Recent advances in the production, properties and applications of alginate oligosaccharides - a mini review

Construction and characterization of a novel fusion alginate lyase with endolytic and exolytic cleavage activity for industrial preparation of alginate oligosaccharides

Alginate lyases with high activity and good thermostability are lacking for the preparation of alginate oligosaccharides (AOS) with various biological activities. We constructed a fusion alginate lyase with both endo-and exo-activities. AlyRm6A-Zu7 was successfully constructed by connecting the highly thermostable AlyRm6A to a new exotype lyase, AlyZu7. The fusion enzyme exhibited high catalytic activity and thermostability. It transformed sodium alginate into oligosaccharides with degrees of polymerization (DP) of 2-4 while producing 4-deoxy-L-erythro-5-hexoseulose uronic acid (DEH). The maximum reducing sugar, AOS, and DP1 + DEH yields were 75 %, 45 %, and 40 %, respectively. Molecular docking confirmed the formation of a stable complex between the substrate and AlyRm6A-Zu7. Protein interactions increased the thermostability of AlyZu7. This work provides new insights into the industrial formation of AOS and monosaccharide DEH using thermally stable fusion enzymes, which has a positive effect in the fields of functional oligosaccharide production and biofuel formation.

Efficient preparation of alginate oligosaccharides by using alginate lyases and evaluation of the development promoting effects on Brassica napus L. in saline-alkali environment

Enzymatic degradation of alginate for the preparation of alginate oligosaccharides (AOS) is currently receiving significant attention in the field. AOS has been shown to promote crop growth and improve plant resistance to abiotic stresses. In this study, two PL6 family alginate lyases, AlyRmA and AlyRmB, were expressed and characterized. These enzymes demonstrate exceptional activity and stable thermophilicity compared to other known alginate lyases. AlyRmA (8855.34 U/mg) and AlyRmB (7879.44 U/mg) exhibited excellent degradation activity towards sodium alginate even at high temperatures (70 °C). The AlyRmA and AlyRmB were characterized and utilized to efficiently produce AOS. The study investigated the promotional effect of AOS on the growth of Brassica napus L. seedlings in a saline-alkaline environment. The results of this study demonstrate the high activity and thermal stability of AlyRmA and AlyRmB, highlighting their potential in the preparation of AOS. Moreover, the application of AOS prepared by AlyRmB could enhance the resistance of Brassica napus L. to saline-alkali environments, thereby broadening the potential applications of AOS.

Low-cost and efficient strategy for brown algal hydrolysis: Combination of alginate lyase and cellulase

Brown algae are rich in biostimulants that not only stimulate the overall development and growth of plants but also have great beneficial effects on the whole soil-plant system. However, alginate, the major component of brown algae, is comparatively difficult to degrade. The cost of preparing alginate oligosaccharides (AOSs) is still too high to produce seaweed fertilizer. In this work, the marine bacterium Vibrio sp. B1Z05 is found to be capable of efficient alginate depolymerization and harbors an extended pathway for alginate metabolism. The B1Z05 extracellular cell-free supernatant exhibited great potential for AOS production at low cost, which, together with cellulase, can efficiently hydrolyze seaweed. The brown algal hydrolysis rates were significantly greater than those of the commercial alginate lyase product CE201, and the obtained seaweed extracts were rich in phytohormones. This work provides a low-cost but efficient strategy for the sustainable production of desirable AOSs and seaweed fertilizer.

Separation, purification and structural characterization of marine oligosaccharides: A comprehensive and systematic review of chromatographic methods

Marine oligosaccharides have now been applied in a wide range of industry due to various kinds of physiological activities. However, the oligosaccharides with different polymeric degrees (Dps) differed in physiological activities and applicable fields. So it is promising and essential to separate, purify and structurally characterize these oligosaccharides for understanding their structure-function relationship. This review will summarize the lasted developments in the separation, purification and structural characterization of marine oligosaccharides, including the alginate oligosaccharides, carrageenan oligosaccharides, agar oligosaccharides, chitin oligosaccharides and chitosan oligosaccharides, emphasizing the successful examples of methods for separation and purification. Furthermore, an outlook for preparation of functional oligosaccharides in food biotechnology and agriculture fields is also included. This comprehensive review could definitely promote the utilization of marine functional polysaccharides for food and agriculture.

Advances in alginate lyases and the potential application of enzymatic prepared alginate oligosaccharides: A mini review

Alginate is mainly a linear polysaccharide composed of randomly arranged β-D-mannuronic acid and α-L-guluronic acid linked by α, β-(1,4)-glycosidic bonds. Alginate lyases degrade alginate mainly adopting a β-elimination mechanism, breaking the glycosidic bonds between the monomers and forming a double bond between the C4 and C5 sugar rings to produce alginate oligosaccharides consisting of 2-25 monomers, which have various physiological functions. Thus, it can be used for the continuous industrial production of alginate oligosaccharides with a specific degree of polymerization, in accordance with the requirements of green exploitation of marine resources. With the development of structural analysis, the quantity of characterized alginate lyase structures is progressively growing, leading to a concomitant improvement in understanding the catalytic mechanism. Additionally, the use of molecular modification methods including rational design, truncated expression of non-catalytic domains, and recombination of conserved domains can improve the catalytic properties of the original enzyme, enabling researchers to screen out the enzyme with the expected excellent performance with high success rate and less workload. This review presents the latest findings on the catalytic mechanism of alginate lyases and outlines the methods for molecular modifications. Moreover, it explores the connection between the degree of polymerization and the physiological functions of alginate oligosaccharides, providing a reference for enzymatic preparation development and utilization.

How alginate lyase produces quasi-monodisperse oligosaccharides: A normal-mode-based docking and molecular dynamics simulation study

Oligosaccharide degradation products of alginate (AOS) hold significant potential in diverse fields, including pharmaceuticals, health foods, textiles, and agricultural production. Enzymatic alginate degradation is appealing due to its mild conditions, predictable activity, high yields, and controllability. However, the alginate degradation often results in a complex mixture of oligosaccharides, necessitating costly purification to isolate highly active oligosaccharides with a specific degree of polymerization (DP). Addressing this, our study centers on the alginate lyase AlyB from Vibrio Splendidus OU02, which uniquely breaks down alginate into mono-distributed trisaccharides. This enzyme features a polysaccharide lyase family 7 domain (PL-7) and a CBM32 carbohydrate-binding module connected by a helical structure. Through normal-mode-based docking and all-atom molecular simulations, we demonstrate that AlyB's substrate and product specificities are influenced by the spatial conformation of the catalytic pocket and the flexibility of its structure. The helically attached CBM is pivotal in releasing trisaccharides, which is crucial for avoiding further degradation. This study sheds light on AlyB's specificity and efficiency and contributes to the evolving field of enzyme design for producing targeted oligosaccharides, with significant implications for various bioindustries.

Biphasic Porous Bijel-Like Structures with Hydrogel Domains as Controlled Drug Delivery Systems

Bijels are a peculiar type of Pickering emulsion that have a bicontinuous morphology and are stabilised by a jammed layer of nanoparticles (NPs). Due to their double nature, their usage has increased in recent years in various fields, such as biological and food applications. In fact, they can release both hydrophilic and hydrophobic compounds simultaneously. An improvement to this structure is the use of a hydrophobic monomer like polycaprolactone as the organic phase, which is able to polymerise during the formation of the structure. Unfortunately, the structures formed in this way always have some drawbacks, such as their thermal stability or degradation when submerged in an aqueous medium. A number of studies have been carried out in which some parameters, such as the NPs or the monomer, were changed and their effect on the final product evaluated. In this work, the effect of modifying the aqueous phase was studied. In particular, the effect of adding alginate, a biopolymer capable of forming a stable hydrogel in the presence of divalent cations, was analysed, as was the difference between soaking or not in CaCl2, the final system. Specific attention was paid to their swelling behaviour (150% vs. 25% of the blank sample), rheological properties (G' 100 kPa vs. 20 kPa of the blank sample) and their release performances. In this framework, complete release of hydrophilic drug vs. 20% in the blank sample was observed together with improved release of the hydrophobic one with 35% in 8 h vs. 5% in the case of the blank sample. This strategy has been proven to influence bijels' properties, opening the doors to many different uses.

Identification and characterization of a critical loop for the high activity of alginate lyase VaAly2 from the PL7_5 subfamily

As the major component in the cell wall of brown algae, alginates are degradable by alginate lyases via β-elimination. Alginate lyases can be categorized into various polysaccharide lyase (PL) families, and PL7 family alginate lyases are the largest group and can be divided into six subfamilies. However, the major difference among different PL7 subfamilies is not fully understood. In this work, a marine alginate lyase, VaAly2, from Vibrio alginolyticus ATCC 17749 belonging to the PL7_5 subfamily was identified and characterized. It displayed comparatively high alginolytic activities toward different alginate substrates and functions as a bifunctional lyase. Molecular docking and biochemical analysis suggested that VaAly2 not only contains a key catalyzing motif (HQY) conserved in the PL7 family but also exhibits some specific characters limited in the PL7_5 subfamily members, such as the key residues and a long loop1 structure around the active center. Our work provides insight into a loop structure around the center site which plays an important role in the activity and substrate binding of alginate lyases belonging to the PL7_5 subfamily.

The effect of alginate oligosaccharides on intestine barrier function and Vibrio parahaemolyticus infections in the white shrimp Litopenaeus vannamei

The intestine is a host-pathogen interaction site and improved intestinal barrier function help to prevent disease in shrimp. Alginate oligosaccharides (AOS) are derived from resourceful brown algae. The intestine protection properties of AOS were widely recognized, and their benefits in fish have been reported. Nevertheless, there are no reports on AOS in shrimp and other crustaceans. In the present work, we measured the effects of AOS on growth performance and disease resistance in the white shrimp Litopenaeus vannamei and investigated their effects on intestinal health. Shrimps with an initial weight of about 2 g were fed with diets supplemented with 0 (control), 0.07%, 0.2%, 0.6%, or 1.2% of AOS for 56 days and were sampled and challenged with Vibrio parahaemolyticus. Dietary AOS did not significantly influence weight gain or feed utilization (P > 0.05). However, AOS considerably decreased the seven-day cumulative mortality after the challenge at any dose (P < 0.05). Dietary AOS improved the intestinal structure, significantly boosted the intestinal villus height at 0.6% and 1.2% levels, and increased intestinal wall thickness by 0.2%, 0.6%, and 1.2%. The alkaline phosphatase and maltase activities were also increased, suggesting that AOS improved the intestinal condition. Redox homeostasis in intestinal was improved by AOS, as expressed by the enhanced total antioxidant capacity and decreased malonaldehyde content, partly due to the increased superoxide dismutase and catalase activities. Compared with the antioxidant system, AOS's stimulating effects on immunity were more significant. At any level, AOS significantly activated lysozyme activity, the expression of propo and two antimicrobial peptide genes (pen-3 and crusin). However, the lowest concentration of AOS did not stimulate the gene expression of all three assayed pattern recognition receptors (LGBP, Toll, and IMD), and only the highest concentration of AOS increased the expression of imd. These findings suggest that AOS are highly efficient immunostimulants, and various immune pathways in shrimp are differentially sensitive to AOS. Finally, our findings suggest that AOS significantly alter the gut microbiota and their relative abundance at the phylum, family, and genus levels. In conclusion, AOS significantly enhances disease resistance in L. vannamei, possibly attributed to improved intestinal development, increased intestinal immunity and altered microbiota. These findings could provide a basis for future studies on the practical use of AOS and its mechanisms of action.