Purification and characterization of five alkaline, thermotolerant, and maltotetraose-producing α-amylases from Bacillus halodurans MS-2-5, and production of recombinant enzymes in Escherichia coli

Propitious catalytic response of immobilized α-amylase from G. thermoleovorans in modified APTES-Fe3O4 NPs for industrial bio-processing

Challenges in enzyme and product recovery are currently intriguing in modern biotechnology. Coping enzyme stability, shelf life and efficiency, nanomaterials-based immobilization were epitomized of industrial practice. Herein, a α-amylase from Geobacillus thermoleovorans was purified and bound effectively on to a modified 3-Aminopropyltriethoxysilane (APTES)-Fe3O4 nanoparticle. It was revealed that the carrier-bound enzyme catalysis (pH 8 and 60 °C) was significant in contrast to the free enzyme (pH 7.5 and 55 °C). Furthermore, Zn2+ and Cu2+ were shown to cause inhibitory effects in both enzyme states. Unlike chloroform, toluene, benzene, and butanol, minimal effects were observed with ethanol, acetone, and hexane. The bound enzyme retained 27.4 % of its initial activity after being stored for 36 days. In addition, the reusability of the bound enzyme showed a gradual decline in activity after the first cycle; however, after 13 cycles, its residual activity at 53 % was observed. These data proved significant enough to use this enzyme for industrial starch and analogous substrate bio-processing.

High-Level Expression and Biochemical Characterization of a Maltotetraose Amylase in Pichia pastoris X-33 for Maltotetraose Production

Maltotetraose amylase, which catalyzes the hydrolysis of amylaceous polysaccharides into maltooligosaccharides with maltotetraose as the main product, is extensively used in the food industry. However, the lack of efficient expression system for maltotetraose amylase has hampered its production and application. In this study, high-level production of a maltotetraose amylase mutant (referred to as Pp-Mta∆CBM) from Pseudomonas saccharophila was achieved in Pichia pastoris X-33. First, the gene of maltotetraose amylase with the carbohydrate-binding module (CBM) removed was codon-optimized and cloned into the pPICZαA vector, followed by transformation into P. pastoris X-33 for expression. Using the promoter PAOX1 and signal peptide α-factor, high-level production of Pp-Mta∆CBM with minimal extracellular impurity proteins was achieved, resulting in an extracellular activity of 367.9 U/mL after 7 days of cultivation in shake flasks. Next, the expressed Pp-Mta∆CBM was purified and characterized. This recombinant enzyme was glycosylated and has maximum activity at 55 ℃ and pH 7.0. Its Km for soluble starch was 4.1 g/L, and its kcat was 3237.6 s-1. Finally, the Pp-Mta∆CBM was found to produce a maximum maltotetraose yield of 57.1% in the presence of 200 g/L of substrate. The findings presented in this study demonstrate the efficient production of Pp-Mta∆CBM in P. pastoris, providing a new expression system for maltotetraose amylase and laying the foundation for its scale-up production and industrial application.

Heterologous Expression and Characterization of a Novel Mesophilic Maltogenic α-Amylase AmyFlA from Flavobacterium sp. NAU1659

A novel amylase AmyFlA from Flavobacterium sp. NAU1659, AmyFlA, was cloned and expressed in Esherichia coli. Based on phylogenetic and functional analysis, it was identified as a novel member of the subfamily GH13_46, sharing high sequence identity. The protein was predicted to consist of 620 amino acids, with a putative signal peptide of 25 amino acids. The enzyme was able to hydrolyze soluble starch with a specific activity of 352.97 U/mg at 50 °C in 50 mM phosphate buffer (pH 6.0). The Km and Vmax values of AmyFlA were respectively 3.15 mg/ml and 566.36 µmol·ml-1·min-1 under optimal conditions. Its activity towards starch was enhanced by 63% in the presence of 1 mM Ca2+, indicating that AmyFlA was a Ca2+-dependent amylase. Compared to the reported maltogenic amylases, AmyFlA produced a lower variety of intermediate oligosaccharides at the start of the reaction so that the product mixture contained a higher proportion of maltose. These results indicate that AmyFlA may be potential application value in the production of high-maltose syrup.

Maltooligosaccharides: Properties, Production and Applications

Maltooligosaccharides (MOS) are homooligosaccharides that consist of 3-10 glucose molecules linked by α-1,4 glycosidic bonds. As they have physiological functions, they are commonly used as ingredients in nutritional products and functional foods. Many researchers have investigated the potential applications of MOS and their derivatives in the pharmaceutical industry. In this review, we summarized the properties and methods of fabricating MOS and their derivatives, including sulfated and non-sulfated alkylMOS. For preparing MOS, different enzymatic strategies have been proposed by various researchers, using α-amylases, maltooligosaccharide-forming amylases, or glycosyltransferases as effective biocatalysts. Many researchers have focused on using immobilized biocatalysts and downstream processes for MOS production. This review also provides an overview of the current challenges and future trends of MOS production.

A novel low temperature active maltooligosaccharides-forming amylase from Bacillus koreensis HL12 as biocatalyst for maltooligosaccharide production

Maltooligosaccharide-forming amylases (MFAses) are promising enzymes for a variety of industrial applications. In this study, a maltooligosaccharide-forming amylase (BkAmy) isolated from Bacillus koreensis HL12 was first heterologous expressed and characterized. According to structural-sequence alignment, BkAmy contained seven conserved regions which are the signature of a novel GH13 subfamily. The gene was expressed in Pichia pastoris KM71 as an extracellular protein with a volumetric activity of 3.38 U/mL culture medium after 72 h induction by 3% (w/v) of methanol. The recombinant BkAmy migrated as a single protein band with an expected size approximately of 55 kDa. BkAmy exhibited the highest catalytic activity on soluble starch with a specific activity of 42.2 U/mg at 40 °C, pH 7.0. The enzyme exhibited 65% relative activity at 30 °C, indicating its advantage on application at moderate reaction temperature desirable for energy saving and reduction of side unwanted reactions. The enzyme exhibited a specific cleavage pattern by releasing maltose (G2), maltotriose (G3) and maltotetraose (G4) from cassava starch with the highest yield of 363 mg/g substrate equivalent to 36% conversion using 40 U/g substrate at 60 min. The work demonstrates the potential of this enzyme on maltooligosaccharide production from starch to create high value-added products in starch processing industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03188-1.

Production, purification and applications of raw starch degrading and calcium-independent α-amylase from soil rich in extremophile

Calcium independent, raw starch hydrolyzing, acidic α-amylase (66 kDa) was synthesized by Bacillus subtilis S113 that is an aerobic, rod-shaped and Gram +ve bacteria. Purification of the enzyme was performed by HiTrap Capto Q (Ion-exchange chromatography; 19.28 fold; 22.41% yield). The purified enzyme was found stable at broad acidic pH (4-6.5) and high-temperature range (40-80 °C), that fulfilled the necessary criteria and laid the foundation to be utilized in starch saccharification industry. Kinetic studies of the enzyme revealed that K_m and V_max of the enzyme was 0.22% and 357.14 U/mg respectively. Scanning electron microscopy studies showed that the enzyme was capable of completely hydrolyzing raw wheat and potato starch, further confirming its role in the starch industry. It was found that only 7.93% of the activity was loss at 4 °C when kept for one year.

Recombinant expression, characterization and application of maltotetraohydrolase from Pseudomonas saccharophila

BACKGROUND

Maltotetraohydrolase, widely used in food and medical fields, possesses the ability to hydrolyze starch to produce maltooligosaccharides with maltotetraose as the main product. It also has the potential usage in delaying bread aging.

RESULTS

Pseudomonas saccharophila maltotetraohydrolase was expressed in Bacillus subtilis WS11. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed obvious bands at 57 kDa (maltotetraohydrolase I) and 47 kDa (maltotetraohydrolase II). Both showed similar enzymatic properties, although the catalytic efficiency of maltotetraohydrolase I was 4.93 fold higher than that of maltotetraohydrolase II using soluble starch as substrate. In addition, the maltotetraohydrolase production was further scaled up in a 3-L fermentor, and the highest activity reached 1907 U mL^-1 . Then, the recombinant maltotetraohydrolase was used to produce maltotetraose. The maltotetraose yields catalyzed by maltotetraohydrolase I and II reached 73.2% and 69.7%, respectively. Finally, when recombinant maltotetraohydrolase was used in bread-making, texture profile analysis of the bread indicated recombinant maltotetraohydrolase I exhibited a significant anti-aging effect.

CONCLUSION

This is the first describing high-efficient expression of P. saccharophila maltotetraohydrolase in the food safety strain B. subtilis, and the yield represented the highest level ever reported. Excellent results were also obtained with respect to the preparation of maltotetraose and delaying bread aging using the recombinant maltotetraohydrolase. The present study will help lay the foundation for the industrial production and application of maltotetraohydrolase. © 2020 Society of Chemical Industry.

Low molecular weight alkaline thermostable α-amylase from Geobacillus sp. nov

Industrial demands for enzymes that are stable in a broad range of conditions are increasing. Such enzymes, one of which is α-amylase, could be produced by extremophiles. This study reports a thermostable α-amylase produced by a newly isolated Geobacillus sp. nov. from a geothermal area. The phylogenetic analysis of the 16S rRNA gene showed that the isolate formed a separate branch with 95% homology to Geobacillus sp. After precipitation using ammonium sulphate followed by ion-exchange chromatography, the enzyme produced a specific activity of 25.1 (U/mg) with a purity of 6.5-fold of the crude extract. The molecular weight of the enzyme was approximately 12.2 kDa. The optimum activity was observed at 75 °C and pH 8. The activity increased in the presence of Ba²⁺ and Fe²⁺ but decreased in the presence of K⁺ and Mg²⁺. Ca²⁺ and Mn²⁺ increased the activity slightly. The activity completely diminished with the addition of Cu²⁺. EDTA and PMSF also sharply reduced enzyme activity. Although the stability was moderate, the low molecular weight could be an important feature for its future applications.

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).

Significantly enhancing recombinant alkaline amylase production in Bacillus subtilis by integration of a novel mutagenesis-screening strategy with systems-level fermentation optimization

Background

Alkaline amylase has significant potential for applications in the textile, paper and detergent industries, however, low yield of which cannot meet the requirement of industrial application. In this work, a novel ARTP mutagenesis-screening method and fermentation optimization strategies were used to significantly improve the expression level of recombinant alkaline amylase in B. subtilis 168.

Results

The activity of alkaline amylase in mutant B. subtilis 168 mut-16# strain was 1.34-fold greater than that in the wild-type, and the highest specific production rate was improved from 1.31 U/(mg·h) in the wild-type strain to 1.57 U/(mg·h) in the mutant strain. Meanwhile, the growth of B. subtilis was significantly enhanced by ARTP mutagenesis. When the agitation speed was 550 rpm, the highest activity of recombinant alkaline amylase was 1.16- and 1.25-fold of the activities at 450 and 650 rpm, respectively. When the concentration of soluble starch and soy peptone in the initial fermentation medium was doubled, alkaline amylase activity was increased 1.29-fold. Feeding hydrolyzed starch and soy peptone mixture or glucose significantly improved cell growth, but inhibited the alkaline amylase production in B. subtilis 168 mut-16#. The highest alkaline amylase activity by feeding hydrolyzed starch reached 591.4 U/mL, which was 1.51-fold the activity by feeding hydrolyzed starch and soy peptone mixture. Single pulse feeding-based batch feeding at 10 h favored the production of alkaline amylase in B. subtilis 168 mut-16#.

Conclusion

The results indicated that this novel ARTP mutagenesis-screening method could significantly improve the yield of recombinant proteins in B. subtilis. Meanwhile, fermentation optimization strategies efficiently promoted expression of recombinant alkaline amylase in B. subtilis 168 mut-16#. These findings have great potential for facilitating the industrial-scale production of alkaline amylase and other enzymes, using B. subtilis cultures as microbial cell factories.

Bacterial and Archaeal α-Amylases: Diversity and Amelioration of the Desirable Characteristics for Industrial Applications

Industrial enzyme market has been projected to reach US$ 6.2 billion by 2020. Major reasons for continuous rise in the global sales of microbial enzymes are because of increase in the demand for consumer goods and biofuels. Among major industrial enzymes that find applications in baking, alcohol, detergent, and textile industries are α-amylases. These are produced by a variety of microbes, which randomly cleave α-1,4-glycosidic linkages in starch leading to the formation of limit dextrins. α-Amylases from different microbial sources vary in their properties, thus, suit specific applications. This review focuses on the native and recombinant α-amylases from bacteria and archaea, their production and the advancements in the molecular biology, protein engineering and structural studies, which aid in ameliorating their properties to suit the targeted industrial applications.

Aspergillus Oryzae S2 α-Amylase Domain C Involvement in Activity and Specificity: In Vivo Proteolysis, Molecular and Docking Studies

We previously reported that Aspergillus oryzae strain S2 had produced two α-amylase isoforms named AmyA and AmyB. The apparent molecular masses revealed by SDS-PAGE were 50 and 42 kDa, respectively. Yet AmyB has a higher catalytic efficiency. Based on a monitoring study of the α-amylase production in both the presence and absence of different protease inhibitors, a chymotrypsin proteolysis process was detected in vivo generating AmyB. A. oryzae S2 α-amylase gene was amplified, cloned and sequenced. The sequence analysis revealed nine exons, eight introns and an encoding open reading frame of 1500 bp corresponding to AmyA isoform. The amino-acid sequence analysis revealed aY371 potential chymotrypsin cleaving site, likely to be the AmyB C-Terminal end and two other potential sites at Y359, and F379. A zymogram with a high acrylamide concentration was used. It highlighted two other closed apparent molecular mass α-amylases termed AmyB1 and AmyB2 reaching40 kDa and 43 kDa. These isoforms could be possibly generated fromY359, and F379secondary cut, respectively. The molecular modeling study showed that AmyB preserved the (β/α)8 barrel domain and the domain B but lacked the C-terminal domain C. The contact map analysis and the docking studies strongly suggested a higher activity and substrate binding affinity for AmyB than AmyA which was previously experimentally exhibited. This could be explained by the easy catalytic cleft accessibility.

Aspergillus oryzae S2 alpha-amylase production under solid state fermentation: optimization of culture conditions

Aspergillus oryzae S2 was assayed for alpha-amylase production under solid state fermentation (SSF). In addition to AmyA and AmyB already produced in monitored submerged culture, the strain was noted to produce new AmyB oligomeric forms, in particular a dominant tetrameric form named AmyC. The latter was purified to homogeneity through fractional acetone precipitation and size exclusion chromatography. SDS-PAGE and native PAGE analyses revealed that, purified AmyC was an approximately 172 kDa tetramer of four 42 kDa subunits. AmyC was also noted to display the same NH2-terminal amino acid sequence residues and approximately the same physico-chemical properties of AmyA and AmyB, to exhibit maximum activity at pH 5.6 and 60 °C, and to produce maltose and maltotriose as major starch hydrolysis end-products. Soyabean meal was the best substitute to yeast extract compared to fish powder waste and wheat gluten waste. AmyC production was optimized under SSF using statistical design methodology. Moisture content of 76.25%, C/N substrate ratio of 0.62, and inoculum size of 10(6.87) spores allowed maximum activity of 22118.34 U/g of dried substrate, which was 33 times higher than the one obtained before the application of the central composite design (CCD).

Production and biochemical characterization of a high maltotetraose (G4) producing amylase from Pseudomonas stutzeri AS22

Amylase production and biochemical characterization of the crude enzyme preparation from Pseudomonas stutzeri AS22 were evaluated. The highest α-amylase production was achieved after 24 hours of incubation in a culture medium containing 10 g/L potato starch and 5 g/L yeast extract, with initial pH 8.0 at 30°C under continuous agitation at 200 rpm. The optimum temperature and pH for the crude α -amylase activity were 60°C and 8.0, respectively. The effect of different salts was evaluated and it was found that both α -amylase production and activity were Ca(2+)-dependent. The amylolytic preparation was found to catalyze exceptionally the formation of very high levels of maltotetraose from starch (98%, w/w) in the complete absence of glucose since the initial stages of starch hydrolysis (15 min) and hence would have a potential application in the manufacturing of maltotetraose syrups.

Structure-based engineering of alkaline α-amylase from alkaliphilic Alkalimonas amylolytica for improved thermostability

This study aimed to improve the thermostability of alkaline α-amylase from Alkalimonas amylolytica through structure-based rational design and systems engineering of its catalytic domain. Separate engineering strategies were used to increase alkaline α-amylase thermostability: (1) replace histidine residues with leucine to stabilize the least similar region in domain B, (2) change residues (glycine, proline, and glutamine) to stabilize the highly conserved α-helices in domain A, and (3) decrease the free energy of folding predicted by the PoPMuSiC program to stabilize the overall protein structure. A total of 15 single-site mutants were obtained, and four mutants - H209L, Q226V, N302W, and P477V - showed enhanced thermostability. Combinational mutations were subsequently introduced, and the best mutant was triple mutant H209L/Q226V/P477V. Its half-life at 60 °C was 3.8-fold of that of the wild type and displayed a 3.2 °C increase in melting temperature compared with that of the wild type. Interestingly, other biochemical properties of this mutant also improved: the optimum temperature increased from 50 °C to 55 °C, the optimum pH shifted from 9.5 to 10.0, the stable pH range expanded from 7.0-11.0 to 6.0-12.0, the specific activity increased by 24 %, and the catalytic efficiency (k cat/K m) increased from 1.8×10(4) to 3.5 × 10(4) l/(g min). Finally, the mechanisms responsible for the increased thermostability were analyzed through comparative analysis of structure models. The structure-based rational design and systems engineering strategies in this study may also improve the thermostability of other industrial enzymes.

In silico rational design and systems engineering of disulfide bridges in the catalytic domain of an alkaline α-amylase from Alkalimonas amylolytica to improve thermostability

High thermostability is required for alkaline α-amylases to maintain high catalytic activity under the harsh conditions used in textile production. In this study, we attempted to improve the thermostability of an alkaline α-amylase from Alkalimonas amylolytica through in silico rational design and systems engineering of disulfide bridges in the catalytic domain. Specifically, 7 residue pairs (P35-G426, Q107-G167, G116-Q120, A147-W160, G233-V265, A332-G370, and R436-M480) were chosen as engineering targets for disulfide bridge formation, and the respective residues were replaced with cysteines. Three single disulfide bridge mutants-P35C-G426C, G116C-Q120C, and R436C-M480C-of the 7 showed significantly enhanced thermostability. Combinational mutations were subsequently assessed, and the triple mutant P35C-G426C/G116C-Q120C/R436C-M480C showed a 6-fold increase in half-life at 60°C and a 5.2°C increase in melting temperature compared with the wild-type enzyme. Interestingly, other biochemical properties of this mutant also improved: the optimum temperature increased from 50°C to 55°C, the optimum pH shifted from 9.5 to 10.0, the stable pH range extended from 7.0 to 11.0 to 6.0 to 12.0, and the catalytic efficiency (kcat/Km) increased from 1.8 × 10(4) to 2.4 × 10(4) liters/g · min. The possible mechanism responsible for these improvements was explored through comparative analysis of the model structures of wild-type and mutant enzymes. The disulfide bridge engineering strategy used in this work may be applied to improve the thermostability of other industrial enzymes.

Structure-guided systems-level engineering of oxidation-prone methionine residues in catalytic domain of an alkaline α-amylase from Alkalimonas amylolytica for significant improvement of both oxidative stability and catalytic efficiency

High oxidative stability and catalytic efficiency are required for the alkaline α-amylases to keep the enzymatic performance under the harsh conditions in detergent industries. In this work, we attempted to significantly improve both the oxidative stability and catalytic efficiency of an alkaline α-amylase from Alkalimonas amylolytica by engineering the five oxidation-prone methionine residues around the catalytic domain via a systematic approach. Specifically, based on the tertiary structure analysis, five methionines (Met 145, Met 214, Met 229, Met 247 and Met 317) were individually substituted with oxidation-resistant threonine, isoleucine and alaline, respectively. Among the created 15 mutants, 7 mutants M145A, M145I, M214A, M229A, M229T, M247T and M317I showed significantly enhanced oxidative stability or catalytic efficiency. In previous work, we found that the replacement of M247 with leucine could significantly improve the oxidative stability. Thus, these 8 positive mutants (M145A, M145I, M214A, M229A, M229T, M247T, M247L and M317I) were used to conduct the second round of combinational mutations. Among the constructed 85 mutants (25 two-point mutants, 36 three-point mutants, 16 four-point mutants and 8 five-point mutants), the mutant M145I-214A-229T-247T-317I showed a 5.4-fold increase in oxidative stability and a 3.0-fold increase in catalytic efficiency. Interestingly, the specific activity, alkaline stability and thermal stability of this mutant were also increased. The increase of salt bridge and hydrogen bonds around the catalytic domain contributed to the significantly improved catalytic efficiency and stability, as revealed by the three-dimensional structure model of wild-type alkaline α-amylase and its mutant M145I-214A-229T-247T-317I. With the significantly improved oxidative stability and catalytic efficiency, the mutant M145I-214A-229T-247T-317I has a great potential as a detergent additive, and this structure-guided systems engineering strategy may be useful for the protein engineering of the other microbial enzymes to fulfill industrial requirements.

Fusion of an oligopeptide to the N terminus of an alkaline α-amylase from Alkalimonas amylolytica simultaneously improves the enzyme's catalytic efficiency, thermal stability, and resistance to oxidation

In this study, we constructed and expressed six fusion proteins composed of oligopeptides attached to the N terminus of the alkaline α-amylase (AmyK) from Alkalimonas amylolytica. The oligopeptides had various effects on the functional and structural characteristics of AmyK. AmyK-p1, the fusion protein containing peptide 1 (AEAEAKAKAEAEAKAK), exhibited improved specific activity, catalytic efficiency, alkaline stability, thermal stability, and oxidative stability compared with AmyK. Compared with AmyK, the specific activity and catalytic constant (kcat) of AmyK-p1 were increased by 4.1-fold and 3.5-fold, respectively. The following properties were also improved in AmyK-p1 compared with AmyK: kcat/Km increased from 1.8 liter/(g·min) to 9.7 liter/(g·min), stable pH range was extended from 7.0 to 11.0 to 7.0 to 12.0, optimal temperature increased from 50°C to 55°C, and the half-life at 60°C increased by ∼2-fold. Moreover, AmyK-p1 showed improved resistance to oxidation and retained 54% of its activity after incubation with H2O2, compared with 20% activity retained by AmyK. Finally, AmyK-p1 was more compatible than AmyK with the commercial solid detergents tested. The mechanisms responsible for these changes were analyzed by comparing the three-dimensional (3-D) structural models of AmyK and AmyK-p1. The significantly enhanced catalytic efficiency and stability of AmyK-p1 suggests its potential as a detergent ingredient. In addition, the oligopeptide fusion strategy described here may be useful for improving the catalytic efficiency and stability of other industrial enzymes.

Comparative analysis of heterologous expression, biochemical characterization optimal production of an alkaline α-amylase from alkaliphilic Alkalimonas amylolytica in Escherichia coli and Pichia pastoris

An alkaline α-amylase gene from alkaliphilic Alkalimonas amylolytica was synthesized based on the preferred codon usage of Escherichia coli and Pichia pastoris, respectively, and then was expressed in the according heterologous host, E. coli BL21 (DE3) and P. pastoris GS115. The alkaline α-amylase expressed in E. coli was designated AmyA, whereas that produced by P. pastoris was designated AmyB. The specific activity of AmyA and AmyB was 16.0 and 16.6 U/mg at pH 9.5 and 50°C, respectively. The optimal pH and pH stability of AmyA and AmyB were similar, whereas the optimum temperature and thermal stability of AmyB were slightly enhanced compared with those of AmyA. The AmyA and AmyB had a similar melting temperature of 64°C and the same catalytic efficiency (k(cat) /K(m) ) of 2.0 × 10(6) L/(mol min). AmyA and AmyB were slightly activated by 1 mM Co(2+) , Ca(2+) , or Na(+) , but inhibited by all other metal ions (K(+) , Mg(2+) , Fe(3+) , Fe(2+) , Zn(2+) , Mn(2+) , and Cu(2+) ). Tween 80 or Tween 60 (10% (w/v)) had little influence on the stability of AmyA and AmyB, while the 10% (w/v) sodium dodecyl sulfate caused the complete loss of AmyA and AmyB activities. The AmyA and AmyB were stable in the presence of solid detergents (washing powder), while were less stable in liquid detergents. Under the optimal conditions in 3-L bioreactor, the extracellular AmyB activity reached 600 U/mL, which was about 10 times as that of AmyA. These results indicated that P. pastoris was a preferable host for alkaline α-amylase expression and the produced alkaline α-amylase had a certain application potential in solid detergents.

Structure-based engineering of methionine residues in the catalytic cores of alkaline amylase from Alkalimonas amylolytica for improved oxidative stability

This work aims to improve the oxidative stability of alkaline amylase from Alkalimonas amylolytica through structure-based site-directed mutagenesis. Based on an analysis of the tertiary structure, five methionines (Met 145, Met 214, Met 229, Met 247, and Met 317) were selected as the mutation sites and individually replaced with leucine. In the presence of 500 mM H(2)O(2) at 35°C for 5 h, the wild-type enzyme and the M145L, M214L, M229L, M247L, and M317L mutants retained 10%, 28%, 46%, 28%, 72%, and 43% of the original activity, respectively. Concomitantly, the alkaline stability, thermal stability, and catalytic efficiency of the M247L mutant were also improved. The pH stability of the mutants (M145L, M214L, M229L, and M317L) remained unchanged compared to that of the wild-type enzyme, while the stable pH range of the M247L mutant was extended from pH 7.0 to 11.0 for the wild type to pH 6.0 to 12.0 for the mutant. The wild-type enzyme lost its activity after incubation at 50°C for 2 h, and the M145L, M214L, M229L, and M317L mutants retained less than 14% of the activity, whereas the M247L mutant retained 34% of the activity under the same conditions. Compared to the wild-type enzyme, the k(cat) values of the M145L, M214L, M229L, and M317L mutants decreased, while that of the M247L mutant increased slightly from 5.0 × 10(4) to 5.6 × 10(4) min(-1). The mechanism responsible for the increased oxidative stability, alkaline stability, thermal stability, and catalytic efficiency of the M247L mutant was further analyzed with a structure model. The combinational mutants were also constructed, and their biochemical properties were characterized. The resistance of the wild-type enzyme and the mutants to surfactants and detergents was also investigated. Our results indicate that the M247L mutant has great potential in the detergent and textile industries.

Cloning and characterization of two new thermostable and alkalitolerant α-amylases from the Anoxybacillus species that produce high levels of maltose

Two genes that encode α-amylases from two Anoxybacillus species were cloned and expressed in Escherichia coli. The genes are 1,518 bp long and encode 506 amino acids. Both sequences are 98% similar but are distinct from other well-known α-amylases. Both of the recombinant enzymes, ASKA and ADTA, were purified using an α-CD-Sepharose column. They exhibited an optimum activity at 60°C and pH 8. Both amylases were stable at pH 6-10. At 60°C in the absence of Ca²⁺, negligible reduction in activity for up to 48 h was observed. The activity half-life at 65°C was 48 and 3 h for ASKA and ADTA, respectively. In the presence of Ca²⁺ ions, both amylases were highly stable for at least 48 h and had less than a 10% decrease in activity at 70°C. Both enzymes exhibited similar end-product profiles, and the predominant yield was maltose (69%) from starch hydrolysis. To the best of our knowledge, most α-amylases that produce high levels of maltose are active at an acidic to neutral pH. This is the first report of two thermostable, alkalitolerant recombinant α-amylases from Anoxybacillus that produce high levels of maltose and have an atypical protein sequence compared with known α-amylases.

Heterologous expression, biochemical characterization, and overproduction of alkaline α-amylase from Bacillus alcalophilus in Bacillus subtilis

BACKGROUND

Alkaline α-amylases have potential applications for hydrolyzing starch under high pH conditions in the starch and textile industries and as ingredients in detergents for automatic dishwashers and laundries. While the alkaline α-amylase gains increased industrial interest, the yield of alkaline α-amylases from wild-type microbes is low, and the combination of genetic engineering and process optimization is necessary to achieve the overproduction of alkaline α-amylase.

RESULTS

The alkaline α-amylase gene from Bacillus alcalophilus JN21 (CCTCC NO. M 2011229) was cloned and expressed in Bacillus subtilis strain WB600 with vector pMA5. The recombinant alkaline α-amylase was stable at pH from 7.0 to 11.0 and temperature below 40°C. The optimum pH and temperature of alkaline α-amylase was 9.0 and 50°C, respectively. Using soluble starch as the substrate, the Km and Vmax of alkaline α-amylase were 9.64 g/L and 0.80 g/(L·min), respectively. The effects of medium compositions (starch, peptone, and soybean meal) and temperature on the recombinant production of alkaline α-amylase in B. subtilis were investigated. Under the optimal conditions (starch concentration 0.6% (w/v), peptone concentration 1.45% (w/v), soybean meal concentration 1.3% (w/v), and temperature 37°C), the highest yield of alkaline α-amylase reached 415 U/mL. The yield of alkaline α-amylase in a 3-L fermentor reached 441 U/mL, which was 79 times that of native alkaline α-amylase from B. alcalophilus JN21.

CONCLUSIONS

This is the first report concerning the heterologous expression of alkaline α-amylase in B. subtilis, and the obtained results make it feasible to achieve the industrial production of alkaline α-amylase with the recombinant B. subtilis.