Characterization of amylomaltase from Thermus filiformis and the increase in alkaline and thermo-stability by E27R substitution

Identification of crucial amino acid residues involved in large ring cyclodextrin synthesis by amylomaltase from Corynebacterium glutamicum

Amylomaltase can be used to synthesize large ring cyclodextrins (LR-CDs), applied as drug solubilizer, gene delivery vehicle and protein aggregation suppressor. This study aims to determine the functional amino acid positions of Corynebacterium glutamicum amylomaltase (CgAM) involved in LR-CD synthesis by site-directed mutagenesis approach and molecular dynamic simulation. Mutants named Δ167, Y23A, P228Y, E231Y, A413F and G417F were constructed, purified, and characterized. The truncated CgAM, Δ167 exhibited no starch transglycosylation activity, indicating that the N-terminal domain of CgAM is necessary for enzyme activity. The P228Y, A413F and G417F produced larger LR-CDs from CD36-CD40 as compared to CD29 by WT. A413F and G417F mutants produced significantly low LR-CD yield compared to the WT. The A413F mutation affected all tested enzyme activities (starch tranglycosylation, disproportionation and cyclization), while the G417F mutation hindered the cyclization activity. P228Y mutation significantly lowered the k _cat of disproportionation activity, while E231Y mutant exhibited much higher k _cat and K _m values for starch transglycosylation, compared to that of the WT. In addition, Y23A mutation affected the kinetic parameters of starch transglycosylation and cyclization. Molecular dynamic simulation further confirmed these mutations' impacts on the CgAM and LR-CD interactions. Identified functional amino acids for LR-CD synthesis may serve as a model for future modification to improve the properties and yield of LR-CDs.

Production of Large-Ring Cyclodextrins by Amylomaltases

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

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

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

Enhancement of large ring cyclodextrin production using pretreated starch by glycogen debranching enzyme from Corynebacterium glutamicum

Synthesis of large-ring cyclodextrins (LR-CDs) in any significant amount has been challenging. This study enhanced the LR-CDs production by Thermus filiformis amylomaltase (TfAM) enzyme by starch pretreatment using glycogen debranching enzyme from Corynebacterium glutamicum (CgGDE). CgGDE pretreated tapioca starch gave LR-CD conversion of 31.2 ± 2.2%, compared with LR-CDs produced from non-treated tapioca starch (16.0 ± 2.4%). CgGDE pretreatment enhanced amylose content by approximately 30%. Notably, a shorter incubation time of 1 h is sufficient for CgGDE starch pretreatment to produce high LR-CD yield, compared with 6 h required for the commercial isoamylase. High-Performance Anion Exchange Chromatography coupled with Pulsed Amperometric Detection (HPAEC-PAD) and Gel Permeable Chromatography (GPC) revealed that CgGDE is more efficient than the commercial isoamylase in debranching tapioca starch and gave lower molecular weight products. In addition, lower amount of by-products (linear oligosaccharides) were detected in cyclization reaction when using CgGDE-pretreated starch. In conclusion, CgGDE is a highly effective enzyme to promote LR-CD synthesis from starch with a shorter incubation time than the commercial isoamylase.

Amylomaltases in Extremophilic Microorganisms

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

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

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

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

Amylomaltase from Thermus filiformis: expression in Saccharomyces cerevisiae and its use in starch modification

AIM

To express amylomaltase from Thermus filiformis (TfAM) in a generally recognized as safe (GRAS) organism and to use the enzyme in starch modification.

METHODS AND RESULTS

TfAM was expressed in Saccharomyces cerevisiae, using 2% (w/v) galactose inducer under GAL1 promoter. The enzyme was thermostable with high disproportionation and cyclization activities. The main large-ring cyclodextrin (CD) products were CD24-CD29, with CD26 as maximum at all incubation times. TfAM was used to modify cassava and pea starches, the amylose content decreased 18% and 30%, respectively, when 5% (w/v) starch was treated with 0·5 U TfAM g-1 starch. The increase in short branched chain (DP, degree of polymerization, 1-5) and the broader chain length distribution pattern which extended to the longer chain (DP40) after TfAM treatment were observed. The thermal property was changed, with an increase in retrogradation of starch as suggested by a lower enthalpy.

CONCLUSIONS

TfAM was successfully expressed in S. cerevisiae and was used to make starches with new functionality.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the expression of AM in the GRAS yeast and the production of a modified starch gel from pea starch to improve the versatility of starch for food use.

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

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

Improving the thermostability by introduction of arginines on the surface of α-L-rhamnosidase (r-Rha1) from Aspergillus niger

To improve the thermostability of α-L-rhamnosidase (r-Rha1), an enzyme previously identified from Aspergillus niger JMU-TS528, multiple arginine (Arg) residues were introduced into the r-Rha1 sequence to replace several lysine (Lys) residues that located on the surface of the folded r-Rha1. Hinted by in silico analysis, five surface Lys residues (K134, K228, K406, K440, K573) were targeted to produce a list of 5 single-residue mutants and 4 multiple-residue mutants using site-directed mutagenesis. Among these mutants, a double Lys to Arg mutant, i.e. K406R/K573R, showed the best thermostability improvement. The half-life of this mutant's enzyme activity increased 3 h at 60 °C, 23 min at 65 °C, and 3.5 min at 70 °C, when compared with the wild type. The simulated protein structure based interaction analysis and molecular dynamics calculation indicate that the thermostability improvement of the mutant K406R-K573R was possibly due to the extra hydrogen bonds, the additional cation-π interactions, and the relatively compact conformation. With the enhanced thermostability, the α-L-rhamnosidase mutant, K406R-K573R, has potentially broadened the r-Rha1 applications in food processing industry.

Roles of N287 in catalysis and product formation of amylomaltase from Corynebacterium glutamicum

Amylomaltase catalyzes intermolecular and intramolecular transglucosylation reactions to form linear and cyclic oligosaccharides, respectively. The aim of this work is to investigate the structure-function relationship of amylomaltase from a mesophilic Corynebacterium glutamicum (CgAM). Site-directed mutagenesis was performed to substitute Tyr for Asn287 (N287Y) to determine its role in controlling amylomaltase activity and product formation. Expression of the wild-type (WT) and N287Y was achieved by cultivating recombinant cells in the medium containing lactose at 16 °C for 14 h. The purified mutated enzyme showed a significant decrease in all transglucosylation activities while hydrolysis activity was not changed. Optimum temperature and pH for disproportionation reaction were slightly changed upon mutation while those for cyclization reaction were not changed. Interestingly, N287Y showed a change in large-ring cyclodextrin (LR-CD) product profile in which the larger size was observed together with an increase in thermostability and substrate preference for G5 in addition to G3. The secondary structure of the mutated enzyme was slightly changed in related to the WT as evidenced from circular dichroism analysis. This work thus demonstrates that N287 is required for transglucosylation activities of CgAM. Having an aromatic residue in this position increased thermostability, changed product profile and substrate preference but demolished most enzyme activities.

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

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

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

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