marker enzymes was studied using two different density gradient systems, i.e., Percoll and Nycodenz. Furthermore, the subcellular localization of various types of antigens was analyzed using indirect immunofluorescence and immuno-electron microscopy. All methods revealed the existence of partial co-localization of melanosomal and lysosomal proteins and different localization of peroxisomal markers. The results suggest that melanosomes may share a common origin with lysosomal structures.

Role of pH in determining the cell-type-specific residual activity of glucocerebrosidase in type 1 Gaucher disease

The properties of control and 370Asn-->Ser glucocerebrosidase, the frequently encountered mutated form of the enzyme in type 1 Gaucher disease, were studied in vitro as well as in situ. The catalytic properties of purified 370Asn-->Ser glucocerebrosidase were highly dependent on the assay conditions. The enzyme was deficient in activity towards substrate and in reactivity with the irreversible inhibitor conduritol B-epoxide (CBE) when activated by the bile salt taurocholate. In the presence of more physiological activators, the lysosomal activator protein saposin C and phosphatidylserine, the 370Asn-->Ser enzyme was near normal in kinetic properties at pH values approximately 5, but not at higher pH. In intact fibroblasts, the enzymic activity of the 370Asn-->Ser glucocerebrosidase and its reactivity with CBE were found to be clearly deficient. However, in intact lymphoblasts from the same patients, the behavior of the mutant enzyme was near normal. The catalytic efficiency of 370Asn-->Ser glucocerebrosidase in situ was also found to be highly pH dependent. When intact lymphoblasts were cultured in the presence of permeant weak bases, which increase the pH of acidic intracellular compartments, the catalytic efficiency of the mutant enzyme, as assessed by its reactivity with CBE, became markedly impaired. Our findings indicate that the intralysosomal pH in the intact cell can be expected to have a critical influence on the activation state of 370Asn-->Ser glucocerebrosidase and its ability to hydrolyse substrate. This phenomenon may partly underly the marked heterogeneity in clinical manifestation of Gaucher disease among patients with this mutated form of glucocerebrosidase.

Fluorescence assay of glucosylceramide glucosidase using NBD-cerebroside

A sensitive fluorometric assay for glucocerebroside beta-glucosidase [Dinur, T., Grabowski, G.A., Desnick, R.J., and Gatt, S. (1984) Anal. Biochem. 136, 223-234] has been reexamined. It was found that the lipids containing the NBD moiety (12-[N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] used for standardization of the assay are light-sensitive and that the yield of fluorescent light is very sensitive to the composition of the solvent used in the fluorometric measurement. Some protection against fading could be obtained by adding a free-radical trapping agent, SlowFade. The fading of the free NBD-acid, when used for standardization, could be prevented by adding ethanol to the solvent, but this reduced the fluorescence yield. It is recommended that some of the fluorescent substrate be enzymatically hydrolyzed completely to NBD-ceramide, which can be utilized as the standard without the need to add ethanol. A warning about enzyme reaction rate stability with time is given, with a suggestion for ensuring constancy of activity.

Retroviral-mediated transfer of the human glucocerebrosidase gene into cultured Gaucher bone marrow

Gaucher disease, a lysosomal glycolipid storage disorder, results from the genetic deficiency of an acidic glucosidase, glucocerebrosidase (GC). The beneficial effects of allogeneic bone marrow transplantation (BMT) for Gaucher disease suggest that GC gene transduction and the transplantation of autologous hematopoietic stem cells (gene therapy) may similarly alleviate symptoms. We have constructed a retroviral vector, L-GC, produced by a clone of the amphotropic packaging cell line PA317, which transduces the normal human GC cDNA with high efficiency. Whole-marrow mononuclear cells and CD34-enriched cells from a 4-yr-old female with type 3 Gaucher disease were transduced by the L-GC vector and studied in long-term bone marrow culture (LTBMC). Prestimulation of marrow with IL-3 and IL-6, followed by co-cultivation with vector-producing fibroblasts, produced gene transfer into 40-45% of the hematopoietic progenitor cells. The levels of GC expression in progeny cells (primarily mature myelomonocytic) produced by the LTBMC were quantitatively analyzed by Northern blot, Western blot, and glucocerebrosidase enzyme assay. Normal levels of GC RNA, immunoreactive protein, and enzymatic activity were detected throughout the duration of culture. These studies demonstrate that retroviral vectors can efficiently transfer the GC gene into long-lived hematopoietic progenitor cells from the bone marrow of patients with Gaucher disease and express physiologically relevant levels of GC enzyme activity.

Clinical phenotype of Gaucher disease in relation to properties of mutant glucocerebrosidase in cultured fibroblasts

We have investigated several parameters of glucocerebrosidase in cultured skin fibroblasts from patients with various clinical phenotypes of Gaucher disease. In this study no strict correlation was found between the clinical manifestations of Gaucher disease and the parameters investigated in fibroblasts. These parameters included the specific activity of the enzyme in extracts towards natural lipid and artificial substrate in the presence of different activators; the enzymic activity per unit of glucocerebrosidase protein; the rate of synthesis of the enzyme and its stability; and the post-translational processing of the enzyme. In addition, the activity in situ of glucocerebrosidase in fibroblasts was investigated using a novel method by analysis of the catabolism of NBD-glucosylceramide in cells that were loaded with bovine serum albumin-lipid complexes. Again, no complete correlation with the clinical phenotype of patients was detectable. Glucocerebrosidase in fibroblasts from most non-neuronopathic (type 1) Gaucher disease patients differs in some aspects from enzyme in cells from patients with neurological forms (types 2 and 3). The stimulation by activator protein and phospholipid is clearly more pronounced in type 1 than in types 2 and 3; the enzymic activity per unit of glucocerebrosidase protein in type 1 is severely reduced in the presence of taurocholate and the amount of glucocerebrosidase appears (near) normal in contrast to the situation in types 2 and 3 Gaucher fibroblasts. However, this distinction was not always consistent; glucocerebrosidase in fibroblasts from some type 1 Gaucher patients, particularly some South African cases, was comparable in properties to enzyme in type 2 and 3 patients.

Effect of experimental conditions on the appearance of distinct forms of placental glucosylceramidase: use of gel filtration analysis as a means of ascertaining their occurrence

We have found that, under some experimental conditions, the placental glucosylceramidase shows an anomalous behaviour on gel filtration chromatography. At pH 5.6, the optimal pH of the enzymatic assay, the purified enzyme remains bound to either Superose 6 or TSK-40-XL HPLC columns, while the interaction of the crude glucosylceramidase contained in the water extract of the lysosome-mitochondrial fraction of placenta with the two HPLC gel matrices is much weaker. The quite different behaviour of the crude compared to the purified enzyme may be explained by the formation in the crude preparation of associated form(s) of glucosylceramidase with suitable endogenous compound(s), which compete with the gel matrices for the binding to the enzyme. The most likely one component of the enzyme complex is the placental activating factor, previously reported by us (Vaccaro et al. (1985) Biochim. Biophys. Acta 836, 157-166), as indicated by the negligible stimulation of the crude enzyme activity on addition of the factor, either before or after passage through the HPLC columns. On the assumption that the behaviour of crude glucosylceramidase on gel filtration becomes similar to that of the purified enzyme when its interaction with endogenous substance(s) is impaired, we have identified some conditions which prevent the formation of the enzyme associated form(s): (a) the addition of guanidine chloride (0.2 M), a cahotropic agent, to the crude preparation; and (b) the increase of pH up to 8. In conclusion, taking advantage of the anomalous behaviour of glucosylceramidase on gel filtration chromatography, evidence has been obtained that placental glucosylceramidase may occur under several forms which had not been previously reported; a difference in experimental conditions can promote the formation of one or another form, by possibly affecting the composition and/or the stoichiometry and/or the stability of the enzyme complex.

Conditions affecting the activity of glucocerebrosidase purified from spleens of control subjects and patients with type 1 Gaucher disease

Glucocerebrosidase was purified to homogeneity from spleens of control subjects and Type 1 Gaucher disease patients by immunoaffinity chromatography. Activation of the enzyme by taurocholate, phosphatidylserine and sphingolipid activator protein 2 (saposin C; SAP-2) was investigated by titration of combinations of various effectors in the absence and presence of Triton X-100. The specific activity of Type 1 Gaucher glucocerebrosidase was found to be less than 20% of the corresponding control value under most conditions. However, in the presence of optimal amounts of activator protein SAP-2 and phosphatidylserine (and in the absence of Triton X-100 and/or taurocholate), the specific activity of mutant enzyme towards artificial and natural lipid substrates was close to normal when measured at pH 5.0-5.5. At pH values below 5.0, the specific activity of mutant enzyme decreased more rapidly compared to that of control enzyme. The activity of Type 1 Gaucher glucocerebrosidase in the intact cell might, in a comparable manner, be highly dependent on the extent of activation by endogenous activators and on the intralysosomal pH. Values for residual glucocerebrosidase activity, as measured in vitro in extracts of cells and tissues from Type 1 Gaucher disease patients, are indeed highly dependent on the assay conditions employed. Consequently such measurements are of little value in the assessment of the actual capacity for glucosylceramide hydrolysis and for prediction of the clinical severity of the disease.

Activity of glucocerebrosidase in extracts of different cell types from type 1 Gaucher disease patients

Glucocerebrosidase activity in extracts of leukocytes, Epstein-Barr virus transformed lymphocytes and fibroblasts from Portuguese Type 1 Gaucher disease patients was studied. The residual glucocerebrosidase activity in all extracts from patients was less than 25% if measured in the presence of bile salt taurocholate. However, if measured in the absence of bile salt the residual enzyme activity in extracts from patients was cell type specific: it was severely reduced in the case of fibroblasts, mildly reduced in the case of lymphoblasts and not significantly reduced in the case of leukocytes. The glucocerebrosidase activity in extracts from all control cell types was stimulated by taurocholate. In the patients the enzyme activity in fibroblasts extracts was also stimulated but that in lymphoblasts and leukocytes was inhibited by the bile salt. The differences in glucocerebrosidase activity (in the absence of taurocholate) in extracts from different cell types from Gaucher disease patients are attributable to differences in the proportion of glucocerebrosidase present as a monomer with low activity (form I) and as a highly active aggregate (form II) that may also contain sphingolipid activator protein 2 (SAP-2). In extracts from leukocytes and lymphocytes from Type 1 Gaucher disease patients, but not in those from fibroblasts, a relatively high proportion of enzyme is present in aggregated form with near normal specific activity.

Function of oligosaccharide modification in glucocerebrosidase, a membrane-associated lysosomal hydrolase

The nature and function of oligosaccharide modification in glucocerebrosidase, a membrane-associated lysosomal hydrolase, have been investigated in cultured human skin fibroblasts. Glucocerebrosidase is synthesised as a 62.5-kDa precursor with high-mannose-type oligosaccharide chains and an apparent native isoelectric point of 6.0-7.0. Subsequent processing of the oligosaccharide moieties to sialylated complex-type structures results in formation of 65-68-kDa forms of the enzyme with apparent native isoelectric points of 4.3-5.0. These forms are transported to lysosomes and subsequently modified by the sequential action of lysosomal exoglycosidases, finally resulting in a 59-kDa form with an isoelectric point near neutrality. The existence of oligosaccharide modification of the enzyme in the lysosomes is illustrated by the accumulation of different intermediate forms of glucocerebrosidase in mutant cell lines deficient in lysosomal exoglycosidases. The enzyme does not undergo proteolytic modification during maturation. The possible physiological relevance of the oligosaccharide modification of glucocerebrosidase in the lysosomes was investigated by studying the properties of the enzyme in fibroblasts deficient in lysosomal exoglycosidases, and also the properties of homogeneous pure glucocerebrosidase from placenta, modified in the oligosaccharide moieties by digestion in vitro with glycosidases. Modification of the oligosaccharide moieties of glucocerebrosidase had no significant effect on the catalytic activity of the enzyme as measured with either artificial or natural substrates in the presence of artificial or natural activators. There was also no effect of modification of the oligosaccharide chains on the intracellular stability of the enzyme or on its apparent hydrophobicity. We conclude that oligosaccharide modification of glucocerebrosidase in the lysosomes simply reflects further maturation of the enzyme in the lysosome and is of no importance to its function.

Comparative study on glucocerebrosidase in spleens from patients with Gaucher disease

In Gaucher disease (glucosylceramide lipidosis), deficiency of glucocerebrosidase causes pathological storage of glucosylceramide, particularly in the spleen. A comparative biochemical and immunological analysis has therefore been made of glucocerebrosidase in spleens from normal subjects (n = 4) and from Gaucher disease patients with non-neuronopathic (n = 5) and neuronopathic (n = 5) phenotypes. The spleens from all Gaucher disease patients showed markedly decreased glucocerebrosidase activity. Discrimination of different phenotypes of Gaucher disease was not possible on the basis of the level of residual enzyme activity, or by measurements, using the immunopurified enzyme, of kinetic constants, pI or molecular mass forms. A severe decrease was found in the specific activity of glucocerebrosidase purified to homogeneity from the spleen of a patient with the non-neuronopathic phenotype of Gaucher disease, as compared with that of the enzyme purified from the spleen of a normal subject. This finding was confirmed by an immunological method developed for accurate assessment of the relative enzyme activity per molecule of glucocerebrosidase protein. The method revealed that the residual enzyme in the spleens of all investigated patients with a non-neuronopathic course of Gaucher disease had a more than 7-fold decreased activity of glucocerebrosidase (measured in the presence of taurocholate) per molecule of enzyme, and that the concentration of glucocerebrosidase molecules in the spleens of these patients was near normal. Observations made with immunoblotting experiments were consistent with these findings. In contrast, in the spleens of patients with neuronopathic phenotypes of Gaucher disease, the concentration of glucocerebrosidase molecules was severely decreased.

Properties of acid ceramidase from human spleen

We have characterised ceramidase activity in extracts of human spleen from control subjects and from patients with Gaucher disease. In Triton X-100 extracts of control spleens, a broad pH optimum of pH 3.5-5.0 was found; no ceramidase activity was detectable at neutral or alkaline pH. About 45-60% of acid ceramidase could be extracted from spleen without detergents, but for complete extraction, Triton X-100 was required. For the radiolabelled substrate oleoylsphingosine, a Km of 0.22 +/- 0.09 mM and a Vmax of 57 +/- 11 nmol/h per mg protein was calculated in spleen from a control subject. Flat-bed isoelectric focussing in the presence of Triton X-100 revealed a pI of 6.0-7.0 for acid ceramidase; similar values were found for sphingomyelinase and glucerebrosidase. HPLC-gel filtration indicated that in the presence of Triton X-100, acid ceramidase has an Mr of about 100 kDa. In the absence of detergents, the enzyme forms high-molecular-weight aggregates. Similar aggregation behaviour was observed for sphingomyelinase, while the elution of beta-hexosaminidase was not affected by detergents. The elution profile of glucocerebrosidase was only slightly altered by Triton X-100. There was no difference in the properties of acid ceramidase present in spleen from control subjects and from patients with type I Gaucher disease.

Characterization of glucocerebrosidase in peripheral blood cells and cultured blastoid cells

We have characterized glucocerebrosidase in various cell types of peripheral blood of control subjects and in cultured human blastoid cells. The intracellular level of glucocerebrosidase in cultured blastoid cells (10-30 nmol substrate hydrolyzed/h.mg protein) resembles closely values observed for leukocyte cell types and various tissues and is significantly lower than that observed in cultured fibroblasts (150-500 nmol substrate hydrolyzed/h.mg protein). Glucocerebrosidase is extracted from leukocyte cell types and cultured blastoid cells almost exclusively in a monomeric, nonactivated form with enzymatic properties identical to those of the tissue enzyme. In contrast, extracts of platelets are rich in an aggregated, activated form of the enzyme. Glucocerebrosidase in blood cells and cultured blastoid cells is heterogeneous with respect to Mr and pI due to a heterogeneous oligosaccharide composition of the enzyme. The different forms seen represent intermediates in the biosynthesis and maturation of the enzyme. Blastoid cells should thus be an attractive model system for studying the natural history of glucocerebrosidase in a cell type related to those cells involved in the pathology of Gaucher disease.

Heterogeneity in human acid beta-glucosidase revealed by cellulose-acetate electrophoresis

Cellulose-acetate gel electrophoresis, a technique commonly used for the separation of human acid hydrolases, was applied to study heterogeneity in acid beta-glucosidase (EC 3.2.1.45). With this technique, three forms of beta-glucosidase were distinguishable in extracts of several tissues. The most anodic beta-glucosidase activity (band 3) represents the broad-specificity beta-glucosidase that is not deficient in Gaucher disease and is not inhibited by conduritol B-epoxide (CBE). The beta-glucosidase activity was deficient in Gaucher disease. A third beta-glucosidase activity with an intermediate mobility (band 2) was also inhibited by CBE and deficient in Gaucher disease. Band 1 and band 2 beta-glucosidase thus represent different forms of glucocerebrosidase. By adding phosphatidylserine and sphingolipid activator protein (SAP-2), monomeric glucocerebrosidase could be completely converted into a form that comigrated with band 2 beta-glucosidase of tissue extracts. The addition of phosphatidylserine only also resulted in a changed mobility of the monomeric enzyme, but the migration in this case differed from that of band 2 beta-glucosidase of tissue extracts. The electrophoretic profile of beta-glucosidase activity of tissue extracts changed upon ethanol/chloroform extraction: the two glucocerebrosidase forms were converted into a band with a mobility identical to that of band 1 beta-glucosidase. Our findings indicate that the interaction of glucocerebrosidase with phospholipid and SAP-2 has major effects on the mobility of the enzyme in the cellulose-acetate gel electrophoresis system. The findings with the cellulose-acetate gel electrophoretic system are discussed in relation to the heterogeneity in glucocerebrosidase observed with sucrose density gradient analysis, immunochemical methods and isoelectric focussing studies.

Glycosylation and processing of high levels of active human glucocerebrosidase in invertebrate cells using a baculovirus expression vector

A human cDNA containing the complete coding region for the lysosomal glycoprotein glucocerebrosidase (EC 3.2.1.45) was introduced into the genome of Autographa californica nuclear polyhedrosis virus downstream from the polyhedrin promoter. Infection of Spodoptera frugiperda cells (SF9) with recombinant virus produced high levels of glucocerebrosidase, 40% of which was in the culture medium. The amino-terminal amino acid sequence of the recombinantly produced enzyme was identical to that of mature, human placental glucocerebrosidase, demonstrating that the signal sequence of the human preenzyme was recognized and appropriately removed in the SF9 invertebrate cells. The glucocerebrosidase in both the culture supernatant and SF9 cell pellet was glycosylated and contained, in part, high mannose oligosaccharide. These results demonstrate that insect cells can be used to produce abundant quantities of active mature human glucocerebrosidase that contains high mannose oligosaccharide as a consequence of post-translational processing.

Structural analysis of the human glucocerebrosidase genes

Two different genomic clones containing the entire coding sequence of human glucocerebrosidase were isolated from a fetal liver library using a cDNA probe previously cloned by us. These clones correspond to two human glucocerebrosidase genes, designated 6-1 and 10-2. Clone 6-1 contains sequences homologous to the cDNA we cloned previously. The promoter regions of the genes were identified by S1 analysis and sequenced. They contain TATA- and CAAT-like boxes, but lack a GGCGGG motif. When coupled to the bacterial gene coding for chloramphenicol acetyl transferase (CAT) and transfected to Gaucher skin fibroblast lines, both promoter fragments enhanced CAT activity. The promoter of gene 6-1 was eight times more efficient than the promoter of gene 10-2. Northern blot analysis revealed three human glucocerebrosidase RNA species of 6, 2.6, and 2.2 kb in size. The 6-kb transcript is probably a nuclear transcript whereas the 2.6-kb and 2.2-kb transcripts are cytoplasmic species which emerge from polyadenylation at different sites.

An improved procedure for the isolation of lamellar bodies from human lung. Lamellar bodies free of lysosomes contain a spectrum of lysosomal-type hydrolases

We have recently shown that lamellar body fractions purified from human lung contain a distinct acid alpha-glucosidase distinguishable from lysosomal acid alpha-glucosidase in that it does not cross-react with antibodies raised against the lysosomal enzyme and does not bind to concanavalin A (De Vries, A.C.J., Schram, A.W., Tager, J.M., Batenburg, J.J. and Van Golde, L.M.G. (1985) Biochim. Biophys. Acta 837, 230-238). In order to study the relationship between the non-concanavalin A-binding alpha-glucosidase and lamellar bodies more closely a method was developed for the further purification of the organelles. A purified lamellar body preparation isolated from human lung homogenate by discontinuous sucrose density centrifugation was subjected to gel filtration with Sepharose 4B followed by Percoll density gradient centrifugation, which yielded a lamellar body preparation with a phospholipid phosphorus/protein ratio of 12.57 +/- 0.38 (mumol/mg) (n = 3) as compared to a ratio of 3.34 +/- 0.16 (mumol/mg) (n = 3) in the sucrose density gradient preparation. Concomitantly there was a 3.3 +/- 0.1 (n = 3)-fold enrichment in the content of total acid alpha-glucosidase and a 3.2 +/- 0.1 (n = 3) -fold enrichment of non-concanavalin A-binding acid alpha-glucosidase. The new purification method removes adhering proteins without changing the phospholipid composition. During the successive purification steps the concanavalin A-sensitive and -insensitive alpha-glucosidases remained fully lamellar body fraction associated. Differences between a lysosome-enriched fraction and a lamellar body preparation at varying stages of purification with respect to the ratio between soluble acid hydrolases and the membrane-associated lysosomal enzyme glucocerebrosidase indicate that the purified lamellar bodies were not contaminated with lysosomes. The absence of lysosomes in the purified lamellar body fraction was confirmed by experiments with the weak base glycyl-L-phenylalanine-beta-naphthylamide, which is an artificial substrate for the lysosomal enzyme cathepsin C and brings about lysis of lysosomes. Morphological examination by electron microscopy endorses the absence of contaminating vesicles and organelles and showed a structural integrity of the lamellar bodies in the final preparation. The improved isolation procedure strongly suggests that the concanavalin A-insensitive acid alpha-glucosidase is endogenous to lamellar bodies and supports our earlier idea that it can be used as a lamellar body-specific marker enzyme. In addition, the experiments show that lamellar bodies free of lysosomes contain a spectrum of lysosomal-type enzymes.

Human acid beta-glucosidase: use of inhibitors, alternative substrates and amphiphiles to investigate the properties of the normal and Gaucher disease active sites

Comparative studies with lipoidal inhibitors and alternative substrates were conducted to investigate the properties of the active site of human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) from normal placenta and spleens of Type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients. With the normal enzyme, the inhibitory potencies of series of alkyl(Cn; n = 0-18)amines, alkyl beta-glucosides and alkyl-1-deoxynojirimycins were a biphasic function of increasing chain length: i.e., large decreases in Ki,app or IC50 were found only with n greater than 4 and limiting values were approached with n = 12-14. This biphasic function of alkyl chain length was observed in the presence or absence of detergents and/or negatively charged lipids. In the presence of Triton X-100 concentrations greater than the critical micellar concentration, the relative (to deoxynojirimycin) inhibitory potencies of the N-Cn-deoxynojirimycins (n greater than 4) were decreased about 3-5-fold, due to an energy requirement to extract the inhibitors from Triton X-100 micelles. The Ki,app or IC50 of N-hexylglucosylsphingosine was inversely related to the Triton X-100 concentration and was not affected by the presence of 'co-glucosidase'. The mutual exclusion of glucon, N-Cn-deoxynojirimycin and sphingosine derivatives from the normal enzyme suggested a shared region for binding in the active site. Increasing the fatty-acid acyl chain length of glucosyl ceramide from 1 to 24 carbons had minor effects on Km,app ( = Kis,app) (8-40 microM), but increased Vmax,app up to 13-fold. With the AJGD enzyme, the inhibitor and alternative substrate findings were similar to those with the normal enzyme, except that Kis,app(AJGD)/Kis,app(normal) = 4 to 11 for the Cn-glycons and sphingosine derivatives. These results indicated that (1) the Ki,app or Km,app values for amphiphilic inhibitors or substrates reflect a balance of binding energies for two hydrophobic subsites within the enzyme's active site and Triton X-100 micelles and (2) the abnormal properties of the AJGD enzyme result from an amino-acid alteration(s) within or near a hydrophilic region which is shared by the glycon-binding site and the two hydrophobic sites of the active site.