The Characterization and Modification of a Novel Bifunctional and Robust Alginate Lyase Derived from Marinimicrobium sp. H1

Expression, Purification, and Characterisation of Recombinant Alginate Lyase (Flammeovirga AL2) for the Bioconversion of Alginate into Alginate Oligosaccharides

Alginate, a polysaccharide found in brown seaweeds, has regularly gained attention for its potential use as a source of bioactive compounds. However, it is structurally complex with a high molecular weight, limiting its application. Alginate oligosaccharides (AOS) are small, soluble fragments, making them more bioavailable. Alginate hydrolysis by enzymes is the preferred method for AOS production. Commercially available alginate lyases are limited, expensive, and sometimes exhibit unsatisfactory activity, making the search for novel alginate lyases with improved activity indispensable. The aims of this study were to codon-optimise, synthesise, express, purify, and characterise a recombinant alginate lyase, AL2, from Flammeovirga sp. strain MY04 and to compare it to a commercial alginate lyase. Expression was successfully performed using Escherichia coli ArcticExpress (DE3) RP cells, and the protein was purified through affinity chromatography. The recombinant enzyme was characterised by pH optimum studies, and temperature optimum and stability experiments. The optimal reaction conditions for AL2 were pH 9.0 and 37 °C, while for the commercial enzyme, the optimal conditions were pH 8.0 and 37 °C. At optimal reaction conditions, the specific activity of AL2 was 151.6 ± 12.8 µmol h-1 mg-1 protein and 96.9 ± 13.1 µmol h-1 mg-1 protein for the commercial alginate lyase. Moreover, AL2 displayed impressive activity in breaking down alginate into AOS. Hence, AL2 shows potential for use as an industrial enzyme for the hydrolysis of alginate into alginate oligosaccharides. Additional studies should be carried out to further characterise this enzyme, improve its purity, and optimise its activity.

The therapeutic effect and possible mechanisms of alginate oligosaccharide on metabolic syndrome by regulating gut microbiota

Metabolic syndrome (MetS) is a disease condition incorporating the abnormal accumulation of various metabolic components, including overweight or abdominal obesity, insulin resistance and abnormal glucose tolerance, hypertension, atherosclerosis, or dyslipidemia. It has been proved that the gut microbiota and microbial-derived products play an important role in regulating lipid metabolism and thus the onset and development of MetS. Previous studies have demonstrated that oligosaccharides with prebiotic effects, such as chitosan oligosaccharides, can regulate the structure of the microbial community and its derived products to control weight and reduce MetS associated with obesity. Alginate oligosaccharides (AOS), natural products extracted from degraded alginate salts with high solubility and extensive biological activity, have also been found to modulate gut microbiota. This review aims to summarize experimental evidence on the positive effects of AOS on different types of MetS while providing insights into mechanisms through which AOS regulates gut microbiota for preventing and treating MetS.

Sustainable Production of Ulva Oligosaccharides via Enzymatic Hydrolysis: A Review on Ulvan Lyase

Ulvan is a water-soluble sulfated polysaccharide extracted from the green algae cell wall. Compared with polysaccharides, oligosaccharides have drawn increasing attention in various industries due to their enhanced biocompatibility and solubility. Ulvan lyase degrades polysaccharides into low molecular weight oligosaccharides through the β-elimination mechanism. The elucidation of the structure, catalytic mechanism, and molecular modification of ulvan lyase will be helpful to obtain high value-added products from marine biomass resources, as well as reduce environmental pollution caused by the eutrophication of green algae. This review summarizes the structure and bioactivity of ulvan, the microbial origin of ulvan lyase, as well as its sequence, three-dimensional structure, and enzymatic mechanism. In addition, the molecular modification of ulvan lyase, prospects and challenges in the application of enzymatic methods to prepare oligosaccharides are also discussed. It provides information for the preparation of bioactive Ulva oligosaccharides through enzymatic hydrolysis, the technological bottlenecks, and possible solutions to address these issues within the enzymatic process.

Catalytic properties characterization and degradation mode elucidation of a polyG-specific alginate lyase OUC-FaAly7

Polymerized guluronates (polyG)-specific alginate lyase with lower polymerized mannuronates (polyM)-degrading activity, superior stability, and clear action mode is a powerful biotechnology tool for the preparation of AOSs rich in M blocks. In this study, we expressed and characterized a polyG-specific alginate lyase OUC-FaAly7 from Formosa agariphila KMM3901. OUC-FaAly7 belonging to polysaccharide lyase (PL) family 7 had highest activity (2743.7 ± 20.3 U/μmol) at 45 °C and pH 6.0. Surprisingly, its specific activity against polyG reached 8560.2 ± 76.7 U/μmol, whereas its polyM-degrading activity was nearly 0 within 10 min reaction. Suggesting that OUC-FaAly7 was a strict polyG-specific alginate lyase. Importantly, OUC-FaAly7 showed a wide range of temperature adaptations and remarkable temperature and pH stability. Its relative activity between 20 °C and 45 °C reached >90 % of the maximum activity. The minimum identifiable substrate of OUC-FaAly7 was guluronate tetrasaccharide (G4). Action process and mode showed that it was a novel alginate lyase digesting guluronate hexaose (G6), guluronate heptaose (G7), and polymerized guluronates, with the preferential generation of unsaturated guluronate pentasaccharide (UG5), although which could be further degraded into unsaturated guluronate disaccharide (UG3) and trisaccharide (UG2). This study contributes to illustrating the catalytic properties, substrate recognition, and action mode of novel polyG-specific alginate lyases.

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.

A Novel Bifunctional Alginate Lyase and Antioxidant Activity of the Enzymatic Hydrolysates

Alginate lyase Aly448, a potential new member of the polysaccharide lyase (PL) 7 family, which was cloned and identified from the macroalgae-associated bacterial metagenomic library, showed bifunctionality. The molecular docking results revealed that Aly448 has two completely different binding sites for alginate (polyMG), poly-α-l-guluronic acid (polyG), and poly-β-d-mannuronic acid (polyM) substrates, respectively, which might be the molecular basis for the enzyme's bifunctionality. Truncational results confirmed that predicted key residues affected the bifunctionality of Aly448, but did not wholly explain. Besides, Aly448 presented excellent biochemical characteristics, such as higher thermal stability and pH tolerance. Degradation of polyMG, polyM, and polyG substrates by Aly448 produced tetrasaccharide (DP4), disaccharide (DP2), and galactose (DP1), which exhibited excellent antioxidant activity. These findings provide novel insights into the substrate recognition mechanism of bifunctional alginate lyases and pave a new path for the exploitation of natural antioxidant agents.

Computer-Aided Rational Design Strategy to Improve the Thermal Stability of Alginate Lyase AlyMc

Alginate lyase degrades alginate by the β-elimination mechanism to produce unsaturated alginate oligosaccharides (UAOS), which have better bioactivities than saturated AOS. Enhancing the thermal stability of alginate lyases is crucial for their industrial applications. In this study, a feasible and efficient rational design strategy was proposed by combining the computer-aided ΔΔG value calculation with the B-factor analysis. Two thermal stability-enhanced mutants, Q246V and K249V, were obtained by site-directed mutagenesis. Particularly, the t1/2, 50 °C for mutants Q246V and K249V was increased from 2.36 to 3.85 and 3.65 h, respectively. Remarkably, the specific activities of Q246V and K249V were enhanced to 2.41- and 2.96-fold that of alginate lyase AlyMc, respectively. Structural analysis and molecular dynamics simulations suggested that mutations enhanced the hydrogen bond networks and the overall rigidity of the molecular structure. Notably, mutant Q246V exhibited excellent thermal stability among the PL-7 alginate lyase family, especially considering the heightened enzymatic activity. Moreover, the rational design strategy used in this study can effectively improve the thermal stability of enzymes and has important significance in advancing applications of alginate lyase.

A repertoire of alginate lyases in the alginate polysaccharide utilization loci of marine bacterium Wenyingzhuangia fucanilytica: biochemical properties and action pattern

BACKGROUND

Alginate lyases are important tools for alginate biodegradation and oligosaccharide production, which have great potential in food and biofuel fields. The alginate polysaccharide utilization loci (PUL) typically encode a series of alginate lyases with a synergistic action pattern. Exploring valuable alginate lyases and revealing the synergistic effect of enzymes in the PUL is of great significance.

RESULTS

An alginate PUL was discovered from the marine bacterium Wenyingzhuangia fucanilytica CZ1127T , and a repertoire of alginate lyases within it was cloned, expressed and characterized. The four alginate lyases in PUL demonstrated similar optimal reaction conditions: maximum enzyme activity at 35-50 °C and pH 8.0-9.0. The results of action pattern indicated that they were two PL7 endolytic bifunctional enzymes (Aly7A and Aly7B), a PL6 exolytic bifunctional enzyme (Aly6A) and a PL17 exolytic M-specific enzyme (Aly17A). Ultra-performance liquid chromatography-mass spectrometry was employed to reveal the synergistic effect of the four enzymes. The end products of Aly7A were further degraded by Aly7B and eventually generated oligosaccharides, from disaccharide to heptasaccharide. The oligosaccharide products were completely degraded to monosaccharides by Aly6A, but it was unable to directly degrade alginate. Aly17A could also produce monosaccharides by cleaving the M-blocks of oligosaccharide products, as well as the M-blocks of polysaccharides. The combination of these enzymes resulted in the complete degradation of alginate to monosaccharides.

CONCLUSION

A new alginate PUL was mined and four novel alginate lyases in the PUL were expressed and characterized. The four cooperative alginate lyases provide novel tools for alginate degradation and biological fermentation. © 2023 Society of Chemical Industry.

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.

Rational design for thermostability improvement of a novel PL-31 family alginate lyase from Paenibacillus sp. YN15

Currently, alginate oligosaccharides (AOS) become attractive due to their excellent physiological effects. AOS has been widely used in food, pharmaceutical, and cosmetic industries. Generally, AOS can be produced from alginate using alginate lyase (ALyase) as the biocatalyst. However, most ALyase display poor thermostability. In this study, a thermostable ALyase from Paenibacillus sp. YN15 (Payn ALyase) was characterized. It belonged to the polysaccharide lyase (PL) 31 family and displayed poly β-D-mannuronate (Poly M) preference. Under the optimum condition (pH 8.0, 55 °C, 50 mM NaCl), it exhibited maximum activity of 90.3 U/mg and efficiently degraded alginate into monosaccharides and AOS with polymerization (DP) of 2-4. Payn ALyase was relatively stable at 55 °C, but the thermostability dropped rapidly at higher temperatures. To further improve its thermostability, rational design mutagenesis was carried out based on a combination of FireProt, Consensus Finder, and PROSS analysis. Finally, a triple-point mutant K71P/Y129G/S213G was constructed. The optimum temperature was increased from 55 to 70 °C, and the Tm was increased from 62.7 to 64.1 °C. The residual activity after 30 min incubation at 65 °C was enhanced from 36.0 % to 83.3 %. This study provided a promising ALyase mutant for AOS industrial production.

Characterization of bifunctional alginate lyase Aly644 and antimicrobial activity of enzymatic hydrolysates

An alginate lyase gene aly644 encoding a member of polysaccharide lyase family 6 was obtained from a metagenome of Antarctic macroalgae-associated microbes. The gene was expressed heterologously in Escherichia coli, and the recombinant protein was purified using a Ni-NTA His Tag Kit. With sodium alginate as the substrate, recombinant Aly644 exhibited an optimum reaction temperature of 50°C and an optimum reaction pH of 7.0. The Vmax and Km values of Aly644 toward sodium alginate were 112.36 mg/mL·min and 16.75 mg/mL, respectively. Substrate specificity analysis showed that Aly644 was a bifunctional alginate lyase that hydrolyzed both polyguluronic acid and polymannuronic acid. The hydrolysis products of Aly644 with sodium alginate as the substrate were detected by thin-layer chromatography, and were mainly di- and trisaccharides. The oligosaccharides produced by degradation of sodium alginate by Aly644 inhibited the mycelial growth of the plant pathogens Phytophthora capsici and Fulvia fulva; the 50% maximal effective concentration (EC50) values were 297.45 and 452.89 mg/L, and the 90% maximal effective concentration (EC90) values were 1341.45 and 2693.83 mg/L, respectively. This highlights that Aly644 is a potential candidate enzyme for the industrial production of alginate oligosaccharides with low degree of polymerization. Enzyme-hydrolyzed alginate oligosaccharides could support the development of green agriculture as natural antimicrobial agents. KEY POINTS: • An alginate lyase was obtained from a metagenome of Antarctic macroalgae-associated microbes. • Aly644 is a bifunctional alginate lyase with excellent thermostability and pH stability. • The enzymatic hydrolysates of Aly644 directly inhibited Phytophthora capsici and Fulvia fulva.

Characterization of a thermostable PL-31 family alginate lyase from Paenibacillus ehimensis and its application for alginate oligosaccharides bioproduction

Currently, people pay more attention to marine sugars, because of their unique physiological effects. Alginate oligosaccharides (AOS) are the degradation products of alginate and have been used in food, cosmetic, and medicine fields. AOS display good physical characteristics (low relative molecular weight, good solubility, high safety, and high stability) and excellent physiological functions (immunomodulatory, antioxidant, antidiabetic, and prebiotic activities). Alginate lyase plays a key role in the AOS bioproduction. In this study, a novel PL-31 family alginate lyase from Paenibacillus ehimensis (paeh-aly) was identified and characterized. It was extracellularly secreted in E. coli and exhibited a preference for the substrate poly β-D-mannuronate. Using sodium alginate as the substrate, it showed the maximum catalytic activity (125.7 U/mg) at pH 7.5 and 55 °C with 50 mM NaCl. Compared with other alginate lyases, paeh-aly exhibited good stability. About 86.6% and 61.0% residual activity could be maintained after 5 h incubation at 50 and 55 °C respectively, and its T_m value was 61.5 °C. The degradation products were AOS with DP 2-4. Paeh-aly demonstrated strong promise for AOS industrial production because of its excellent thermostability and efficiency.

Genomic analysis of Marinimicrobium sp. C6131 reveals its genetic potential involved in chitin metabolism

Marinimicrobium sp. C6131, which had the ability to degrade chitin, was isolated from deep-sea sediment of the southwest Indian Ocean. Here, the genome of strain C6131 was sequenced and the chitin metabolic pathways were constructed. The genome contained a circular chromosome of 4,207,651 bp with a G + C content of 58.50%. A total of 3471 protein-coding sequences were predicted. Gene annotation and metabolic pathway reconstruction showed that strain C6131 possessed genes and two metabolic pathways involved in chitin catabolism: the hydrolytic chitin utilization pathway initiated by chitinases and the oxidative chitin utilization pathway initiated by lytic polysaccharide monooxygenases. Chitin is the most abundant polysaccharide in the ocean. Degradation and recycling of chitin driven by marine bacteria are crucial for biogeochemical cycles of carbon and nitrogen in the ocean. The genomic information of strain C6131 revealed its genetic potential involved in chitin metabolism. The strain C6131 could grow with colloidal chitin as the sole carbon source, indicating that these genes would have functions in chitin degradation and utilization. The genomic sequence of Marinimicrobium sp. C6131 could provide fundamental information for future studies on chitin degradation, and help to improve our understanding of the chitin degradation process in deep-sea environments.

Process and applications of alginate oligosaccharides with emphasis on health beneficial perspectives

Alginates are linear polymers comprising 40% of the dry weight of algae possess various applications in food and biomedical industries. Alginate oligosaccharides (AOS), a degradation product of alginate, is now gaining much attention for their beneficial role in food, pharmaceutical and agricultural industries. Hence this review was aimed to compile the information on alginate and AOS (prepared from seaweeds) during 1994-2020. As per our knowledge, this is the first review on the potential use of alginate oligosaccharides in different fields. The alginate derivatives are grouped according to their applications. They are involved in the isolation process and show antimicrobial, antioxidant, anti-inflammatory, antihypertension, anticancer, and immunostimulatory properties. AOS also have significant applications in prebiotics, nutritional supplements, plant growth development and others products.

Characterization of a bifunctional and endolytic alginate lyase from Microbulbifer sp. ALW1 and its application in alginate oligosaccharides production from Laminaria japonica

The diverse biological activities of alginate oligosaccharides attracted extensive exploration of alginate lyases with various substrate specificity and enzymatic properties. In this study, an alginate lyase from Microbulbifer sp. ALW1, namely AlgL7, was phylogenetically classified into the polysaccharide lyase family 7 (PL7). The conserved amino acid residues Tyr606 and His499 in AlgL7 were predicted to act as the general acid/base catalysts. The enzyme was enzymatically characterized after heterologous expression and purification in E. coli. AlgL7 displayed optimal activity at 40 °C and pH 7.0. It had good stability at temperature below 35 °C and within a pH range of 5.0-10.0. AlgL7 exhibited good stability against the reducing reagent β-ME and the surfactants of Tween-20 and Triton X-100. The degradation profiles of alginate indicated AlgL7 was a bifunctional endolytic alginate lyase generating alginate oligosaccharides with the degrees of polymerization 2-4. The degradation products of sodium alginate exhibited stronger antioxidant activities than the untreated polysaccharide. In addition, AlgL7 could directly digest Laminaria japonica to produce alginate oligosaccharides. These characteristics of AlgL7 offer a great potential of its application in high-value utilization of brown algae resources.

Characterization of a Novel Polysaccharide Lyase Family 5 Alginate Lyase with PolyM Substrate Specificity

Alginate lyases (ALyases) have been widely applied in enzymatically degrading alginate for the preparation of alginate oligosaccharides (AOS), which possess a range of excellent physiological benefits including immunoregulatory, antivirus, and antidiabetic properties. Among the characterized ALyases, the number of ALyases with strict substrate specificity which possess potential in directed preparation of AOS is quite small. ALyases of polysaccharides lyase (PL) 5 family have been reported to perform poly-β-D-mannuronic acid (Poly-M) substrate specificity. However, there have been fewer studies with a comprehensive characterization and comparison of PL 5 family ALyases. In this study, a putative PL 5 family ALyase PMD was cloned from Pseudomonas mendocina and expressed in Escherichia coli. The novel ALyase presented maximum activity at 30 °C and pH 7.0. PMD displayed pH stability properties under the range of pH 5 to pH 9, which retained more than 80% relative activity, even when incubated for 48 h. Product analysis indicated that PMD might be an endolytic ALyase with strict Poly M substrate specificity and yield disaccharide and trisaccharide as main products. In addition, residues K58, R66, Y248, and R344 were proposed to be the potential key residues for catalysis via site-directed mutation. Detailed characterization of PMD and comprehensive comparisons could supply some different information about properties of PL 5 ALyases which might be helpful for its application in the directed production of AOS.

Improving the thermostability of alginate lyase FlAlyA with high expression by computer-aided rational design for industrial preparation of alginate oligosaccharides

FlAlyA, a PL7 alginate lyase with industrial potential, is widely applied in the preparation the alginate oligosaccharide because of its high activity of degradation the alginate. However, heat inactivation still limits the industrial application of FlAlyA. To further enhance its thermostability, a group of mutants were designed, according to evaluating the B-factor value and free energy change via computer-aided calculation. 25 single-point mutants and one double-points mutant were carried out by site-directed mutagenesis. The optimal two single-point mutants H176D and H71K showed 1.20 and 0.3°C increases in the values of T m, while 7.58 and 1.73 min increases in the values of half-life (t 1/2) at 50°C, respectively, compared with that of the wild-type enzyme. Interestingly, H71K exhibits the comprehensive improvement than WT, including expression level, thermal stability and specific activity. In addition, the mechanism of these two mutants is speculated by multiple sequence alignment, structural basis and molecular dynamics simulation, which is likely to be involved in the formation of new hydrogen bonds and decrease the SASA of the mutants. These results indicate that B-factor is an efficient approach to improves the thermostability of alginate lyase composed of β-sheet unit. Furthermore, the highest yield of the mutant reached about 650 mg/L, which was nearly 36 times that of previous studies. The high expression, excellent activity and good thermal stability make FlAlyA a potential candidate for the industrial production of alginate oligosaccharides.

Cloning and Characterization of a Novel Endo-Type Metal-Independent Alginate Lyase from the Marine Bacteria Vibrio sp. Ni1

The applications of alginate lyase are diverse, but efficient commercial enzymes are still unavailable. In this study, a novel alginate lyase with high activity was obtained from the marine bacteria Vibrio sp. Ni1. The ORF of the algB gene has 1824 bp, encoding 607 amino acids. Homology analysis shows that AlgB belongs to the PL7 family. There are two catalytic domains with the typical region of QIH found in AlgB. The purified recombinant enzyme of AlgB shows highest activity at 35 °C, pH 8.0, and 50 mmol/L Tris-HCl without any metal ions. Only K⁺ slightly enhances the activity, while Fe²⁺ and Cu²⁺ strongly inhibit the activity. The AlgB preferred polyM as substrate. The end products of enzymatic mixture are DP2 and DP3, without any metal ion to assist them. This enzyme has good industrial application prospects.

Alginate Lyases from Marine Bacteria: An Enzyme Ocean for Sustainable Future

The cell wall of brown algae contains alginate as a major constituent. This anionic polymer is a composite of β-d-mannuronate (M) and α-l-guluronate (G). Alginate can be degraded into oligosaccharides; both the polymer and its products exhibit antioxidative, antimicrobial, and immunomodulatory activities and, hence, find many commercial applications. Alginate is attacked by various enzymes, collectively termed alginate lyases, that degrade glycosidic bonds through β-elimination. Considering the abundance of brown algae in marine ecosystems, alginate is an important source of nutrients for marine organisms, and therefore, alginate lyases play a significant role in marine carbon recycling. Various marine microorganisms, particularly those that thrive in association with brown algae, have been reported as producers of alginate lyases. Conceivably, the marine-derived alginate lyases demonstrate salt tolerance, and many are activated in the presence of salts and, therefore, find applications in the food industry. Therefore, this review summarizes the structural and biochemical features of marine bacterial alginate lyases along with their applications. This comprehensive information can aid in the expansion of future prospects of alginate lyases.

Alginate oligosaccharides: The structure-function relationships and the directional preparation for application

Alginate oligosaccharides (AOS) are degradation products of alginate extracted from brown algae. With low molecular weight, high water solubility, and good biological activity, AOS present anti-inflammatory, antimicrobial, antioxidant, and antitumor properties. They also exert growth-promoting effects in animals and plants. Three types of AOS, mannuronate oligosaccharides (MAOS), guluronate oligosaccharides (GAOS), and heterozygous mannuronate and guluronate oligosaccharides (HAOS), can be produced from alginate by enzymatic hydrolysis. Thus far, most studies on the applications and biological activities of AOS have been based mainly on a hybrid form of HAOS. To improve the directional production of AOS for practical applications, systematic studies on the structures and related biological activities of AOS are needed. This review provides a summary of current understanding of structure-function relationships and advances in the production of AOS. The current challenges and opportunities in the application of AOS is suggested to guide the precise application of AOS in practice.

Effects of Module Truncation of a New Alginate Lyase VxAly7C from Marine Vibrio xiamenensis QY104 on Biochemical Characteristics and Product Distribution

Alginate lyase has received extensive attention as an important tool for oligosaccharide preparation, pharmaceutical production, and energy biotransformation. Noncatalytic module carbohydrate-binding modules (CBM) have a major impact on the function of alginate lyases. Although the effects of two different families of CBMs on enzyme characteristics have been reported, the effect of two combined CBM32s on enzyme function has not been elucidated. Herein, we cloned and expressed a new multimodular alginate lyase, VxAly7C, from Vibrioxiamenensis QY104, consisting of two CBM32s at N-terminus and a polysaccharide lyase family 7 (PL7) at C-terminus. To explore the function of CBM32s in VxAly7C, full-length (VxAly7C-FL) and two truncated mutants, VxAly7C-TM1 (with the first CBM32 deleted) and VxAly7C-TM2 (with both CBM32s deleted), were characterized. The catalytic efficiency of recombinant VxAly7C-TM2 was 1.82 and 4.25 times higher than that of VxAly7C-TM1 and VxAly7C-FL, respectively, indicating that CBM32s had an antagonistic effect. However, CBM32s improved the temperature stability, the adaptability in an alkaline environment, and the preference for polyG. Moreover, CBM32s contributed to the production of tri- and tetrasaccharides, significantly affecting the end-product distribution. This study advances the understanding of module function and provides a reference for broader enzymatic applications and further enzymatic improvement and assembly.

Biochemical Characterization and Cold-Adaption Mechanism of A PL-17 Family Alginate Lyase Aly23 from Marine Bacterium Pseudoalteromonas sp. ASY5 and Its Application for Oligosaccharides Production

As an important enzyme involved in the marine carbon cycle, alginate lyase has received extensive attention because of its excellent degradation ability on brown algae, which is widely utilized for alginate oligosaccharide preparation or bioethanol production. In comparison with endo-type alginate lyases (PL-5, PL-7, and PL-18 families), limited studies have focused on PL-17 family alginate lyases, especially for those with special characteristics. In this study, a novel PL-17 family alginate lyase, Aly23, was identified and cloned from the marine bacterium Pseudoalteromonas carrageenovora ASY5. Aly23 exhibited maximum activity at 35 °C and retained 48.93% of its highest activity at 4 °C, representing an excellent cold-adaptation property. Comparative molecular dynamics analysis was implemented to explore the structural basis for the cold-adaptation property of Aly23. Aly23 had a high substrate preference for poly β-D-mannuronate and exhibited both endolytic and exolytic activities; its hydrolysis reaction mainly produced monosaccharides, disaccharides, and trisaccharides. Furthermore, the enzymatic hydrolyzed oligosaccharides displayed good antioxidant activities to reduce ferric and scavenge radicals, such as hydroxyl, ABTS⁺, and DPPH. Our work demonstrated that Aly23 is a promising cold-adapted biocatalyst for the preparation of natural antioxidants from brown algae.

Evolving strategies for marine enzyme engineering: recent advances on the molecular modification of alginate lyase

Alginate, an acidic polysaccharide, is formed by β-d-mannuronate (M) and α-l-guluronate (G). As a type of polysaccharide lyase, alginate lyase can efficiently degrade alginate into alginate oligosaccharides, having potential applications in the food, medicine, and agriculture fields. However, the application of alginate lyase has been limited due to its low catalytic efficiency and poor temperature stability. In recent years, various structural features of alginate lyase have been determined, resulting in modification strategies that can increase the applicability of alginate lyase, making it important to summarize and discuss the current evidence. In this review, we summarized the structural features and catalytic mechanisms of alginate lyase. Molecular modification strategies, such as rational design, directed evolution, conserved domain recombination, and non-catalytic domain truncation, are also described in detail. Lastly, the application of alginate lyase is discussed. This comprehensive summary can inform future applications of alginate lyases.

The Function of CBM32 in Alginate Lyase VxAly7B on the Activity on Both Soluble Sodium Alginate and Alginate Gel

Carbohydrate-binding modules (CBMs), as an important auxiliary module, play a key role in degrading soluble alginate by alginate lyase, but the function on alginate gel has not been elucidated. Recently, we reported alginate lyase VxAly7B containing a CBM32 and a polysaccharide lyase family 7 (PL7). To investigate the specific function of CBM32, we characterized the full-length alginate lyase VxAly7B (VxAly7B-FL) and truncated mutants VxAly7B-CM (PL7) and VxAly7B-CBM (CBM32). Both VxAly7B-FL and native VxAly7B can spontaneously cleavage between CBM32 and PL7. The substrate-binding capacity and activity of VxAly7B-CM to soluble alginate were 0.86- and 1.97-fold those of VxAly7B-FL, respectively. Moreover, CBM32 could accelerate the expansion and cleavage of alginate gel beads, and the degradation rate of VxAly7B-FL to alginate gel beads was threefold that of VxAly7B-CM. Results showed that CBM32 is not conducive to the degradation of soluble alginate by VxAly7B but is helpful for binding and degradation of insoluble alginate gel. This study provides new insights into the function of CBM32 on alginate gel, which may inspire the application strategy of CBMs in insoluble substrates.

Comparison of Biochemical Characteristics, Action Models, and Enzymatic Mechanisms of a Novel Exolytic and Two Endolytic Lyases with Mannuronate Preference

Recent explorations of tool-like alginate lyases have been focused on their oligosaccharide-yielding properties and corresponding mechanisms, whereas most were reported as endo-type with α-L-guluronate (G) preference. Less is known about the β-D-mannuronate (M) preference, whose commercial production and enzyme application is limited. In this study, we elucidated Aly6 of Flammeovirga sp. strain MY04 as a novel M-preferred exolytic bifunctional lyase and compared it with AlgLs of Pseudomonas aeruginosa (Pae-AlgL) and Azotobacter vinelandii (Avi-AlgL), two typical M-specific endolytic lyases. This study demonstrated that the AlgL and heparinase_II_III modules play indispensable roles in determining the characteristics of the recombinant exo-type enzyme rAly6, which is preferred to degrade M-enriched substrates by continuously cleaving various monosaccharide units from the nonreducing end, thus yielding various size-defined ΔG-terminated oligosaccharides as intermediate products. By contrast, the endolytic enzymes Pae-rAlgL and Avi-rAlgL varied their action modes specifically against M-enriched substrates and finally degraded associated substrate chains into various size-defined oligosaccharides with a succession rule, changing from ΔM to ΔG-terminus when the product size increased. Furthermore, site-directed mutations and further protein structure tests indicated that H¹⁹⁵NHSTW is an active, half-conserved, and essential enzyme motif. This study provided new insights into M-preferring lyases for novel resource discoveries, oligosaccharide preparations, and sequence determinations.

Structure Characteristics, Biochemical Properties, and Pharmaceutical Applications of Alginate Lyases

Alginate, the most abundant polysaccharides of brown algae, consists of various proportions of uronic acid epimers α-L-guluronic acid (G) and β-D-mannuronic acid (M). Alginate oligosaccharides (AOs), the degradation products of alginates, exhibit excellent bioactivities and a great potential for broad applications in pharmaceutical fields. Alginate lyases can degrade alginate to functional AOs with unsaturated bonds or monosaccharides, which can facilitate the biorefinery of brown algae. On account of the increasing applications of AOs and biorefinery of brown algae, there is a scientific need to explore the important aspects of alginate lyase, such as catalytic mechanism, structure, and property. This review covers fundamental aspects and recent developments in basic information, structural characteristics, the structure-substrate specificity or catalytic efficiency relationship, property, molecular modification, and applications. To meet the needs of biorefinery systems of a broad array of biochemical products, alginate lyases with special properties, such as salt-activated, wide pH adaptation range, and cold adaptation are outlined. Withal, various challenges in alginate lyase research are traced out, and future directions, specifically on the molecular biology part of alginate lyases, are delineated to further widen the horizon of these exceptional alginate lyases.

Purification and Characterization of a Novel Alginate Lyase from a Marine Streptomyces Species Isolated from Seaweed

Alginate, a natural polysaccharide derived from brown seaweed, is finding multiple applications in biomedicine via its transformation through chemical, physical, and, increasingly, enzymatic processes. In this study a novel alginate lyase, AlyDS44, was purified and characterized from a marine actinobacterium, Streptomyces luridiscabiei, which was isolated from decomposing seaweed. The purified enzyme had a specific activity of 108.6 U/mg, with a molecular weight of 28.6 kDa, and was composed of 260 amino acid residues. AlyDS44 is a bifunctional alginate lyase, active on both polyguluronate and polymannuronate, though it preferentially degrades polyguluronate. The optimal pH of this enzyme is 8.5 and the optimal temperature is 45 °C. It is a salt-tolerant alginate lyase with an optimal activity at 0.6 M NaCl. Metal ions Mn²⁺, Co²⁺, and Fe²⁺ increased the alginate degrading activity, but it was inhibited in the presence of Zn²⁺ and Cu²⁺. The highly conserved regions of its amino acid sequences indicated that AlyDS44 belongs to the polysaccharide lyase family 7. The main breakdown products of the enzyme on alginate were disaccharides, trisaccharides, and tetrasaccharides, which demonstrated that this enzyme acted as an endo-type alginate lyase. AlyDS44 is a novel enzyme, with the potential for efficient production of alginate oligosaccharides with low degrees of polymerization.

Secretory Expression of an Alkaline Alginate Lyase With Heat Recovery Property in Yarrowia lipolytica

Alginate lyase possesses wide application prospects for the degradation of brown algae and preparation of alginate oligosaccharides, and its degradation products display a variety of biological activities. Although many enzymes of this type have been reported, alginate lyases with unique properties are still relatively rare. In the present work, an alginate lyase abbreviated as Alyw203 has been cloned from Vibrio sp. W2 and expressed in food-grade Yarrowia lipolytica. The Alyw203 gene consists of an open reading frame (ORF) of 1,566 bp containing 521 amino acids, of which the first 17 amino acids are considered signal peptides, corresponding to secretory features. The peak activity of the current enzyme appears at 45°C with a molecular weight of approximately 57.0 kDa. Interestingly, Alyw203 exhibits unique heat recovery performance, returning above 90% of its initial activity in the subsequent incubation for 20 min at 10°C, which is conducive to the recovery of current enzymes at low-temperature conditions. Meanwhile, the highest activity is obtained under alkaline conditions of pH 10.0, showing outstanding pH stability. Additionally, as an alginate lyase independent of NaCl and resistant to metal ions, Alyw203 is highly active in various ionic environments. Moreover, the hydrolyzates of present enzymes are mainly concentrated in the oligosaccharides of DP1–DP2, displaying perfect product specificity. The alkali suitability, heat recovery performance, and high oligosaccharide yield of Alyw203 make it a potential candidate for industrial production of the monosaccharide and disaccharide.

Biochemical Characterization of a Novel Exo-Type PL7 Alginate Lyase VsAly7D from Marine Vibrio sp. QY108

Brown algae is a kind of renewable resource for biofuels production. As the major component of carbohydrate in the cell walls of brown algae, alginate can be degraded into unsaturated monosaccharide by exo-type alginate lyases, then converted into 4-deoxy-L-erythro-5-hexoseulose uronate (DEH) by a non-enzyme reaction, which is an important raw material for the preparation of bioethanol. In our research, a novel exo-type alginate lyase, VsAly7D, belonging to the PL7 family was isolated from marine bacterium Vibrio sp. QY108 and recombinantly expressed in Escherichia coli. The purified VsAly7D demonstrated the highest activity at 35 °C, whereas it still maintained 46.5% and 83.1% of its initial activity at 20 °C and 30 °C, respectively. In addition, VsAly7D exhibited the maximum activity under alkaline conditions (pH 8.0), with the simultaneously remaining stability between pH 8.0 and 10.0. Compared with other reported exo-type enzymes, VsAly7D could efficiently degrade alginate, poly-β-D-mannuronate (polyM) and poly-α-L-guluronate (polyG) with highest specific activities (663.0 U/mg, 913.6 U/mg and 894.4 U/mg, respectively). These results showed that recombinant VsAly7D is a suitable tool enzyme for unsaturated alginate monosaccharide preparation and holds great promise for producing bioethanol from brown algae.

Alginate degrading enzymes: an updated comprehensive review of the structure, catalytic mechanism, modification method and applications of alginate lyases

Alginate, a kind of linear acidic polysaccharide, consists of α-L-guluronate (G) and β-D-mannuronate (M). Both alginate and its degradation products (alginate oligosaccharides) possess abundant biological activities such as antioxidant activity, antitumor activity, and antimicrobial activity. Therefore, alginate and alginate oligosaccharides have great value in food, pharmaceutical, and agricultural fields. Alginate lyase can degrade alginate into alginate oligosaccharides via the β-elimination reaction. It plays an important role in marine carbon recycling and the deep utilization of brown algae. Elucidating the structural features of alginate lyase can improve our knowledge of its catalytic mechanisms. With the development of structural analysis techniques, increasing numbers of alginate lyases have been characterized at the structural level. Hence, it is essential and helpful to summarize and discuss the up-to-date findings. In this review, we have summarized progress on the structural features and the catalytic mechanisms of alginate lyases. Furthermore, the molecular modification strategies and the applications of alginate lyases have also been discussed. This comprehensive information should be helpful to expand the applications of alginate lyases.

Alginate derived functional oligosaccharides: Recent developments, barriers, and future outlooks

Alginate is a biopolymer used extensively in the food, pharmaceutical, and chemical industries. Alginate oligosaccharides (AOS) derived from alginate exhibit superior biological activities and therapeutic potential. Alginate lyases with characteristic substrate specificity can facilitate the production of a broad array of AOS with precise structure and functionality. By adopting innovative analytical tools in conjunction with focused clinical studies, the structure-bioactivity relationship of a number of AOS has been brought to light. This review covers fundamental aspects and recent developments in AOS research. Enzymatic and microbial processes involved in AOS production from brown algae and sequential steps involved in AOS structure elucidation are outlined. Biological mechanisms underlying the health benefits of AOS and their potential industrial and therapeutic applications are elaborated. Withal, various challenges in AOS research are traced out, and future directions, specifically on recombinant systems for AOS preparation, are delineated to further widen the horizon of these exceptional oligosaccharides.

Characteristics and applications of alginate lyases: A review

Brown algae, as the main source of alginate, are a type of marine biomass with a very high output. Alginate, a polysaccharide composed of β-D-mannuronic acid (M) and α-L-guluronic acid (G), has great potential for applications in the food, cosmetic and pharmaceutical industries. Alginate lyases (Alys) can degrade alginate polymers into oligosaccharides or monosaccharides, resulting in a broad application field. Alys can be used for both the production of alginate oligosaccharides and the biorefinery of brown algae. In view of their important functions, an increasing number of Alys have been isolated and characterized. For better application, a comprehensive understanding of Alys is essential. Therefore, in this paper, we summarized recently discovered Alys, discussed their characteristics, and introduced their structural properties, degradation patterns and biological roles in alginate-degrading organisms. In addition, applications of Alys have been illustrated with examples. This paper provides a relatively comprehensive description of Alys, which is significant for Alys exploration and application.

Characterization of a New Intracellular Alginate Lyase with Metal Ions-Tolerant and pH-Stable Properties

Alginate lyases play an important role in alginate oligosaccharides (AOS) preparation and brown seaweed processing. Many extracellular alginate lyases have been characterized to develop efficient degradation tools needed for industrial applications. However, few studies focusing on intracellular alginate lyases have been conducted. In this work, a novel intracellular alkaline alginate lyase Alyw202 from Vibrio sp. W2 was cloned, expressed and characterized. Secretory expression was performed in a food-grade host, Yarrowia lipolytica. Recombinant Alyw202 with a molecular weight of approximately 38.3 kDa exhibited the highest activity at 45 °C and more than 60% of the activity in a broad pH range of 3.0 to 10.0. Furthermore, Alyw202 showed remarkable metal ion-tolerance, NaCl independence and the capacity of degrading alginate into oligosaccharides of DP2-DP4. Due to the unique pH-stable and high salt-tolerant properties, Alyw202 has potential applications in the food and pharmaceutical industries.

Characterization of a New Bifunctional and Cold-Adapted Polysaccharide Lyase (PL) Family 7 Alginate Lyase from Flavobacterium sp

Alginate oligosaccharides produced by enzymatic degradation show versatile physiological functions and biological activities. In this study, a new alginate lyase encoding gene alyS02 from Flavobacterium sp. S02 was recombinantly expressed at a high level in Yarrowia lipolytica, with the highest extracellular activity in the supernatant reaching 36.8 ± 2.1 U/mL. AlyS02 was classified in the polysaccharide lyase (PL) family 7. The optimal reaction temperature and pH of this enzyme were 30 °C and 7.6, respectively, indicating that AlyS02 is a cold-adapted enzyme. Interestingly, AlyS02 contained more than 90% enzyme activity at 25 °C, higher than other cold-adapted enzymes. Moreover, AlyS02 is a bifunctional alginate lyase that degrades both polyG and polyM, producing di- and trisaccharides from alginate. These findings suggest that AlyS02 would be a potent tool for the industrial applications.

Expression and Characterization of an Alginate Lyase and Its Thermostable Mutant in Pichia pastoris

Alginate is one of the most abundant polysaccharides in algae. Alginate lyase degrades alginate through a β-elimination mechanism to produce alginate oligosaccharides with special bioactivities. Improving enzyme activity and thermal stability can promote the application of alginate lyase in the industrial preparation of alginate oligosaccharides. In this study, the recombinant alginate lyase cAlyM and its thermostable mutant 102C300C were expressed and characterized in Pichia pastoris. The specific activities of cAlyM and 102C300C were 277.1 U/mg and 249.6 U/mg, respectively. Both enzymes showed maximal activity at 50 °C and pH 8.0 and polyG preference. The half-life values of 102C300C at 45 °C and 50 °C were 2.6 times and 11.7 times the values of cAlyM, respectively. The degradation products of 102C300C with a lower degree of polymerization contained more guluronate. The oligosaccharides with a polymerization degree of 2–4 were the final hydrolytic products. Therefore, 102C300C is potentially valuable in the production of alginate oligosaccharides with specific M/G ratio and molecular weights.

Cloning, Secretory Expression and Characterization of a Unique pH-Stable and Cold-Adapted Alginate Lyase

Cold-adapted alginate lyases have unique advantages for alginate oligosaccharide (AOS) preparation and brown seaweed processing. Robust and cold-adapted alginate lyases are urgently needed for industrial applications. In this study, a cold-adapted alginate lyase-producing strain Vibrio sp. W2 was screened. Then, the gene ALYW201 was cloned from Vibrio sp. W2 and expressed in a food-grade host, Yarrowia lipolytica. The secreted Alyw201 showed the activity of 64.2 U/mL, with a molecular weight of approximate 38.0 kDa, and a specific activity of 876.4 U/mg. Alyw201 performed the highest activity at 30 °C, and more than 80% activity at 25-40 °C. Furthermore, more than 70% of the activity was obtained in a broad pH range of 5.0-10.0. Alyw201 was also NaCl-independent and salt-tolerant. The degraded product was that of the oligosaccharides of DP (Degree of polymerization) 2-6. Due to its robustness and its unique pH-stable property, Alyw201 can be an efficient tool for industrial production.