Complete Amino Acid Sequence of Crystalline (α–Glucosidase fromAspergillus niger

Modification of the transglucosylation properties of α-glucosidases from Aspergillus oryzae and Aspergillus sojae via a single critical amino acid replacement

We constructed enzyme variants of the α-glucosidases from Aspergillus oryzae (AoryAgdS) and Aspergillus sojae (AsojAgdL) by mutating the amino acid residue at position 450. AoryAgdS_H450R acquired the ability to produce considerable amounts of α-1,6-transglucosylation products, whereas AsojAgdL_R450H changed to produce more α-1,3- and α-1,4-transglucosylation products than α-1,6-products. The 450th amino acid residue is critical for the transglucosylation of these α-glucosidases.

A Novel α-Glucosidase of the Glycoside Hydrolase Family 31 from Aspergillus sojae

We characterized an α-glucosidase belonging to the glycoside hydrolase family 31 from Aspergillus sojae. The α-glucosidase gene was cloned using the whole genome sequence of A. sojae, and the recombinant enzyme was expressed in Aspergillus nidulans. The enzyme was purified using affinity chromatography. The enzyme showed an optimum pH of 5.5 and was stable between pH 6.0 and 10.0. The optimum temperature was approximately 55 °C. The enzyme was stable up to 50 °C, but lost its activity at 70 °C. The enzyme acted on a broad range of maltooligosaccharides and isomaltooligosaccharides, soluble starch, and dextran, and released glucose from these substrates. When maltose was used as substrate, the enzyme catalyzed transglucosylation to produce oligosaccharides consisting of α-1,6-glucosidic linkages as the major products. The transglucosylation pattern with maltopentaose was also analyzed, indicating that the enzyme mainly produced oligosaccharides with molecular weights higher than that of maltopentaose and containing continuous α-1,6-glucosidic linkages. These results demonstrate that the enzyme is a novel α-glucosidase that acts on both maltooligosaccharides and isomaltooligosaccharides, and efficiently produces oligosaccharides containing continuous α-1,6-glucosidic linkages.

The gold-standard genome of Aspergillus niger NRRL 3 enables a detailed view of the diversity of sugar catabolism in fungi

The fungal kingdom is too large to be discovered exclusively by classical genetics. The access to omics data opens a new opportunity to study the diversity within the fungal kingdom and how adaptation to new environments shapes fungal metabolism. Genomes are the foundation of modern science but their quality is crucial when analysing omics data. In this study, we demonstrate how one gold-standard genome can improve functional prediction across closely related species to be able to identify key enzymes, reactions and pathways with the focus on primary carbon metabolism.

Based on this approach we identified alternative genes encoding various steps of the different sugar catabolic pathways, and as such provided leads for functional studies into this topic. We also revealed significant diversity with respect to genome content, although this did not always correlate to the ability of the species to use the corresponding sugar as a carbon source.

Synthesis of Isomalto-Oligosaccharides by Pichia pastoris Displaying the Aspergillus niger α-Glucosidase

We explored the ability of an Aspergillus niger α-glucosidase displayed on P. pastoris to act as a whole-cell biocatalyst (Pp-ANGL-GCW61) system to synthesize isomalto-oligosaccharides (IMOs). IMOs are a mixture that includes isomaltose (IG₂), panose (P), and isomaltotriose (IG₃). In this study, the IMOs were synthesized by a hydrolysis-transglycosylation reaction in an aqueous system of maltose. In a 2 mL reaction system, the IMOs were synthesized with a conversion rate of approximately 49% in 2 h when 30% maltose was utilized under optimal conditions by Pp-ANGL-GCW61. Additionally, the 0.5-L reaction system was conducted in a 2-L stirred reactor with a conversion rate of approximately 44% in 2 h. Moreover, the conversion rate was relatively stable after the whole-cell catalyst was reused three times. In conclusion, Pp-ANGL-GCW61 has a high reaction efficiency and operational stability, which makes it a powerful biocatalyst available for industrial scale synthesis.

α-Glucosidases and α-1,4-glucan lyases: structures, functions, and physiological actions

α-Glucosidases (AGases) and α-1,4-glucan lyases (GLases) catalyze the degradation of α-glucosidic linkages at the non-reducing ends of substrates to release α-glucose and anhydrofructose, respectively. The AGases belong to glycoside hydrolase (GH) families 13 and 31, and the GLases belong to GH31 and share the same structural fold with GH31 AGases. GH13 and GH31 AGases show diverse functions upon the hydrolysis of substrates, having linkage specificities and size preferences, as well as upon transglucosylation, forming specific α-glucosidic linkages. The crystal structures of both enzymes were determined using free and ligand-bound forms, which enabled us to understand the important structural elements responsible for the diverse functions. A series of mutational approaches revealed features of the structural elements. In particular, amino-acid residues in plus subsites are of significance, because they regulate transglucosylation, which is used in the production of industrially valuable oligosaccharides. The recently solved three-dimensional structure of GLase from red seaweed revealed the amino-acid residues essential for lyase activity and the strict recognition of the α-(1 → 4)-glucosidic substrate linkage. The former was introduced to the GH31 AGase, and the resultant mutant displayed GLase activity. GH13 and GH31 AGases hydrate anhydrofructose to produce glucose, suggesting that AGases are involved in the catabolic pathway used to salvage unutilized anhydrofructose.

Bulk Segregant Analysis Reveals the Genetic Basis of a Natural Trait Variation in Fission Yeast

Although the fission yeast Schizosaccharomyces pombe is a well-established model organism, studies of natural trait variations in this species remain limited. To assess the feasibility of segregant-pool-based mapping of phenotype-causing genes in natural strains of fission yeast, we investigated the cause of a maltose utilization defect (Mal(-)) of the S. pombe strain CBS5557 (originally known as Schizosaccharomyces malidevorans). Analyzing the genome sequence of CBS5557 revealed 955 nonconservative missense substitutions, and 61 potential loss-of-function variants including 47 frameshift indels, 13 early stop codons, and 1 splice site mutation. As a side benefit, our analysis confirmed 146 sequence errors in the reference genome and improved annotations of 27 genes. We applied bulk segregant analysis to map the causal locus of the Mal(-) phenotype. Through sequencing the segregant pools derived from a cross between CBS5557 and the laboratory strain, we located the locus to within a 2.23-Mb chromosome I inversion found in most S. pombe isolates including CBS5557. To map genes within the inversion region that occupies 18% of the genome, we created a laboratory strain containing the same inversion. Analyzing segregants from a cross between CBS5557 and the inversion-containing laboratory strain narrowed down the locus to a 200-kb interval and led us to identify agl1, which suffers a 5-bp deletion in CBS5557, as the causal gene. Interestingly, loss of agl1 through a 34-kb deletion underlies the Mal(-) phenotype of another S. pombe strain CGMCC2.1628. This work adapts and validates the bulk segregant analysis method for uncovering trait-gene relationship in natural fission yeast strains.

Molecular Cloning of cDNAs and Genes for Three α-Glucosidases from European Honeybees,Apis melliferaL., and Heterologous Production of Recombinant Enzymes inPichia pastoris

cDNAs encoding three alpha-glucosidases (HBGases I, II, and III) from European honeybees, Apis mellifera, were cloned and sequenced, two of which were expressed in Pichia pastoris. The cDNAs for HBGases I, II, and III were 1,986, 1,910, and 1,915 bp in length, and included ORFs of 1,767, 1,743, and 1,704 bp encoding polypeptides comprised of 588, 580, and 567 amino acid residues, respectively. The deduced proteins of HBGases I, II, and III contained 18, 14, and 8 putative N-linked glycosylation sites, respectively, but at least 2 sites in HBGase II were unmodified by N-linked oligosaccharide. In spite of remarkable differences in the substrate specificities of the three HBGases, high homologies (38-44% identity) were found in the deduced amino acid sequences. In addition, three genomic DNAs, of 13,325, 2,759, and 27,643 bp, encoding HBGases I, II, and III, respectively, were isolated from honeybees, and the sequences were analyzed. The gene of HBGase I was found to be composed of 8 exons and 7 introns. The gene of HBGase II was not divided by intron. The gene of HBGase III was confirmed to be made up of 9 exons and 8 introns, and to be located in the region upstream the gene of HBGase I.

Optimization of the production of Aspergillus niger α-glucosidase expressed in Pichia pastoris

The α-glucosidase (AGL) from Aspergillus niger has been applied to produce isomaltooligosaccharides. In the present study, various factors which affect the yield of recombinant AGL, produced by engineered Pichia pastoris, were investigated. The expression level reached 5.5 U ml(-1) in bioreactor after optimization of parameters of initial induction cell density, induction temperature and methanol concentration. In addition, it was found that coexpression of protein disulfide isomerase (PDI) inhibited the growth of the engineered P. pastoris strains and had an adverse effect on the production of AGL, while codon optimization of native A. niger α-glucosidase encoding gene (aglu) resulted in a significant enhancement of enzyme production, which reached 10.1 U ml(-1). We believe that yield of AGL is increased by codon optimization as a result of enhanced translation efficiency as well as more stable mRNA secondary structure. In contrast, PDI coexpression under the control of alcohol oxidase promoter (PAOX1) seems to be less efficient in helping disulfide bond formation in AGL while probably induce unfolded protein response, which further leads to cell apoptosis and increased protein degradation.

A novel metabolic pathway for glucose production mediated by α-glucosidase-catalyzed conversion of 1,5-anhydrofructose

α-Glucosidase is in the glycoside hydrolase family 13 (13AG) and 31 (31AG). Only 31AGs can hydrate the D-glucal double bond to form α-2-deoxyglucose. Because 1,5-anhydrofructose (AF), having a 2-OH group, mimics the oxocarbenium ion transition state, AF may be a substrate for α-glucosidases. α-Glucosidase-catalyzed hydration produced α-glucose from AF, which plateaued with time. Combined reaction with α-1,4-glucan lyase and 13AG eliminated the plateau. Aspergillus niger α-glucosidase (31AG), which is stable in organic solvent, produced ethyl α-glucoside from AF in 80% ethanol. The findings indicate that α-glucosidases catalyze trans-addition. This is the first report of α-glucosidase-associated glucose formation from AF, possibly contributing to the salvage pathway of unutilized AF.

Heterologous expression and biochemical characterization of alpha-glucosidase from Aspergillus niger by Pichia pastroris

The aglu of Aspergillus niger encodes the pro-protein of alpha-glucosidase, and the mature form of wild-type enzyme is a heterosubunit protein. In the present study, the cDNA of alpha-glucosidase was cloned and expressed in Pichia pastoris strain KM71. The activity of recombinant enzyme in a 3 L fermentor reached 2.07 U/mL after 96 h of induction. The recombinant alpha-glucosidase was able to produce oligoisomaltose. The molecular weight of the recombinant enzyme was estimated to be about 145 kDa by SDS-PAGE, and it reduced to 106 kDa after deglycosylation. The enzymatic activity of recombinant alpha-glucosidase was not significantly affected by a range of metal ions. The optimum temperature of the enzyme was 60 degrees C, and it was stable below 50 degrees C. The enzyme was active over the range of pH 3.0-7.0 with maximal activity at pH 4.5. Using pNPG as substrate, the K(m) and V(max) values were 0.446 mM and 43.48 U/mg, respectively. These studies provided the basis for the application of recombinant alpha-glucosidase in the industry of functional oligosaccharides.

Endoplasmic reticulum alpha-glycosidases of Candida albicans are required for N glycosylation, cell wall integrity, and normal host-fungus interaction

The cell surface of Candida albicans is enriched in highly glycosylated mannoproteins that are involved in the interaction with the host tissues. N glycosylation is a posttranslational modification that is initiated in the endoplasmic reticulum (ER), where the Glc(3)Man(9)GlcNAc(2) N-glycan is processed by alpha-glucosidases I and II and alpha1,2-mannosidase to generate Man(8)GlcNAc(2). This N-oligosaccharide is then elaborated in the Golgi to form N-glycans with highly branched outer chains rich in mannose. In Saccharomyces cerevisiae, CWH41, ROT2, and MNS1 encode for alpha-glucosidase I, alpha-glucosidase II catalytic subunit, and alpha1,2-mannosidase, respectively. We disrupted the C. albicans CWH41, ROT2, and MNS1 homologs to determine the importance of N-oligosaccharide processing on the N-glycan outer-chain elongation and the host-fungus interaction. Yeast cells of Cacwh41Delta, Carot2Delta, and Camns1Delta null mutants tended to aggregate, displayed reduced growth rates, had a lower content of cell wall phosphomannan and other changes in cell wall composition, underglycosylated beta-N-acetylhexosaminidase, and had a constitutively activated PKC-Mkc1 cell wall integrity pathway. They were also attenuated in virulence in a murine model of systemic infection and stimulated an altered pro- and anti-inflammatory cytokine profile from human monocytes. Therefore, N-oligosaccharide processing by ER glycosidases is required for cell wall integrity and for host-fungus interactions.

Multiple forms of α-glucosidase in rice seeds (Oryza sativa L., var Nipponbare)

Two isoforms of alpha-glucosidases (ONG2-I and ONG2-II) were purified from dry rice seeds (Oryza sativa L., var Nipponbare). Both ONG2-I and ONG2-II were the gene products of ONG2 mRNA expressed in ripening seeds. Each enzyme consisted of two components of 6kDa-peptide and 88kDa-peptide encoded by this order in ONG2 cDNA (ong2), and generated by post-translational proteolysis. The 88kDa-peptide of ONG2-II had 10 additional N-terminal amino acids compared with the 88kDa-peptide of ONG2-I. The peptides between 6kDa and 88kDa components (26 amino acids for ONG2-I and 16 for ONG2-II) were removed by post-translational proteolysis. Proteolysis induced changes in adsorption and degradation of insoluble starch granules. We also obtained three alpha-glucosidase cDNAs (ong1, ong3, and ong4) from ripening seeds. The ONG1, ONG2, and ONG4 genes were situated in distinct locus of rice genome. The transcripts encoding ONG2 and ONG3 were generated by alternative splicing. Members of alpha-glucosidase multigene family are differentially expressed during ripening and germinating stages in rice.

Purification and characterization of Acremonium implicatum α-glucosidase having regioselectivity for α-1,3-glucosidic linkage

alpha-Glucosidase with a high regioselectivity for alpha-1,3-glucosidic linkages for hydrolysis and transglucosylation was purified from culture broth of Acremonium implicatum. The enzyme was a tetrameric protein (M.W. 440,000), of which the monomer (M.W. 103,000; monomeric structure was expected from cDNA sequence) was composed of two polypeptides (M.W. 51,000 and 60,000) formed possibly by posttranslational proteolysis. Nigerose and maltose were hydrolyzed by the enzyme rapidly, but slowly for kojibiose. The k(0)/K(m) value for nigerose was 2.5-fold higher than that of maltose. Isomaltose was cleaved slightly, and sucrose was not. Maltotriose, maltotetraose, p-nitrophenyl alpha-maltoside and soluble starch were good substrates. The enzyme showed high affinity for maltooligosaccharides and p-nitrophenyl alpha-maltoside. The enzyme had the alpha-1,3- and alpha-1,4-glucosyl transfer activities to synthesize oligosaccharides, but no ability to form alpha-1,2- and alpha-1,6-glucosidic linkages. Ability for the formation of alpha-1,3-glucosidic linkage was two to three times higher than that for alpha-1,4-glucosidic linkage. Eight kinds of transglucosylation products were synthesized from maltose, in which 3(2)-O-alpha-nigerosyl-maltose and 3(2)-O-alpha-maltosyl-maltose were novel saccharides.

Two potent competitive inhibitors discriminating α-glucosidase family I from family II

The inhibition kinetics for isoacarbose (a pseudotetrasaccharide, IsoAca) and acarviosine-glucose (pseudotrisaccharide, AcvGlc), both of which are derivatives of acarbose, were investigated with various types of alpha-glucosidases obtained from microorganisms, plants, and insects. IsoAca and AcvGlc, competitive inhibitors, allowed classification of alpha-glucosidases into two groups. Enzymes of the first group were strongly inhibited by AcvGlc and weakly by IsoAca, in which the K(i) values of AcvGlc (0.35-3.0 microM) were 21- to 440-fold smaller than those of IsoAca. However, the second group of enzymes showed similar K(i) values, ranging from 1.6 to 8.0 microM for both compounds. This classification for alpha-glucosidases is in total agreement with that based on the similarity of their amino acid sequences (family I and family II). This indicated that the alpha-glucosidase families I and II could be clearly distinguished based on their inhibition kinetic data for IsoAca and AcvGlc. The two groups of alpha-glucosidases seemed to recognize distinctively the extra reducing-terminal glucose unit in IsoAca.

Identification of the catalytic nucleophile of the Family 31 alpha-glucosidase from Aspergillus niger via trapping of a 5-fluoroglycosyl-enzyme intermediate

The mechanism-based reagent 5-fluoro-alpha-d-glucopyranosyl fluoride (5F alpha GlcF) was used to trap a glycosyl-enzyme intermediate and identify the catalytic nucleophile at the active site of Aspergillus niger alpha-glucosidase (Family 31). Incubation of the enzyme with 5F alpha GlcF, followed by peptic proteolysis and comparative liquid chromatography/MS mapping allowed the isolation of a labelled peptide. Fragmentation analysis of this peptide by tandem MS yielded the sequence WYDMSE, with the label located on the aspartic acid residue (D). Comparison with the known protein sequence identified the labelled amino acid as Asp-224 of the P2 subunit.

Carboxyl group of residue Asp647 as possible proton donor in catalytic reaction of alpha-glucosidase from Schizosaccharomyces pombe

cDNA encoding Schizosaccharomyces pombe alpha-glucosidase was cloned from a library constructed from mRNA of the fission yeast, and expressed in Saccharomyces cerevisiae. The cDNA, 4176 bp in length, included a single ORF composed of 2910 bp encoding a polypeptide of 969 amino-acid residues with M(r) 106 138. The deduced amino-acid sequence showed a high homology to those of alpha-glucosidases from molds, plants and mammals. Therefore, the enzyme was categorized into the alpha-glucosidase family II. By site-directed mutagenesis, Asp481, Glu484 and Asp647 residues were confirmed to be essential in the catalytic reaction. The carboxyl group (-COOH) of the Asp647 residue was for the first time shown to be the most likely proton donor acting as the acid catalyst in the alpha-glucosidase of family II. Studies with the chemical modifier conduritol B epoxide suggested that the carboxylate group (-COO-) of the Asp481 residue was the catalytic nucleophile, although the role of the Glu484 residue remains obscure.

Purification and characterization of an extracellular alpha-glucosidase protein from Trichoderma viride which degrades a phytotoxin associated with sheath blight disease in rice

AIMS

To purify and characterize an extracellular alpha-glucosidase from Trichoderma viride capable of inactivating a host-specific phytotoxin, designated RS toxin, produced by the rice sheath blight pathogen, Rhizoctonia solani Kühn.

METHODS AND RESULTS

The host-specific RS toxin was purified from both culture filtrates (culture filtrate toxin, CFTox) and R. solani-inoculated rice sheaths (sheath blight toxin, SBTox). Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analyses of extracellular proteins, purified from a biocontrol fungus T. viride (TvMNT7) grown on SBTox and CFTox separately, were carried out. The antifungal activity of the purified high molecular weight protein (110 kDa) was studied against RS toxin as well as on the sclerotial germination and mycelial growth of R. solani. Enzyme assay and Western blot analysis with the antirabbit TvMNT7 110-kDa protein indicated that the protein was an alpha-glucosidase. The 110-kDa protein was highly specific to RS toxin and its Michaelis-Menten constant value was 0.40 mmol l-1 when p-nitrophenyl alpha-D-glucopyranoside was used as the substrate. The isoelectric point of the protein was 5.2. N-terminal sequencing of the alpha-glucosidase protein showed that its amino acid sequence showed no homology with other known alpha-glucosidases.

CONCLUSION

This appears to be the first report of the purification and characterization of an alpha-glucosidase capable of inactivating a host-specific toxin of fungal origin. The alpha-glucosidase is specific to RS toxin and is different from the known alpha-glucosidases.

SIGNIFICANCE AND IMPACT OF THE STUDY

As RS toxin could be inactivated by the microbial alpha-glucosidase enzyme, isolation of the gene that codes for the enzyme from T. viride and transfer of the gene to rice plants would lead to enhanced resistance against sheath blight pathogen by inactivation of RS toxin.

Regiospecific transglycolytic synthesis and structural characterization of 6-O-alpha-glucopyranosyl-glucopyranose (isomaltose)

The enzymatic synthesis of 6-O-alpha-glucopyranosyl-glucopyranose (isomaltose) was achieved. The regiospecific transglycosylation reaction was catalyzed by a crude preparation of alpha-D-glucosidase from Aspergillus niger, using p-nitrophenyl alpha-D-glucopyranose as the donor and glucopyranose as the acceptor. The yield of the reaction was 59% on a molar basis with respect to the donor. The structural identity of the product was fully determined by HPLC, HPAEC-PAD, ionspray mass spectrometry and (13)C NMR.

The alpha- and beta-subunits are required for expression of catalytic activity in the hetero-dimeric glucosidase II complex from human liver

The alpha- and beta-subunits of the hetero-dimeric glucosidase II complex from human liver were cloned and expressed in COS-1 cells. The 4106 bp full-length cDNA for the alpha-subunit contained a 2835 bp ORF encoding a 107 kDa polypeptide. The 2095 bp cDNA for the beta-subunit encodes a approximately 60 kDa protein in a continuous 1605 bp ORF. The alpha- and beta-subunits each contain two potential Asn-Xaa-Thr/Ser acceptor sites, with only one site in the alpha-subunit (Asn97) being glycosylated. Additional lambda-clones were isolated for each subunit containing in-frame insertions/deletions within the coding region, indicating alternative splicing. Analysis of different human tissues revealed approximately 4.4 kb and approximately 2.4 kb transcripts for alpha- and beta-subunit, respectively, consistent with their full-length cDNA. Coexpression of the alpha- and beta-subunits in COS-1 cells resulted in >4-fold increase of glucosidase II activity. An inactive protein was obtained, however, after transfection with the alpha-subunit alone, showing that both subunits are essential for expression of active glucosidase II. The observation that the enzyme, previously purified from pig liver and lacking the beta-subunit, was catalytically active indicates that the beta-subunit is involved in alpha-subunit maturation rather than being required for enzymatic activity once the alpha-subunit has acquired its mature form. The alpha-subunit is expressed in COS-1 cells as an ER-located protein, whether inactive or part of a catalytically active complex. This suggests that ER-localization of the alpha-subunit, when associated with the dimeric enzyme complex, is mediated by the C-terminal HDEL-signal in the beta-subunit, whereas the apparently incompletely folded form of the inactive alpha-subunit could be retained in the ER by the putative "glycoprotein-specific quality control machinery. "

Molecular basis of glucoamylase overproduction by a mutagenised industrial strain of Aspergillus niger

We have compared a mutagenized strain of Aspergillus niger (S1), used industrially for glucoamylase production, and a related low glucoamylase-producing strain (S2) with a laboratory strain of A. niger (AB4.1). Our aim was to assess the properties of S1 in relation to the laboratory strain and to account at the molecular level for the basis of its glucoamylase overproduction. Both S1 and S2 have similar multiple copies of the glucoamylase-encoding gene (glaA) but only S1 has enhanced glaA transcript and glucoamylase levels compared to AB4.1 that has a single copy of the glaA gene. Glucoamylase production by S1 and AB4.1 was repressed by xylose and induced by starch but, in S2, remained unaffected by carbon source. S1 also secreted elevated levels of alpha-amylase relative to both S2 and AB4.1 but the production of alpha-glucosidase was low in all three strains. The gene encoding aspergillopepsin (pepA), an abundant secreted aspartyl protease, was present as a single copy in all strains but no aspergillopepsin could be detected by Western blotting in either S1 or S2 culture supernatants. We conclude that A. niger strain improvement by mutagenesis and screening for glucoamylase overproduction has led to glaA gene multiplication and an expression defect in the pepA gene.

Glycogen storage disease type II: identification of four novel missense mutations (D645N, G648S, R672W, R672Q) and two insertions/deletions in the acid alpha-glucosidase locus of patients of differing phenotype

Glycogen storage disease type II (GSDII), an autosomal recessive myopathic disorder, results from deficiency of lysosomal acid alpha-glucosidase. We searched for mutations in an evolutionarily conserved region in 54 patients of differing phenotype. Four novel mutations (D645N, G448S, R672W, and R672Q) and a previously described mutation (C647W) were identified in five patients and their deleterious effect on enzyme expression demonstrated in vitro. Two novel frame-shifting insertions/deletions (delta nt766-785/insC and +insG@nt2243) were identified in two patients with exon 14 mutations. The remaining three patients were either homozygous for their mutations (D645N/D645 and C647W/C647W) or carried a previously described leaky splice site mutation (IVS1-13T-->G). For all patients "in vivo" enzyme activity was consistent with clinical phenotype. Agreement of genotype with phenotype and in vitro versus in vivo enzyme was seen in three patients (two infantile patients carrying C647W/C647W and D645N/+insG@nt2243 and an adult patient heteroallelic for G648S/IVS1-13T-->G). Relative discordance was found in a juvenile patient homozygous for the non-expressing R672Q and an adult patient heterozygous for the minimally expressing R672W and delta nt766-785/+insC. Possible explanations include differences in in vitro assays vs in vivo enzyme activity, tissue specific expression with diminished enzyme expression/stability in fibroblasts vs muscle, somatic mosaicism, and modifying genes.

Human small intestinal maltase-glucoamylase cDNA cloning. Homology to sucrase-isomaltase

It has been hypothesized that human mucosal glucoamylase (EC 3.2.1. 20 and 3.2.1.3) activity serves as an alternate pathway for starch digestion when luminal alpha-amylase activity is reduced because of immaturity or malnutrition and that maltase-glucoamylase plays a unique role in the digestion of malted dietary oligosaccharides used in food manufacturing. As a first step toward the testing of this hypothesis, we have cloned human small intestinal maltase-glucoamylase cDNA to permit study of the individual catalytic and binding sites for maltose and starch enzyme hydrolase activities in subsequent expression experiments. Human maltase-glucoamylase was purified by immunoisolation and partially sequenced. Maltase-glucoamylase cDNA was amplified from human intestinal RNA using degenerate and gene-specific primers with the reverse transcription-polymerase chain reaction. The 6,513-base pair cDNA contains an open reading frame that encodes a 1,857-amino acid protein (molecular mass 209,702 Da). Maltase-glucoamylase has two catalytic sites identical to those of sucrase-isomaltase, but the proteins are only 59% homologous. Both are members of glycosyl hydrolase family 31, which has a variety of substrate specificities. Our findings suggest that divergences in the carbohydrate binding sequences must determine the substrate specificities for the four different enzyme activities that share a conserved catalytic site.

Cloning and sequencing of an alpha-glucosidase gene from Aspergillus niger and its expression in A. nidulans

We have cloned an extracellular alpha-glucosidase gene from Aspergillus niger with oligonucleotide probes synthesized on the basis of the determined peptide sequences. The nucleotide sequence revealed an open reading frame of 985 amino acids split with three introns, and the deduced amino acid sequence was nearly identical to that of the alpha-glucosidase previously determined. The cloned gene was introduced into Aspergillus nidulans, and its expression in the transformants was shown to be regulated by the carbon sources in the medium, suggesting that a common regulatory expression system is shared by these two species as is the case of other starch-degrading enzymes of Aspergillus species.

Purification and characterization of the cell-wall-associated and extracellular alpha-glucosidases from Saccharomycopsis fibuligera

Cell-wall-associated and extracellular alpha-glucosidases were purified to homogeneity from Saccharomycopsis fibuligera KZ growing on a medium containing cellobiose as the sole source of carbon; this substrate has the greatest inducing effect on the production of both forms of the enzyme. Depending on the source of carbon, 75-90% of the enzyme is associated with cell wall, from which it can be completely released by 1% Triton X-100 at 25 degrees C in 2 h. Both enzymes are glycoproteins in monomeric form with an apparent molecular mass of 132 kDa estimated by SDS/PAGE and 135 kDa estimated by gel filtration. N-linked carbohydrate accounts for 12% of the total mass. Both forms exhibited optimum activity at pH 5.5 and seem to be stable in the pH range 4.0-8.0 on incubation at 4 degrees C for 24 h. The cell-wall-associated form had an optimum activity at 42.5 degrees C and was stable in the absence of substrate up to 30 degrees C, while the extracellular form had optimal activity at 52.5 degrees C and was stable up to 40 degrees C. Both forms are unable to renature after thermal inactivation. The cell-wall-associated and extracellular alpha-glucosidases cleaved the same kind of substrates, from maltose to maltoheptaose, isomaltase and panose, although showing different rates of hydrolysis, and had little or no activity with polysaccharides. The extracellular form cross-reacts with antibody raised against the cell-wall-associated form, and both forms show the same peptide pattern after cleavage with chymotrypsin. The amino acid sequences of six peptides from both forms show marked similarity to those of Schwanniomyces occidentalis glucoamylase.

Novel structures of N-linked high-mannose type oligosaccharides containing alpha-D-galactofuranosyl linkages in Aspergillus niger alpha-D-glucosidase

Seven oligosaccharides were isolated from alpha-D-glucosidase (EC 3.2.1.20) from Aspergillus niger, and the structures of these oligosaccharides were studied by 1H NMR spectroscopy. After treatment of the alpha-D-glucosidase with N-glycosidase F, seven major oligosaccharide peaks were detected by Dionex anion-exchange HPLC. The structures corresponding to the three peaks OS-1, OS-2, and OS-4 were determined to be Man8GlcNAc2, Man9GlcNAc2, and GlcMan9GlcNAc2, respectively, from 1H NMR spectra of the isolated fractions. Each of the four oligosaccharides OS-5, OS-6, OS-7-1, and OS-7-2 contained an alpha-D-galactofuranosyl residue (Galf) linked to Man(A) via an alpha-(1-->2)-linkage. OS-7 was found to consist of two oligosaccharides. The structures of these four oligosaccharides were determined to be GalfMan5GlcNAc2, GalfMan6GlcNAc2, GalfMan7GlcNAc2, and GalfMan8GlcNAc2 by 1H NMR spectroscopy and compositional analysis. The Galf structure of GalfMan5GlcNAc2 was found to be identical to that of an oligosaccharide previously isolated from the alpha-D-galactosidase of the same strain. The structure of OS-3 remains undetermined.

Structure and expression of a gene coding for thermostable alpha-glucosidase with a broad substrate specificity from Bacillus sp. SAM1606

We cloned an alpha-glucosidase gene from thermophilic Bacillus sp. SAM1606 to overexpress it in Escherichia coli transformants. Deletion of the 5'-noncoding region as well as expression of the alpha-glucosidase gene under the control of the icp promotor of the insecticidal crystal protein gene from Bacillus thuringiensis subsp. sotto enhanced the enzyme productivity to 23.5 U/ml, which was 12,000-fold higher than that obtained by the strain SAM1606. The open reading frame corresponding to the alpha-glucosidase encoded 587 amino acid residues including a residue coded by the initiation codon TTG, and the molecular mass of the alpha-glucosidase from N-terminal serine was calculated to be 68,886 Da. Sequence analysis revealed that the SAM1606 alpha-glucosidase belonged to the alpha-amylase family. The SAM1606 alpha-glucosidase showed extremely high sequence identity (62-65%) to the Bacillus cereus and Bacillus thermoglucosidasius oligo-1,6-glucosidases, which were 72% identical to each other. Sequence identity in the suggested active site regions were essentially the same (80-82%) among these three enzymes. However, the substrate specificity of the SAM1606 alpha-glucosidase was significantly different from those of the oligo-1,6-glucosidases. The thermostability of these three alpha-glucosidases could be correlated with the increase in the number of proline residues, whose occurrence was predicted at beta turns and coils in the enzymes.