A cycloamylose-forming hyperthermostable 4-α-glucanotransferase of Aquifex aeolicus expressed in Escherichia coli

Designing starch derivatives with desired structures and functional properties via rearrangements of glycosidic linkages by starch-active transglycosylases

Modification of starch by transglycosylases from glycoside hydrolase families has attracted much attention recently; these enzymes can produce starch derivatives with novel properties, i.e. processability and functionality, employing highly efficient and safe methods. Starch-active transglycosylases cleave starches and transfer linear fragments to acceptors introducing α-1,4 and/or linear/branched α-1,6 glucosidic linkages, resulting in starch derivatives with excellent properties such as complexing and resistance to digestion characteristics, and also may be endowed with new properties such as thermo-reversible gel formation. This review summarizes the effects of variations in glycosidic linkage composition on structure and properties of modified starches. Starch-active transglycosylases are classified into 4 groups that form compounds: (1) in cyclic with α-1,4 glucosidic linkages, (2) with linear chains of α-1,4 glucosidic linkages, (3) with branched α-1,6 glucosidic linkages, and (4) with linear chains of α-1,6 glucosidic linkages. We discuss potential processability and functionality of starch derivatives with different linkage combinations and structures. The changes in properties caused by rearrangements of glycosidic linkages provide guidance for design of starch derivatives with desired structures and properties, which promotes the development of new starch products and starch processing for the food industry.

A 4-α-Glucanotransferase from Thermus thermophilus HB8: Secretory Expression and Characterization

4-α-glucanotransferase (4GT, EC 2.4.1.25) catalyzes the breakdown of the α-1,4 glycosidic bonds of the starch main chain and forms new α-1,4 glycosidic bonds in the side chain, which is often used to optimize the physical and chemical properties of starch and to improve the quality of starch-based food. However, the low enzyme activity of 4GT limits its production and widespread application. Herein, the 4GT gene encoding 500 amino acids from Thermus thermophilus HB8 was cloned and expressed in Escherichia coli. The purified 4GT exhibited maximum activity at pH 7.0 and 60 °C and had a good stability at pH 6.0-8.0 and 30-60 °C. It was confirmed that 4GT possessed the catalytic function of extending the branch length of potato starch. Furthermore, the 4GT gene was successfully expressed extracellularly in Bacillus subtilis. Then, the enzyme yield of 4GT increased by 4.1 times through screening of different plasmids and hosts. Additionally, the fermentation conditions were optimized to enhance 4GT extracellular enzyme yield. Finally, a recombinant Bacillus subtilis with 299.9 U/mL enzyme yield of 4GT was obtained under the optimized fermentation process. In conclusion, this study provides a valuable reference for characterization and expression of food-grade enzymes.

Production of Large-Ring Cyclodextrins by Amylomaltases

Amylomaltase is a well-known glucan transferase that can produce large ring cyclodextrins (LR-CDs) or so-called cycloamyloses via cyclization reaction. Amylomaltases have been found in several microorganisms and their optimum temperatures are generally around 60–70 °C for thermostable amylomaltases and 30–45 °C for the enzymes from mesophilic bacteria and plants. The optimum pHs for mesophilic amylomaltases are around pH 6.0–7.0, while the thermostable amylomaltases are generally active at more acidic conditions. Size of LR-CDs depends on the source of amylomaltases and the reaction conditions including pH, temperature, incubation time, and substrate. For example, in the case of amylomaltase from Corynebacterium glutamicum, LR-CD productions at alkaline pH or at a long incubation time favored products with a low degree of polymerization. In this review, we explore the synthesis of LR-CDs by amylomaltases, structural information of amylomaltases, as well as current applications of LR-CDs and amylomaltases.

Heterologous expression of 4α-glucanotransferase: overproduction and properties for industrial applications

4α-Glucanotransferase (4α-GTase) is unique in its ability to form cyclic oligosaccharides, some of which are of industrial importance. Generally, low amount of enzymes is produced by or isolated from their natural sources: animals, plants, and microorganisms. Heterologous expressions of these enzymes, in an attempt to increase their production for applicable uses, have been widely studied since 1980s; however, the expressions are mostly performed in the prokaryotic bacteria, mostly Escherichia coli. Site-directed mutagenesis has added more value to these expressed enzymes to display the desired properties beneficial for their applications. The search for further suitable properties for food application leads to an extended research in expression by another group of host organism, the generally-recognized as safe host including the Bacillus and the eukaryotic yeast systems. Herein, our review focuses on two types of 4α-GTase: the cyclodextrin glycosyltransferase and amylomaltase. The updated studies on the general structure and properties of the two enzymes with emphasis on heterologous expression, mutagenesis for property improvement, and their industrial applications are provided.

Amylomaltases in Extremophilic Microorganisms

Amylomaltases (4-α-glucanotransferases, E.C. 2.4.1.25) are enzymes which can perform a double-step catalytic process, resulting in a transglycosylation reaction. They hydrolyse glucosidic bonds of α-1,4'-d-glucans and transfer the glucan portion with the newly available anomeric carbon to the 4'-position of an α-1,4'-d-glucan acceptor. The intramolecular reaction produces a cyclic α-1,4'-glucan. Amylomaltases can be found only in prokaryotes, where they are involved in glycogen degradation and maltose metabolism. These enzymes are being studied for possible biotechnological applications, such as the production of (i) sugar substitutes; (ii) cycloamyloses (molecules larger than cyclodextrins), which could potentially be useful as carriers and encapsulating agents for hydrophobic molecules and also as effective protein chaperons; and (iii) thermoreversible starch gels, which could be used as non-animal gelatin substitutes. Extremophilic prokaryotes have been investigated for the identification of amylomaltases to be used in the starch modifying processes, which require high temperatures or extreme conditions. The aim of this article is to present an updated overview of studies on amylomaltases from extremophilic Bacteria and Archaea, including data about their distribution, activity, potential industrial application and structure.

Streptococcus agalactiae amylomaltase offers insight into the transglycosylation mechanism and the molecular basis of thermostability among amylomaltases

Amylomaltase (AM) catalyzes transglycosylation of starch to form linear or cyclic oligosaccharides with potential applications in biotechnology and industry. In the present work, a novel AM from the mesophilic bacterium Streptococcus agalactiae (SaAM), with 18–49% sequence identity to previously reported AMs, was characterized. Cyclization and disproportionation activities were observed with the optimum temperature of 30 °C and 40 °C, respectively. Structural determination of SaAM, the first crystal structure of small AMs from the mesophiles, revealed a glycosyl-enzyme intermediate derived from acarbose and a second acarbose molecule attacking the intermediate. This pre-transglycosylation conformation has never been before observed in AMs. Structural analysis suggests that thermostability in AMs might be mainly caused by an increase in salt bridges since SaAM has a lower number of salt bridges compared with AMs from the thermophiles. Increase in thermostability by mutation was performed. C446 was substituted with A/S/P. C446A showed higher activities and higher k_cat/K_m values for starch in comparison to the WT enzyme. C446S exhibited a 5 °C increase in optimum temperature and the threefold increase in half-life time at 45 °C, most likely resulting from H-bonding interactions. For all enzymes, the main large-ring cyclodextrin (LR-CD) products were CD24-CD26 with CD22 as the smallest. C446S produced more CD35-CD42, especially at a longer incubation time.

Properties of recombinant 4-α-glucanotransferase from Bifidobacterium longum subsp. longum JCM 1217 and its application

To determine the physiochemical properties of the 4-α-glucanotransferase from Bifidobacterium sp., the bllj_0114 gene encoding 4-α-glucanotransferase was cloned from Bifidobacterium longum subsp. longum JCM 1217 and expressed in Escherichia coli. The amino acid sequence alignment indicated that the recombinant protein, named BL-αGTase, belongs to the glycoside hydrolase (GH) family 77. BL-αGTase was purified using nickel-nitrilotriacetic acid affinity chromatography and characterized using various substrates. The enzyme catalyzed the disproportionation activity, which transfers a glucosyl unit from oligosaccharides to acceptor molecules, and had the highest activity at 40 °C and pH 6.0. In the presence of 5 mM metal ions, in particular Cu²⁺, Zn²⁺, and Fe²⁺, BL-αGTase activity was reduced. To determine whether BL-αGTase can be used to generate thermoreversible gels, potato starch was treated with BL-αGTase for various reaction times. The BL-αGTase-treated starches showed sol-gel reversibility and melted at 59.6-75.7 °C.

Efficient production of aggregation prone 4-α-glucanotransferase by combined use of molecular chaperones and chemical chaperones in Escherichia coli

In this study, a combined optimization strategy, based on co-expression of molecular chaperones and supplementation of osmolytes, was used to reduce the formation of inclusion bodies and enhance the expression of the soluble form of 4-α-glucanotransferase. The 4-α-glucanotransferase yield was enhanced by co-expression with pGro7 and supplementation of trimetlylamine oxide. Subsequently, the effects of process conditions (temperature, inducer concentration, and arabinose concentration) on cell growth and 4-α-glucanotransferase production were also investigated in shake flasks. In addition, a modified high-cell-density fermentation approach was proposed and applied in 3-L fermentor supplied with l-arabinose and trimetlylamine oxide, which achieved a dry cell weight of 65.92 g·L^-1. Through this cultivation approach at 28 °C, the activity of 4-α-glucanotransferase reached 332.5 U·g^-1 dry cell weight, which was 24.6-fold greater than the initial activity in shake flask cultivation. This combined strategy is expected to provide an efficient and economical approach to overproduction of aggregation prone proteins on a large scale.

Significance of H461 at subsite +1 in substrate binding and transglucosylation activity of amylomaltase from Corynebacterium glutamicum

Amylomaltase (AM) catalyzes inter- and intra-molecular transglycosylation reactions of glucan to yield linear and cyclic oligosaccharide products. The functional roles of the conserved histidine at position 461 in the active site of AM from Corynebacterium glutamicum (CgAM) was investigated. H461 A/S/D/R/W were constructed, their catalytic properties were compared to the wild-type (WT). A significant decrease in transglucosylation activities was observed, especially in H461A mutant, while hydrolysis activity was barely affected. The transglucosylation factor of the H461A-CgAM was decreased by 8.6 folds. WT preferred maltotriose (G3) as substrate for disproportionation reaction, but all H461 mutants showed higher preference for maltose (G2). Using G3 substrate, k_cat/K_m values of H461 mutated CgAMs were 40-64 folds lower, while the K_m values were twice higher than those of WT. All mutants could not produce large-ring cyclodextrin (LR-CD) product. The heat capacity profile indicated that WT had higher thermal stability than H461A. The X-ray structure of WT showed two H-bonds between H461 and heptasaccharide analog at subsite +1, while no such bonding was observed from the model structure of H461A. The importance of H461 on substrate binding with CgAM was evidenced. We are the first to mutate an active site histidine in AM to explore its function.

Y418 in 410s loop is required for high transglucosylation activity and large-ring cyclodextrin production of amylomaltase from Corynebacterium glutamicum

Amylomaltase catalyzes α-1,4 glucosyl transfer reaction to yield linear or cyclic oligosaccharide products. The aim of this work is to investigate functional roles of 410s loop unique to amylomaltase from Corynebacterium glutamicum (CgAM). Site-directed mutagenesis of Y418, the residue at the loop tip, was performed. Y418A/S/D/R/W/F - CgAMs were characterized and compared to the wild-type (WT). A significant decrease in starch transglucosylation, disproportionation and cyclization activities was observed. Specificity for G3 substrate in disproportionation reaction was not changed; however, Y418F showed an increase in preference for longer oligosaccharides G5 to G7. The catalytic efficiency of Y418 mutated CgAMs, except for Y418F, was significantly lower (up to 8- and 12- fold for the W and R mutants, respectively) than that of WT. The change was in the k_cat, not the K_m values which were around 16-20 mM. The profile of large-ring cyclodextrin (LR-CD) product was different; the principal product of Y418A/D/S was shifted to the larger size (CD36-CD40) while that of the WT and Y418F peaked at CD29-CD33. The product yield was reduced especially in W and R mutants. Hence Y418 in 410s loop of CgAM not only contributes to transglucosylation activities but also controls the amount and size of LR-CD products through the proposed hydrophobic stacking interaction and the suitable distance of loop channel for substrate entering. This is the first report to show the effect of the loop tip residue on LR-CD product formation.

Crystal Structure of Amylomaltase from Corynebacterium glutamicum

Amylomaltase is an essential enzyme in maltose utilization and maltodextrin metabolism, and it has been industrially used for the production of cyclodextrin and modification of starch. We determined the crystal structure of amylomaltase from Corynebacterium glutamicum (CgAM) at a resolution of 1.7 Å. Although CgAM forms a dimer without NaCl, it exists as a monomer in physiological concentration of NaCl. CgAM is composed of N- and C-terminal domains, which can be further divided into two and four subdomains, respectively. It exhibits a unique structural feature at the functionally unknown N-domain and also shows two striking differences at the C-domain compared to other amylomaltases. These differences at extended edge of the substrate-binding site might affect substrate specificity for large cyclodextrin formation. The bis-tris methane and sulfate molecules bound at the substrate-binding site of our current structure mimic the binding of the hydroxyl groups of glucose bound at subsites -1 and -2, respectively.

Remarkable evolutionary relatedness among the enzymes and proteins from the α-amylase family

The α-amylase is a ubiquitous starch hydrolase catalyzing the cleavage of the α-1,4-glucosidic bonds in an endo-fashion. Various α-amylases originating from different taxonomic sources may differ from each other significantly in their exact substrate preference and product profile. Moreover, it also seems to be clear that at least two different amino acid sequences utilizing two different catalytic machineries have evolved to execute the same α-amylolytic specificity. The two have been classified in the Cabohydrate-Active enZyme database, the CAZy, in the glycoside hydrolase (GH) families GH13 and GH57. While the former and the larger α-amylase family GH13 evidently forms the clan GH-H with the families GH70 and GH77, the latter and the smaller α-amylase family GH57 has only been predicted to maybe define a future clan with the family GH119. Sequences and several tens of enzyme specificities found throughout all three kingdoms in many taxa provide an interesting material for evolutionarily oriented studies that have demonstrated remarkable observations. This review emphasizes just the three of them: (1) a close relatedness between the plant and archaeal α-amylases from the family GH13; (2) a common ancestry in the family GH13 of animal heavy chains of heteromeric amino acid transporter rBAT and 4F2 with the microbial α-glucosidases; and (3) the unique sequence features in the primary structures of amylomaltases from the genus Borrelia from the family GH77. Although the three examples cannot represent an exhaustive list of exceptional topics worth to be interested in, they may demonstrate the importance these enzymes possess in the overall scientific context.

Pcal_0768, a hyperactive 4-α-glucanotransferase from Pyrobacculum calidifontis

Genome sequence of hyperthermophilic archaeon Pyrobaculum calidifontis revealed the presence of an open reading frame, Pcal_0768, corresponding to a putative 4-α-glucanotranferase belonging to glycoside hydrolases (GH) family 77. We have produced, in Escherichia coli, and purified recombinant Pcal_0768 which exhibited high disproportionation (690 U mg(-1)) activity. To the best of our knowledge, this is the highest ever reported activity for any member of family GH77. Maltooligosaccharides, when used as sole substrates, were disproportionated into linear maltooligohomologues. The analysis of the reaction end products revealed no evidence for the production of cycloamyloses. Catalytic activity of the enzyme remained unchanged in the presence or the absence of ionic and nonionic detergents. γ-cyclodextrin, an inhibitor of 4-α-glucanotransferases, did not show any inhibitory effect on Pcal_0768 activity. These properties make Pcal_0768 a potential candidate for starch processing industry.

Mutagenesis for improvement of activity and thermostability of amylomaltase from Corynebacterium glutamicum

This work aims to improve thermostability of amylomaltase from a mesophilic Corynebacterium glutamicum (CgAM) by random and site-directed mutagenesis. From error prone PCR, a mutated CgAM with higher thermostability at 50 °C compared to the wild-type was selected and sequenced. The result showed that the mutant contains a single mutation of A406V. Site-directed mutagenesis was then performed to construct A406V and A406L. Both mutated CgAMs showed higher intermolecular transglucosylation activity with an upward shift in the optimum temperature and a slight increase in the optimum pH for disproportionation and cyclization reactions. Thermostability of both mutated CgAMs at 35-40 °C was significantly increased with a higher peak temperature from DSC spectra when compared to the wild-type. A406V had a greater effect on activity and thermostability than A406L. The catalytic efficiency values kcat/Km of A406V- and A406L-CgAMs were 2.9 and 1.4 times higher than that of the wild-type, respectively, mainly due to a significant increase in kcat. LR-CD product analysis demonstrated that A406V gave higher product yield, especially at longer incubation time and higher temperature, in comparison to the wild-type enzyme.

In silico analysis of family GH77 with focus on amylomaltases from borreliae and disproportionating enzymes DPE2 from plants and bacteria

The CAZy glycoside hydrolase (GH) family GH77 is a monospecific family containing 4-α-glucanotransferases that if from prokaryotes are known as amylomaltases and if from plants including algae are known as disproportionating enzymes (DPE). The family GH77 is a member of the α-amylase clan GH-H. The main difference discriminating a GH77 4-α-glucanotransferase from the main GH13 α-amylase family members is the lack of domain C succeeding the catalytic (β/α)8-barrel. Of more than 2400 GH77 members, bacterial amylomaltases clearly dominate with more than 2300 sequences; the rest being approximately equally represented by Archaea and Eucarya. The main goal of the present study was to deliver a detailed bioinformatics study of family GH77 (416 collected sequences) focused on amylomaltases from borreliae (containing unique sequence substitutions in functionally important positions) and plant DPE2 representatives (possessing an insert of ~140 residues between catalytic nucleophile and proton donor). The in silico analysis reveals that within the genus of Borrelia a gradual evolutionary transition from typical bacterial Thermus-like amylomaltases may exist to family-GH77 amylomaltase versions that currently possess progressively mutated the most important and otherwise invariantly conserved positions. With regard to plant DPE2, a large group of bacterial amylomaltases represented by the amylomaltase from Escherichia coli with a longer N-terminus was identified as a probable intermediary connection between Thermus-like and DPE2-like (existing also among bacteria) family GH77 members. The presented results concerning both groups, i.e. amylomaltases from borreliae and plant DPE2 representatives (with their bacterial counterpart), may thus indicate the direction for future experimental studies.

One-pot synthesis of cycloamyloses from sucrose by dual enzyme treatment: combined reaction of amylosucrase and 4-α-glucanotransferase

Amylose-like α-(1,4)-glucan known as the most favorable substrate for the enzymatic production of cycloamyloses (CAs) using 4-α-glucanotransferase has a solubility issue, which requires an additional solubilization process. In our study, two glucosyltransferases, Synechocystis 4-α-glucanotransferase and Neisseria amylosucrase, were adopted to develop an efficient biocatalytic production process of CAs directly from sucrose. From one-pot synthesis, the maximum CA yield (9.6%, w/w) with 0.3 M sucrose was achieved with 10 units/mL of amylosucrase and 0.1 unit/mL of 4-α-glucanotransferase at 40 °C for a 3 h reaction in a simultaneous dual enzyme reaction mode. The size of linear α-(1,4)-glucan was positively related to the CA productivity by 4-α-glucanotransferase in a hyperbolic manner. Using our innovative bioprocess, there was no practical limitation on the initial sucrose concentration and no use of insoluble linear α-(1,4)-glucan substrate. Consequently, the concomitant dual enzyme reaction converted sucrose directly to CAs via in situ transient linear α-(1,4)-glucan as an soluble intermediate.

Characterization of 4-alpha-glucanotransferase from Synechocystis sp. PCC 6803 and its application to various corn starches

A putative 4-alpha-glucanotransferase (alphaGTase) gene from Synechocystis sp. PCC 6803 was identified being composed of 1505 nucleotides, and the overexpressed protein was purified with an affinity chromatography. The recombinant alphaGTase had about 57kDa of molecular mass when judged by SDS-PAGE analysis. The optimum reaction condition of the alphaGTase was shown to be pH 7 at 45 degrees C in 50mm phosphate buffer. This enzyme displayed transglycosylating activity on various maltooligosaccharides, of which the smallest donor and acceptor molecules were determined to be maltose and glucose, respectively. Various corn starches consisting of different proportions of amylopectin and amylose were incubated with the recombinant alphaGTase. The change in molecular weight distribution of alphaGTase-modified starch was analyzed by HPSEC. The reaction pattern of alphaGTase showed substantial decrease in amylopectin and increase in the peak corresponding to cycloamylose (CA). The production yield of CA tended to increase from 5 to 30% along with the increase in the apparent amylose content in corn starch, which suggested that linear amylose chain would be preferred to produce CA in the alphaGTase treatment. The detectable minimum degree of polymerization (DP) of CA was shown to be 22 by MALDI-TOF-MS analysis. As another action mode of alphaGTase, the rearrangement of amylopectin branch-chain distribution occurred without hydrolysis to small oligosaccharides. After isoamylolysis, alphaGTase-treated starch displayed the increase in DP 4-9 and longer than DP 21 when the relative proportion of branch chains in amylopectin was determined by HPAEC.

Enzymatic synthesis and properties of highly branched rice starch amylose and amylopectin cluster

We enzymatically modified rice starch to produce highly branched amylopectin and amylose and analyzed the resulting structural changes. To prepare the highly branched amylopectin cluster (HBAPC), we first treated waxy rice starch with Thermus scotoductus alpha-glucanotransferase (TSalphaGT), followed by treatment with Bacillus stearothermophilus maltogenic amylase (BSMA). Highly branched amylose (HBA) was prepared by incubating amylose with Bacillus subtilis 168 branching enzyme (BBE) and subsequently treating it with BSMA. The molecular weight of TSalphaGT-treated waxy rice starch was reduced from 8.9 x 10(8) to 1.2 x 10(5) Da, indicating that the alpha-1,4 glucosidic linkage of the segment between amylopectin clusters was hydrolyzed. Analysis of the amylopectin cluster side chains revealed that a rearrangement in the side-chain length distribution occurred. Furthermore, HBAPC and HBA were found to contain significant numbers of branched maltooligosaccharide side chains. In short, amylopectin molecules of waxy rice starch were hydrolyzed into amylopectin clusters by TSalphaGT in the enzymatic modification process, and then further branched by transglycosylation using BSMA. HBAPC and HBA showed higher water solubility and stability against retrogradation than amylopectin clusters or branched amylose. The hydrolysis rates of HBAPC and HBA by glucoamylase and alpha-amylase greatly decreased. The k cat/ K m value of glucoamylase acting on the amylopectin cluster was 45.94 s(-1)(mg/mL)(-1) and that for glucoamylase acting on HBAPC was 11.10 s(-1)(mg/mL)(-1), indicating that HBAPC was 4-fold less susceptible to glucoamylase. The k cat/ K m value for HBA was 15.90 s(-1)(mg/mL)(-1), or about three times less than that for branched amylose. The k cat/ K m values of porcine pancreatic alpha-amylase for HBAPC and HBA were 496 and 588 s(-1)(mg/mL)(-1), respectively, indicating that HBA and HBAPC are less susceptible to hydrolysis by glucoamylase and alpha-amylase. HBAPC and HBA show potential as novel glucan polymers with low digestibility and high water solubility.

Three-way Stabilization of the Covalent Intermediate in Amylomaltase, an α-Amylase-like Transglycosylase

Amylomaltases are glycosyl hydrolases belonging to glycoside hydrolase family 77 that are capable of the synthesis of large cyclic glucans and the disproportionation of oligosaccharides. Using protein crystallography, we have generated a flip book movie of the amylomaltase catalytic cycle in atomic detail. The structures include a covalent glycosyl enzyme intermediate and a covalent intermediate in complex with an analogue of a co-substrate and show how the structures of both enzyme and substrate respond to the changes required by the catalytic cycle as it proceeds. Notably, the catalytic nucleophile changes conformation dramatically during the reaction. Also, Gln-256 on the 250s loop is involved in orienting the substrate in the +1 site. The absence of a suitable base in the covalent intermediate structure explains the low hydrolysis activity.

Amylomaltase of Pyrobaculum aerophilum IM2 produces thermoreversible starch gels

Amylomaltases are 4-alpha-glucanotransferases (EC 2.4.1.25) of glycoside hydrolase family 77 that transfer alpha-1,4-linked glucans to another acceptor, which can be the 4-OH group of an alpha-1,4-linked glucan or glucose. The amylomaltase-encoding gene (PAE1209) from the hyperthermophilic archaeon Pyrobaculum aerophilum IM2 was cloned and expressed in Escherichia coli, and the gene product (PyAMase) was characterized. PyAMase displays optimal activity at pH 6.7 and 95 degrees C and is the most thermostable amylomaltase described to date. The thermostability of PyAMase was reduced in the presence of 2 mM dithiothreitol, which agreed with the identification of two possible cysteine disulfide bridges in a three-dimensional model of PyAMase. The kinetics for the disproportionation of malto-oligosaccharides, inhibition by acarbose, and binding mode of the substrates in the active site were determined. Acting on gelatinized food-grade potato starch, PyAMase produced a thermoreversible starch product with gelatin-like properties. This thermoreversible gel has potential applications in the food industry. This is the first report on an archaeal amylomaltase.