HEPES activates a MiT/TFE-dependent lysosomal-autophagic gene network in cultured cells: A call for caution

In recent years, the lysosome has emerged as a highly dynamic, transcriptionally regulated organelle that is integral to nutrient-sensing and metabolic rewiring. This is coordinated by a lysosome-to-nucleus signaling nexus in which MTORC1 controls the subcellular distribution of the microphthalmia-transcription factor E (MiT/TFE) family of “master lysosomal regulators”. Yet, despite the importance of the lysosome in cellular metabolism, the impact of traditional in vitro culture media on lysosomal dynamics and/or MiT/TFE localization has not been fully appreciated. Here, we identify HEPES, a chemical buffering agent that is broadly applied in cell culture, as a potent inducer of lysosome biogenesis. Supplementation of HEPES to cell growth media is sufficient to decouple the MiT/TFE family members–TFEB, TFE3 and MITF–from regulatory mechanisms that control their cytosolic retention. Increased MiT/TFE nuclear import in turn drives the expression of a global network of lysosomal-autophagic and innate host-immune response genes, altering lysosomal dynamics, proteolytic capacity, autophagic flux, and inflammatory signaling. In addition, siRNA-mediated MiT/TFE knockdown effectively blunted HEPES-induced lysosome biogenesis and gene expression profiles. Mechanistically, we show that MiT/TFE activation in response to HEPES requires its macropinocytic ingestion and aberrant lysosomal storage/pH, but is independent of MTORC1 signaling. Altogether, our data underscore the cautionary use of chemical buffering agents in cell culture media due to their potentially confounding effects on experimental results.

In vitro and in vivo comparative and competitive activity-based protein profiling of GH29 α-l-fucosidases

GH29 α-l-fucosidases catalyze the hydrolysis of α-l-fucosidic linkages. Deficiency in human lysosomal α-l-fucosidase (FUCA1) leads to the recessively inherited disorder, fucosidosis. Herein we describe the development of fucopyranose-configured cyclophellitol aziridines as activity-based probes (ABPs) for selective in vitro and in vivo labeling of GH29 α-l-fucosidases from bacteria, mice and man. Crystallographic analysis on bacterial α-l-fucosidase confirms that the ABPs act by covalent modification of the active site nucleophile. Competitive activity-based protein profiling identified l-fuconojirimycin as the single GH29 α-l-fucosidase inhibitor from eight configurational isomers.

Potent and selective activity-based probes for GH27 human retaining α-galactosidases

Lysosomal degradation of glycosphingolipids is mediated by the consecutive action of several glycosidases. Malfunctioning of one of these hydrolases can lead to a lysosomal storage disorder such as Fabry disease, which is caused by a deficiency in α-galactosidase A. Herein we describe the development of potent and selective activity-based probes that target retaining α-galactosidases. The fluorescently labeled aziridine-based probes 3 and 4 inhibit the two human retaining α-galactosidases αGal A and αGal B covalently and with high affinity. Moreover, they enable the visualization of the endogenous activity of both α-galactosidases in cell extracts, thereby providing a means to study the presence and location of active enzyme levels in different cell types, such as healthy cells versus those derived from Fabry patients.

Exploring functional cyclophellitol analogues as human retaining beta-glucosidase inhibitors

Of six cyclophellitol analogues, the N-pentylaziridine is the most effective retaining human beta-glucosidase inhibitor considering potency and compound stability.

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.

Activity-based profiling of retaining β-glucosidases: a comparative study

Activity-based protein profiling (ABPP) is a versatile strategy to report on enzyme activity in vitro, in situ, and in vivo. The development and use of ABPP tools and techniques has met with considerable success in monitoring physiological processes involving esterases and proteases. Activity-based profiling of glycosidases, on the other hand, has proven more difficult, and to date no broad-spectrum glycosidase activity-based probes (ABPs) have been reported. In a comparative study, we investigated both 2-deoxy-2-fluoroglycosides and cyclitol epoxides for their utility as a starting point towards retaining β-glucosidase ABP. We also investigated the merits of direct labeling and two-step bio-orthogonal labeling in reporting on glucosidase activity under various conditions. Our results demonstrate that 1) in general cyclitol epoxides are the superior glucosidase ABPs, 2) that direct labeling is the more efficient approach but it hinges on the ability of the glucosidase to be accommodated in the active site of the reporter (BODIPY) entity, and 3) that two-step bio-orthogonal labeling can be achieved on isolated enzymes but translating this protocol to cell extracts requires more investigation.

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.

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.

Common G102S polymorphism in chitotriosidase differentially affects activity towards 4-methylumbelliferyl substrates

Chitotriosidase (CHIT1) is a chitinase that is secreted by activated macrophages. Plasma chitotriosidase activity reflects the presence of lipid-laden macrophages in patients with Gaucher disease. CHIT1 activity can be conveniently measured using fluorogenic 4-methylumbelliferyl (4MU)-chitotrioside or 4MU-chitobioside as the substrate, however, nonsaturating concentrations have to be used because of apparent substrate inhibition. Saturating substrate concentrations can, however, be used with the newly designed substrate 4MU-deoxychitobioside. We studied the impact of a known polymorphism, G102S, on the catalytic properties of CHIT1. The G102S allele was found to be common in type I Gaucher disease patients in the Netherlands ( approximately 24% of alleles). The catalytic efficiency of recombinant Ser102 CHIT1 was approximately 70% that of wild-type Gly102 CHIT1 when measured with 4MU-chitotrioside at a nonsaturating concentration. However, the activity was normal with 4MU-deoxychitobioside as the substrate at saturating concentrations, consistent with predictions from molecular dynamics simulations. In conclusion, interpretation of CHIT1 activity measurements with 4MU-chitotrioside with respect to CHIT1 protein concentrations depends on the presence of Ser102 CHIT1 in an individual, complicating estimation of the body burden of storage macrophages. Use of the superior 4MU-deoxychitobioside substrate avoids such complications because activity towards this substrate under saturating conditions is not affected by the G102S substitution.

Treatment of Fabry disease with different dosing regimens of agalsidase: effects on antibody formation and GL-3

Two different enzyme preparations are used for the treatment of Fabry disease patients, agalsidase alpha (Replagal, Shire) and agalsidase beta (Fabrazyme, Genzyme). Therapeutic efficacy of both products has been variable probably due to differences in gender, severity, age and other patient characteristics. We studied the occurrence of alpha-Gal A antibodies and their effect on urinary and plasma globotriaosylceramide (GL-3), plasma chitotriosidase and clinical outcome in 52 patients after 12 months of treatment with either 0.2mg/kg agalsidase alppha (10 males, 8 females) or beta (8 males, 5 females) or 1.0mg/kg agalsidase beta (10 males, 11 females). Antibodies were detected in 18/28 male patients after 6 months. None of the females developed antibodies. Following 12 months of 0.2mg/kg treatment, urinary GL-3 decreased in antibody negative (AB-) but increased in antibody positive (AB+) patients. Treatment with 1.0mg/kg gave a reduction in urinary GL-3 in both AB- and AB+ patients. Levels of plasma GL-3 and chitotriosidase decreased in all patient groups. Twelve months of 0.2mg/kg treatment did not change renal function or left ventricular mass. Further, no change in renal function was seen following 1.0mg/kg treatment and left ventricular mass decreased in both AB- and AB+ patients. In summary, alpha-Gal A antibodies frequently develop in male Fabry disease patients and interfere with urinary GL-3 excretion. Infusion of a dose of 1.0mg/kg results in a more robust decline in GL-3, less impact, if any of antibodies, stable renal function and reduction of LVMass.

CCL18: a urinary marker of Gaucher cell burden in Gaucher patients

Glucosylceramide-laden tissue macrophages in Gaucher patients secrete large quantities of chitotriosidase and CC chemokine ligand 18 (CCL18), resulting in markedly increased plasma levels. We have comparatively investigated the occurrence of both parameters in plasma and urine samples of Gaucher patients. Chitotriosidase was high in urine samples of some symptomatic patients, but elevations did not correlate with increased plasma concentrations. Urinary chitotriosidase was particularly high in a patient with severe kidney involvement and local storage cell infiltration. Urinary levels of CCL18 were also highly elevated in samples from Gaucher patients as compared to controls. The median value of the CCL18/creatinine ratio in urine samples of 31 Gaucher patients was 143.3 pg/micromol (range 32-551) and in those of 12 normal subjects was 4.1 pg/micromol (range 1.3-6.8). In sharp contrast to chitotriosidase, increases in the low-molecular-mass chemokine CCL18 in urine and plasma specimens of Gaucher patients correlated well. A correlation was also observed for reductions in urinary and plasma CCL18 following therapy. It is concluded that assessment of urinary CCL18 of Gaucher patients gives insight into the total body burden on Gaucher cells, whereas that of chitotriosidase does not. Urinary chitotriosidase appears rather to be a reflection of renal pathology.

Enzyme therapy for Fabry disease: Neutralizing antibodies toward agalsidase alpha and beta

BACKGROUND

Fabry disease is an X-linked inherited disorder that is caused by excessive lysosomal globotriaosylceramide (CTH) storage due to a deficiency in alpha-galactosidase A (alpha-Gal A). Two recombinant enzyme preparations have been approved as treatment modality. We studied emergence and properties of alpha-Gal A antibodies in treated patients.

METHODS

During the first 6 to 12 months of intravenous administration of recombinant enzymes (rh-alpha-Gal A) formation of antibodies was studied in 18 adult Fabry patients (two females).

RESULTS

The female patients did not develop detectable amounts of antibodies following enzyme therapy. After 6 months of treatment with either agalsidase alpha or beta, 11/16 male patients showed high titers of immunoglobulin G (IgG) antibodies that cross-react in vitro similarly with both recombinant enzymes. The anti-rh-alpha-Gal A IgG neutralizes rh-alpha-Gal A activity in vitro for 65% to 95%. During infusion with rh-alpha-Gal A, circulating enzyme-antibody complexes are formed and these complexes are taken up by leukocytes in the peripheral blood. After 6 months of treatment all IgG-negative patients showed a significant (P < 0.01) reduction of urinary CTH (1890 +/- 797 to 603 +/- 291 nmol CTH/24hr urine), compared to IgG-positive patients (mean increase from 2535 +/- 988 to 2723 +/- 1212), suggesting a negative effect of circulating antibodies on renal tubular CTH clearance.

CONCLUSION

Emergence of antibodies with in vivo neutralizing capacities is frequently encountered in treated Fabry disease patients. Complete cross-reactivity of these antibodies suggests that it is unlikely that switching from one to the other recombinant protein prevents the immune response and related effects. Further studies on the clinical implications of alpha-Gal A antibodies are essential.

Transglycosidase activity of chitotriosidase: improved enzymatic assay for the human macrophage chitinase

Chitotriosidase is a chitinase that is massively expressed by lipid-laden tissue macrophages in man. Its enzymatic activity is markedly elevated in serum of patients suffering from lysosomal lipid storage disorders, sarcoidosis, thalassemia, and visceral Leishmaniasis. Monitoring of serum chitotriosidase activity in Gaucher disease patients during progression and therapeutic correction of their disease is useful to obtain insight in changes in body burden on pathological macrophages. However, accurate quantification of chitotriosidase levels by enzyme assay is complicated by apparent substrate inhibition, which prohibits the use of saturating substrate concentrations. We have therefore studied the catalytic features of chitotriosidase in more detail. It is demonstrated that the inhibition of enzyme activity at excess substrate concentration can be fully explained by transglycosylation of substrate molecules. The potential physiological consequences of the ability of chitotriosidase to hydrolyze as well as transglycosylate are discussed. The novel insight in transglycosidase activity of chitotriosidase has led to the design of a new substrate molecule, 4-methylumbelliferyl-(4-deoxy)chitobiose. With this substrate, which is no acceptor for transglycosylation, chitotriosidase shows normal Michaelis-Menten kinetics, resulting in major improvements in sensitivity and reproducibility of enzymatic activity measurements. The novel convenient chitotriosidase enzyme assay should facilitate the accurate monitoring of Gaucher disease patients receiving costly enzyme replacement therapy.

Chitotriosidase, a chitinase, and the 39-kDa human cartilage glycoprotein, a chitin-binding lectin, are homologues of family 18 glycosyl hydrolases secreted by human macrophages

In various mammals, enzymatically active and inactive members of family 18 glycosyl hydrolases, containing chitinases, have been identified. In man, chitotriosidase is the functional chitinolytic enzyme, whilst the homologous human cartilage 39-kDa glycoprotein (HC gp-39) does not exhibit chitinase activity and its function is unknown. This study establishes that HC gp-39 is a chitin-specific lectin. It is experimentally demonstrated that a single amino acid substitution in the catalytic centre of the 39-kDa isoform of chitotriosidase, which generates a similar sequence to that in HC gp-39, results in a loss of hydrolytic activity and creates the capacity to bind to chitin. The possible implication of the finding for chitinolytic and chitin-binding proteins that are produced in high quantities by activated macrophages are discussed.

Synthesis, sorting, and processing into distinct isoforms of human macrophage chitotriosidase

Chitotriosidase, the human analogue of chitinases from non-vertebrate species, has recently been identified. The macrophage-derived enzyme is remarkably heterogeneous in molecular mass and isoelectric point. The synthesis and modification of the enzyme in cultured macrophages is reported. Chitotriosidase is synthesized as a 50-kDa protein with a pI of about 6.5 and 7.2. It is predominantly secreted, but in part processed into a 39-kDa form with a pI of 8.0 that accumulates in lysosomes. In the C-terminal extension of the 50-kDa chitotriosidase, sialic-acid containing O-linked glycans are present, causing its heterogeneous acidic isoelectric point. Chitotriosidase lacks N-linked glycans and the mechanism of routing to lysosomes proves to be distinct from that of soluble, N-glycosylated, lysosomal enzymes. It was observed that, in macrophages, alternative splicing generates a distinct chitotriosidase mRNA species, encoding a 40-kDa chitotriosidase that is C-terminally truncated. This enzyme is almost identical to the 39-kDa chitotriosidase formed from the 50-kDa precursor by proteolytic processing. It is concluded that the C-terminus present in the 50-kDa chitotriosidase, but absent in the 39-kDa isoform, was found to mediate tight binding to chitin. In the blood stream the secretory 50-kDa chitotriosidase occurs predominantly, whilst in tissues the 39-kDa form is also abundant. These findings are consistent with the data on the synthesis and processing of chitotriosidase in the cultured macrophage model.

Purification and characterization of human chitotriosidase, a novel member of the chitinase family of proteins

Recently we noted (Hollak, C.E.M., van Weely, S., van Oers, M.H.J., and Aerts, J.M.F.G. (1994) J. Clin. Invest. 93, 1288-1292) that the clinical manifestation of Gaucher disease is associated with a several hundred-fold increase in chitotriosidase activity in plasma. We report on the purification and characterization of the protein. Two major isoforms of chitotriosidase with isoelectric points of 7.2 and 8.0 and molecular masses of 50 and 39 kDa, respectively, were purified from the spleen of a Gaucher patient. The N-terminal amino acid sequence of the two forms proved to be identical. An antiserum raised against the purified 39-kDa chitotriosidase precipitated all isozymes. Chitotriosidase activity was earlier found to be completely absent in some individuals. These findings in combination suggest that a single gene may encode the different isoforms of chitotriosidase. Both the N-terminal sequence and an internal sequence chitotriosidase proved to be homologous to sequences in proteins that are members of the chitinase family (Hakala, B.E., White,C., and Recklies, A.D. (1993) J. Biol. Chem. 268, 25803-25810). The human chitotriosidase described here showed chitinolytic activity toward artificial substrates as well as chitin and may therefore be considered to be a chitinase.

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.

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.

Relationship between the two immunologically distinguishable forms of glucocerebrosidase in tissue extracts

Extracts of human spleen contain two immunologically distinguishable forms of glucocerebrosidase: form I is precipitable by polyclonal or monoclonal anti-(placental glucocerebrosidase) antibodies, whereas form II is not [Aerts, J. M. F. G., Donker-Koopman, W. E., Van der Vliet, M. F. K., Jonsson, L. M. V., Ginns, E. I., Murray, G. J., Barranger, J. A., Tager, J. M. & Schram, A. W. (1985) Eur. J. Biochem. 150, 565-574]. The proportion of form II glucocerebrosidase was high in extracts of spleen, liver and kidney and low in extracts of brain, placenta and fibroblasts. Furthermore, the proportion of form II enzyme was higher in a detergent-free aqueous extract of spleen than in a Triton X-100 extract of total spleen or splenic membranes. When form II glucocerebrosidase in a splenic extract was separated from form I enzyme by immunoaffinity chromatography and stored at 4 degrees C, a gradual conversion to form I enzyme occurred. The conversion was almost immediate if 30% (v/v) ethylene glycol was present. In the denatured state both forms of glucocerebrosidase reacted with anti-(placental glucocerebrosidase) antibodies. Form I glucocerebrosidase was stimulated by sodium taurocholate or sphingolipid-activator protein 2 (SAP-2), whereas form II enzyme exhibited maximal activity in the absence of the effectors. The pH activity profile of form II glucocerebrosidase was almost identical to that of form I enzyme in the presence of SAP-2. In the native state, form I glucocerebrosidase had a molecular mass of 60 kDa whereas that of form II glucocerebrosidase was about 200 kDa. After gel-permeation high-performance liquid chromatography of splenic extracts, the fractions with form II glucocerebrosidase contained material cross-reacting with both anti-(placental glucocerebrosidase) and anti-(SAP-2) antibodies. Preincubation of form I glucocerebrosidase with SAP-2 at pH 4.5 led to masking of the epitope on glucocerebrosidase reacting with monoclonal anti-(placental glucocerebrosidase) antibody 2C7. Furthermore, preincubation of form I glucocerebrosidase with monoclonal antibody 2C7 prevented activation of the enzyme by SAP-2. We propose that form I glucocerebrosidase is a monomeric form of the enzyme, whereas form II glucocerebrosidase is a high-Mr complex of the enzyme in association with sphingolipid-activator protein 2.

Efficient routing of glucocerebrosidase to lysosomes requires complex oligosaccharide chain formation

The biosynthesis and intracellular transport of the membrane-associated lysosomal enzyme glucocerebrosidase was studied in the monoblast cell line U937. Addition to the cultures of the oligosaccharide trimming inhibitors swainsonine or deoxymannojirimycin led to an increased intracellular activity of glucocerebrosidase. This was due to prevention of the lysosomal degradation of the enzyme. When homogenates of control cells were fractionated on Percoll gradients glucocerebrosidase, like beta-hexosaminidase, was distributed in two peaks, one at low density and one at high density. When homogenates of cells cultured in the presence of oligosaccharide trimming inhibitors were fractionated beta-hexosaminidase was still distributed in two peaks but glucocerebrosidase was found mainly in low density fractions also containing galactosyltransferase activity. It is concluded that complex type oligosaccharide chain formation is required for efficient routing of glucocerebrosidase to the lysosomes in U937 cells.

Comparison of the properties of a soluble form of glucocerebrosidase from human urine with those of the membrane-associated tissue enzyme

Human urine contains a soluble form of glucocerebrosidase, an enzyme associated with the lysosomal membrane in cells and tissues. Urinary glucocerebrosidase is identical to the enzyme extracted from tissues with respect to the following parameters: Km for natural and artificial substrates, inhibition by conduritol B-epoxide, and stimulation by taurocholate. The enzyme is greater than 90% precipitable by polyclonal anti-(placental glucocerebrosidase) antiserum. Upon isoelectric focussing of urinary glucocerebrosidase multiple peaks of activity were observed. Partial deglycosylation (removal of sialic acid, N-acetylglucosamine and galactose) of the urinary enzyme increased the isoelectric point to a value identical to that of the main form found after partial deglycosylation of the placental enzyme. Upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate followed by immunoblotting, the immunopurified urinary enzyme shows the same molecular mass forms as the enzyme immunopurified from brain and kidney. In placenta the apparent molecular mass is somewhat higher but upon removal of sialic acid, N-acetylglucosamine and galactose the urinary and the placental enzyme show identical molecular masses of 57 kDa. We conclude that the enzymes extracted from urine and tissue are identical and that differences in apparent molecular mass and isoelectric point are probably due to heterogeneity in the oligosaccharide moieties of the molecules.

Deficient activity of glucocerebrosidase in urine from patients with type 1 Gaucher disease

Glucocerebrosidase is present in considerable amounts in human urine. The enzyme is stable in concentrated urine for several days when stored at 0 degrees C. Like tissue glucocerebrosidase, the urinary enzyme is inhibited by conduritol B-epoxide and hydrolyses not only glucocerebroside but also the synthetic substrate 4-methyl-umbelliferyl-beta-D-glucoside. The enzyme is deficient in urine from patients with Gaucher disease (type 1). It is possible to discriminate completely between patients with type 1 Gaucher disease and control subjects by measuring the ratio glucocerebrosidase/beta-hexosaminidase in urine. The value of this ratio (mean +/- SE) with the synthetic substrates 4-methylumbelliferyl-beta-glucoside and p-nitrophenyl-beta-N-acetylglucosaminide, respectively, was 34.2 +/- 3.7 (n = 24) in the controls and 2.1 +/- 0.9 (n = 21) in the patients.

A procedure for the rapid purification in high yield of human glucocerebrosidase using immunoaffinity chromatography with monoclonal antibodies

A novel chromatographic immunoaffinity procedure is described for the purification of Form I glucocerebrosidase (see J. M. F. G. Aerts, W. E. Donker-Koopman, M. K. Van der Vliet, L. M. V. Jonsson, E. I. Ginns, G. J. Murray, J. A. Barranger, J. M. Tager, and A. W. Schram, 1985, Eur. J. Biochem. 150, 565-574) from extracts of human tissues. The affinity support consists of two monoclonal anti-(glucocerebrosidase) antibodies immobilized by covalent coupling to CNBr-activated Sepharose 4B. After adsorption of the enzyme from a crude detergent extract, the column is washed successively with 30% ethylene glycol in citrate buffer (pH 6), 1% Triton X-100 in citrate phosphate buffer (pH 5.2), and 50% ethylene glycol in citrate buffer. The enzyme is eluted with 90% ethylene glycol in citrate buffer. After dilution to 30% ethylene glycol, the immunoaffinity purification is repeated. The procedure can be completed within less than 18 h. The final preparations have a high specific activity (50 U/mg protein (n = 4) for the placental enzyme) and contain no detectable impurities after polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The yield is high (81 +/- 8% for the placental enzyme). The immunoaffinity column has a high capacity, can be regenerated easily, and can be utilized repeatedly without loss of activity.

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

The beta-glucosidase activity in spleen from control subjects and patients with different clinical phenotypes of Gaucher's disease was characterized. The occurrence of a soluble non-specific beta-glucosidase with a neutral pH optimum and two membrane-associated beta-glucocerebrosidases with an acid pH optimum was demonstrated. The two beta-glucocerebrosidases can be distinguished on the basis of their ability to react with anti-(placental beta-glucocerebrosidase) antibodies bound to protein-A--Sepharose 4B beads. One of the splenic beta-glucocerebrosidases (form I) is precipitated by the immobilized antibodies and the other (form II) is not. The two forms also differ in binding affinity to concanavalin A, degree of stimulation of enzymic activity by taurocholate and isoelectric point. In contrast, the Km values of the two beta-glucocerebrosidases for natural and artificial substrates are similar and both are inhibited by conduritol B-epoxide. In spleen from three patients with type 1, one patient with type 2 and one patient with type 3 Gaucher's disease form I beta-glucocerebrosidase was found to be clearly deficient, whereas the activity of form II was 25-50% of that in control spleen. The non-specific, neutral beta-glucosidase was not deficient in these Gaucher spleens. The distinct biochemical and immunological properties of non-specific beta-glucosidase and the fact that normal levels of the enzyme are present in patients with Gaucher's disease indicate, in confirmation of previous reports, that non-specific beta-glucosidase is not related to beta-glucocerebrosidase.

Immunological studies on lysosomal sphingomyelinase: identification of a 28 000-Da component deficient in urine from patients with Niemann-Pick disease types A and B

The immunoblotting technique was used to identify sphingomyelinase protein in samples of tissue and urine after subjection to polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. In a sphingomyelinase preparation purified from control urine a prominent band was seen with an Mr of 28 000 Da. Glycoprotein fractions from urine and placenta, a membrane extract from spleen, and a partially purified sphingomyelinase preparation from placenta contained the 28 000-Da band plus additional, higher-Mr bands. The 28 000-Da band was detectable in urine from a patient with Niemann-Pick disease type C, but not in urine from patients with Niemann-Pick disease types A and B. It is concluded that sphingomyelinase is composed of at least one polypeptide with an Mr of 28 000 Da and that this polypeptide is deficient in the urine of patients with Niemann-Pick disease types A and B.

Subcellular Localization of Anthocyanin Methyltransferase in Flowers of Petunia hybrida

The subcellular localization of the enzyme anthocyanin-methyltransferase was studied in cells (protoplasts) obtained from the upper epidermis of petals of Petunia hybrida Hort. Vacuoles were isolated from protoplasts to ascertain the possible presence of the enzyme in these organelles. The recovery of methyltransferase activity in vacuole-enriched fractions equalled that of the cytosolic marker enzyme glucose-6-phosphate dehydrogenase. The relative activity of methyltransferase in the vacuole fraction was one tenth of that in the protoplast. Neither whole protoplasts nor isolated vacuoles contained inhibitors of methyltransferase activity. Examination of fractions obtained by differential centrifugation of a protoplast lysate showed that the major part of the methyltransferase activity was cytosolic. Activity found in a 130,000g pellet was due to nonspecific adhesion to membranes. The results indicate that terminal steps of anthocyanin biosynthesis take place in the cytosol. They do not lend support to the notion that the vacuole might be involved in (part of) this process.

Use of immobilized antibodies in investigating acid alpha-glucosidase in urine in relation to Pompe's disease

(1) A simple method is described for the isolation of the lysosomal enzyme, acid alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) from normal human liver. Antibodies raised against the purified enzyme were immobilized by covalent coupling to Sepharose 4B. (2) Acid alpha-glucosidase can be quantitatively removed from normal urine by incubating with an excess of immobilized antibody. With p-nitrophenyl-alpha-glucoside as substrate, acid alpha-glucosidase accounts for 91 +/- 3% of the total alpha-glucosidase activity at pH 4.0 IN Normal urine. (3) In urine from a patient with the infantile form of Pompe's disease ('acid maltase deficiency'), no alpha-glucosidase activity could be removed by the immobilized antibody, in agreement with the fact that acid alpha-glucosidase is absent in these patients. (4) In urine from patients with the late-onset form of Pompe's disease, 46 +/- 11% of the alpha-glucosidase activity at pH 4.0 can be removed by incubation with immobilized antibodies, indicating that residual acid alpha-glucosidase activity is present in urine of these patients. The residual acid alpha-glucosidase activity amounts to about 5% of that in the urine of control persons. (5) If acid alpha-glucosidase is adsorbed to immobilized antibodies, the activity can still be measured with p-nitrophenyl-alpha-glucoside as substrate. The Km for p-nitrophenyl-alpha-glucoside is not significantly changed by adsorbing purified acid alpha-glucosidase to immobilized antibodies. (6) The properties of acid alpha-glucosidase from urine of patients with late-onset Pompe's disease were compared with those of acid alpha-glucosidase from normal urine, both adsorbed to immobilized antiserum. The pH-activity profile of the enzyme from urine of patients with late-onset Pompe's disease can not be distinguished from that of the normal urinary enzyme. The Km for p-nitro-phenyl-alpha-glucoside of the two enzymes is identical, both at pH 4 and 3. The titration curves of the two enzymes with immobilized antibodies are identical.

Enzymological properties and immunological characterization of alpha-galactosidase isoenzymes from normal and Fabry human liver

1. A method is described for the rapid isolation of alpha-galactosidases A and B (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) from normal human liver. 2. When the same method is applied to Fabry liver, most of the alpha-galactosidase activity is recovered in the fraction corresponding to normal alpha-galactosidase B. In agreement with Romeo, G., D'Urso, M., Pisacane, A., Blum, E., De Falco, A. and Ruffilli, A. (1975) Biochem. Genet. 13, 615-628) [18], a small amount of alpha-galactosidase activity is found in the fraction corresponding to normal alpha-galactosidase A. 3. The kinetic properties of the B-like activity from Fabry liver are similar to those of normal alpha-galactosidase B. In agreement with Romeo et al. [18], it was found that the kinetic properties of the A-like activity from Fabry liver are similar to those of normal alpha-galactosidase A. 4. Using antisera raised against normal alpha-galactosidase A and normal alpha-galactosidase B, it is shown that the normal alpha-galactosidase isoenzymes are immunologically distinct and that the B-like activity from Fabry liver is immunologically related to normal alpha-galactosidase B. Furthermore, the A-like activity from Fabry liver is immunologically related to normal alpha-galactosidase B and not to normal alpha-galactosidase A. 5. Normal alpha-galactosidase B is converted into an A-like form during storage. 6. It is concluded that the B-like alpha-galactosidase in Fabry tissues is identical to normal alpha-galactosidase B, and that the small amount of A-like activity found in Fabry material is due to a modified form of alpha-galactosidase B.