Characterization of Properties and Transglycosylation Abilities of Recombinant α-Galactosidase from Cold-Adapted Marine Bacterium Pseudoalteromonas KMM 701 and Its C494N and D451A Mutants.

A novel wild-type recombinant cold-active α-d-galactosidase (α-PsGal) from the cold-adapted marine bacterium Pseudoalteromonas sp. KMM 701, and its mutants D451A and C494N, were studied in terms of their structural, physicochemical, and catalytic properties. Homology models of the three-dimensional α-PsGal structure, its active center, and complexes with D-galactose were constructed for identification of functionally important amino acid residues in the active site of the enzyme, using the crystal structure of the α-galactosidase from Lactobacillus acidophilus as a template. The circular dichroism spectra of the wild α-PsGal and mutant C494N were approximately identical. The C494N mutation decreased the efficiency of retaining the affinity of the enzyme to standard p-nitrophenyl-α-galactopiranoside (pNP-α-Gal). Thin-layer chromatography, matrix-assisted laser desorption/ionization mass spectrometry, and nuclear magnetic resonance spectroscopy methods were used to identify transglycosylation products in reaction mixtures. α-PsGal possessed a narrow acceptor specificity. Fructose, xylose, fucose, and glucose were inactive as acceptors in the transglycosylation reaction. α-PsGal synthesized -α(1→6)- and -α(1→4)-linked galactobiosides from melibiose as well as -α(1→6)- and -α(1→3)-linked p-nitrophenyl-digalactosides (Gal2-pNP) from pNP-α-Gal. The D451A mutation in the active center completely inactivated the enzyme. However, the substitution of C494N discontinued the Gal-α(1→3)-Gal-pNP synthesis and increased the Gal-α(1→4)-Gal yield compared to Gal-α(1→6)-Gal-pNP.

Hydrolysis of oligosaccharides by a fungal α-galactosidase from fruiting bodies of a wild mushroom Leucopaxillus tricolor.

A novel acidic α-galactosidase (EC 3.2.1.22) designated as Leucopaxillus tricolor α-galactosidase (LTG) has been purified to homogeneity from the fruiting bodies of L. tricolor to 855-fold with a specific activity of 956 U mg-1 by the application of chromatography and gel filtration. The molecular mass of LTG was estimated to be 60 kDa as determined by both SDS-PAGE and by gel filtration. The purified enzyme was identified by LC-MS/MS and four inner amino acid sequences were obtained. When 4-nitrophenyl α-D-glucopyranoside (pNPGal) was used as substrate, the optimal pH and optimal temperature of LTG were pH 5.0 and 50 °C, respectively. The enzyme activity was strongly inhibited by Hg2+ , Fe3 , Cu2+ , Cd2+ , and Mn2+ ions. The chemical modification agent N-bromosuccinimide (NBS) completely inhibited the enzyme activity of LTG, indicating the paramount importance of tryptophan residue(s) to its enzymatic activity. Besides, LTG displayed wide substrate diversity with activity toward a variety of substrates such as stachyose, raffinose, melibiose, locust bean gum, and guar gum. Given the good ability of degrading the non-digestible and flatulence-causing oligosaccharides, this fungus may become a useful source of α-galactosidase for multiple applications.

Characterization of a long-chain α-galactosidase from Papiliotrema flavescens.

α-Galactosidases are assigned to the class of hydrolases and the subclass of glycoside hydrolases (GHs). They belong to six GH families and include the only characterized α-galactosidases from yeasts (GH 27, Saccharomyces cerevisiae). The present study focuses on an investigation of the lactose-inducible α-galactosidase produced by Papiliotrema flavescens. The enzyme was present on the surface of cells and in the cytosol. Its temperature optimum was about 60 °C and the pH optimum was 4.8; the pH stability ranged from 3.2 to 6.6. This α-galactosidase also exhibited transglycosylation activity. The cytosol α-galactosidase with a molecular weight about 110 kDa, was purified using a combination of liquid chromatography techniques. Three intramolecular peptides were determined by the partial structural analysis of the sequences of the protein isolated, using MALDI-TOF/TOF mass spectrometry. The data obtained recognized the first yeast α-galactosidase, which belongs to the GH 36 family. The bioinformatics analysis and homology modeling of a 210 amino acids long C-terminal sequence (derived from cDNA) confirmed the correctness of these findings. The study was also supplemented by the screening of capsular cryptococcal yeasts, which produce the surface lactose-inducible α- and ß-galactosidases. The production of the lactose-inducible α-galactosidases was not found to be a general feature within the yeast strains examined and, therefore, the existing hypothesis on the general function of this enzyme in cryptococcal capsule rearrangement cannot be confirmed.

Thermus thermophilus as source of thermozymes for biotechnological applications: homologous expression and biochemical characterization of an α-galactosidase.

BACKGROUND: The genus Thermus, which has been considered for a long time as a fruitful source of biotechnological relevant enzymes, has emerged more recently as suitable host to overproduce thermozymes. Among these, α-galactosidases are widely used in several industrial bioprocesses that require high working temperatures and for which thermostable variants offer considerable advantages over their thermolabile counterparts. RESULTS: Thermus thermophilus HB27 strain was used for the homologous expression of the TTP0072 gene encoding for an α-galactosidase (TtGalA). Interestingly, a soluble and active histidine-tagged enzyme was produced in larger amounts (5 mg/L) in this thermophilic host than in Escherichia coli (0.5 mg/L). The purified recombinant enzyme showed an optimal activity at 90 °C and retained more than 40% of activity over a broad range of pH (from 5 to 8). CONCLUSIONS: TtGalA is among the most thermoactive and thermostable α-galactosidases discovered so far, thus pointing to T. thermophilus as cell factory for the recombinant production of biocatalysts active at temperature values over 90 °C.

Is it Fabry disease?

Fabry disease is caused by mutations in the GLA gene that lower α-galactosidase A activity to less than 25-30% of the mean normal level. Several GLA variants have been identified that are associated with relatively elevated residual α-galactosidase A. The challenge is to determine which GLA variants can cause clinical manifestations related to Fabry disease. Here, we review the various types of GLA variants and recommend that pathogenicity be considered only when associated with elevated globotriaosylceramide in disease-relevant organs and tissues as analyzed by mass spectrometry. This criterion is necessary to ensure that very costly and specific therapy is provided only when appropriate.Genet Med 18 12, 1181-1185.

Purification of thermostable α-galactosidase from Irpex lacteus and its use for hydrolysis of oligosaccharides.

A monomeric α-galactosidase (ILGI) from the mushroom Irpex lacteus was purified 94.19-fold to electrophoretic homogeneity. ILGI exhibited a specific activity of 18.36 U mg(-1) and demonstrated a molecular mass of 60 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). ILGI was optimally active at 80 °C and pH 5.0, and it was stable over a temperature range of 4-70 °C and a wide pH range of 2.0-12.0. ILGI was completely inactivated by Ag(+) and Hg(2+) ions and N-bromosuccinimide (NBS). Moreover, ILGI exhibited good resistance to proteases. Galactose acted as a noncompetitive inhibitor with Ki and Kis of 3.34 and 0.29 mM, respectively. The α-galactosidase presented a broad substrate specificity, which included p-nitrophenyl α-D-galactopyranoside (pNPGal), melibiose, stachyose, and raffinose with Km values of 1.27, 3.24, 7.1, and 22.12 mM, correspondingly. ILGI exhibited efficient and complete hydrolysis to raffinose and stachyose. The aforementioned features of this enzyme suggest its potential value in food and feed industries.

High-level expression of a novel α-galactosidase gene from Rhizomucor miehei in Pichia pastoris and characterization of the recombinant enyzme.

The second α-galactosidase gene (designated as RmgalB) was cloned from the thermophilic fungus Rhizomucor miehei and expressed in Pichia pastoris. The gene belonging to glycoside hydrolase (GH) family 36 has an open reading frame (ORF) of 2241bp encoding 746 amino acids with two introns. The recombinant α-galactosidase (RmgalB) was secreted at high levels of 1953.9Uml(-1) in high cell density fermentor, which is the highest yield obtained for a α-galactosidase. The purified enzyme as a tetramer gave a single band corresponding to a molecular mass of 83.1kDa in SDS-PAGE. The enzyme exhibited a very high specific activity of 505.5Umg(-1). The optimum temperature and pH of RmgalB were determined to be 55°C and pH 5.5, respectively. It was stable within pH 5.5-9.5 and up to 55°C. RmgalB displayed specificity toward raffinose and stachyose, and completely hydrolyzed the anti-nutritive raffinose family oligosaccharides (RFOs). These properties make RmgalB useful in the food and feed industries.

Hydrolysis of Oligosaccharides by a Thermostable α-Galactosidase from Termitomyces eurrhizus.

The genus of Termitomyces purchased from the market has been identified as Termitomyces eurrhizus using the Internal Transcribed Spacer (ITS) method. An α-galactosidase from T. eurrhizus (TEG), a monomeric protein with a molecular mass of 72 kDa, was purified 146 fold by employing ion exchange chromatography and gel filtration. The optimum pH and temperature was 5.0 and 60 °C, respectively. TEG was stable over pH 2-6, and also exhibited good thermostablility, retaining 100% of the original activity after incubation at 60 °C for 2 h. Inhibition of the enzyme activity by N-bromosuccinimide (NBS) constituted evidence for an essential role of tryptophan in the catalytic action of the isolated enzyme. Besides 4-nitro-phenyl α-d-galactophyranoside (pNPGal), natural substrates could also be effectively hydrolyzed by TEG. Results of thin-layer chromatography (TLC) revealed complete enzymatic hydrolysis of raffinose and stachyose to galactose at 50 °C within 6 h. These properties of TEG advocate its utilization for elevating the nutritional value of soymilk.

A Fungal α-Galactosidase from Tricholoma matsutake with Broad Substrate Specificity and Good Hydrolytic Activity on Raffinose Family Oligosaccharides.

An acidic α-galactosidase designated as TMG was purified from the fruiting bodies The purification protocol entailed ion exchange chromatography on Q-Sepharose and of Tricholoma matsutake with 136-fold purification and a specific activity of 909 units/mg. Mono-Q and fast protein liquid chromatography on Superdex 75. TMG is a monomeric protein exhibiting a molecular mass of 47 kDa in SDS-PAGE and gel filtration. The purified enzyme was identified by LC-MS/MS and three inner amino acid sequences were obtained. The optimum pH and temperature for TMG with pNPGal as substrate were pH 4.5 and 55 °C, respectively. The α-galactosidase activity was strongly inhibited by K+, Ca2+, Cd2+, Hg2+, Ag+ and Zn2+ ions. The enzyme activity was inhibited by the chemical modification agent N-bromosuccinimide (NBS), indicating the importance of tryptophan residue(s) at or near the active site. Besides hydrolyzing pNPGal, TMG also efficaciously catalyzed the degradation of natural substrates such as stachyose, raffinose, and melibiose. Thus TMG can be exploited commercially for improving the nutritional value of soy milk by degradation of indigestible oligosaccharides.

Purification an α-galactosidase from Coriolus versicolor with acid-resistant and good degradation ability on raffinose family oligosaccharides.

An acid-tolerant α-galactosidase (CVGI) was isolated from the fruiting bodies of Coriolus versicolor with a 229-fold of purification and a specific activity of 398.6 units mg⁻¹. It was purified to electrophoretic homogeneity by ion exchange chromatography and gel filtration chromatography. The purified enzyme gave a single band corresponding to a molecular mass of 40 kDa in SDS-PAGE and gel filtration. The α-galactosidase was identified by MALDI-TOF-MS and its inner peptides were sequenced by ESI-MS/MS. The optimum temperature and pH of the enzyme were determined as 60 °C and 3.0, respectively. The enzyme was very stable at a temperature range of 4-50 °C and at a pH range of 2-5. Among the metal ions tested, Cu²âº, Cd²âº and Hg²âº ions have been shown to partially inhibit the activity of α-galactosidase, while the activity of CVGI was completely inactivated by Ag⁺ ions. N-bromosuccinamide inhibited enzyme activity by 100 %, indicating the importance of tryptophan residue(s) at or near the active site. CVGI had wide substrate specificity (p-nitrophenyl galactoside, melidiose, raffinose and stachyose). After treatment with CVGI, raffinose family oligosaccharide was hydrolyzed effectively to yield galactose and sucrose. The results showed that the general properties of the enzyme offer potential for use of this α-galactosidase in several production processes.

Bifidobacterial α-galactosidase with unique carbohydrate-binding module specifically acts on blood group B antigen.

Bifidobacterium bifidum is one of the most frequently found bifidobacteria in the intestines of newborn infants. We previously reported that B. bifidum possesses unique metabolic pathways for O-linked glycans on gastrointestinal mucin (Yoshida E, Sakurama H, Kiyohara M, Nakajima M, Kitaoka M, Ashida H, Hirose J, Katayama T, Yamamoto K, Kumagai H. 2012. Bifidobacterium longum subsp. infantis uses two different ß-galactosidases for selectively degrading type-1 and type-2 human milk oligosaccharides. Glycobiology. 22:361-368). The nonreducing termini of O-linked glycans on mucin are frequently covered with histo-blood group antigens. Here, we identified a gene agabb from B. bifidum JCM 1254, which encodes glycoside hydrolase (GH) family 110 α-galactosidase. AgaBb is a 1289-amino acid polypeptide containing an N-terminal signal sequence, a GH110 domain, a carbohydrate-binding module (CBM) 51 domain, a bacterial Ig-like (Big) 2 domain and a C-terminal transmembrane region, in this order. The recombinant enzyme expressed in Escherichia coli hydrolyzed α1,3-linked Gal in branched blood group B antigen [Galα1-3(Fucα1-2)Galß1-R], but not in a linear xenotransplantation antigen (Galα1-3Galß1-R). The enzyme also acted on group B human salivary mucin and erythrocytes. We also revealed that CBM51 specifically bound blood group B antigen using both isothermal titration calorimetry and a solid-phase binding assay, and it enhanced the affinity of the enzyme toward substrates with multivalent B antigens. We suggest that this enzyme plays an important role in degrading B antigens to acquire nutrients from mucin oligosaccharides in the gastrointestinal tracts.

A thermostable α-galactosidase from Lenzites elegans (Spreng.) ex Pat. MB445947: purification and properties.

An α-galactosidase was isolated from a culture filtrate of Lenzites elegans (Spreng.) ex Pat. MB445947 grown on citric pectin as carbon source. It was purified to electrophoretic homogeneity by ammonium sulfate precipitation, gel filtration chromatography and anion-exchange chromatography. The relative molecular mass of the native purified enzyme was 158 kDa determined by gel filtration and it is a homodimer (Mr subunits = 61 kDa). The optimal temperature for enzyme activity was in the range 60-80 °C. This α-galactosidase showed a high thermostability, retaining 94 % of its activity after preincubation at 60 °C for 2 h. The optimal pH for the enzyme was 4.5 and it was stable from pH 3 to 7.5 when the preincubation took place at 60 °C for 2 h. It was active against several α-galactosides such as p-nitrophenyl-α-D-galactopyranoside, α-D-melibiose, raffinose and stachyose. The α-galactosidase is a glycoprotein with 26 % of structural sugars. Galactose was a non-competitive inhibitor with a Ki = 22 mM versus p-nitrophenyl-α-D-galactoside and 12 mM versus α-D-melibiose as substrates. Glucose was a simple competitive inhibitor with a Ki = 10 mM. Cations such as Hg(2+) and p-chloromercuribenzoate were also inhibitors of this activity, suggesting the presence of -SH groups in the active site of the enzyme. On the basis of the sequence of the N-terminus (SPDTIVLDGTNFALN) the studied α-galactosidase would be a member of glycosyl hydrolase family 36 (GH 36). Given the high optimum temperature and heat stability of L. elegans α-galactosidase, this fungus may become a useful source of α-galactosidase production for multiple applications.

Purification and characterization of a thermostable α-galactosidase from Thielavia terrestris NRRL 8126 in solid state fermentation.

Several seeds and husks of some plants belonging to leguminosae, Graminae, Compositae and Palmae were evaluated as carbon substrates to produce α-galactosidase (α-Gal) by the thermophilic fungus, Thielavia terrestris NRRL 8126 in solid substrate fermentation. The results showed that Cicer arietinum (chick pea seed) was the best substrate for α-Gal production. The crude enzyme was precipitated by ammonium sulphate (60%) and purified by gel filtration on sephadex G-100 followed by ion exchange chromatography on DEAE-Cellulose. The final purification fold of the enzyme was 30.42. The temperature and pH optima of purified α-Gal from Thielavia terrestris were 70 °C and 6.5, respectively. The enzyme showed high thermal stability at 70 °C and 75 °C and the half-life of the α-Gal at 90 °C was 45 min. Km of the purified enzyme was 1.31 mM. The purified enzyme was inhibited by Ag2+, Hg2+, Zn2+, Ba2+, Mg2+, Mn2+ and Fe2+ at 5 mM and 10 mM. Also, EDTA, sodium arsenate, L-cysteine and iodoacetate inhibited the enzyme activity. On the other hand, Ca2+, Cu2+, K+ and Na+ slightly enhanced the enzyme activity at 5 mM while at 10 mM they caused inhibition. The molecular weight of the α-Gal was estimated to be 82 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This enzyme displays a number of biochemical properties that make it a potentially strong candidate for biotechnological and medicinal applications.

[A novel alpha-galactosidase from Arthrobacter sp. GN14 isolated from Grus nigricollis feces: gene cloning, heterologous expression and characterization].

OBJECTIVE: Cloning and heterologously expressing the alpha-galactosidase gene (agaAGN14) from Arthrobacter sp. GN14 isolated from feces of black-neck crane (Grus nigricollis). METHODS: The full-length agaAGN14 was cloned based on degenerate PCR and GC TAIL-PCR (thermal asymmetric interlaced PCR), ligated into pET-28a (+) vector and expressed in Escherichia coli BL21 (DE3) cells. The recombinant alpha-galactosidase (rAgaAGN14) was purified to electrophoretic homogeneity by Ni(2+)-NTA metal chelating affinity chromatography, and then the enzyme characterizations were determined. Amino acids sequences of agaAGN14 (AgaAGN14) and alpha-galactosidases from Actinobacteria and gastrointestinal microorganisms were aligned and used for constructing a neighbor-joining phylogenetic tree. RESULTS: The 2109-bp full-length agaAGN14 (66.8% GC content) encodes a 702-residue polypeptide (AgaAGN14; 77.5 kDa). AgaAGN14 showed the highest identity of 53.7% with alpha-galactosidases in public databases, and < 43% identities with alpha-galactosidases from gastrointestinal microorganisms. AgaAGN14 was put in a phylogenetic branch sharing the catalytic motifs KWD and SDXXDXXXR, and close to alpha-galactosidases from soil microorganisms and far from alpha-galactosidases from gastrointestinal microorganisms. The purified rAgaAGN14 efficiently hydrolyzed pNPG, raffinose, melibiose, stachyose, rapeseed meal and cottonseed meal; showed apparent optimal at pH 6.0 and 45 degrees C, stability and activity (> 50%) at pH 6.0-9.0, and activities of 28%, 30% and 80% at 10 degrees C, 20 degrees C and 37 degrees C, respectively; exhibited K(m), V(max) and k(cat) values of 0.41 mmol/L, 18.28 micromol/min/mg and 25.36 s(-1), respectively, using pNPG as the substrate at 45 degrees C and pH 6.5; strongly inhibited by Ag+, Hg2+ and SDS, partial inhibited by K+, Ca2+, Mn2+, Fe3+, Ni2+, Cu2+ and beta-mercaptoethanol, and little influenced by Co2+, Pb2+, Zn2+, Mg2+, Na+ and EDTA. CONCLUSION: The Arthrobacter strain isolated from feces of Grus nigricollis, and the sequence analysis, phylogenetic analysis, heterologous expression and recombinant enzyme's biochemical characterizations of an alpha-galactosidase from Arthrobacter strain were first reported. rAgaAGN14 was a novel alpha-galactosidase.

Purification, biochemical and biophysical characterization of an acidic α-galactosidase from the seeds of Annona squamosa (custard apple).

Alpha galactosidase is an exoglycosidase that cleaves α-D-galactose and has numerous applications in medicine, biotechnology, food and pharma industries. In this study, a low molecular weight acidic α-galactosidase was identified from the seeds of custard apple. The purification of α-galactosidase from the crude extract of defatted seeds was achieved by employing ammonium sulphate fractionation, hydrophobic interaction and gel filtration chromatographic techniques. The purified custard apple α-galactosidase (CaG) migrated as a single band in native PAGE corresponding to molecular weight of ~67 kDa and cleaved chromogenic, fluorogenic and natural substrates. CaG was found to be a heterodimer with subunit masses of 40 and 30 kDa. The kinetic parameters such as KM and Vmax were found to be 0.67 mM and 1.5 U/mg respectively with p-nitrophenyl α-D-galactopyranoside. Galactose, methyl α-D-galactopyranoside and D-galacturonic acid inhibited CaG activity in mixed mode. The CD spectral analysis at far UV region showed that purified CaG exists predominantly as helix (35%), beta sheets (16.3%) and random coils (32.3%) in its secondary structure. These biochemical and biophysical properties of CaG provide leads to understand its primary sequence and glycan structures which will eventually define its novel physiological roles in plants and potential industrial applications.

A new α-galactosidase from symbiotic Flavobacterium sp. TN17 reveals four residues essential for α-galactosidase activity of gastrointestinal bacteria.

The α-galactosidase gene, galA17, was cloned from Flavobacterium sp. TN17, a symbiotic bacterium isolated from the gut of Batocera horsfieldi larvae. The 2,205-bp full-length gene encodes a 734-residue polypeptide (GalA17) containing a putative 28-residue signal peptide and a catalytic domain belonging to glycosyl hydrolase family 36 (GH 36). The deduced amino acid sequence of galA17 was most similar to a putative α-galactosidase from Pedobacter sp. BAL39 (EDM38577; 66.6% identity) and a characterized α-galactosidase from Carnobacterium piscicola BA (AAL27305; 30.1%). Phylogenetic analysis revealed that GalA17 was similar to GH 36 α-galactosidases from symbiotic bacteria sharing two putative catalytic motifs, KWD and SDXXDXXXR, in which D480, S548, D549, and R556 were essential for α-galactosidase activity based on site-directed mutagenesis. Purified recombinant GalA17 showed apparent optimal activity at pH 5.5 and 45°C; exhibited strong resistance to digestion by trypsin, α-chymotrypsin, collagenase, and proteinase K; and efficiently hydrolyzed several synthetic and natural substrates (p-nitrophenyl-α-D-galactopyranoside, stachyose, melibiose, raffinose, soybean meal, locust bean gum, and guar gum).

Good hydrolysis activity on raffinose family oligosaccharides by a novel α-galactosidase from Tremella aurantialba.

An α-galactosidase designated as TAG was purified from the dried fruit bodies of Tremella aurantialba with 182.5-fold purification. The purification procedure involved ion exchange chromatography on Q-sepharose, DEAE-Cellulose, and Mono Q and gel filtration by FPLC on Superdex 75. The purified α-galactosidase was a monomeric protein with a molecular mass of 88 kDa. The optimal pH of TAG was 5.0 and more than 60% of the original enzyme activity remained at pH 2.0 and 3.0. Its optimal temperature was 54 °C with good thermo-stability, 30.8% of the original activity was retained after exposure to a temperature of 70 °C for 1 h. The metal ions Hg2+, Cu2+, Fe3+ and Mg2+ strongly inhibited the enzyme activity. The enzyme activity was found to be inhibited by N-bromosuccinimide indicating that tryptophan was essential to the catalytic activity of α-galactosidase. The enzyme completely hydrolysed stachyose and partially hydrolysed raffinose to galactose at 50 °C within 6 h as detected by thin layer chromatography and the dinitrosalicylic acid method and the content of reducing sugar reached 4.36 mg/mL.

Overexpression of human alpha-galactosidase A results in its intracellular aggregation, crystallization in lysosomes, and selective secretion.

Human lysosomal alpha-galactosidase A (alpha-Gal A) was stably overexpressed in CHO cells and its biosynthesis and targeting were investigated. Clone AGA5.3-1000Mx, which was the highest enzyme overexpressor, produced intracellular alpha-Gal A levels of 20,900 U/mg (approximately 100 micrograms of enzyme/10(7) cells) and secreted approximately 13,000 U (or 75 micrograms/10(7) cells) per day. Ultrastructural examination of these cells revealed numerous 0.25-1.5 microns crystalline structures in dilated trans-Golgi network (TGN) and in lysosomes which stained with immunogold particles using affinity-purified anti-human alpha-Gal A antibodies. Pulse-chase studies revealed that approximately 65% of the total enzyme synthesized was secreted, while endogenous CHO lysosomal enzymes were not, indicating that the alpha-Gal A secretion was specific. The recombinant intracellular and secreted enzyme forms were normally processed and phosphorylated; the secreted enzyme had mannose-6-phosphate moieties and bound the immobilized 215-kD mannose-6-phosphate receptor (M6PR). Thus, the overexpressed enzyme's selective secretion did not result from oversaturation of the M6PR-mediated pathway or abnormal binding to the M6PR. Of note, the secreted alpha-Gal A was sulfated and the percent of enzyme sulfation decreased with increasing amplification, presumably due to the inaccessibility of the enzyme's tyrosine residues for the sulfotransferase in the TGN. Overexpression of human lysosomal alpha-N-acetylgalactosaminidase and acid sphingomyelinase in CHO cell lines also resulted in their respective selective secretion. In vitro studies revealed that purified secreted alpha-Gal A was precipitated as a function of enzyme concentration and pH, with 30% of the soluble enzyme being precipitated when 10 mg/ml of enzyme was incubated at pH 5.0. Thus, it is hypothesized that these overexpressed lysosomal enzymes are normally modified until they reach the TGN where the more acidic environment of this compartment causes the formation of soluble and particulate enzyme aggregates. A significant proportion of these enzyme aggregates are unable to bind the M6PR and are selectively secreted via the constitutive secretory pathway, while endogenous lysosomal enzymes bind the M6PRs and are transported to lysosomes.

Synthesis of polyfunctional quinolizidine alkaloids: development towards selective glycosidase inhibitors.

A highly divergent route to a variety of quinolizidine alkaloids is described. The enantiomeric precursors and utilized for the synthesis of these alkaloids were constructed stereospecifically from the PET cyclization of the corresponding acetylene tethered alpha-trimethylsilyl amine moieties and , respectively, both of which were synthesised from D-ribose. The polyhydroxy quinolizidine alkaloid was found to be a selective inhibitor of alpha-galactosidase with Ki 83.9 microM. The amine analogs , and are found to be selective and potent inhibitors of alpha-glucosidase with Ki 28, 120 and 140 microM, respectively.

A novel alpha-galactosidase from Bifidobacterium bifidum with transgalactosylating properties: gene molecular cloning and heterologous expression.

A genomic library of Bifidobacterium bifidum (NCIMB 41171) DNA was constructed in Escherichia coli RA11r (melA(-)B(+)) and one alpha-galactosidase encoding gene was isolated. Conceptual translation combined with insertional mutagenesis analysis indicated an open reading frame (ORF) of 759 amino acid (aa) residues encoding an alpha-galactosidase (named as MelA) of 82.8 kDa. Partial purification and characterisation showed that the enzyme had an apparent native molecular mass of approximately 243 kDa and a subunit size of approximately 85 kDa. The enzyme belongs to glycosyl hydrolases 36 family with high aa sequence similarities (approximately 73%) to other known alpha-galactosidases of bifidobacterial origin. Under optimum pH conditions for activity (pH 6.0) and high melibiose concentration (40% w/v), the enzyme was able to form oligosaccharides with degree of polymerisation (DP) > or = 3 at higher concentration than DP = 2, with a total yield of 20.5% (w/w).