Study on expression and action mode of recombinant alginate lyases based on conserved domains reconstruction

Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

Microbulbifer is a genus of halophilic bacteria that are commonly detected in the commensal marine microbiomes. These bacteria have been recognized for their ability to degrade polysaccharides and other polymeric materials. Increasingly, Microbulbifer genomes indicate these bacteria to be an untapped reservoir for novel natural product discovery and biosynthetic novelty. In this review, we summarize the distribution of Microbulbifer bacteria, activities of the various polymer degrading enzymes that these bacteria produce, and an up-to-date summary of the natural products that have been isolated from Microbulbifer strains. We argue that these bacteria have been hiding in plain sight, and contemporary efforts into their genome and metabolome mining are going to lead to a proliferation of Microbulbifer-derived natural products in the future. We also describe, where possible, the ecological interactions of these bacteria in marine microbiomes.

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.

Characterization of a multi-domain exo-β-1,3-galactanase from Paenibacillus xylanexedens

β-1,3-Galactanases selectively degrade β-1,3-galactan, thus it is an attractive enzyme technique to map high-galactan structure and prepare galactooligosaccharides. In this work, a gene encoding exo-β-1,3-galactanase (PxGal43) was screened form Paenibacillus xylanexedens, consisting of a GH43 domain, a CBM32 domain and α-L-arabinofuranosidase B (AbfB) domain. Using β-1,3-galactan (AG-II-P) as substrate, the recombined enzyme expressed in Escherichia coli BL21 (DE3) exhibited an optimal activity at pH 7.0 and 30 °C. The enzyme was thermostable, retaining >70 % activity after incubating at 50 °C for 2 h. In addition, it showed high tolerance to various metal ions, denaturants and detergents. Substrate specificity indicated that PxGal43 hydrolysis only β-1,3-linked galactosyl oligosaccharides and polysaccharides, releasing galactose as an exo-acting manner. The function of the CBM32 and AbfB domain was revealed by their sequential deletion and suggested that their connection to the catalytic domain was crucial for the oligomerization, catalytic activity, substrate binding and thermal stability of PxGal43. The substrate docking and site-directed mutagenesis proposed that Glu191, Gln244, Asp138 and Glu81 served as the catalytic acid, catalytic base, pKa modulator, and substrate identifier in PxGal43, respectively. These results provide a better understanding and optimization of multi-domain bacterial GH43 β-1,3-galactanase for the degradation of arabinogalactan.

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.

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.

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.

A Recombinant Alginate Lyase Algt1 with Potential in Preparing Alginate Oligosaccharides at High-Concentration Substrate

Alginate lyase has been demonstrated as an efficient tool in the preparation of functional oligosaccharides (AOS) from alginate. The high viscosity resulting from the high concentration of alginate poses a limiting factor affecting enzymatic hydrolysis, particularly in the preparation of the fragments with low degrees of polymerization (DP). Herein, a PL7 family alginate lyase Algt from Microbulbifer thermotolerans DSM 19189 was developed and expressed in Pichia pastoris. The recombinant alginate lyase Algt1 was constructed by adopting the structural domain truncation strategy, and the enzymatic activity towards the alginate was improved from 53.9 U/mg to 212.86 U/mg compared to Algt. Algt1 was stable when incubated at 40 °C for 90 min, remaining with approximately 80.9% of initial activity. The analyses of thin-layer chromatography (TLC), fast protein liquid chromatography (FPLC), and electrospray ionization mass spectrometry (ESI-MS) demonstrated that the DP of the minimum identifiable substrate of Algt1 was five, and the main hydrolysis products were AOS with DP 1-4. Additionally, 1-L the enzymatic hydrolysis system demonstrated that Algt1 exhibited an effective degradation at alginate concentrations of up to 20%, with the resulting products of monosaccharides (14.02%), disaccharides (21.10%), trisaccharides (37.08%), and tetrasaccharides (27.80%). These superior properties of Algt1 make it possible to efficiently generate functional AOS with low DP in industrial processing.

Efficient Degradation of Alginate and Preparation of Alginate Oligosaccharides by a Novel Biofunctional Alginate Lyase with High Activity and Excellent Thermophilic Features

The enzymatic degradation of seaweed polysaccharides is gaining interest for its potential in the production of functional oligosaccharides and fermentable sugars. Herein, a novel alginate lyase, AlyRm3, was cloned from a marine strain, Rhodothermus marinus DSM 4252. The AlyRm3 showed optimal activity (37,315.08 U/mg) at 70 °C and pH 8.0, with the sodium alginate used as a substrate. Noticeably, AlyRm3 was stable at 65 °C and also exhibited 30% of maximal activity at 90 °C. These results indicated that AlyRm3 is a thermophilic alginate lyase that efficiently degrades alginate at high industrial temperatures (>60 °C). The FPLC and ESI−MS analyses suggested that AlyRm3 primarily released disaccharides and trisaccharides from the alginate, polyM, and polyG in an endolytic manner. In the saccharification process of sodium alginate (0.5%, w/v), the AlyRm3 yielded numerous reducing sugars (1.73 g/L) after 2 h of reaction. These results indicated that AlyRm3 has a high enzymatic capacity for saccharifying the alginate, and could be used to saccharify the alginate biomass before the main fermentation process for biofuels. These properties make AlyRm3 a valuable candidate for both fundamental research and industrial applications.

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.

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.

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.

Recent Advancements in Microbial Polysaccharides: Synthesis and Applications

Polysaccharide materials are widely applied in different applications including food, food packaging, drug delivery, tissue engineering, wound dressing, wastewater treatment, and bioremediation sectors. They were used in these domains due to their efficient, cost-effective, non-toxicity, biocompatibility, and biodegradability. As is known, polysaccharides can be synthesized by different simple, facile, and effective methods. Of these polysaccharides are cellulose, Arabic gum, sodium alginate, chitosan, chitin, curdlan, dextran, pectin, xanthan, pullulan, and so on. In this current article review, we focused on discussing the synthesis and potential applications of microbial polysaccharides. The biosynthesis of polysaccharides from microbial sources has been considered. Moreover, the utilization of molecular biology tools to modify the structure of polysaccharides has been covered. Such polysaccharides provide potential characteristics to transfer toxic compounds and decrease their resilience to the soil. Genetically modified microorganisms not only improve yield of polysaccharides, but also allow economically efficient production. With the rapid advancement of science and medicine, biosynthesis of polysaccharides research has become increasingly important. Synthetic biology approaches can play a critical role in developing polysaccharides in simple and facile ways. In addition, potential applications of microbial polysaccharides in different fields with a particular focus on food applications have been assessed.

Bacterial alginate metabolism: an important pathway for bioconversion of brown algae

Brown macroalgae have attracted great attention as an alternative feedstock for biorefining. Although direct conversion of ethanol from alginates (major components of brown macroalgae cell walls) is not amenable for industrial production, significant progress has been made not only on enzymes involved in alginate degradation, but also on metabolic pathways for biorefining at the laboratory level. In this article, we summarise recent advances on four aspects: alginate, alginate lyases, different alginate-degrading systems, and application of alginate lyases and associated pathways. This knowledge will likely inspire sustainable solutions for further application of both alginate lyases and their associated pathways.

Potential applications of alginate oligosaccharides for biomedicine - A mini review

Extensive research on marine algae, especially on their health-promoting properties, has been conducted. Various ingredients with potential biomedical applications have been discovered and extracted from marine algae. Alginate oligosaccharides are low molecular weight alginate polysaccharides present in cell walls of brown algae. They exhibit various health benefits such as anti-inflammatory, anti-microbial, anti-oxidant, anti-tumor and immunomodulation. Their low-toxicity, non-immunogenicity, and biodegradability make them an excellent material in biomedicine. Alginate oligosaccharides can be chemically or biochemically modified to enhance their biological activity and potential in pharmaceutical applications. This paper provides a brief overview on alginate oligosaccharides characteristics, modification patterns and highlights their vital health promoting properties.

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.

Characterization of an organic solvent-tolerant polysaccharide lyase from Microbulbifer thermotolerans DAU221

Alginate and its derivatives are annually produced approximately 30,000 tons or more and are applied to various industries as they are natural polymers. The global market for alginate and its derivatives has been growing steadily. There is little research compared to other enzymes produced through biomass degradation or modification. An alginate lyase, MtAl138, from Microbulbifer thermotolerans DAU221 was cloned and identified in Escherichia coli BL21 (DE3). MtAl138 contains a highly conserved motif (R⁵³⁸TELR, Q⁶⁰⁷IH⁶⁰⁹, and YFKAGVY⁷¹⁶NQ), which indicates that it belongs to the polysaccharide lyase family 7 (PL7). MtAl138, with a molecular weight of 77 kDa worked optimally at 45 °C and pH 7.4. MtAl138 showed twice as much activity as when there was no NaCl when there was between 100 and 600 mM NaCl. Moreover, its activity increased in organic solvents such as benzene, hexane, methanol, and toluene. Based on the thin layer chromatography analyses, MtAl38 is an endo-type enzyme that produces di-, tri-, or tetrasaccharides from polyG and polyM. This study provided that MtAl138 is an endoenzyme that showed outstanding enzymatic activity at concentrated salt solutions and organic solvents, which makes it a reasonably attractive enzyme for use in various industries.

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.

Construction and biochemical characterization of a novel hybrid alginate lyase with high activity by module recombination to prepare alginate oligosaccharides

Alginate lyases are essential tools to prepare alginate oligosaccharides with various biological activities. However, alginate lyases with excellent properties such as high activity and good thermal stability are still in shortage. Therefore, it is crucial to exploit new alginate lyases with high activity and polysaccharide-degrading efficiency for alginate oligosaccharide preparation. Herein, we proposed to construct a novel hybrid alginate lyase with improved property by module recombination. The hybrid alginate lyase, designated as Aly7C, was successfully constructed by recombining the carbohydrate binding module (CBM) of Aly7A with the catalytic module of Aly7B. Interestingly, the hybrid enzyme Aly7C exhibited higher activity than the catalytic domain. Moreover, it could degrade sodium alginate, polyM and polyG into oligosaccharides with degrees of polymerization (Dps) 2-5, which exhibit perfect product specificity. This work provides a new insight into well-defined generation of alginate oligosaccharides with associated CBMs and enhances the understanding of functions of the modules.

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.

Enzymatic preparation of a low-molecular-weight polysaccharide rich in uronic acid from the seaweed Laminaria japonica and evaluation of its hypolipidemic effect in mice

Here, we describe a method combining thermo-acid pretreatment and alginate lyase hydrolysis to prepare a low-molecular-weight polysaccharide from the seaweed Laminaria japonica (SP). The in vitro results showed that SP displayed obvious absorption of oil (2.95 g g-1) and cholesterol (21.87 g g-1 at pH 2.0). In addition, the in vivo assessment of SP-related anti-obesity effects in C57BL/6J mice fed a high-fat diet and treated with SP for 8 weeks revealed that SP significantly reduced weight gain and lipid accumulation in white adipose and liver tissues, improved serum lipid profiles, and ameliorated intestinal damage. Moreover, SP activated the AMP-activated protein kinase pathway in liver tissues, downregulated sterol regulatory element-binding protein and fatty acid synthase, and suppressed lipid synthesis. These findings indicated that SP extracted from L. japonica might represent a potent functional food exhibiting anti-obesity effects.

Elucidation of a Unique Pattern and the Role of Carbohydrate Binding Module of an Alginate Lyase

Alginate oligosaccharides with different degrees of polymerization (DPs) possess diverse physiological activities. Therefore, in recent years, increasing attention has been drawn to the use of enzymes for the preparation of alginate oligosaccharides for food and industrial applications. Previously, we identified and characterized a novel bifunctional alginate lyase Aly7A, which can specifically release trisaccharide from three different substrate types with a unique degradation pattern. Herein, we investigated its degradation pattern by modular truncation and molecular docking. The results suggested that Aly7A adopted a unique action mode towards different substrates with the substrate chain sliding into the binding pocket of the catalytic domain to position the next trisaccharide for cleavage. Deletion of the Aly7A carbohydrate binding module (CBM) domain resulted in a complex distribution of degradation products and no preference for trisaccharide formation, indicating that the CBM may act as a “controller” during the trisaccharide release process. This study further testifies CBM as a regulator of product distribution and provides new insights into well-defined generation of alginate oligosaccharides with associated CBMs.

Rational Design of Alginate Lyase from Microbulbifer sp. Q7 to Improve Thermal Stability

Alginate lyase degrades alginate by the β-elimination mechanism to produce oligosaccharides with special bioactivities. The low thermal stability of alginate lyase limits its industrial application. In this study, introducing the disulfide bonds while using the rational design methodology enhanced the thermal stability of alginate lyase cAlyM from Microbulbifer sp. Q7. Enzyme catalytic sites, secondary structure, spatial configuration, and molecular dynamic simulation were comprehensively analyzed. When compared with cAlyM, the mutants D102C-A300C and G103C-T113C showed an increase by 2.25 and 1.16 h, respectively, in half-life time at 45 °C, in addition to increases by 1.7 °C and 0.4 °C in the melting temperature, respectively. The enzyme-specific activity and k_cat/K_m values of D102C-A300C were 1.8- and 1.5-times higher than those of cAlyM, respectively. The rational design strategy that was used in this study provides a valuable method for improving the thermal stability of the alginate lyase.

Effects of module truncation on biochemical characteristics and products distribution of a new alginate lyase with two catalytic modules

In this work, we investigated the functions of structural modules within alginate lyase by truncating an endo-type alginate lyase into two successive catalytic modules. The effects of module deletion on biochemical characteristics and product distributions were further investigated. The N-terminal module (Aly7B-CDI) exhibited no activity toward alginate, polyM or polyG, but the C-terminal module (Aly7B-CDII) retained its activity. The full-length enzyme (Aly7B) and its truncated counterpart (Aly7B-CDII) had similar substrate specificities, but Aly7B-CDII had lower activity. Moreover, the activity of Aly7B was much higher than Aly7B-CDII at 30°C. Aly7B-CDII, however, possessed higher optimal pH and better pH stability than the full-length enzyme. The final degradation products for Aly7B were unsaturated di-, tri- and tetra-oligosaccharides, and those for Aly7B-CDII were unsaturated mono-, di-, tri-, tetra- and penta-oligosaccharides. Therefore, the potential impact of the noncatalytic module Aly7B-CDI on the catalytic module Aly7B-CDII was further elucidated by characterizing Aly7B and its truncations. These data contribute to the functional understanding of these differing modules.