Metal Content of α-Amylases of Various Origins

α-Amylase purified and characterized from fenugreek (Trigonella foenum-graecum) showed substantial anti-biofilm activity against Staphylococcus aureus MTCC740

Starch hydrolyzing α-amylase from germinated fenugreek (Trigonella foenum-graecum) has been purified 104-fold to apparent electrophoretic homogeneity with a final specific activity of 297.5 units/mg. SDS-PAGE of the final preparation revealed a single protein band of 47.5 kDa, supported by LC/MS analysis and size-exclusion chromatography on the Superdex 200 (ÄKTA-FPLC). α-Amylase exhibited maximum activity at pH 5.5. An activation energy (Ea) of 9.12 kcal/mol was found to exist in the temperature range of 20 to 90 °C. When substrate concentrations were evaluated between 0.5 and 10 mg/mL, the Km and Vmax values for starch were observed to be 1.12 mg/mL and 384.14 μmol/min/mg, respectively. The major substrate starch exhibited high specificity for fenugreek α-amylase. In the presence of EDTA (5 mM), the activity was lost, however, it could be largely reversed with the addition of calcium. Furthermore, an effort was made to assess the ability of fenugreek seed-derived partially purified (DEAE-cellulose enzyme) and purified α-amylase to disperse inside 48 h-old biofilms of Staphylococcus aureus MTCC740. The outcomes clearly demonstrated that the purified and partially purified α-amylase both exhibited strong biofilm dispersion activity.

Molecular modeling, docking and dynamics studies of fenugreek (Trigonella foenum-graecum) α-amylase

α-Amylase catalyses the hydrolysis of glucosidic bonds in polysaccharides such as starch, glycogen and their degradation products. In the present study, the three-dimensional structure of fenugreek (Trigonella foenum-graecum) α-amylase was determined using a homology modeling-based technique. The best predicted model was deposited in PMDB server with PMDB ID PM0084364. The phylogenetic tree was created using the UPGMA method with 8 homologous protein sequences, Trigonella foenum-graecum was utilized as the target protein. Alignment of the phylogenetic tree identified two primary functional groupings (A and B). α-Amylase from the target genome Trigonella foenum-graecum (Acc. No: GHNA01022531.1) was clustered with Medicago truncatula (Acc. No: XP003589186.1), Cicer arietinum (Acc. No: XP004499059.1), Cajanus cajan (Acc. No: XP020231823.1), Vigna angularis (Acc. No: NP001316768.1) and Vigna mungo (Acc. No: P17859.1), in group A cluster, while Hordeum vulgare (Acc. No: Q40015) and Oryza sativa (PDB ID: 3WN6) were in cluster B. The molecular dynamics simulations were performed to understand the molecular basis and mode of action of Trigonella foenum-graecum α-amylase. Additionally, a geometry-based molecular docking technique was used to evaluate potential binding interactions between the modeled structure of α-amylase and maltose. The results show that Trp228, Glu226, Arg199, His308, Tyr165, Asp309, Phe202 and Asp201 from Trigonella foenum-graecum α-amylase enzyme is involved in the binding to the substrate maltose. Our study provides a 3D model of Trigonella foenum-graecum α-amylase and aids in understanding the atomic level molecular underpinnings of the mechanism of α-amylase interaction with substrate maltose. Ca2+ are essential for the stability of domain B since they are connected to it. Ca2+ site ligands are Asp139, Glu130, Thr133, Asp135 and Gly131 residues. HIGHLIGHTSIn silico analysis, gene prediction of α-amylase was carried from Trigonella foenum-graecum.Analysis of the structure of α-amylase was carried out using homology modelling.Calcium binding sites and their interactions with α-amylase were visualised using BIOVIA DISCOVERY STUDIO 2019.The molecular interaction between Trigonella foenum-graecum α-amylase and maltose was studied in silico using a molecular docking-based method.To give the required simulation parameters, RMSD, RMSF, and Total Energy were calculated using BIOVIA DISCOVERY STUDIO 2019.[Figure: see text]Communicated by Ramaswamy H. Sarma.

Analyzing the potential of selected plant extracts and their structurally diverse secondary metabolites for α-glucosidase inhibitory activity: in vitro and in silico approach

Inhibiting α-glucosidase activity is a therapeutic method to regulate post-prandial hyperglycemia in humans. Here, in-vitro and in-silico studies were used to find α-glucosidase inhibitory plant secondary metabolites (PSM). Among 408 solvent extracts from 70 plants tested for α-glucosidase inhibition, 174 had IC50 ≤ 3 mg/ml. α-glucosidase inhibitory PSM is found in several plant species and solvent extracts, indicating their diversity. Further, ensemble molecular docking and structural activity relationship analysis supported this hypothesis where the top 100 PSM with the least binding energy (BE) among the 539 PSM belonged to sesquiterpenoids (34%), catechols (11%), flavonoids (9%) and steroidal lactones (8%). Shortlisted 11 PSM were subjected to molecular dynamic simulation. Withanolide J recorded the least BE of -66.424 ± 22.333 kJ/mol, followed by Withacoagulin I (-64.665 ± 24.030 kJ/mol). When different simulation frames were analyzed, PSM of withanolide groups was stabilized in the narrow entrance of the active pocket forming H-bond with LYS156, TYR158, PHE159, PHE303 PRO312, LEU313, ARG315 and PHE134. Similarly, Hydroxytuberosone and 1, 8-Dihydroxy-3-carboxy-9, 10-anthraquinone (DHCA) formed H-bond with ASP307 located on the loop at the entrance of the active pocket. In the case of Neoliquiritin and Kaempferol-3-o-alpha-L-rhamnoside (KALR), glucose moiety interacted with the GLU277 and ASP215 (catalytic amino acid residues) through H-bonds. In addition, these 11 PSM were found to fulfil the criteria of drug-likeness as per Lipinski's rule of five and pharmacokinetic profile. The present study strengthens the library of α-glucosidase inhibitory plants and PSM, providing valuable information for Type-II Diabetes mellitus management.Communicated by Ramaswamy H. Sarma.

New Insights into the Latest Advancement in α-Amylase Inhibitors of Plant Origin with Anti-Diabetic Effects

The rising predominance of type 2 diabetes, combined with the poor medical effects seen with commercially available anti-diabetic medications, has motivated the development of innovative treatment approaches for regulating postprandial glucose levels. Natural carbohydrate digestion enzyme inhibitors might be a viable option for blocking dietary carbohydrate absorption with fewer side effects than manufactured medicines. Alpha-amylase is a metalloenzyme that facilitates digestion by breaking down polysaccharides into smaller molecules such as maltose and maltotriose. It also contributes to elevated blood glucose levels and postprandial hyperglycemia. As a result, scientists are being urged to target α-amylase and create inhibitors that can slow down the release of glucose from carbohydrate chains and prolong its absorption, thereby resulting in lower postprandial plasma glucose levels. Natural α-amylase inhibitors derived from plants have gained popularity as safe and cost-effective alternatives. The bioactive components responsible for the inhibitory actions of various plant extracts have been identified through phytochemical research, paving the way for further development and application. The majority of the findings, however, are based on in vitro investigations. Only a few animal experiments and very few human investigations have confirmed these findings. Despite some promising results, additional investigation is needed to develop feasible anti-diabetic drugs based on plant-derived pancreatic α-amylase inhibitors. This review summarizes the most recent findings from research on plant-derived pancreatic α-amylase inhibitors, including plant extracts and plant-derived bioactive compounds. Furthermore, it offers insights into the structural aspects of the crucial therapeutic target, α-amylases, in addition to their interactions with inhibitors.

Structures of two novel crystal forms of Aspergillus oryzae alpha amylase (taka-amylase)

The structures of Aspergillus oryzae α-amylase were determined in a tetragonal crystal, having one molecule as asymmetric unit, and a monoclinic crystal with two molecules as asymmetric unit. Both crystal forms were obtained from trace contaminants of an old commercial lipase preparation. Structures were determined and refined to 1.65 Å and 1.43 Å resolution respectively. The latter crystal has a non-crystallographic (NCS) twofold axis within the asymmetric unit. Glycosylation at Asn197 is evident, and in the tetragonal crystal can be seen to include three, partially disordered sugar residues following the initial N-acetyl glucosamine (NAG). Superposition of the tetragonal crystal model on the α-amylases from Bacillus subtilis (PDB:1BAG), pig pancreas (PDB:3L2L), and barley (PDB:1AMY), show a high degree of coincidence, particularly for the (β/α)8-barrel domains, and especially within the active site. Using this structural agreement between amylases, we extrapolated the binding model of a six residue, limit dextrin found in pig pancreas α-amylase to the A. oryzae enzyme model, which predicts substrate interacting amino acid residues.

A Novel Digestive α-Amylase from Blue Crab (Portunus segnis) Viscera: Purification, Biochemical Characterization and Application for the Improvement of Antioxidant Potential of Oat Flour

This study reports on the purification and characterization of a digestive α-amylase from blue crab (Portunussegnis) viscera designated Blue Crab Amylase (BCA). The enzyme was purified to homogeneity by ultrafiltration, Sephadex G-100 gel filtration and Sepharose mono Q anion exchange chromatography, with the final purification fold of 424.02, specific activity of 1390.8 U mg⁻¹ and 27.8% recovery. BCA, showing a molecular weight of approximately 45 kDa, possesses desirable biotechnological features, such as optimal temperature of 50 °C, interesting thermal stability which is enhanced in the presence of starch, high stability towards surfactants (Tween 20, Tween 80 and Triton X-100), high specific activity, quite high storage and broad pH range stability. The enzyme displayed Km and Vmax values, of 7.5 ± 0.25 mg mL⁻¹ and 2000 ± 23 μmol min⁻¹ mg⁻¹ for potato starch, respectively. It hydrolyzed various carbohydrates and produced maltose, maltotriose and maltotetraose as the major end products of starch hydrolysis. In addition, the purified enzyme was successfully utilized for the improvement of the antioxidant potential of oat flour, which could be extended to other cereals. Interestingly, besides its suitability for application in different industrial sectors, especially food industries, the biochemical properties of BCA from the blue crab viscera provide novel features with other marine-derived enzymes and better understanding of the biodegradability of carbohydrates in marine environments, particularly in invasive alien crustaceans.

Crystal structure of a maltooligosaccharide-forming amylase from Bacillus stearothermophilus STB04

To better understand structure-function relationships, an X-ray crystal structure of the maltooligosaccharide-forming amylase from Bacillus stearothermophilus STB04 (Bst-MFA) with bound acarbose has been determined at 2.2 Å. The structure revealed a classical three-domain fold stabilized by four calcium ions, in which CaI-CaIII form an unprecedented linear metal triad in the interior of domain B. Catalytic residues are deduced to be two aspartic acids and one glutamic acid (Asp234, Glu264, Asp331), and the acarbose is bound to surrounding amino acid residues, mainly through extensive hydrogen bonds. Furthermore, analysis of the structure indicates the existence of at least 8 subsites in Bst-MFA, six glycone sites (-6, -5, -4, -3, -2, -1) and two aglycone sites (+1, +2). Subsite +3 remains to be further explored. Sugar-binding subsites contribute to further presentation of the oligosaccharide-binding mode, which explains the product specificity of Bst-MFA to some extent. In addition, we propose a mechanism by which maltooligosaccharide-forming amylases produce particular maltooligosaccharide products, a result different from that seen with typical α-amylases. Finally, the three-dimensional structure of Bst-MFA complexed with acarbose provides the basis for further studies, designed to increase product specificity.

Starch-Modifying Enzymes

Starch is a carbohydrate polymer found abundantly on earth. It is synthesized in plants as a short-term storage compound for respiration in the leaves and for long-term storage in the tubers, seeds and roots of plants. A wide variety of enzymes modify or convert starch into various products. The classes of enzymes that act on starch include endoamylases, exoamylases, debranching enzymes and transferases. Starch-modifying enzymes of microbial origin are utilized in a wide variety of industrial applications. Alkaline-active amylases are diverse in terms of optimum reaction conditions, substrate and product specificity. Amylases that are active at lower temperatures and alkaline conditions are most suited for detergent formulation. Other notable starch-modifying enzymes from alkaliphiles include maltooligosaccharide-forming amylases and cyclodextrin glycosyltransferases (CGTases), which produce a variety of maltooligosaccharides and cyclodextrins, respectively. Such compounds are used in the food, fine chemical, pharmaceutical and cosmetic industries, among others. Alkaline-active amylases are also applicable in the paper, textile and leather industries and also in bioremediation and alkaline waste water treatment. Their application in these fields is further enhanced through stabilization and improving their specificity and catalytic action by employing nanotechnology and genetic engineering. Graphical Abstract *Alkaline alpha-amylase AmyK from Bacillus sp. KSM-1378. Shirai T, Igarashi K, Ozawa T, Hagihara H, Kobayashi T, Ozaki K, Ito S (2007) Proteins 66:600-610. Source: Protein Data Bank in Europe (PDBe).

Purification, biochemical, and molecular characterization of a novel extracellular thermostable and alkaline α-amylase from Tepidimonas fonticaldi strain HB23

The present study investigated the purification, biochemical, and molecular characterization of a novel thermostable α-amylase (TfAmy48) from Tepidimonas fonticaldi strain HB23. MALDI-TOF/MS analysis indicated that the purified enzyme is a monomer with a molecular mass of 48,138.10 Da. The results from amino-acid sequence analysis revealed high homology between the 25 NH₂-terminal residues of TfAmy48 and those of Gammaproteobacteria α-amylases. The optimum pH and temperature values for α-amylase activity were pH 8 and 80 °C, respectively. Thin-layer chromatography (TLC) analysis showed that the final hydrolyzed products of the enzyme from soluble potato starch were maltopentaose, maltose, and maltotriose, which indicate that TfAmy48 possessed an endo-acting pattern. Compared to Termamyl®300 L, TfAmy48 showed extreme stability and tolerance towards organic solvents and excellent compatibility with some commercial laundry detergents. These proprieties make TfAmy48 enzyme a potential candidate as a cleaning bioadditive in detergent composition. The Tfamy48 gene encoding TfAmy48 was cloned, sequenced, and heterologously-expressed in the extracellular fraction of Escherichia coli strain BL21(DE3)pLysS. The biochemical properties of the extracellular purified recombinant enzyme (rTfAmy48) were similar to those of native one. The highest sequence identity value (97%) was obtained with PsAmy1 α-amylase from Pseudomonas sp. strain KFCC10818, with only 16 amino-acid (aa) residues of difference.

Marine Microbiological Enzymes: Studies with Multiple Strategies and Prospects

Marine microorganisms produce a series of promising enzymes that have been widely used or are potentially valuable for our daily life. Both classic and newly developed biochemistry technologies have been broadly used to study marine and terrestrial microbiological enzymes. In this brief review, we provide a research update and prospects regarding regulatory mechanisms and related strategies of acyl-homoserine lactones (AHL) lactonase, which is an important but largely unexplored enzyme. We also detail the status and catalytic mechanism of the main types of polysaccharide-degrading enzymes that broadly exist among marine microorganisms but have been poorly explored. In order to facilitate understanding, the regulatory and synthetic biology strategies of terrestrial microorganisms are also mentioned in comparison. We anticipate that this review will provide an outline of multiple strategies for promising marine microbial enzymes and open new avenues for the exploration, engineering and application of various enzymes.

Comprehensive enzymatic analysis of the amylolytic system in the digestive fluid of the sea hare, Aplysia kurodai: Unique properties of two α-amylases and two α-glucosidases

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The amylolytic system of the digestive fluid of sea hare (Aplysia kurodai) was studied.

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Two α-amylases and two α-glucosidases were purified from the digestive fluid.

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Sea hare efficiently digests sea lettuce to glucose by a combination of these enzymes.

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Starch in sea lettuce is a predominant glucose source for sea hare.

Sea lettuce (Ulva pertusa) is a nuisance species of green algae that is found all over the world. East-Asian species of the marine gastropod, the sea hare Aplysia kurodai, shows a clear feeding preference for sea lettuce. Compared with cellulose, sea lettuce contains a higher amount of starch as a storage polysaccharide. However, the entire amylolytic system in the digestive fluid of A. kurodai has not been studied in detail. We purified α-amylases and α-glucosidases from the digestive fluid of A. kurodai and investigated the synergistic action of these enzymes on sea lettuce. A. kurodai contain two α-amylases (59 and 80 kDa) and two α-glucosidases (74 and 86 kDa). The 59-kDa α-amylase, but not the 80-kDa α-amylase, was markedly activated by Ca²⁺ or Cl⁻. Both α-amylases degraded starch and maltoheptaose, producing maltotriose, maltose, and glucose. Glucose production from starch was higher with 80-kDa α-amylase than with 59-kDa α-amylase. Kinetic analysis indicated that 74-kDa α-glucosidase prefers short α-1,4-linked oligosaccharide, whereas 86-kDa α-glucosidase prefers large α-1,6 and α-1,4-linked polysaccharides such as glycogen. When sea lettuce was used as a substrate, a 2-fold greater amount of glucose was released by treatment with 59-kDa α-amylase and 74-kDa α-glucosidase than by treatment with 45-kDa cellulase and 210-kDa β-glucosidase of A. kurodai. Unlike mammals, sea hares efficiently digest sea lettuce to glucose by a combination of two α-amylases and two α-glucosidases in the digestive fluids without membrane-bound maltase–glucoamylase and sucrase–isomaltase complexes.

Crystal structure of α-amylase from Oryza sativa: molecular insights into enzyme activity and thermostability

AmyI-1 is an α-amylase from Oryza sativa (rice) and plays a crucial role in degrading starch in various tissues and at various growth stages. This enzyme is a glycoprotein with an N-glycosylated carbohydrate chain, a unique characteristic among plant α-amylases. In this study, we report the first crystal structure of AmyI-1 at 2.2-Å resolution. The structure consists of a typical (β/α)8-barrel, which is well-conserved among most α-amylases in the glycoside hydrolase family-13. Structural superimposition indicated small variations in the catalytic domain and carbohydrate-binding sites between AmyI-1 and barley α-amylases. By contrast, regions around the N-linked glycosylation sites displayed lower conservation of amino acid residues, including Asn-263, Asn-265, Thr-307, Asn-342, Pro-373, and Ala-374 in AmyI-1, which are not conserved in barley α-amylases, suggesting that these residues may contribute to the construction of the structure of glycosylated AmyI-1. These results increase the depths of our understanding of the biological functions of AmyI-1.

Identification and characterization of a novel alkaline α-amylase Amy703 belonging to a new clade from Bacillus pseudofirmus

Alkaline α-amylases are of great interest in desizing processes and detergent industries. Here, an alkaline α-amylase gene amy703 from an alkaliphilic Bacillus pseudofirmus strain was cloned and sequenced. Its encoding product, Amy703, might represent a new clade of α-amylase family, because it shared only 35 % highest identity with all amylases characterized up to date and was not clustered into any subfamilies with amylase activity in glycoside hydrolase family 13. Heterologous expression and characterization of Amy703 showed that it is a metalloenzyme with maximal activity at 40 °C and pH 9.0. Its activity was significantly enhanced by 2- and 2.48-fold at the presence of 10 mM Ca2+ and Mg2+, respectively, while Hg2+ was a strong inhibitor of Amy703. Amy703 has a higher affinity (K  m = 3.92 mg/ml) for soluble starch compared to many other alkaline amylases. The computer modeling of its structure indicated that Amy703 contains typical amylase domains and a loop region appearing to bind the substrates. Site-directed mutagenesis suggested that a conserved residue Glu550 was essential for the activity of Amy703, and proposed it working together with other two residues to constitute a catalytic triad (Asp521, Glu550, and Asp615).

Α-amylase from wheat (Triticum aestivum) seeds: its purification, biochemical attributes and active site studies

Glycosylated α-amylase from germinated wheat seeds (Triticum aestivum) has been purified to apparent electrophoretic homogeneity with a final specific activity of 1,372 U/mg. The enzyme preparation when analysed on SDS-PAGE, displayed a single protein band with Mr 33 kDa; Superdex 200 column showed Mr of 32 kDa and MS/MS analysis further provided support for these values. The enzyme displayed its optimum catalytic activity at pH 5.0 and 68 °C with an activation energy of 6.66 kcal/mol and Q10 1.42. The primary substrate for this hydrolase appears to be starch with Km 1.56 mg/mL, Vmax 1666.67 U/mg and kcat 485 s(-1) and hence is suitable for application in starch based industries. Thermal inactivation of α-amylase at 67 °C resulted in first-order kinetics with rate constant (k) 0.0086 min(-1) and t1/2 80 min. The enzyme was susceptible to EDTA (10mM) with irreversible loss of hydrolytic power. In the presence of 1.0mM SDS, the enzyme lost only 14% and 23% activity in 24 and 48 h, respectively. Chemical modification studies showed that the enzyme contains histidine and carboxylic residues at its active site for its catalytic activity and possibly conserved areas.

Similarities and differences in the biochemical and enzymological properties of the four isomaltases from Saccharomyces cerevisiae

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Isomaltases (Imap) preferably cleave α-(1,6) bonds, yet show clear substrate ambiguity.

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With only 3 different aa, Ima3p activities and thermostability diverge from Ima2p.

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The most distant protein, Ima5p, is extremely sensitive to temperature.

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Ima5p nevertheless displays most of the same catalytic properties as Ima1p and Ima2p.

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Ima5p challenges previous conclusions about specific aa needs for the active site.

The yeast Saccharomyces cerevisiae IMA multigene family encodes four isomaltases sharing high sequence identity from 65% to 99%. Here, we explore their functional diversity, with exhaustive in-vitro characterization of their enzymological and biochemical properties. The four isoenzymes exhibited a preference for the α-(1,6) disaccharides isomaltose and palatinose, with Michaëlis–Menten kinetics and inhibition at high substrates concentration. They were also able to hydrolyze trisaccharides bearing an α-(1,6) linkage, but also α-(1,2), α-(1,3) and α-(1,5) disaccharides including sucrose, highlighting their substrate ambiguity. While Ima1p and Ima2p presented almost identical characteristics, our results nevertheless showed many singularities within this protein family. In particular, Ima3p presented lower activities and thermostability than Ima2p despite only three different amino acids between the sequences of these two isoforms. The Ima3p_R279Q variant recovered activity levels of Ima2p, while the Leu-to-Pro substitution at position 240 significantly increased the stability of Ima3p and supported the role of prolines in thermostability. The most distant protein, Ima5p, presented the lowest optimal temperature and was also extremely sensitive to temperature. Isomaltose hydrolysis by Ima5p challenged previous conclusions about the requirement of specific amino acids for determining the specificity for α-(1,6) substrates. We finally found a mixed inhibition by maltose for Ima5p while, contrary to a previous work, Ima1p inhibition by maltose was competitive at very low isomaltose concentrations and uncompetitive as the substrate concentration increased. Altogether, this work illustrates that a gene family encoding proteins with strong sequence similarities can lead to enzyme with notable differences in biochemical and enzymological properties.

The structure of the Mycobacterium smegmatis trehalose synthase reveals an unusual active site configuration and acarbose-binding mode

Trehalose synthase (TreS) catalyzes the reversible conversion of maltose into trehalose in mycobacteria as one of three biosynthetic pathways to this nonreducing disaccharide. Given the importance of trehalose to survival of mycobacteria, there has been considerable interest in understanding the enzymes involved in its production; indeed the structures of the key enzymes in the other two pathways have already been determined. Herein, we present the first structure of TreS from Mycobacterium smegmatis, thereby providing insights into the catalytic machinery involved in this intriguing intramolecular reaction. This structure, which is of interest both mechanistically and as a potential pharmaceutical target, reveals a narrow and enclosed active site pocket within which intramolecular substrate rearrangements can occur. We also present the structure of a complex of TreS with acarbose, revealing a hitherto unsuspected oligosaccharide-binding site within the C-terminal domain. This may well provide an anchor point for the association of TreS with glycogen, thereby enhancing its role in glycogen biosynthesis and degradation.

Purification, characterization and cloning of a thermotolerant isoamylase produced from Bacillus sp. CICIM 304

A novel thermostable isoamylase, IAM, was purified to homogeneity from the newly isolated thermophilic bacterium Bacillus sp. CICIM 304. The purified monomeric protein with an estimated molecular mass of 100 kDa displayed its optimal temperature and pH at 70 °C and 6.0, respectively, with excellent thermostability between 30 and 70 °C and pH values from 5.5 to 9.0. Under the conditions of temperature 50 °C and pH 6.0, the K  m and V  max on glycogen were 0.403 ± 0.018 mg/mg and 0.018 ± 0.001 mg/(min mg), respectively. Gene encoding IAM, BsIam was identified from genomic DNA sequence with inverse PCRs. The open reading frame of the BsIam gene was 2,655 base pairs long and encoded a polypeptide of 885 amino acids with a calculated molecular mass of 101,155 Da. The deduced amino acid sequence of IAM shared less than 40 % homology with that of microbial isoamylase ever reported, which indicated it was a novel isoamylase. This enzyme showed its obvious superiority in the industrial starch conversion process.

Enzymatic conversions of starch

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

A new nanobiocatalytic system based on allosteric effect with dramatically enhanced enzymatic performance

We report a rational design of CaHPO(4)-α-amylase hybrid nanobiocatalytic system based on allosteric effect and an explanation of the increase in catalytic activity when certain enzymes are immobilized in specific nanomaterials. Employing a calcification approach in aqueous solutions, we acquired such new nanobiocatalytic systems with three different morphologies, i.e., nanoflowers, nanoplates, and parallel hexahedrons. Through studying enzymatic performance of these systems and free α-amylase with/without Ca(2+), we demonstrated how two factors, allosteric regulation and morphology of the as-synthesized nanostructures, predominantly influence enzymatic activity. Benefiting from both the allosteric modulation and its hierarchical structure, CaHPO(4)-α-amylase hybrid nanoflowers exhibited dramatically enhanced enzymatic activity. As a bonus, the new system we devised was found to enjoy higher stability and durability than free α-amylase plus Ca(2+).

Production, Purification, and Characterization of Thermostableα-Amylase Produced byBacillus licheniformisIsolate AI20

An optimization strategy, based on statistical experimental design, is employed to enhance the production of thermostableα-amylase by a thermotolerantB. licheniformisAI20 isolate. Using one variant at time (OVAT) method, starch, yeast extract, and CaCl2were observed to influence the enzyme production significantly. Thereafter, the response surface methodology (RSM) was adopted to acquire the best process conditions among the selected variables, where a three-level Box-Behnken design was employed to create a polynomial quadratic model correlating the relationship between the three variables andα-amylase activity. The optimal combination of the major constituents of media forα-amylase production was 1.0% starch, 0.75% yeast extract, and 0.02% CaCl2. The predicted optimumα-amylase activity was 384 U/mL/min, which is two folds more than the basal medium conditions. The producedα-amylase was purified through various chromatographic techniques. The estimated enzyme molecular mass was 55 kDa and theα-amylase had an optimal temperature and pH of 60–80°C and 6–7.5, respectively. Values ofVmaxandKmfor the purified enzyme were 454 mU/mg and 0.709 mg/mL. Theα-amylase enzyme showed great stability against different solvents. Additionally, the enzyme activity was slightly inhibited by detergents, sodium dodecyl sulphate (SDS), or chelating agents such as EDTA and EGTA. On the other hand, great enzyme stability against different divalent metal ions was observed at 0.1 mM concentration, but 10 mM of Cu2+or Zn2+reduced the enzyme activity by 25 and 55%, respectively.

High external pH enables more efficient secretion of alkaline α-amylase AmyK38 by Bacillus subtilis

Background

Bacillus subtilis genome-reduced strain MGB874 exhibits enhanced production of exogenous extracellular alkaline cellulase Egl-237 and subtilisin-like alkaline protease M-protease. Here, we investigated the suitability of strain MGB874 for the production of α-amylase, which was anticipated to provoke secretion stress responses involving the CssRS (Control secretion stress Regulator and Sensor) system.

Results

Compared to wild-type strain 168, the production of a novel alkaline α-amylase, AmyK38, was severely decreased in strain MGB874 and higher secretion stress responses were also induced. Genetic analyses revealed that these phenomena were attributable to the decreased pH of growth medium as a result of the lowered expression of rocG, encoding glutamate dehydrogenase, whose activity leads to NH₃ production. Notably, in both the genome-reduced and wild-type strains, an up-shift of the external pH by the addition of an alkaline solution improved AmyK38 production, which was associated with alleviation of the secretion stress response. These results suggest that the optimal external pH for the secretion of AmyK38 is higher than the typical external pH of growth medium used to culture B. subtilis. Under controlled pH conditions, the highest production level (1.08 g l^-1) of AmyK38 was obtained using strain MGB874.

Conclusions

We demonstrated for the first time that RocG is an important factor for secretory enzyme production in B. subtilis through its role in preventing acidification of the growth medium. As expected, a higher external pH enabled a more efficient secretion of the alkaline α-amylase AmyK38 in B. subtilis. Under controlled pH conditions, the reduced-genome strain MGB874 was demonstrated to be a beneficial host for the production of AmyK38.

Partial characterization of a novel amylase activity isolated from Tunisian Ficus carica latex

CONTEXT

A large number of plants still need to be investigated through screening of amylases suitable for industry. In the present study, and for the first time, we describe the amylolytic activity of Saint Pedro Ficus carica L. (Moraceae) crude latex of Kahli and Bidhi varieties.

OBJECTIVE

Effects of temperature, pH, metal ions, and inhibitors and compatibility with some commercial detergents were investigated for amylase activity.

MATERIALS AND METHODS

Amylase activity was screened in crude latex using the DNS method and potato starch as a substrate. Analyses of amylolytic reaction products by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) were performed.

RESULTS

Bidhi and Kahli amylases were active in optimal pH of 6.5 and 7 at 45°C, respectively, displaying a half life of 85 and 60 min, respectively, at 80°C, and they were very stable in a wide range of pH (4-12). Bidhi amylase activity increased to 260% by addition of 10(-3) mM Fe(2+) or 10(-2) mM Cu(2+), and was strongly inhibited by Mg(2+) and EDTA. In the presence of Ca(2+) and Mg(2+), Kahli amylase activity was dramatically enhanced by 220 and 260%, respectively. The compatibility of both amylases with certain commercial detergents was also shown to be good as enzymes retained up to 98% of their activities after 30 min of incubation at 80°C.

DISCUSSION AND CONCLUSION

Analysis of amylolytic reaction products by TLC and HPLC suggested that Kahli amylase was an amyloglucosidase and Bidhi amylase was β-fructose, α(1-4) glucose. Bidhi amylase is a good choice for application in starch, food, detergents and medical industries.

Calcium ion-dependent increase in thermostability of dextran glucosidase from Streptococcus mutans

Dextran glucosidase from Streptococcus mutans (SmDG), which belongs to glycoside hydrolase family 13 (GH13), hydrolyzes the non-reducing terminal glucosidic linkage of isomaltooligosaccharides and dextran. Thermal deactivation of SmDG did not follow the single exponential decay but rather the two-step irreversible deactivation model, which involves an active intermediate having 39% specific activity. The presence of a low concentration of CaCl2 increased the thermostability of SmDG, mainly due to a marked reduction in the rate constant of deactivation of the intermediate. The addition of MgCl2 also enhanced thermostability, while KCl and NaCl were not effective. Therefore, divalent cations, particularly Ca2+, were considered to stabilize SmDG. On the other hand, CaCl2 had no significant effect on catalytic reaction. The enhanced stability by Ca2+ was probably related to calcium binding in the β→α loop 1 of the (β/α)(8) barrel of SmDG. Because similar structures and sequences are widespread in GH13, these GH13 enzymes might have been stabilized by calcium ions.

Crystal structures of isomaltase from Saccharomyces cerevisiae and in complex with its competitive inhibitor maltose

The structures of isomaltase from Saccharomyces cerevisiae and in complex with maltose were determined at resolutions of 1.30 and 1.60 Å, respectively. Isomaltase contains three domains, namely, A, B, and C. Domain A consists of the (β/α)(8) -barrel common to glycoside hydrolase family 13. However, the folding of domain C is rarely seen in other glycoside hydrolase family 13 enzymes. An electron density corresponding to a nonreducing end glucose residue was observed in the active site of isomaltase in complex with maltose; however, only incomplete density was observed for the reducing end. The active site pocket contains two water chains. One water chain is a water path from the bottom of the pocket to the surface of the protein, and may act as a water drain during substrate binding. The other water chain, which consists of six water molecules, is located near the catalytic residues Glu277 and Asp352. These water molecules may act as a reservoir that provides water for subsequent hydrolytic events. The best substrate for oligo-1,6-glucosidase is isomaltotriose; other, longer-chain, oligosaccharides are also good substrates. However, isomaltase shows the highest activity towards isomaltose and very little activity towards longer oligosaccharides. This is because the entrance to the active site pocket of isomaltose is severely narrowed by Tyr158, His280, and loop 310-315, and because the isomaltase pocket is shallower than that of other oligo-1,6-glucosidases. These features of the isomaltase active site pocket prevent isomalto-oligosaccharides from binding to the active site effectively.

X-ray crystallographic analyses of pig pancreatic alpha-amylase with limit dextrin, oligosaccharide, and alpha-cyclodextrin

Further refinement of the model using maximum likelihood procedures and reevaluation of the native electron density map has shown that crystals of pig pancreatic alpha-amylase, whose structure we reported more than 15 years ago, in fact contain a substantial amount of carbohydrate. The carbohydrate fragments are the products of glycogen digestion carried out as an essential step of the protein's purification procedure. In particular, the substrate-binding cleft contains a limit dextrin of six glucose residues, one of which contains both alpha-(1,4) and alpha-(1,6) linkages to contiguous residues. The disaccharide in the original model, shared between two amylase molecules in the crystal lattice, but also occupying a portion of the substrate-binding cleft, is now seen to be a tetrasaccharide. There are, in addition, several other probable monosaccharide binding sites. Furthermore, we have further reviewed our X-ray diffraction analysis of alpha-amylase complexed with alpha-cyclodextrin. alpha-Amylase binds three cyclodextrin molecules. Glucose residues of two of the rings superimpose upon the limit dextrin and the tetrasaccharide. The limit dextrin superimposes in large part upon linear oligosaccharide inhibitors visualized by other investigators. By comprehensive integration of these complexes we have constructed a model for the binding of polysaccharides having the helical character known to be present in natural substrates such as starch and glycogen.

Production and properties of α-amylase fromBacillussp. BKL20

As a result of screening Bacillus sp. strains isolated from different natural substrates, strain BKL20 was identified as a producer of a thermostable alkaline α-amylase. Maximum production of this α-amylase was achieved by optimizing culture conditions. Production of α-amylase seemed to be independent of the presence of starch in the culture medium and was stimulated by the presence of peptone (0.3%, m/v) and yeast extract (0.2%, m/v). The enzyme was thermostable and retained amylolytic activity after 30 min of incubation at 60 and 70 °C. High activity was maintained over a broad pH range, from 6.0 to 11.0, and the enzyme remained active after alkaline incubation for 24 h. Bacillus sp. BKL20 α-amylase was not stimulated by Ca2+or other bivalent metal cations and was not inhibited by EGTA or EDTA at 1–10 mmol/L, suggesting that this α-amylase is a Ca2+-independent enzyme. It also showed good resistance to both oxidizing (H2O2) and denaturating (urea) agents.

Engineering of a Bacillus alpha-amylase with improved thermostability and calcium independency

Successful industrial use of amylases requires that they are sufficiently stable and active at application conditions, e.g., at high temperature in starch-liquefaction process. In the present study, site-directed mutagenesis was used to enhance the thermal stability and calcium independency of a mesophilic alpha-amylase from Bacillus megaterium WHO. Mutations (A53S and H58I) were designed at the calcium-binding site based on the sequence alignment. Kinetic and thermostability parameters of the mutants were analyzed and compared with that of the wild type. In the presence of calcium, the affinity of the enzymes (wild type and mutants) toward starch was increased. In comparison to the wild type, calcium ion had more effect on the catalytic efficiency, k (cat)/K (m), and half-life (at 60 degrees C) of A53S mutant. In A53S, the dependence of half-life on calcium concentration showed that the enhanced calcium binding is likely to be responsible for the increased stability. In contrast, calcium-independent mutant (H58I) possessed high thermostability. In addition, thermodynamic parameters of amylolytic reaction exhibited an increase in the activation energy and the entropy of the system. Kinetics of irreversible thermal inactivation suggests that the activation energy increased by 1.4-fold in the most stable variant.

alpha-Amylase: an ideal representative of thermostable enzymes

The conditions prevailing in the industrial applications in which enzymes are used are rather extreme, especially with respect to temperature and pH. Therefore, there is a continuing demand to improve the stability of enzymes and to meet the requirements set by specific applications. In this respect, thermostable enzymes have been proposed to be industrially relevant. In this review, alpha-amylase, a well-established representative of thermostable enzymes, providing an attractive model for the investigation of the structural basis of thermostability of proteins, has been discussed.

Study of the inhibition of α-amylase by the benzo[c]phenanthridine alkaloids sanguinarine and chelerythrine

Inhibition of porcine pancreas and human saliva alpha-amylase (EC 3.2.1.1) by sanguinarine and chelerythrine was studied. The inhibition of alpha-amylase was assayed using a biosensor method which utilises a flow system equipped with a peroxide electrode. 250 microM sanguinarine and 250 microM chelerythrine cause complete inhibition of 1.9 nkat alpha-amylase from porcine pancreas. The same concentration of sanguinarine and chelerythrine caused 23.9% and 7.5% inhibition, respectively, of 1.9 nkat alpha-amylase from human saliva. Mixed type and partially reversible inhibition was found for both alpha-amylases treated with either alkaloid.

Trehalose synthase converts glycogen to trehalose

Trehalose (alpha,alpha-1,1-glucosyl-glucose) is essential for the growth of mycobacteria, and these organisms have three different pathways that can produce trehalose. One pathway involves the enzyme described in the present study, trehalose synthase (TreS), which interconverts trehalose and maltose. We show that TreS from Mycobacterium smegmatis, as well as recombinant TreS produced in Escherichia coli, has amylase activity in addition to the maltose <--> trehalose interconverting activity (referred to as MTase). Both activities were present in the enzyme purified to apparent homogeneity from extracts of Mycobacterium smegmatis, and also in the recombinant enzyme produced in E. coli from either the M. smegmatis or the Mycobacterium tuberculosis gene. Furthermore, when either purified or recombinant TreS was chromatographed on a Sephacryl S-200 column, both MTase and amylase activities were present in the same fractions across the peak, and the ratio of these two activities remained constant in these fractions. In addition, crystals of TreS also contained both amylase and MTase activities. TreS produced both radioactive maltose and radioactive trehalose when incubated with [(3)H]glycogen, and also converted maltooligosaccharides, such as maltoheptaose, to both maltose and trehalose. The amylase activity was stimulated by addition of Ca(2+), but this cation inhibited the MTase activity. In addition, MTase activity, but not amylase activity, was strongly inhibited, and in a competitive manner, by validoxylamine. On the other hand, amylase, but not MTase activity, was inhibited by the known transition-state amylase inhibitor, acarbose, suggesting the possibility of two different active sites. Our data suggest that TreS represents another pathway for the production of trehalose from glycogen, involving maltose as an intermediate. In addition, the wild-type organism or mutants blocked in other trehalose biosynthetic pathways, but still having active TreS, accumulate 10- to 20-fold more glycogen when grown in high concentrations (> or = 2% or more) of trehalose, but not in glucose or other sugars. Furthermore, trehalose mutants that are missing TreS do not accumulate glycogen in high concentrations of trehalose or other sugars. These data indicate that trehalose and TreS are both involved in the production of glycogen, and that the metabolism of trehalose and glycogen is interconnected.