Bioconversion of sucrose to maltooligosaccharides by the synergistic action of amylosucrase and α-amylase

Engineering hyperthermophilic pullulanase to efficiently utilize corn starch for production of maltooligosaccharides and glucose

Pullulanase is a starch-debranching enzyme that hydrolyzes side chain of starch, oligosaccharides and pullulan. Nevertheless, the limited activities of pullulanases constrain their practical application. Herein, the hyperthermophilic type II pullulanase from Pyrococcus yayanosii CH1 (PulPY2) was evolved by synergistically engineering the substrate-binding pocket and active-site lids. The resulting mutant PulPY2-M2 exhibited 5-fold improvement in catalytic efficiency (kcat/Km) compared to that of PulPY2. PulPY2-M2 was utilized to develop a one-pot reaction system for efficient production of maltooligosaccharides. The maltooligosaccharides conversion rate of PulPY2-M2 reached 96.1%, which was increased by 5.4% compared to that of PulPY2. Furthermore, when employed for glucose production, the glucose productivity of PulPY2-M2 was 25.4% and 43.5% higher than that of PulPY2 and the traditional method, respectively. These significant improvements in maltooligosaccharides and glucose production and the efficient utilization of corn starch demonstrated the potential of the engineered PulPY2-M2 in starch sugar industry.

Glycosylation of flavonoids by sucrose- and starch-utilizing glycoside hydrolases: A practical approach to enhance glycodiversification

Flavonoids are ubiquitous and diverse in plants and inseparable from the human diet. However, in terms of human health, their further research and application in functional food and pharmaceutical industries are hindered by their low water solubility. Therefore, flavonoid glycosylation has recently attracted research attention because it can modulate the physicochemical and biochemical properties of flavonoids. This review represents a comprehensive overview of the O-glycosylation of flavonoids catalyzed by sucrose- and starch-utilizing glycoside hydrolases (GHs). The characteristics of this feasible biosynthesis approach are systematically summarized, including catalytic mechanism, specificity, reaction conditions, and yields of the enzymatic reaction, as well as the physicochemical properties and bioactivities of the product flavonoid glycosides. The cheap glycosyl donor substrates and high yields undoubtedly make it a practical flavonoid modification approach to enhance glycodiversification.

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.

Comprehensive utilization of sucrose resources via chemical and biotechnological processes: A review

Sucrose, one of the most widespread disaccharides in nature, has been available in daily human life for many centuries. As an abundant and cheap sweetener, sucrose plays an essential role in our diet and the food industry. However, it has been determined that many diseases, such as obesity, diabetes, hyperlipidemia, etc., directly relate to the overconsumption of sucrose. It arouses many explorations for the conversion of sucrose to high-value chemicals. Production of valuable substances from sucrose by chemical methods has been studied since a half-century ago. Compared to chemical processes, biotechnological conversion approaches of sucrose are more environmentally friendly. Many enzymes can use sucrose as the substrate to generate functional sugars, especially those from GH68, GH70, GH13, and GH32 families. In this review, enzymatic catalysis and whole-cell fermentation of sucrose for the production of valuable chemicals were reviewed. The multienzyme cascade catalysis and metabolic engineering strategies were addressed.

Association among starch storage, metabolism, related genes and growth of Moso bamboo (Phyllostachys heterocycla) shoots

BACKGROUND

Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. However, the starch storage and utilization mechanisms during bamboo shoot growth remain unclear. This study aimed to reveal in which organs starch was stored, how carbohydrates were transformed among each organ, and how the expression of key genes was regulated during bamboo shoot growth and developmental stages which should lay a foundation for developing new theoretical techniques for bamboo cultivation.

RESULTS

Based on changes of the NSC content, starch metabolism-related enzyme activity and gene expression from S0 to S3, we observed that starch grains were mainly elliptical in shape and proliferated through budding and constriction. Content of both soluble sugar and starch in bamboo shoot peaked at S0, in which the former decreased gradually, and the latter initially decreased and then increased as shoots grew. Starch synthesis-related enzymes (AGPase, GBSS and SBE) and starch hydrolase (α-amylase and β-amylase) activities exhibited the same dynamic change patterns as those of the starch content. From S0 to S3, the activity of starch synthesis-related enzyme and starch amylase in bamboo rhizome was significantly higher than that in bamboo shoot, while the NSC content in rhizomes was obviously lower than that in bamboo shoots. It was revealed by the comparative transcriptome analysis that the expression of starch synthesis-related enzyme-encoding genes were increased at S0, but reduced thereafter, with almost the same dynamic change tendency as the starch content and metabolism-related enzymes, especially during S0 and S1. It was revealed by the gene interaction analysis that AGPase and SBE were core genes for the starch and sucrose metabolism pathway.

CONCLUSIONS

Bamboo shoots were the main organ in which starch was stored, while bamboo rhizome should be mainly functioned as a carbohydrate transportation channel and the second carbohydrate sink. Starch metabolism-related genes were expressed at the transcriptional level during underground growth, but at the post-transcriptional level during above-ground growth. It may be possible to enhance edible bamboo shoot quality for an alternative starch source through genetic engineering.

Thermostable Amylosucrase from Calidithermus timidus DSM 17022: Insight into Its Characteristics and Tetrameric Conformation

Amylosucrase (EC 2.4.1.4, ASase), a typical carbohydrate-active enzyme, can catalyze 5 types of reactions and recognize more than 50 types of glycosyl acceptors. However, most ASases are unstable even at 50 °C, which limits their practical industrial applications. In this study, an extremely thermostable ASase was discovered from Calidithermus timidus DSM 17022 (CT-ASase) with an optimal activity temperature of 55 °C, half-life of 1.09 h at 70 °C, and melting temperature of 74.47 °C. The recombinant CT-ASase was characterized as the first tetrameric ASase, and a structure-based truncation mutation was conducted to confirm the effect of tetrameric conformation on its thermostability. In addition, α-1,4-glucan was found to be the predominant product of CT-ASase at pH 6.0-8.0 and 30-60 °C.