Synthesis of Isomaltooligosaccharides by Saccharomyces cerevisiae Cells Expressing Aspergillus niger α-Glucosidase

Insights into the transglucosylation activity of α-glucosidase from Schwanniomyces occidentalis

The α-glucosidase from Schwanniomyces occidentalis (GAM1p) was expressed in Komagataella phaffii to about 70 mg/L, and its transferase activity studied in detail. Several isomaltooligosaccharides (IMOS) were formed using 200 g/L maltose. The major production of IMOS (81.3 g/L) was obtained when 98% maltose was hydrolysed, of which 34.8 g/L corresponded to isomaltose, 26.9 g/L to isomaltotriose, and 19.6 g/L to panose. The addition of glucose shifted the IMOS synthesis towards products containing exclusively α(1 → 6)-linkages, increasing the production of isomaltose and isomaltotriose about 2-4 fold, enabling the formation of isomaltotetraose, and inhibiting that of panose to about 12 times. In addition, the potential of this enzyme to glycosylate 12 possible hydroxylated acceptors, including eight sugars and four phenolic compounds, was evaluated. Among them, only sucrose, xylose, and piceid (a monoglucosylated derivative of resveratrol) were glucosylated, and the main synthesised products were purified and characterised by MS and NMR. Theanderose, α(1 → 4)-D-glucosyl-xylose, and a mixture of piceid mono- and diglucoside were obtained with sucrose, xylose, and piceid as acceptors, respectively. Maximum production of theanderose reached 81.7 g/L and that of the glucosyl-xylose 26.5 g/L, whereas 3.4 g/L and only 1 g/L were produced of the piceid mono- and diglucoside respectively. KEY POINTS: • Overexpression of a yeast α-glucosidase producing novel molecules. • Yeast enzyme producing the heterooligosaccharides theanderose and glucosyl-xylose. • Glycosylation of the polyphenol piceid by a yeast α-glucosidase.

Biochemical characterization of glycoside hydrolase family 31 α-glucosidases from Myceliophthora thermophila for α-glucooligosaccharide synthesis

The transglucosidase activity of GH31 α-glucosidases is employed to catalyze the synthesis of prebiotic isomaltooligosaccharides (IMOs) using the malt syrup prepared from starch as substrate. Continuous mining for new GH31 α-glucosidases with high stability and efficient transglucosidase activity is critical for enhancing the supply and quality of IMO preparations. In the present study, two α-glucosidases (MT31α1 and MT31α2) from Myceliophthora thermophila were explored for biochemical characterization. The optimum pH and temperature of MT31α1 and MT31α2 were determined to be pH 4.5 and 65 °C, and pH 6.5 and 60 °C, respectively. Both MT31α1 and MT31α2 were shown to be stable in the pH range of 3.0 to 10.0. MT31α1 displayed a high thermostability, retaining 60 % of activity after incubation for 24 h at 55 °C. MT31α1 is highly active on substrates with all types of α-glucosidic linkages. In contrast, MT31α2 showed preference for substrates with α-(1→3) and α-(1→4) linkages. Importantly, MT31α1 was able to synthesize IMOs and the conversion rate of maltose into the main functional IMOs components reached over 40 %. Moreover, MT31α2 synthesizes glucooligosaccharides with (consecutive) α-(1→3) linkages. Taken together, MT31α1 and MT31α2, showing distinct substrate and product specificity, hold clear potential for the synthesis of prebiotic glucooligosaccharides.

Synthesis of isomaltooligosaccharides using 4-O-α-d-isomaltooligosaccharylmaltooligosaccharide 1,4-α-isomaltooligosaccharohydrolase

Isomaltooligosaccharides (IMOs), including isomaltose, are valuable oligosaccharides, and the development of methods to synthesize high-purity IMOs has long been underway. We recently discovered a novel enzyme, 4-O-α-d-isomaltooligosaccharylmaltooligosaccharide 1,4-α-isomaltooligosaccharohydrolase (IMM-4IH), that showed promise for improving the synthesis process. In this study, we establish methods for synthesizing isomaltose and IMOs consisting of a variety of degrees of polymerization from starch using IMM-4IH. With 5% substrate, by combining IMM-4IH with 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75, the yield of isomaltose was 63.0%; incorporating isoamylase and cyclomaltodextrin glucanotransferase increased the yield to 75.3%. On the other hand, by combining IMM-4IH with 1,4-α-glucan 6-α-glucosyltransferase from Paenibacillus sp. PP710, IMOs were synthesized. The inclusion of isoamylase and α-amylase led to the 136 mM IMOs, consisting of oligosaccharides from isomaltose to isomaltodecaose, from 10% starch. The development of these efficient methods will be an important contribution to the industrial production of IMOs.

Production of a Series of Long-Chain Isomaltooligosaccharides from Maltose by Bacillus subtilis AP-1 and Associated Prebiotic Properties

Bacillus subtilis strain AP-1, which produces α-glucosidase with transglucosidase activity, was used to produce a series of long-chain isomaltooligosaccharides (IMOs) with degree of polymerization (DP) ranging from 2 to 14 by direct fermentation of maltose. A total IMOs yield of 36.33 g/L without contabacillusmination from glucose and maltose was achieved at 36 h of cultivation using 50 g/L of maltose, with a yield of 72.7%. IMOs were purified by size exclusion chromatography with a Superdex 30 Increase column. The molecular mass and DP of IMOs were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Subsequently, linkages in produced oligosaccharides were verified by enzymatic hydrolysis with α-amylase and oligo-α-1,6-glucosidase. These IMOs showed prebiotic properties, namely tolerance to acidic conditions and digestive enzymes of the gastrointestinal tract, stimulation of probiotic bacteria growth to produce short-chain fatty acids and no stimulating effect on pathogenic bacteria growth. Moreover, these IMOs were not toxic to mammalian cells at up to 5 mg/mL, indicating their biocompatibility. Therefore, this research demonstrated a simple and economical method for producing IMOs with DP2–14 without additional operations; moreover, the excellent prebiotic properties of the IMOs offer great prospects for their application in functional foods.

Discovery of a novel glucanohydrolase, 4-α-isomaltooligosylglucose 4-glucanohydrolase, that can be used for efficient production of isomaltose

We discovered a novel enzyme in our pursuit of an improved method for the production of isomaltose. The enzyme, 4-α-isomaltooligosylglucose 4-glucanohydrolase from Sarocladium kiliense U4520, recognizes the panose motif (α-d-Glcp-(1 → 6)-α-d-Glcp-(1 → 4)-d-Glcp) and hydrolyzes the α-1,4-glucosidic bond on the reducing end side with respect to the α-1,6-glucosidic bond. The structure on the non-reducing end of the panose motif is important for the recognition of the substrate by the enzyme, and the substrate specificity is unique and distinguished from previously reported enzymes. The enzyme catalyzes the hydrolysis of panose with a k_cat/K_m of 31.2 s^-1mM^-1, and catalysis results in anomeric inversion. These enzymatic properties suggest that this enzyme will pair well with 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75 in the efficient production of isomaltose from starch.

Valorization of renewable resources to functional oligosaccharides: Recent trends and future prospective

Lignocellulosic wastes have the ability to be transformed into oligosaccharides and other value-added products. The synthesis of oligosaccharides from renewable sources bestow to growing bioeconomies. Oligosaccharides are synthesized chemically or biologically from agricultural residues. These oligosaccharides are functional food supplements that have a positive impact on humans and livestock. Non-digestible oligosaccharides, refered as prebiotics are beneficial for the colonic microbiota inhabiting the f the digestive system. These microbiota plays a crucial role in stimulating the host immune system and other physiological responses. The commonly known prebiotics, galactooligosaccharides (GOS), xylooligosaccharides (XOS), fructooligosaccharides (FOS), mannanooligosaccharides (MOS), and isomaltooligosaccharides (IOS) are synthesized either through enzymatic or whole cell-mediated approaches using natural or agricultural waste substrates. This review focusses on recent advancements in biological processes, for the synthesis of oligosaccharides using renewable resources (lignocellulosic substrates) for sustainable circular bioeconomy. The work also addresses the limitations associated with the processes and commercialization of the products.

Efficient production of isomaltose and isomaltooligosaccharides from starch using 1,4-α-glucan 6-α-glucosyltransferase and isopullulanase

We attempted to develop an efficient method for producing isomaltose, a disaccharide consisting of an α-(1→6)-linkage, from starch by combining enzymes of known activity. We found that the combination of 1,4-α-glucan 6-α-glucosyltransferase from Bacillus globisporus N75 and isopullulanase from Aspergillus brasiliensis ATCC 9642 led to the efficient synthesis of isomaltose. Inclusion of isoamylase and cyclomaltodextrin glucanotransferase resulted in increased efficiency, with production yields exceeding 70%. Furthermore, we considered that isomaltooligosaccharides could be synthesized from starch by combining 1,4-α-glucan 6-α-glucosyltransferase from Paenibacillus sp. PP710 and isopullulanase. In reactions that additionally utilized isoamylase and α-amylase, the total concentration of product, which included a series of isomaltooligosaccharides from isomaltose to isomaltodecaose, was 131 m m, and the ratio of 6-linked glucopyranosyl bonds to all bonds was 91.7% at a substrate concentration of 10%. The development of these manufacturing methods will accelerate the industrial production of isomaltose and isomaltooligosaccharides.

The challenges in production technology, health-associated functions, physico-chemical properties and food applications of isomaltooligosaccharides

Isomaltooligosaccharides (IMOs) are recognized as functional food ingredients with prebiotic potential that deliver health benefits. IMOs have attained commercial interest as they are produced from low-cost agricultural products that are widely available and have prospective applications in the food industry. The review examines the various production processes and the main challenges involved in deriving diverse structures of IMO with maximized yield and increased functionality. The different characterization and purification techniques employed for structural elucidation, the physico-chemical importance, technological properties, food-based applications and biological effects (in vitro and in vivo interventions) have been discussed in detail. The key finding is the need for research involving biotechnological and enzymology aspects to simplify the production technologies that meet the industrial and consumer requirements. The knowledge from this article delivers a clear insight to scientists, food technologists and the general public for the improved utilization of IMOs to support the emerging market for functional foods and nutraceuticals.

Bacterial α-diglucoside metabolism: perspectives and potential for biotechnology and biomedicine

In a competitive microbial environment, nutrient acquisition is a major contributor to the survival of any individual bacterial species, and the ability to access uncommon energy sources can provide a fitness advantage. One set of soluble carbohydrates that have attracted increased attention for use in biotechnology and biomedicine is the α-diglucosides. Maltose is the most well-studied member of this class; however, the remaining four less common α-diglucosides (trehalose, kojibiose, nigerose, and isomaltose) are increasingly used in processed food and fermented beverages. The consumption of trehalose has recently been shown to be a contributing factor in gut microbiome disease as certain pathogens are using α-diglucosides to outcompete native gut flora. Kojibiose and nigerose have also been examined as potential prebiotics and alternative sweeteners for a variety of foods. Compared to the study of maltose metabolism, our understanding of the synthesis and degradation of uncommon α-diglucosides is lacking, and several fundamental questions remain unanswered, particularly with regard to the regulation of bacterial metabolism for α-diglucosides. Therefore, this minireview attempts to provide a focused analysis of uncommon α-diglucoside metabolism in bacteria and suggests some future directions for this research area that could potentially accelerate biotechnology and biomedicine developments. KEY POINTS: • α-diglucosides are increasingly important but understudied bacterial metabolites. • Kinetically superior α-diglucoside enzymes require few amino acid substitutions. • In vivo studies are required to realize the biotechnology potential of α-diglucosides.

Alternative splicing regulates the α-glucosidase synthesis in Aspergillus neoniger NCIM 1400

Aspergillus neoniger NCIM 1400 whose cell-free fraction was earlier established for transglycosylation activity conferred by α-glucosidase gene (agdA), was subjected to sequence analysis. Preliminary results revealed certain dynamics in the intron splicing mechanism, and to ascertain these molecular events, a detailed study was carried. The electrophoresis results from the cDNA portion (B-fragment) of agdA showed multiple bands, indicating the amplification of one or more fragments. The sequence results of cDNA cloned vector revealed the retention type of alternative splicing in the agdA. The splicing mechanism of agdA in NCIM 1400 was compared to different A. niger strains, which harbours agdA orthologues, using PCR. It was observed that effective intron splicing leads to higher α-glucosidase activity from these selected Aspergillus spp. To explore the dynamics of intron retention in A. neoniger NCIM 1400, time-course analysis of intron retention, enzyme activity, and sugar consumption were carried over a period of 168 h of fungal growth. RT-qPCR results revealed that introns retention was not detected during the initial growth phase when the maltose and its hydrolysed product, glucose were consumed. Here we demonstrate that exhaustion of maltose causes increase in retention of introns in the mRNA transcripts of agdA gene, and this could be the possible mode of regulating this gene.

Expression and function of an Hac1-regulated multi-copy xylanase gene in Saccharomyces cerevisiae

Saccharomyces cerevisiae-based expression systems, which rely on safe, food-grade strains, are low cost, simple to operate, and can be used for large-scale fermentation. However, low levels of foreign protein expression by S. cerevisiae have limited their widespread application. The ability of the endoplasmic reticulum (ER) to fold and process foreign proteins is an important factor restricting the expression of foreign proteins. In the current study, the effects of transcription factor Hac1p, which is involved in the unfolded protein response pathway, on S. cerevisiae-based expression of xylanase gene xynB from Aspergillus niger were examined. Overlap extension polymerase chain reaction (PCR), rDNA integration and droplet digital PCR technology were used to generate a S. cerevisiae strain (S8) containing eight copies of xynB, allowing high-yield secretory expression of xylanase. The effects of subsequent overexpression of HAC1 in strain S8 on the expression of genes associated with protein folding in the ER were then examined using the GeXP system. Results confirmed the constitutive secretory expression of the multiple copies of xynB following rDNA-based integration of the expression cassette, with a maximum xylanase yield of 325 U/mL. However, overexpression of HAC1 further improved xylanase production by strain S8, resulting in a yield of 381 U/mL.

Characterization of a Maltase from an Early-Diverged Non-Conventional Yeast Blastobotrys adeninivorans

Genome of an early-diverged yeast Blastobotrys (Arxula) adeninivorans (Ba) encodes 88 glycoside hydrolases (GHs) including two α-glucosidases of GH13 family. One of those, the rna_ARAD1D20130g-encoded protein (BaAG2; 581 aa) was overexpressed in Escherichia coli, purified and characterized. We showed that maltose, other maltose-like substrates (maltulose, turanose, maltotriose, melezitose, malto-oligosaccharides of DP 4‒7) and sucrose were hydrolyzed by BaAG2, whereas isomaltose and isomaltose-like substrates (palatinose, α-methylglucoside) were not, confirming that BaAG2 is a maltase. BaAG2 was competitively inhibited by a diabetes drug acarbose (Ki = 0.8 µM) and Tris (Ki = 70.5 µM). BaAG2 was competitively inhibited also by isomaltose-like sugars and a hydrolysis product-glucose. At high maltose concentrations, BaAG2 exhibited transglycosylating ability producing potentially prebiotic di- and trisaccharides. Atypically for yeast maltases, a low but clearly recordable exo-hydrolytic activity on amylose, amylopectin and glycogen was detected. Saccharomyces cerevisiae maltase MAL62, studied for comparison, had only minimal ability to hydrolyze these polymers, and its transglycosylating activity was about three times lower compared to BaAG2. Sequence identity of BaAG2 with other maltases was only moderate being the highest (51%) with the maltase MalT of Aspergillus oryzae.

Heterologous Expression of a Thermostable α-Glucosidase from Geobacillus sp. Strain HTA-462 by Escherichia coli and Its Potential Application for Isomaltose⁻Oligosaccharide Synthesis

Isomaltose-oligosaccharides (IMOs), as food ingredients with prebiotic functionality, can be prepared via enzymatic synthesis using α-glucosidase. In the present study, the α-glucosidase (GSJ) from Geobacillus sp. strain HTA-462 was cloned and expressed in Escherichia coli BL21 (DE3). Recombinant GSJ was purified and biochemically characterized. The optimum temperature condition of the recombinant enzyme was 65 °C, and the half-life was 84 h at 60 °C, whereas the enzyme was active over the range of pH 6.0-10.0 with maximal activity at pH 7.0. The α-glucosidase activity in shake flasks reached 107.9 U/mL and using 4-Nitrophenyl β-D-glucopyranoside (pNPG) as substrate, the K_m and Vmax values were 2.321 mM and 306.3 U/mg, respectively. The divalent ions Mn²⁺ and Ca²⁺ could improve GSJ activity by 32.1% and 13.8%. Moreover, the hydrolysis ability of recombinant α-glucosidase was almost the same as that of the commercial α-glucosidase (Bacillus stearothermophilus). In terms of the transglycosylation reaction, with 30% maltose syrup under the condition of 60 °C and pH 7.0, IMOs were synthesized with a conversion rate of 37%. These studies lay the basis for the industrial application of recombinant α-glucosidase.