Bacillus stearothermophilus ATCC12016 α-glucosidase specific for α-1,4 bonds of maltosaccharides and α-glucans shows high amino acid sequence similarities to seven α-d-glucohydrolases with different substrate specificity

Function and structure of GH13_31 α-glucosidase with high α-(1→4)-glucosidic linkage specificity and transglucosylation activity

α-Glucosidase hydrolyzes α-glucosides and transfers α-glucosyl residues to an acceptor through transglucosylation. In this study, GH13_31 α-glucosidase BspAG13_31A with high transglucosylation activity is reported in Bacillus sp. AHU2216 and biochemically and structurally characterized. This enzyme is specific to α-(1→4)-glucosidic linkage as substrates and transglucosylation products. Maltose is the most preferred substrate. Crystal structures of BspAG13_31A wild-type for the substrate-free form and inactive acid/base mutant E256Q in complexes with maltooligosaccharides were solved at 1.6-2.5 Å resolution. BspAG13_31A has a catalytic domain folded by an (β/α)₈ -barrel. In subsite +1, Ala200 and His203 on β→α loop 4 and Asn258 on β→α loop 5 are involved in the recognition of maltooligosaccharides. Structural basis for specificity of GH13_31 enzymes to α-(1→4)-glucosidic linkage is first described.

A new GH13 α-glucosidase from alkaliphilic Bacillus pseudofirmus 703 with both exo-α-l, 4-glucosidase and oligo-l, 6-glucosidase activities toward amylopectin

Debranching of (1, 6)-α-linkages in starch is of great significance as it is widely used in different industries. In recent years, identifying a single potential enzyme that could debranch (1, 6)-α-linkages and cleave (1, 4)-α-linkages brought great interest as amylopectin possessed both (1, 4)-α- and (1, 6)-α-linkages. In the present study, a 64\,kDa exo-α-l, 4-glucosidase from Bacillus pseudofirmus 703, annotated as Amy112, was cloned and characterized. Biochemical analysis indicated that heterologous Amy112 expressed in Escherichia coli exhibited a high activity against amylopectin, with the optimal temperature and pH of 40°C and pH 7.0, respectively. Addition of K⁺ ions improved the amy112 activity by 12%, but Li⁺, Ca²⁺ and Mg²⁺ ions showed no significant effect. Amy112 sequence homology revealed that it belonged to glycoside hydrolase family 13, showing 65% identity with α-glucosidase GSJ from Geobacillus sp. HTA-462. This is the first report indicating that Amy112 from B. pseudofirmus 703 belongs to GH13 enzyme family, having both exo-α-1, 4-glucosidase and oligo-l, 6-glucosidase activities. However, no transglycosylation activity was detected in LC-MS analysis. Amy112 would be of great significance of being utilized to debranch starch in different industries in a cost effective manner.

Thielavins A, J and K: α-Glucosidase inhibitors from MEXU 27095, an endophytic fungus from Hintonia latiflora

Bioassay-guided fractionation of the bio-active organic extract obtained from solid-media culture of MEXU 27095, an endophytic fungus isolated from the Mexican medicinal plant Hintonia latiflora (Rubiaceae), led to separation of three tridepsides which were identified as thielavins A, J and K. All three compounds inhibited Saccharomyces cerevisieae α-glucosidase (αGHY) in a concentration-dependent manner with IC50 values of 23.8, 15.8, and 22.1μM, respectively. Their inhibitory action was higher than that of acarbose (IC50=545μM), used as a positive control. Kinetic analysis established that the three compounds acted as non-competitive inhibitors with ki values of 27.8, 66.2 and 55.4μM, respectively (α=1.0, 1.2, 0.7, respectively); acarbose behaved as competitive inhibitor with a ki value of 156.1μM. Thielavin J inhibited the activity of α-glucosidase from Bacillus stearothermophilus (αGHBs) with an IC50 of 30.5μM, being less active than acarbose (IC50=0. 015μM); in this case, compound (2) (ki=20.0μM and α=2.9) and acarbose (ki=0.008μM and α=1.9) behaved as non-competitive inhibitors. Docking analysis predicted that all three thielavins and acarbose bind to homologated αGHBs and to αGHY (PDB: 3A4A) in a pocket close to the catalytic site for maltose and isomaltose, respectively. The α-glucosidase inhibitory properties of thielavin K (3) were corroborated in vivo since it induced a noted antihyperglycemic action during an oral sucrose tolerance test (3.1, 10.0 and 31.6mg/kg) in normal and nicotinamide-streptozotocin diabetic mice. In addition, at a dose of 10mg/kg, it provoked a moderate hypoglycemic activity in diabetic mice.

Molecular characterization of the α-glucosidase activity in Enterobacter sakazakii reveals the presence of a putative gene cluster for palatinose metabolism

Enterobacter sakazakii is considered an opportunistic pathogen for premature infants and neonates. Although E. sakazakii has been isolated from various types of food, recontaminated dried infant formula has been epidemiologically identified as the major source of infection. Amongst others, alpha-glucosidase activity is one of the most important biochemical features, which differentiates E. sakazakii from other species in the family Enterobacteriaceae and has therefore been used as a selective marker in the development of differential media. However, it has been shown, that methods based on this biochemical feature are prone to producing false-positive results for presumptive E. sakazakii colonies due to the presence of this enzymatic activity in other species of the Enterobacteriaceae. Therefore, elucidation of the molecular basis responsible for the biochemical feature in E. sakazakii would provide novel targets suitable for the development of more specific and direct identification systems for this organism. By applying the bacterial artificial chromosome (BAC) approach, along with heterologous gene expression in Escherichia coli, the molecular basis of the alpha-glucosidase activity in E. sakazakii was characterized. Here we report the identification of two different alpha-glucosidase encoding genes. Homology searches of the deduced amino acid sequences revealed that the proteins belong to a cluster of gene products putatively responsible for the metabolism of isomaltulose (palatinose; 6-O-alpha-d-glucopyranosyl-d-fructose). The glycosyl-hydrolyzing activity of each protein was demonstrated by subcloning the respective open reading frames and screening of E. coli transformants for their ability to hydrolyze 4-methyl-umbelliferyl-alpha-d-glucoside. Analysis at the protein level revealed that both enzymes belong to the intracellular fraction of cell proteins. The presence of the postulated palatinose metabolism was proven by growth experiments using this sugar as a sole carbon source.

alpha-Glucosidase from a strain of deep-sea Geobacillus: a potential enzyme for the biosynthesis of complex carbohydrates

An alpha-glucosidase from Geobacillus sp. strain HTA-462, one of the deepest sea bacteria isolated from the sediment of the Mariana Trench, was purified to homogeneity and estimated to be a 65-kDa protein by SDS-PAGE. At low ion strength, the enzyme exists in the homodimeric form (130 kDa). It is a thermo- and alkaline-stable enzyme with a half-life of 13.4 h and a maximum hydrolytic activity at 60 degrees C and pH 9.0 in 15 mM glycine-NaOH buffer. The enzyme exclusively hydrolyzed alpha-1,4-glycosidic linkages of oligosaccharides in an exo-type manner. The enzyme had an overwhelming transglycosylation activity and glycosylated various non-sugar molecules when maltose was used as a sugar donor. It converted maltose to isomaltose. The gene encoding the enzyme was cloned and sequenced. The recombinant enzyme could be extracellularly overproduced by Bacillus subtilis harboring its gene and preserved the primary properties of the native enzyme. Site-directed mutagenesis experiments showed that Asp98 is essential for the enzyme activity in addition to Asp199, Asp326, and Glu256.

Cloning and characterization of the gene cluster for palatinose metabolism from the phytopathogenic bacterium Erwinia rhapontici

Erwinia rhapontici is able to convert sucrose into isomaltulose (palatinose, 6-O-alpha-D-glucopyranosyl-D-fructose) and trehalulose (1-O-alpha-D-glucopyranosyl-D-fructose) by the activity of a sucrose isomerase. These sucrose isomers cannot be metabolized by plant cells and most other organisms and therefore are possibly advantageous for the pathogen. This view is supported by the observation that in vitro yeast invertase activity can be inhibited by palatinose, thus preventing sucrose consumption. Due to the lack of genetic information, the role of sucrose isomers in pathogenicity has not been evaluated. Here we describe for the first time the cloning and characterization of the palatinose (pal) genes from Erwinia rhapontici. To this end, a 15-kb chromosomal DNA fragment containing nine complete open reading frames (ORFs) was cloned. The pal gene products of Erwinia rhapontici were shown to be homologous to proteins involved in uptake and metabolism of various sugars from other microorganisms. The palE, palF, palG, palH, palK, palQ, and palZ genes were oriented divergently with respect to the palR and palI genes, and sequence analysis suggested that the first set of genes constitutes an operon. Northern blot analysis of RNA extracted from bacteria grown under various conditions implies that the expression of the palI gene and the palEFGHKQZ genes is oppositely regulated at the transcriptional level. Genes involved in palatinose uptake and metabolism are down regulated by sucrose and activated by palatinose. Palatinose activation is inhibited by sucrose. Functional expression of palI and palQ in Escherichia coli revealed sucrose isomerase and palatinase activity, respectively.

Relationship of sequence and structure to specificity in the alpha-amylase family of enzymes

The hydrolases and transferases that constitute the alpha-amylase family are multidomain proteins, but each has a catalytic domain in the form of a (beta/alpha)(8)-barrel, with the active site being at the C-terminal end of the barrel beta-strands. Although the enzymes are believed to share the same catalytic acids and a common mechanism of action, they have been assigned to three separate families - 13, 70 and 77 - in the classification scheme for glycoside hydrolases and transferases that is based on amino acid sequence similarities. Each enzyme has one glutamic acid and two aspartic acid residues necessary for activity, while most enzymes of the family also contain two histidine residues critical for transition state stabilisation. These five residues occur in four short sequences conserved throughout the family, and within such sequences some key amino acid residues are related to enzyme specificity. A table is given showing motifs distinctive for each specificity as extracted from 316 sequences, which should aid in identifying the enzyme from primary structure information. Where appropriate, existing problems with identification of some enzymes of the family are pointed out. For enzymes of known three-dimensional structure, action is discussed in terms of molecular architecture. The sequence-specificity and structure-specificity relationships described may provide useful pointers for rational protein engineering.

Analysis of the Bacillus subtilis genome: cloning and nucleotide sequence of a 62 kb region between 275 degrees (rrnB) and 284 degrees (pai)

In the framework of the international project aimed at the sequencing of the Bacillus subtilis genome, five DNA fragments in the region between rrnB (275 degrees) and pai (284 degrees) were cloned by inverse and combinatorial long-range PCR and their nucleotide sequences were determined and analysed. Together these sequences constituted a contig of 62229 bp. On the basis of the position of Not1 and Stil restriction sites, the orientation and order of known genetic markers was determined to be pai (284 degrees)-degQ comQ comP comAA comAB-pbpD-kapB kinB patB-mcpB tipA mcpA tipB-rrnB (275 degrees). Fifty-four ORFs were detected. Thirteen of these coincided with known B. subtilis genes, and 41 new ORFs were found. Of the predicted new gene products, 12 showed no significant similarity to other known proteins, whereas ten showed strong similarity to proteins of other organisms with unknown function. Nineteen predicted proteins showed strong similarity to known proteins of other organisms, for instance a Na+/H+ antiporter system of Bacillus alcalophilus, a sugar transport system found in Mycoplasma genitalium, NADH-dependent butanol dehydrogenase of Clostridium acetobutylicum, glucose-6-phosphate isomerase A of B, subtilis, exo-1,4-alpha-glucosidase activity of Bacillus stearothermophilus and L-rhamnose isomerase of Escherichia coli.