Goat liver beta-mannosidases: molecular properties, inhibition and inactivation of the lysosomal and nonlysosomal forms

The two caprine hepatic beta-mannosidases have been partially purified and their properties have been compared. The lysosomal beta-mannosidase A had an apparent molecular weight of 127,000 +/- 10,000 and an isoelectric point of pH 6-7. Its activity was unaffected by incubation with Triton X-100 (0.1%) and cysteine (20 mM) and it hydrolyzed the presumed natural substrates, Man(beta 1-4)GlcNAc and Man(beta 1-4)GlcNAc(beta 1-4)GlcNAc. The nonlysosomal beta-mannosidase B had an apparent molecular weight of 43,000 +/- 2,000 and an isoelectric point of pH 5.5. beta-Mannosidase B was activated by Triton X-100 (0.1%) and was inhibited by cysteine (20 mM). Hydrolysis of Man(beta 1-4)GlcNAc, but not of Man(beta 1-4)GlcNAc(beta 1-4)GlcNAc, followed incubation with beta-mannosidase B. 1,5-Dideoxy-1,5-imino-D-mannitol did not inhibit the A enzyme and only feebly (Ki = 0.3 mM) inhibited the B enzyme; beta-D-mannopyranosylmethyl p-nitrophenyl triazene did not inactivate either enzyme but 1,2-anhydro-1,2,3,5,6/4-cyclohexane hexol inactivated the B enzyme only. The radical mechanistic differences between the two enzymes argue against their having the same genetic origin.     

Gaucher disease types 1, 2, and 3: differential mutations of the acid beta-glucosidase active site identified with conduritol B epoxide derivatives and sphingosine.

To elucidate the genetic heterogeneity in Gaucher disease, the residual beta-glucosidase in cultured fibroblasts from affected patients with each of the major phenotypes was investigated in vitro and/or in viable cells by inhibitor studies using the covalent catalytic site inhibitors, conduritol B epoxide or its bromo derivative, and the reversible cationic inhibitor, sphingosine. These studies delineated three distinct groups (designated A, B, and C) of residual activities with characteristic responses to these inhibitors. Group A residual enzymes had normal I50 values (i.e., the concentration of inhibitor that results in 50% inhibition) for the inhibitors and normal or nearly normal t1/2 values for conduritol B epoxide. All neuronopathic (types 2 and 3) and most non-Jewish nonneuronopathic (type 1) patients had group A residual activities and, thus, could not be distinguished by these inhibitor studies. Group B residual enzymes had about four- to fivefold increased I50 values for the inhibitors and similarly increased t1/2 values for conduritol B epoxide. All Ashkenazi Jewish type 1 and only two non-Jewish type 1 patients had group B residual activities. The differences in I50 values between groups A and B also were confirmed by determining the uninhibited enzyme activity after culturing the cells in the presence of bromo-conduritol B epoxide. Group C residual activity had intermediate I50 values for the inhibitors and represented a single Afrikaner type 1 patient: this patient was a genetic compound for the group A (type 2) and group B (type 1) mutations. These inhibition studies indicated that: Gaucher disease type 1 is biochemically heterogeneous, neuronopathic and non-Jewish nonneuronopathic phenotypes cannot be reliably distinguished by these inhibitor studies, and the Ashkenazi Jewish form of Gaucher disease type 1 results from a unique mutation in a specific active site domain of acid beta-glucosidase that leads to a defective enzyme with a decreased Vmax.     

Partial purification and characterization of Naegleria fowleri beta-glucosidase

Naegleria fowleri cells, grown axenically, contain high levels of beta-D-glucosidase which catalyzes the hydrolysis of 4-methylumbelliferyl-beta-D-glucopyranoside (4MUGlc) (Km, 0.9 mM), octyl-beta-D-glucoside (Km, 0.17 mM), and p-nitrophenyl-beta-D-glucopyranoside at relative rates of 1.00, 2.88, and 1.16, respectively (substrate concentration, 3.0 mM). When the amebae are subjected to freeze-thawing, sonication, and centrifugation (100,000 g, 1 h), 85% of the beta-glucosidase activity appears in the supernatant fraction. The beta-glucosidase was purified 40-fold (34% yield) using a combination of chromatographic steps involving DE-52 cellulose, concanavalin A-Sepharose, and hydroxylapatite followed by isoelectric focusing. The predominant soluble beta-D-galactosidase activity in the Naegleria extract copurifies with the beta-D-glucosidase; the two activities have the same isoelectric point (pI, 6.9), similar heat stabilities, are both inhibited by lactobionic acid (Ki, 0.40 mM), and exhibit optima at pH 4.5, indicating that they are probably the same enzyme. The Naegleria beta-D-glucosidase has an apparent molecular weight of 66,000, a Stokes radius of 25 A, and a sedimentation coefficient of 4.2S. The beta-glucosidase is not inhibited by conduritol beta-epoxide or galactosylsphingosine but is completely inhibited by 1.25 mM bromo conduritol beta-epoxide. The latter compound, when present in the growth medium, inhibits the growth of the organism and profoundly alters its ultrastructure, the main effect being the apparent inhibition of cytokinesis and the generation of multinucleate cells. The issue of the role of the beta-glucosidase in the metabolism of the ameba and its possible role in pathogenic mechanisms are discussed.     

Human acid beta-glucosidase: inhibition studies using glucose analogues and pH variation to characterize the normal and Gaucher disease glycon binding sites

Comparative kinetic studies with glycon inhibitors were used to investigate the properties of the active site of human acid beta-glucosidase (EC 3.2.1.45) from normal placenta and spleens of type 1 Ashkenazi Jewish Gaucher disease (AJGD) patients. With the pure normal enzyme, the specificity of glycon binding was assessed with 35 glucose derivatives and epimers. Most glycons were mixed type inhibitors with a predominantly competitive nature (i.e., Kis much less than Kii) and had low apparent affinity for the enzyme (Kisapp = 20-500 mmol/l). beta-Glucose-1-phosphate was unusual, since it inhibited 4-methylumbelliferyl-beta-glucoside hydrolysis in an uncompetitive pattern (Kiapp = 0.55 mmol/l) but had no effect on glucosyl ceramide hydrolysis. C-1- (1-deoxy-1-amino-beta-D-glucose) and C-3- (3-deoxy-3-amino-D-glucose) amino and C-5-imino [1-deoxynojirimycin (dNM), nojirimycin and castanospermine] substituted sugars were highly potent inhibitors with Kisapp(beta-glucose)/Kisapp approximately equal to 10(3)-10(5); an amine at C-2 did not alter Kisapp compared to beta-glucose. The variation of Kisapp with pH for the 5-imino- and 1-deoxy-1-aminoglycosides conformed to a model for the unprotonated inhibitors binding to the protonated forms (EH and EH2) of the diprotic (Vmaxapp and Vmaxapp/Kmapp) normal enzyme (pK1 = 4.7; pK2 = 6.7) with pH-independent Kisapp values of 2.9-9.0 mumol/l and 0.22 mmol/l, respectively. Several of the amine-containing inhibitors competitively protected the enzyme from inactivation by conduritol B epoxide, a covalent active site-directed inhibitor, indicating interaction with residues at that site. With the partially purified AJGD splenic enzymes, the results were the same except that Kisapp(AJGD)/Kisapp(normal) = 4-17 for dNM and 1-deoxy-1-amino-beta-glucose; this ratio was approximately equal to 1 with most other glycons, and particularly, nojirimycin and castanospermine. The results of these studies indicated that the glycon binding site of the normal acid beta-glucosidase contains important residues for interaction with the C-2, C-3 and C-4 hydroxyl groups of beta-glucose and a residue with pKa = 6.7 which was critical to the binding of amine-containing inhibitors and the hydrolysis of substrates. The findings were consistent with a specific alteration in or near the glycon binding site which results in the functional abnormalities of the mutant AJGD acid beta-glucosidase.     

Synthesis of 5-amino-5-deoxy-D-mannopyranose and 1,5-dideoxy-1,5-imino-D-mannitol, and inhibition of alpha- and beta-D-mannosidases

The title compounds and the corresponding L-gulo derivatives were synthesised in 6 steps from benzyl 2,3:5,6-di-O-isopropylidene-alpha-D-mannofuranoside. The Ki values, determined from inhibition studies with alpha-D-mannosidases from jack beans, almonds, and calf liver, and beta-D-mannosidase from Aspergillus wentii, ranged from 70 to 400 microM for the mannitol derivative and from 1.2 to 20 microM for 5-amino-5-deoxy-D-mannopyranose, i.e., inhibition is 10(2)-10(4)-fold stronger than with D-mannose. Marked enhancement of inhibition with increasing pH is ascribed to the ionisation of a carboxyl group at the active site, forming an ion pair with the protonated inhibitor. The inhibition equilibrium between the jack-bean enzyme and the mannose derivative was approached slowly with kapp 2.0 X 10(5) M-1 X min-1. The mannose-derived inhibitor was also inhibitory against beta-D-glucosidases from almonds and Asp. wentii, with Ki values only 20-150-times larger than those for the inhibition of these enzymes by 5-amino-5-deoxy-D-glucopyranose. This moderate discrimination in binding of D-gluco and D-manno derivatives is in marked contrast to the high specificity shown by the glucosidase in catalysing the hydrolysis of mannosidases. A similar low specificity with respect to binding, combined with highly specific catalysis, was also seen with the mannosidases acting on inhibitors and substrates with the D-gluco configuration.     

Microbial Transport, Survival, and Succession in a Sequence of Buried Sediments

Abstract Two chronosequences of unsaturated, buried loess sediments, ranging in age from <10,000 years to >1 million years, were investigated to reconstruct patterns of microbial ecological succession that have occurred since sediment burial. The relative importance of microbial transport and survival to succession was inferred from sediment ages, porewater ages, patterns of abundance (measured by direct counts, counts of culturable cells, and total phospholipid fatty acids), activities (measured by radiotracer and enzyme assays), and community composition (measured by phospholipid fatty acid patterns and Biolog substrate usage). Core samples were collected at two sites 40 km apart in the Palouse region of eastern Washington State, near the towns of Washtucna and Winona. The Washtucna site was flooded multiple times during the Pleistocene by glacial outburst floods; the Winona site elevation is above flood stage. Sediments at the Washtucna site were collected from near surface to 14.9 m depth, where the sediment age was approximately 250 ka and the porewater age was 3700 years; sample intervals at the Winona site ranged from near surface to 38 m (sediment age: approximately 1 Ma; porewater age: 1200 years). Microbial abundance and activities declined with depth at both sites; however, even the deepest, oldest sediments showed evidence of viable microorganisms. Same-age sediments had equal quantities of microorganisms, but different community types. Differences in community makeup between the two sites can be attributed to differences in groundwater recharge and paleoflooding. Estimates of the microbial community age can be constrained by porewater and sediment ages. In the shallower sediments (<9 m at Washtucna, <12 m at Winona), the microbial communities are likely similar in age to the groundwater; thus, microbial succession has been influenced by recent transport of microorganisms from the surface. In the deeper sediments, the populations may be considerably older than the porewater ages, since microbial transport is severely restricted in unsaturated sediments. This is particularly true at the Winona site, which was never flooded.     

The Gaucher mouse.

A model of Gauchers disease was produced through the administration of conduritol B-expoxide. Tissue levels of glucosylceramide were elevated in the experimental animals. The activity of β-glucosidase in homogenates of brain, liver, and spleen was reduced 93% in the treated animals. Six other lysosomal hydrolases measured were uneffected.     

Epoxyalkyl oligo-(1 leads to 4)- -D-glucosides as active-site-directed inhibitors of cellulases

N-Deacetylation of benzyl 2-acetamido-2-deoxy-6-O-α-D-mannopyranosyl-α-D-glucopyranoside (3) by alkaline hydrolysis, or hydrazinolysis in the presence of hydrazine sulphate, proceeds quantitatively to yield the amine 4. The mannosyl glycosidic linkage in 4 can be selectively hydrolysed by acid, whereas the 2-amino-2-deoxyhexosyl glycosidic linkage is selectively cleaved upon treatment with sodium nitrite in dilute acetic acid. Aspects of the selective cleavage of hexosaminoglycans are discussed.     

Development of a genetic system for the chemolithoautotrophic bacterium Thiobacillus denitrificans

Thiobacillus denitrificans is a widespread, chemolithoautotrophic bacterium with an unusual and environmentally relevant metabolic repertoire, which includes its ability to couple denitrification to sulfur compound oxidation; to catalyze anaerobic, nitrate-dependent oxidation of Fe(II) and U(IV); and to oxidize mineral electron donors. Recent analysis of its genome sequence also revealed the presence of genes encoding two [NiFe]hydrogenases, whose role in metabolism is unclear, as the sequenced strain does not appear to be able to grow on hydrogen as a sole electron donor under denitrifying conditions. In this study, we report the development of a genetic system for T. denitrificans, with which insertion mutations can be introduced by homologous recombination and complemented in trans. The antibiotic sensitivity of T. denitrificans was characterized, and a procedure for transformation with foreign DNA by electroporation was established. Insertion mutations were generated by in vitro transposition, the mutated genes were amplified by the PCR, and the amplicons were introduced into T. denitrificans by electroporation. The IncP plasmid pRR10 was found to be a useful vector for complementation. The effectiveness of the genetic system was demonstrated with the hynL gene, which encodes the large subunit of a [NiFe]hydrogenase. Interruption of hynL in a hynL::kan mutant resulted in a 75% decrease in specific hydrogenase activity relative to the wild type, whereas complementation of the hynL mutation resulted in activity that was 50% greater than that of the wild type. The availability of a genetic system in T. denitrificans will facilitate our understanding of the genetics and biochemistry underlying its unusual metabolism.