Jarunee Kaulpiboon

Purification and Characterization of Two Alkaline, Thermotolerant α-Amylases from Bacillus halodurans 38C-2-1 and Expression of the Cloned Gene in Escherichia coli

A newly isolated strain, 38C-2-1, produced alkaline and thermotolerant α-amylases and was identified as Bacillus halodurans. The enzymes were purified to homogeneity and named α-amylase I and II. These showed molecular masses of 105 and 75 kDa respectively and showed maximal activities at 50–60 °C and pH 10–11, and 42 and 38% relative activities at 30 °C. These results indicate that the enzymes are thermotolerant. The enzyme activity was not inhibited by a surfactant or a bleaching reagent used in detergents. A gene encoding α-amylase I was cloned and named amyI. Production of AmyI with a signal peptide repressed the growth of an Escherichia coli transformant. When enzyme production was induced by the addition of isopropyl β-D(−)-thiogalactopyranoside in the late exponential growth phase, the highest enzyme yield was observed. It was 45-fold that of the parent strain 38C-2-1.

Altered Large-Ring Cyclodextrin Product Profile Due to a Mutation at Tyr-172 in the Amylomaltase of Corynebacterium glutamicum

ABSTRACT Corynebacterium glutamicum amylomaltase (CgAM) catalyzes the formation of large-ring cyclodextrins (LR-CDs) with a degree of polymerization of 19 and higher. The cloned CgAM gene was ligated into the pET-17b vector and used to transform Escherichia coli BL21(DE3). Site-directed mutagenesis of Tyr-172 in CgAM to alanine (Y172A) was performed to determine its role in the control of LR-CD production. Both the recombinant wild-type (WT) and Y172A enzymes were purified to apparent homogeneity and characterized. The Y172A enzyme exhibited lower disproportionation, cyclization, and hydrolysis activities than the WT. The k cat/Km of the disproportionation reaction of the Y172A enzyme was 2.8-fold lower than that of the WT enzyme. The LR-CD product profile from enzyme catalysis depended on the incubation time and the enzyme concentration. Interestingly, the Y172A enzyme showed a product pattern different from that of the WT CgAM at a long incubation time. The principal LR-CD products of the Y172A mutated enzyme were a cycloamylose mixture with a degree of polymerization of 28 or 29 (CD28 or CD29), while the principal LR-CD product of the WT enzyme was CD25 at 0.05 U of amylomaltase. These results suggest that Tyr-172 plays an important role in determining the LR-CD product profile of this novel CgAM.

Production of long-chain isomaltooligosaccharides from maltotriose using the thermostable amylomaltase and transglucosidase enzymes

Amylomaltase and transglucosidase were combined to produce long-chain isomaltooligosaccharides (IMOs). IMOs are effective prebiotics that stimulate the growth of healthy bacteria in human intestines and thus promote better overall health. In this study, the p17bAMY amylomaltase was expressed from its gene, which had been directly isolated from soil samples, while transglucosidase was purchased and purified by a gel-filtration column. Crude amylomaltase was purified by heat treatment, Q-, and phenyl-sepharose column. The purified amylomaltase had a molecular weight of 57 kDa. Specificity on the substrates of the amylomaltase was also studied and it was found that this enzyme was able to catalyze transglucosylation activity using substrates G2 to G7. However, G3 was the most preferred substrate for the enzyme. Here, Km-G3 and kcat/Km were 23 mM and 1.72 × 108 mM/min, respectively. Amylomaltase and transglucosidase were tested both alone and in combination on a G3 substrate to study the efficient process for the IMOs production. The obtained products from the enzymatic reactions were monitored using the TLC analytical method and a densitometer. The amylomaltase led to products containing linear maltooligosaccharides, while the transglucosidase produced short-chain IMOs. Interestingly, when amylomaltase and transglucosidase were used in combination, long-chain IMOs with sizes larger than IMO4 were observed under the determined condition.

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.

Altered product specificity of a cyclodextrin glycosyltransferase by molecular imprinting with cyclomaltododecaose.

Cyclodextrin glycosyltransferases (CGTases), members of glycoside hydrolase family 13, catalyze the conversion of amylose to cyclodextrins (CDs), circular α‐(1,4)‐linked glucopyranose oligosaccharides of different ring sizes. The CD containing 12 α‐D‐glucopyranose residues was preferentially synthesized by molecular imprinting of CGTase from Paenibacillus sp. A11 with cyclomaltododecaose (CD12) as the template molecule. The imprinted CGTase was stabilized by cross‐linking of the derivatized protein. A high proportion of CD12 and larger CDs was obtained with the imprinted enzyme in an aqueous medium. The molecular imprinted CGTase showed an increased catalytic efficiency of the CD12‐forming cyclization reaction, while decreased kcat/Km values of the reverse ring‐opening reaction were observed. The maximum yield of CD12 was obtained when the imprinted CGTase was reacted with amylose at 40°C for 30 min. Molecular imprinting proved to be an effective means toward increase in the yield of large‐ring CDs of a specific size in the biocatalytic production of these interesting novel host compounds for molecular encapsulations. Copyright

Expression and characterization of a fusion protein-containing cyclodextrin glycosyltransferase from Paenibacillus sp. A11.

A recombinant cyclodextrin glycosyltransferase (CGTase) gene fused with thioredoxin (Trx), hexa‐histidine (His6) and S‐protein (S) at the N terminus and a proline‐rich peptide (PRP) at the C terminus, was constructed using the wild‐type gene from Paenibacillus sp. A11, the pET‐32a vector and Escherichia coli BL21(DE3) as the host cell. The expression levels and enzyme characteristics of the Trx‐His6‐CGTase‐PRP fusion protein, the recombinant CGTase without fusion peptides, and the wild‐type CGTase were compared. The maximum specific activity for the Trx‐His6‐CGTase‐PRP fusion enzyme was 2.7 fold higher than that of the non‐fusion form at the optimal IPTG concentration. The Trx‐His6‐CGTase‐PRP fusion protein was purified to homogeneity by starch adsorption and Ni‐NTA affinity chromatography, with a specific activity of 2,268 units/mg protein at a 61% yield. The ease of purification and the higher enzyme yield were obtained with the fusion form when compared to the non‐fusion and wild‐type enzymes. The fusion enzyme was superior than its wild‐type counterpart in terms of stability against high temperature and organic solvents. Moreover, the fusion enzyme could catalyze the synthesis of cyclodextrins in 20% (v/v) dimethylformamide with a higher product yield of CD7 and CD8 compared to that of the wild‐type enzyme in the same buffer‐solvent system. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Molecular imprinting of cyclodextrin glycosyltransferases from Paenibacillus sp. A11 and Bacillus macerans with γ-cyclodextrin

Cyclodextrin glycosyltransferase catalyzes the formation of a mixture of cyclodextrins from starch by an intramolecular transglycosylation reaction. To manipulate the product specificity of the Paenibacillus sp. A11 and Bacillus macerans cyclodextrin glycosyltransferases towards the preferential formation of γ‐cyclodextrin (CD8), crosslinked imprinted proteins of both cyclodextrin glycosyltransferases were prepared by applying enzyme imprinting and immobilization methodologies. The crosslinked imprinted cyclodextrin glycosyltransferases obtained by imprinting with CD8 showed pH and temperature optima similar to those of the native and immobilized cyclodextrin glycosyltransferases. However, the pH and temperature stability of the immobilized and crosslinked imprinted cyclodextrin glycosyltransferases were higher than those of the native cyclodextrin glycosyltransferases. When the catalytic activities of the native, immobilized and crosslinked imprinted cyclodextrin glycosyltransferases were compared, the efficiency of the crosslinked imprinted enzymes for CD8 synthesis was increased 10‐fold, whereas that for cyclodextrin hydrolysis was decreased. Comparison of the product ratios by high‐performance anion exchange chromatography showed that the native cyclodextrin glycosyltransferases from Paenibacillus sp. A11 and Bacillus macerans produced CD6 : CD7 : CD8 : ≥ CD9 ratios of 15 : 65 : 20 : 0 and 43 : 36 : 21 : 0 after 24 h of reaction at 40 °C with starch substrates. In contrast, the crosslinked imprinted cyclodextrin glycosyltransferases from Paenibacillus sp. A11 and Bacillus macerans produced cyclodextrin in ratios of 15 : 20 : 50 : 15 and 17 : 14 : 49 : 20, respectively. The size of the synthesis products formed by the crosslinked imprinted cyclodextrin glycosyltransferases was shifted towards CD8 and ≥ CD9, and the overall cyclodextrin yield was increased by 12% compared to the native enzymes. The crosslinked imprinted cyclodextrin glycosyltransferases also showed higher stability in organic solvents, retaining 85% of their initial activity after five cycles of synthesis reactions.

[Direct cloning of gene encoding a novel amylomaltase from soil bacterial DNA for large-ring cyclodextrin production].

The aim of this study was to isolate a novel amylomaltase gene from community DNA of soil samples collected from Ban Nong Khrok hot spring in Thailand without bacterial cultivation. Using PCR, a 1.5 kb full-length gene was amplified and ligated with pGEM®-T easy vector to transform into Escherichia coli DH5 α for sequencing. The obtained gene encoding an amylomaltase consisted of 1,503 bp that translated into 500 amino acids. Amino acid sequence deduced from this gene was highly homologous with that of amylomaltase from Thermus thermophillus ATCC 33923. In order to express the enzyme, the cloned gene was subcloned into plasmid pET-17b and introduced into E. coli BL21(DE3). The maximum expression was observed when the cloned cells were cultured at 37°C for 6 h with 0.5 mM IPTG induction. By 10% SDS-PAGE, the relative molecular mass of the purified amylomaltase was approximately 58 kDa. This enzyme was optimally active at 70°C and pH 9.0. In addition, the enzyme could hydrolyze pea starch to yield the largering cyclodextrins with degrees of polymerization of 23 and higher. It is noted that CD29 was the product in the largest quantity under all tested conditions.

Enzymatic synthesis of propyl-α-glycosides and their application as emulsifying and antibacterial agents

Alkyl glycosides have been effectively used in many industries because of their biodegradable, emulsification and antibacterial properties. In this study, the alkyl glycoside of propyl glycosides (PGn) was synthesized using β-cyclodextrin (β-CD) and 1-propanol through the transglycosylation reaction of recombinant cyclodextrin glycosyltransferase (CGTase) from the Bacillus circulans A11. The optimal condition for the synthesis of propyl glycosides consisted of an incubation of 1.5% (w/v) β-CD and 500 U/mL of CGTase in a water/propanol content containing 10% (v/v) 1-propanol at pH 6.0, 50°C for 96 h. Upon analysis of the product at the optimal condition by TLC, at least three products which move faster than glucose were observed. These transferred products were formed with molecular weights of 222.1, 384.1 and 546.4 daltons as determined by mass spectrometry analysis; these values were in accordance with propyl glucoside (PG1), propyl maltoside (PG2) and propyl maltotrioside (PG3), respectively. PG1 and PG2 were produced and prepared on a large scale and subsequently purified by preparative TLC. The combined 1H- and 13C-NMR analysis confirmed that the structures of PG1 and PG2 were propyl-α-D-glucopyranoside and propyl-α-D-maltopyranoside, respectively. Both PG1 and PG2 showed emulsification activity and stability in their formation in water and n-hexadecane. Furthermore, the antibacterial activity of both products was determined and it was found that PG2 had a higher antibacterial activity against Staphylococcus aureus and Escherichia coli than that of PG1.

Molecular mutagenesis at Tyr-101 of the amylomaltase transcribed from a gene isolated from soil DNA

The wild-type (WT) amylomaltase gene was directly isolated from soil DNA and cloned into a pET19b vector to express in E. coli BL21(DE3). The ORF of this gene consisted of 1,572 bp, encoding an enzyme of 523 amino acids. Though showing 99% sequence identity to amylomaltse from Thermus thermophilus ATCC 33923, this enzyme is unique in its alkaline optimum pH. In order to alter amylomaltase with less coupling or hydrolytic activity to enhance cycloamylose (CA) formation through cyclization reaction, site-directed mutagenesis of the second glucan binding site involving in CA production was performed at Tyr-101. The result revealed that the mutated Y101S enzyme showed a small increase in cyclization activity while significantly decreased disproportionation, coupling and hydrolytic activities. Mutation also resulted in the change in substrate specificity for disproportionation reaction. The WT enzyme preferred maltotriose, while the activity of mutated enzyme was the highest with maltopentaose substrate. Product analysis by HPAEC-PAD demonstrated that the main CAs of the WT amylomaltase were CA29-CA37. Y101S mutation did not change the product pattern, however, the amount of CAs formed by the mutated enzyme tended to increase especially at long incubation time. The article is published in the original.