Marine-polysaccharide degrading enzymes: Status and prospects

Enzymatic production of diverse N-acetyl chitooligosaccharides employing a novel bifunctional chitinase and its engineered variants

Bioproduction of diverse N-acetyl chitooligosaccharides from chitin is of great value. In the study, a novel GH family 18 bifunctional chitinase gene (PsChi82) from Paenibacillus shirakamiensis was identified, expressed and biochemically characterized. PsChi82 was most active at pH 5.0, and 55 °C, and displayed remarkable pH stability with the broad pH range of 3.0-12.0. It showed high chitosanase activity of 10.6 U mg-1 and diverse hydrolysis products of GlcNAc, (GlcNAc)2, GlcN-GlcNAc and (GlcN)2-GlcNAc, which may facilitate comprehensively understanding of structure-function relationships of N-acetyl COSs. Three engineered variants were then expressed and characterized. Among them, PsChi82-CBM26 possessed specific activity of 25.1 U mg-1 against colloidal chitin, which was 2.1 folds higher than that of PsChi82. The diverse N-acetyl COSs were subsequently produced by PsChi82-CBM26 with a sugar content of 23.2 g L-1. These excellent properties may make PsChi82-CBM26 potentially useful for N-acetyl COSs production in the food and chemical industries.

Polysaccharides from Platycodon grandiflorum: A review of their extraction, structures, modifications, and bioactivities

Platycodon grandiflorum (P. grandiflorum) has long been used as a food and traditional herbal medicine. As a food, P. grandiflorum is often transformed into pickles for consumption, and as a traditional Chinese medicine, P. grandiflorum clears the lung, nourishes the pharynx, dispels phlegm, and discharges pus. Polysaccharides are among the main active components of P. grandiflorum. Recent literature has described the preparation, identification, and pharmacological activity of these polysaccharides. Studies have shown that these polysaccharides exhibit a variety of significant biological effects in vitro and in vivo, such as immune stimulation and antioxidant, anti-liver injury, anti-apoptosis and antitumour effects. However, there is no systematic summary of the related research articles on P. grandiflorum polysaccharide, which undoubtedly brings some difficulties to the future research. The purpose of this review is to comprehensively describe research progress on the extraction, purification, structural characterization, modification, and biological activity of P. grandiflorum polysaccharides. The shortcomings of recent research are summarized, further research on their biological activity is proposed to provide new reference value for the application of P. grandiflorum polysaccharides in drugs and health products in the future.

Efficacious bioconversion of alginate/cellulose to value-added oligosaccharides by alginate-degrading GH5 endoglucanase from Trichoderma asperellum

Enzymatic degradation of lignocellulosic biomass provides an eco-friendly approach to produce value-added macromolecules, e.g., bioactive polysaccharides. A novel acidophilic GH5 β-1,4-endoglucanase (termed TaCel5) from Trichoderma asperellum ND-1 was efficiently expressed in Komagataella phaffii (∼1.5-fold increase, 38.42 U/mL). TaCel5 displayed both endoglucanase (486.3 U/mg) and alginate lyase (359.5 U/mg) enzyme activities. It had optimal pH 3.0 and strong pH stability (exceed 86 % activity retained over pH range 3.0-5.0). 80 % activity (both endoglucanase and alginate lyase) was retained in the presence of 15 % ethanol or 3.42 M NaCl. Analysis of action mode revealed that hydrolytic activity of TaCel5 required at least three glucose (cellotriose) residues, yielding mainly cellobiose. Glu241 and Glu352 are essential catalytic residues, while Asp106, Asp277 and Asp317 play auxiliary roles in cellulose degradation. TaCel5 displayed high hydrolysis efficiency for glucan and alginate substrates. ESI-MS analysis indicated that the enzymatic hydrolysates of alginate mainly contained disaccharides and heptasaccharides. This is the first detailed report of a bifunctional GH5 endoglucanase/alginate lyase enzyme from T. asperellum. Thus TaCel5 has strong potential in food and feed industries as a catalyst for bioconversion of cellulose- and alginate-containing waste materials into value-added products oligosaccharides, which was of great benefit both for the economy and environment.

Genome Analysis of Multiple Polysaccharide-Degrading Bacterium Microbulbifer thermotolerans HB226069: Determination of Alginate Lyase Activity

Polysaccharide-degrading bacteria are key participants in the global carbon cycle and algal biomass recycling. Herein, a polysaccharide lyase-producing strain HB226069 was isolated from Sargassum sp. from Qingge Port, Hainan, China. Results of the phylogenetic of the 16S rRNA gene and genotypic analysis indicated that the isolate should be classified as Microbulbifer thermotolerans. The whole genome is a 4,021,337 bp circular chromosome with a G+C content of 56.5%. Analysis of the predicted genes indicated that strain HB226069 encoded 161 carbohydrate-active enzymes (CAZymes), and abundant putative enzymes involved in polysaccharide degradation were predicted, including alginate lyase, fucosidase, agarase, xylanase, cellulase, pectate lyase, amylase, and chitinase. Three of the putative polysaccharide lyases from PL7 and PL17 families were involved in alginate degradation. The alginate lyases of strain HB226069 showed the maximum activity of 117.4 U/mL at 50 °C, pH 7.0, and 0.05 M FeCl3, while exhibiting the best stability at 30 °C and pH 7.0. The Thin Layer Chromatography (TLC) and Electrospray Ionization Mass Spectrometry (ESI-MS) analyses indicated that the alginate oligosaccharides (AOSs) degraded by the partially purified alginate lyases contained oligosaccharides of DP2-DP5 and monosaccharide while reacting for 36 h. The complete genome of M. thermotolerans HB226069 enriches our understanding of the mechanism of polysaccharide lyase production and supports its potential application in polysaccharide degradation.

Improvement of thermostability by increasing rigidity in the finger regions and flexibility in the catalytic pocket area of Pseudoalteromonas porphyrae κ-carrageenase

Poor thermostability reduces the industrial application value of κ-carrageenase. In this study, the PoPMuSiC algorithm combined with site-directed mutagenesis was applied to improve the thermostability of the alkaline κ-carrageenase from Pseudoalteromonas porphyrae. The mutant E154A with improved thermal stability was successfully obtained using this strategy after screening seven rationally designed mutants. Compared with the wild-type κ-carrageenase (WT), E154A improved the activity by 29.4% and the residual activity by 51.6% after treatment at 50 °C for 30 min. The melting temperature (Tm) values determined by circular dichroism were 66.4 °C and 64.6 °C for E154A and WT, respectively. Molecular dynamics simulation analysis of κ-carrageenase showed that the flexibility decreased within the finger regions (including F1, F2, F3, F5 and F6) and the flexibility improved in the catalytic pocket area of the mutant E154A. The catalytic tunnel dynamic simulation analysis revealed that E154A led to enlarged catalytic tunnel volume and increased rigidity of the enzyme-substrate complex. The increasing rigidity within the finger regions and more flexible catalytic pocket of P. porphyrae κ-carrageenase might be a significant factor for improvement of the thermostability of the mutant κ-carrageenase E154A. The proposed rational design strategy could be applied to improve the enzyme kinetic stability of other industrial enzymes. Moreover, the hydrolysates of κ-carrageenan digested by the mutant E154A demonstrated increased scavenging activities against hydroxyl (OH) radicals and 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radicals compared with the undigested κ-carrageenan.

Expression and Characterization of an Efficient Alginate Lyase from Psychromonas sp. SP041 through Metagenomics Analysis of Rotten Kelp

Alginate is derived from brown algae, which can be cultivated in large quantities. It can be broken down by alginate lyase into alginate oligosaccharides (AOSs), which exhibit a higher added value and better bioactivity than alginate. In this study, metagenomic technology was used to screen for genes that code for high-efficiency alginate lyases. The candidate alginate lyase gene alg169 was detected from Psychromonas sp. SP041, the most abundant species among alginate lyase bacteria on selected rotten kelps. The alginate lyase Alg169 was heterologously expressed in Escherichia coli BL21 (DE3), Ni-IDA-purified, and characterized. The optimum temperature and pH of Alg169 were 25 °C and 7.0, respectively. Metal ions including Mn2+, Co2+, Ca2+, Mg2+, Ni2+, and Ba2+ led to significantly increased enzyme activity. Alg169 exhibited a pronounced dependence on Na+, and upon treatment with Mn2+, its activity surged by 687.57%, resulting in the highest observed enzyme activity of 117,081 U/mg. Bioinformatic analysis predicted that Alg169 would be a double-domain lyase with a molecular weight of 65.58 kDa. It is a bifunctional enzyme with substrate specificity to polyguluronic acid (polyG) and polymannuronic acid (polyM). These results suggest that Alg169 is a promising candidate for the efficient manufacturing of AOSs from brown seaweed.

Improvement of the catalytic performance of chitosanase Csn-PD from Paenibacillus dendritiformis by semi-rational design

Chitooligosaccharides (COS) possess versatile functional properties that have found extensive applications across various fields. Chitosanase can specifically hydrolyze β-1,4 glycosidic bonds in chitosan to produce COS. In this study, Csn-PD, a glycoside hydrolase family 46 chitosanase from Paenibacillus dendritiformis, which produces (GlcN)2 as its main product, was rationally redesigned aiming to improve its catalytic performance. Based on the results of molecular docking analysis and multiple sequence alignment, four amino acid residues in Csn-PD (I101, T120, T220, and Y259) were pinpointed for targeted mutations. Beneficial mutations in terms of enhanced catalytic activity were then combined by site-directed mutagenesis. Notably, the most promising variant, Csn-PDT6 (Csn-PD I101M/T120E/T220G), exhibited an impressive eight-fold surge in activity compared to the wild-type Csn-PD. This heightened enzymatic activity was complemented by an enhanced pH stability profile. A compelling feature of Csn-PDT6 is its preservation of the hydrolytic product profile observed in Csn-PD. This characteristic further accentuates its candidacy for the targeted production of (GlcN)2. The success of our strategic approach is vividly illustrated by the significant improvements achieved in the catalytic performance of the chitosanase, encompassing both its activity and stability. These developments offer a valuable model that may have implications for the semi-rational design of other enzymes.

An enzyme-pHBH method for specific quantification of porphyran

Porphyran, the major polysaccharide extracted from Porphyra, exhibits tremendous potential for development as functional food or pharmaceutical due to its multiple biological activities. The quantitative analysis of porphyran is important for the quality control in product development. However, the specific quantitative method of porphyran has not been established, and the lack of reference substance makes the quantification more challenging. Here, a common component of porphyran, with high purity, similar molecular weight distribution, sourced from different Porphyra producing areas in China was first prepared by a series of isolation and purification steps, and utilized as the reference substance for porphyran quantification. Subsequently, the porphyran was fully degraded into oligosaccharides by using a β-porphyranase, followed by employing para-hydroxybenzoic acid hydrazide (pHBH) method to detect the content of the generated reducing sugar. The enzyme-pHBH method for porphyran specific quantification was established. Results showed that this method was validated with good linearity, high accuracy and precision, and reliability. Addtionally, NaCl with a concentration below 0.5 %, alcohol under 8 % and other polysaccharide including chitosan, agarose, chondrotin sulfate, alginate, hyaluronic acid and κ-carrageenan did not interfere with this method. This approach is promising for quality control of the porphyran products and offers a feasible strategy for the specific quantification of other polysaccharides.

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.

Identification and evaluation of CAZyme genes, along with functional characterization of a new GH46 chitosanase from Streptomyces sp. KCCM12257

The genomic analysis of Streptomyces sp. KCCM12257 presented 233 CAZyme genes with a predominant glycosyl hydrolase family. This contributes degradation of various polysaccharides including chitin and chitosan, and other promising candidates for the production of different oligosaccharides. We screened the strain providing different polysaccharides as a sole source of carbon and strain KCCM12257, showed higher activity towards colloidal chitosan. Further, we identified and characterized a new chitosanase (MDI5907146) of GH46 family. There was no activity towards chitin, carboxymethylcellulose, or even with chitosan powder. This enzyme acts on colloidal chitosan and hydrolyzes it down into monoacetyl chitobiose, which consists of two glucosamine units with an acetyl group attached to them. The maximum enzyme activity was observed at pH 6.5 and 40 °C using colloidal chitosan as a substrate. The Co2+ metal ions almost double the reaction as compared to other metal ions. The dissociation constant (Km) and of colloidal chitosan (≥90 % and ≥75%DD) were 3.03 mg/ml and 5.01 mg/ml respectively, while maximum velocity (Vmax) values were found to be 36 mg/ml, and 30 μM/μg/min, respectively. Similarly, catalytic efficiency (Kcat/Km) of colloidal chitosan with ≥90 %DD was 1.9 fold higher than colloidal chitosan with ≥75%DD.

Enzymatic hydrolysates of κ-carrageenan by κ-carrageenase-CLEA immobilized on amine-modified ZIF-8 confer hypolipidemic activity in HepG2 cells

κ-Carrageenase can degrade κ-carrageenan to produce bioactive κ-carrageenan oligosaccharides (KCOs) that have potential applications in pharmaceutical, food, agricultural, and cosmetics industries. Immobilized enzymes gain their popularity due to their good reusability, enhanced stability, and tunability. In this study, the previously characterized catalytic domain of Pseudoalteromonas purpurea κ-carrageenase was covalently immobilized on the synthesized amine-modified zeolitic imidazolate framework-8 nanoparticles with the formation of cross-linked enzyme aggregates, and the immobilized κ-carrageenase was further characterized. The immobilized κ-carrageenase demonstrated excellent pH stability and good reusability, and exhibited higher optimal reaction temperature, better thermostability, and extended storage stability compared with the free enzyme. The KCOs produced by the immobilized κ-carrageenase could significantly decrease the TC, TG, and LDL-C levels in HepG2 cells, increase the HDL-C level in HepG2 cells, and reduce the free fatty acids level in Caco-2 cells. Biochemical assays showed that the KCOs could activate AMPK activity, increase the ratios of p-AMPK/AMPK and p-ACC/ACC, and downregulate the expression of the lipid metabolism related proteins including SREBP1 and HMGCR in the hyperlipidemic HepG2 cells. This study provides a novel and effective method for immobilization of κ-carrageenase, and the KCOs produced by the immobilized enzyme could be a potential therapeutic agent to prevent hyperlipidemia.

High-Value Utilization of Marine Biological Resources

The ocean covers 71% of the surface of our planet and comprises a diverse variety of biological resources-a combination of marine animals, marine plants, and marine microorganisms that have economic value for human beings [...].

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.

UV/H2O2-Degraded Polysaccharides from Sargassum fusiforme: Purification, Structural Properties, and Anti-Inflammatory Activity

The main purpose of this study was to analyze the structural properties and anti-inflammatory activity of the purified fractions derived from UV/H2O2-degraded polysaccharides from Sargassum fusiforme. Results indicated that twofractions with different monosaccharide compositions and morphological characteristics, PT-0.25 (yield 39.5%) and PT-0.5 (yield 23.9%), were obtained. The average molecular weights of PT-0.25 and PT-0.5 were 14.52 kDa and 22.89 kDa, respectively. In addition, PT-0.5 exhibited better anti-inflammatory activity with a clear dose dependence. The mechanism was associated with the inhibition of LPS-activated Toll-like receptor 4-mediated inflammatory pathways in RAW264.7 cells. The results showed that PT-0.5 was a complex polysaccharide mainly composed of 4-Fucp, t-Manp, 6-Galp, t-Fucp, and 3,4-GlcAp. These results would provide theoretical support for studying the structural properties and biological activities of UV/H2O2-degraded polysaccharides.

Production, Characterization and Application of a Novel Chitosanase from Marine Bacterium Bacillus paramycoides BP-N07

Chitooligosaccharides (COS), a high-value chitosan derivative, have many applications in food, pharmaceuticals, cosmetics and agriculture owing to their unique biological activities. Chitosanase, which catalyzes the hydrolysis of chitosan, can cleave β-1,4 linkages to produce COS. In this study, a chitosanase-producing Bacillus paramycoides BP-N07 was isolated from marine mud samples. The chitosanase enzyme (BpCSN) activity was 2648.66 ± 20.45 U/mL at 52 h and was able to effectively degrade chitosan. The molecular weight of purified BpCSN was approximately 37 kDa. The yield and enzyme activity of BpCSN were 0.41 mg/mL and 8133.17 ± 47.83 U/mg, respectively. The optimum temperature and pH of BpCSN were 50 °C and 6.0, respectively. The results of the high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) of chitosan treated with BpCSN for 3 h showed that it is an endo-chitosanase, and the main degradation products were chitobiose, chitotriose and chitotetraose. BpCSN was used for the preparation of oligosaccharides: 1.0 mg enzyme converted 10.0 g chitosan with 2% acetic acid into oligosaccharides in 3 h at 50 °C. In summary, this paper reports that BpCSN has wide adaptability to temperature and pH and high activity for hydrolyzing chitosan substrates. Thus, BpCSN is a chitosan decomposer that can be used for producing chitooligosaccharides industrially.

N-acetyl-d-glucosamine-based oligosaccharides from chitin: Enzymatic production, characterization and biological activities

Chitin, the second most abundant biopolymer, possesses diverse applications in the food, agricultural, and pharmaceutical industries due to its functional properties. However, the potential applications of chitin are limited owing to its high crystallinity and low solubility. N-acetyl chitooligosaccharides and lacto-N-triose II, the two types of GlcNAc-based oligosaccharides, can be obtained from chitin by enzymatic methods. With their lower molecular weights and improved solubility, these two types of GlcNAc-based oligosaccharides display more various beneficial health effects when compared to chitin. Among their abilities, they have exhibited antioxidant, anti-inflammatory, anti-tumor, antimicrobial, and plant elicitor activities as well as immunomodulatory and prebiotic effects, which suggests they have the potential to be utilized as food additives, functional daily supplements, drug precursors, elicitors for plants, and prebiotics. This review comprehensively covers the enzymatic methods used for the two types of GlcNAc-based oligosaccharides production from chitin by chitinolytic enzymes. Moreover, current advances in the structural characterization and biological activities of these two types of GlcNAc-based oligosaccharides are summarized in the review. We also highlight current problems in the production of these oligosaccharides and trends in their development, aiming to offer some directions for producing functional oligosaccharides from chitin.

Directed preparation, structure-activity relationship and applications of alginate oligosaccharides with specific structures: A systematic review

The alginate oligosaccharides (AOS) possess versatile activities (such as antioxidant, anti-inflammatory, antitumor, and immune-regulatory activities) and have been the research topic in marine bioresource utilization fields. The degree of polymerization (DP) and the β-D-mannuronic acid (M)/α-L-guluronic acid (G)-units ratio strongly affect the functionality of AOS. Therefore, directed preparation of AOS with specific structures is essential for expanding the applications of alginate polysaccharides and has been the research topic in the marine bioresource field. Alginate lyases could efficiently degrade alginate and specifically produce AOS with specific structures. Therefore, enzymatic preparation of AOS with specific structures has drawn increasing attention. Herein, we systematically summarized the current research progress on the structure-function relation of AOS and focuses on the application of the enzymatic properties of alginate lyase to the specific preparation of various types of AOS. At the same time, current challenges and opportunities for AOS applications are presented to guide and improve the preparation and application of AOS in the future.

Identification of a Key Loop for Tuning Transglycosylation Activity in the Substrate-Binding Region of a Chitosanase

Csn-PD, a glycoside family 46 chitosanase from Paenibacillus dendritiformis, exhibits endotype hydrolysis of chitosan and produces (GlcN)₂ as the major product. Here, we report the crystal structure of Csn-PD at 1.68 Å resolution. The structure contains 14 α-helices and two β-strands that fold into two globular domains with the substrate bound between them. To evaluate the function of a loop in the substrate-binding region (residues 112-116, NDKHP), a mutant Csn-PDL1, in which this loop was deleted, was generated. Hydrolysis of chitosan by the mutant yielded chitooligosaccharides (COSs) with higher degrees of polymerization (DP) than the wild-type enzyme. Excitingly, (GlcN)₆ was produced from smaller COSs via transglycosylation activity of the mutant. Hence, the catalytic performance of a chitosanase was altered by modification of a loop in the substrate-binding regions. Our novel data on a chitosanase with transglycosylation activity offer a promising way to produce COSs with high DP.

Simultaneous enhancement of thermostability and catalytic activity of κ-carrageenase from Pseudoalteromonas tetraodonis by rational design

κ-Carrageenase provides an attractive enzymatic approach to preparation of κ-carrageenan oligosaccharides. Pseudoalteromonas tetraodonis κ-carrageenase is active at the alkaline conditions but displays low thermostability. To further improve its enzymatic performance, two mutants of Q42V and I51H exhibiting both improved thermostability and enzyme activity were screened by the PoPMuSiC algorithm. Compared with the wild-type κ-carrageenase (WT), Q42V and I51H increased the enzyme activity by 20.9% and 25.4%, respectively. After treatment at 50 ℃ for 40 min, Q42V and I51H enhanced the residual activity by 31.1% and 25.9%, respectively. The T_m values of Q42V, I51H, and WT determined by differential scanning calorimetry were 58.2 ℃, 54.8 ℃, and 51.2 ℃, respectively. Compared with untreated and HCl-treated κ-carrageenans, Q42V-treated κ-carrageenan exhibited higher pancreatic lipase inhibitory activity. Molecular docking analysis indicated that the additional pi-sigma force and hydrophobic interaction in the enzyme-substrate complex could account for the increased catalytic activity of Q42V and I51H, respectively. Molecular dynamics analysis indicated that the improved thermostability of mutants Q42V and I51H could be attributed to the less structural deviation and the flexible changes of enzyme conformation at high temperature. This study provides new insight into κ-carrageenase performance improvement and identifies good candidates for their industrial applications.

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.

Biochemical Characterization of a GH46 Chitosanase Provides Insights into the Novel Digestion Specificity

Endo-chitosanases (EC 3.2.1.132) are generally considered to selectively release functional chito-oligosaccharides (COSs) with degrees of polymerization (DPs) ≥ 2. Although numerous endo-chitosanases have been characterized, the digestion specificity of endo-chitosanases needs to be further explored. In this study, a GH46 endo-chitosanase OUC-CsnPa was cloned, expressed, and characterized from Paenibacillus sp. 1-18. The digestion pattern analysis indicated that OUC-CsnPa could produce monosaccharides from chitotetraose [(GlcN)₄], the smallest recognized substrate, in a random endo-acting manner. Especially, the enzyme specificities during chitosan digestion including the regulation of product abundance through a transglycosylation reaction were also evaluated. It was hypothesized that an insertion region in OUC-CsnPa may form a strong force to be involved in stabilizing (GlcN)₄ at its negative subsite for efficient hydrolysis. This is the first comprehensive report to reveal the digestion specificity and subsite specificity of monosaccharide production by endo-chitosanases. Overall, OUC-CsnPa described here highlights the previously unknown digestion properties of the endo-acting chitosanases and provides a unique example of possible structure-function relationships.

Marine macroalgae polysaccharides-based nanomaterials: an overview with respect to nanoscience applications

Background

Exploration of marine macroalgae poly-saccharide-based nanomaterials is emerging in the nanotechnology field, such as wound dressing, water treatment, environmental engineering, biosensor, and food technology.

Main body

In this article, the current innovation and encroachments of marine macroalgae polysaccharide-based nanoparticles (NPs), and their promising opportunities, for future prospect in different industries are briefly reviewed. The extraction and advancement of various natural sources from marine polysaccharides, including carrageenan, agarose, fucoidan, and ulvan, are highlighted in order to provide a wide range of impacts on the nanofood technology. Further, seaweed or marine macroalgae is an unexploited natural source of polysaccharides, which involves numerous different phytonutrients in the outermost layer of the cell and is rich in sulphated polysaccharides (SP), SP-based nanomaterial which has an enhanced potential value in the nanotechnology field.

Conclusion

At the end of this article, the promising prospect of SP-based NPs and their applications in the food sector is briefly addressed.

Enzymatic preparation and potential applications of agar oligosaccharides: a review

Oligosaccharides derived from agar, that is, agarooligosaccharides and neoagarooligosaccharides, have demonstrated various kinds of bioactivities which have been utilized in a variety of fields. Enzymatic hydrolysis is a feasible approach that principally allows for obtaining specific agar oligosaccharides in a sustainable way at an industrial scale. This review summarizes recent technologies employed to improve the properties of agarase. Additionally, the relationship between the degree of polymerization, bioactivities, and potential applications of agar-derived oligosaccharides for pharmaceutical, food, cosmetic, and agricultural industries are discussed. Engineered agarase exhibited general improvement of enzymatic performance, which is mostly achieved by truncation. Rational and semi-rational design assisted by computational methods present the latest strategy for agarase improvement with greatest potential to satisfy future industrial needs. Agarase immobilized on magnetic Fe3O4 nanoparticles via covalent bond formation showed characteristics well suited for industry. Additionally, albeit with the relationship between the degree of polymerization and versatile bioactivities like anti-oxidants, anti-inflammatory, anti-microbial agents, prebiotics and in skin care of agar-derived oligosaccharides are discussed here, further researches are still needed to unravel the complicated relationship between bioactivity and structure of the different oligosaccharides.

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.

Agarose-Degrading Characteristics of a Deep-Sea Bacterium Vibrio Natriegens WPAGA4 and Its Cold-Adapted GH50 Agarase Aga3420

Up until now, the characterizations of GH50 agarases from Vibrio species have rarely been reported compared to GH16 agarases. In this study, a deep-sea strain, WPAGA4, was isolated and identified as Vibrio natriegens due to the maximum similarity of its 16S rRNA gene sequence, the values of its average nucleotide identity, and through digital DNA-DNA hybridization. Two circular chromosomes in V. natriegens WPAGA4 were assembled. A total of 4561 coding genes, 37 rRNA, 131 tRNA, and 59 other non-coding RNA genes were predicted in the genome of V. natriegens WPAGA4. An agarase gene belonging to the GH50 family was annotated in the genome sequence and expressed in E. coli cells. The optimum temperature and pH of the recombinant Aga3420 (rAga3420) were 40 °C and 7.0, respectively. Neoagarobiose (NA2) was the only product during the degradation process of agarose by rAga3420. rAga3420 had a favorable stability following incubation at 10-30 °C for 50 min. The Km, Vmax, and kcat values of rAga3420 were 2.8 mg/mL, 78.1 U/mg, and 376.9 s-1, respectively. rAga3420 displayed cold-adapted properties as 59.7% and 41.2% of the relative activity remained at 10 3 °C and 0 °C, respectively. This property ensured V. natriegens WPAGA4 could degrade and metabolize the agarose in cold deep-sea environments and enables rAga3420 to be an appropriate industrial enzyme for NA2 production, with industrial potential in medical and cosmetic fields.

Gene cloning and molecular characterization of a thermostable chitosanase from Bacillus cereus TY24

Background

An important conceptual advance in health and the environment has been recognized that enzymes play a key role in the green processing industries. Of particular interest, chitosanase is beneficial for recycling the chitosan resource and producing chitosan oligosaccharides. Also, chitosan gene expression and molecular characterization will promote understanding of the biological function of bacterial chitosanase as well as explore chitosanase for utilizing chitosan resources.

Results

A chitosanase-producing bacterium TY24 was isolated and identified as Bacillus cereus. Moreover, the chitosanase gene was cloned and expressed in Escherichia coli. Sequence analysis reveals that the recombinant chitosanase (CHOE) belongs to the glycoside hydrolases 8 family. The purified CHOE has a molecular weight of about 48 kDa and the specific activity of 1150 U/mg. The optimal pH and temperature of CHOE were 5.5 and 65 °C, respectively. The enzyme was observed stable at the pH range of 4.5–7.5 and the temperature range of 30–65 °C. Especially, the half-life of CHOE at 65 °C was 161 min. Additionally, the activity of CHOE was remarkably enhanced in the presence of Mn²⁺, Cu²⁺, Mg²⁺ and K⁺, beside Ca²⁺ at 5 mM. Especially, the activity of CHOE was enhanced to more than 120% in the presence of 1% of various surfactants. CHOE exhibited the highest substrate specificity toward colloid chitosan.

Conclusion

A bacterial chitosanase was cloned from B. cereus and successfully expressed in E. coli (BL21) DE3. The recombinant enzyme displayed good stability under acid pH and high-temperature conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-022-00762-6.

A bifunctional exolytic alginate lyase from Microbulbifer sp. ALW1 with salt activation and calcium-dependent catalysis

Alginate lyases can depolymerize alginate to oligomers with potential applications in many fields. Here a new alginate lyase, namely AlgL6, was characterized from Microbulbifer sp. ALW1, phylogenetically classified into the polysaccharide lyase family 6 (PL6). The recombinant alginate lyase AlgL6 exerted enzymatic activities towards polymannuronate, polyguluronate, and sodium alginate in an exolytic manner. AlgL6 had an optimum temperature of 35 °C and good stability at 30 °C or below. Its optimum pH was 8.0, and it had good stability over the pH range of 5.0-9.0. AlgL6 exhibited excellent halo-stability against Na⁺, and its activity can be increased up to about 1.8 times by 0.5 M NaCl. AlgL6 also showed strong stability in the presence of some nonionic detergents such as Tween 20 and Tween 80. The degradation products of sodium alginate by AlgL6 exhibited more effective antioxidant activities than the undigested polysaccharides. Structure analysis illustrated the catalytic mechanism defined by the coordination of the acid/base residues Arg269 and Lys248 of AlgL6. The replacement of Ca²⁺-interacting amino acid residues in AlgL6 and depletion of Ca²⁺ suggested the involvement of Ca²⁺ in the enzyme's catalytic activity. These properties of AlgL6 supply support to its industrial application for development of alginate bioresource.

Research Progress on the Extraction, Structure, and Bioactivities of Polysaccharides from Coriolus versicolor

Coriolus is the dried fruiting body of Coriolus versicolor (L. ex Fr.) Quel. C. versicolor (CV) is a worldwide-distributed fungus, which is common and widely used in primitive forests in the northern hemisphere. Polysaccharide, as the main active ingredient in CV, has a variety of biological activities, such as promoting immune function, antivirus, antitumor, anti-diabetes, and so on. However, Coriolus versicolor polysaccharide (CVP) faces the problems of a single extraction method, lack of research on separation and purification, and the research on structural characterization is limited to the primary structure. Furthermore, the existing research results have not been systematically reviewed. Therefore, this paper summarizes the research status of CVP in terms of extraction technology, separation and purification, structural characterization, and pharmacological activity in recent years, in order to provide a theoretical basis for in-depth research, development, and utilization of CVP.

Draft Genome Sequences of Four Bacterial Strains Isolated from Sediment of the South China Sea

Here, we report the draft genome sequences of four bacterial isolates from sediment of the South China Sea. Three of the isolates belong to the class Alphaproteobacteria and encode complete SoxXAYZBCD gene clusters, related to thiosulfate oxidation, while one isolate belongs to the class Opitutae and possesses a total of 397 carbohydrate active enzymes (CAZymes), related to predicted polysaccharide degradation.

Using One-pot Fermentation Technology to Prepare Enzyme Cocktail to Sustainably Produce Low Molecular Weight Galactomannans from Sesbania cannabina Seeds

Enzymatic hydrolysis using β-mannanase and α-galactosidase is necessary to produce low molecular weight galactomannan (LMW-GM) from galactomannans (GM) in the leguminous seeds. In this study, different ratios of avicel and melibiose were used as the inductors (carbon sources) for Trichoderma reesei to metabolize the enzyme cocktail containing β-mannanase and α-galactosidase using one-pot fermentation technology. The obtained enzyme cocktail was used to efficiently produce LMW-GM from GM in Sesbania cannabina seeds. Results showed that 15 g/L avicel and 10 g/L melibiose were the best carbon sources to prepare enzyme cocktail containing β-mannanase and α-galactosidase with activities of 3.69 ± 0.27 U/mL and 0.51 ± 0.02 U/mL, respectively. Specifically, melibiose could effectively induce the metabolite product of α-galactosidase by T. reesei, which showed good performance in degrading the galactose substituent from GM backbone. The degradation of galactose alleviated the spatial site-blocking effect for enzymatic hydrolysis by β-mannanase and improved the yield of LMW-GM. This research can lay the foundation for the industrial technology amplification of LMW-GM production for further application.

Recent Advances in Bioutilization of Marine Macroalgae Carbohydrates: Degradation, Metabolism, and Fermentation

Marine macroalgae are considered renewable natural resources due to their high carbohydrate content, which gives better utilization value in biorefineries and higher value conversion than first- and second-generation biomass. However, due to the diverse composition, complex structure, and rare metabolic pathways of macroalgae polysaccharides, their bioavailability needs to be improved. In recent years, enzymes and pathways related to the degradation and metabolism of macroalgae polysaccharides have been continuously developed, and new microbial fermentation platforms have emerged. Aiming at the bioutilization and transformation of macroalgae resources, this review describes the latest research results from the direction of green degradation, biorefining, and metabolic pathway design, including summarizing the the latest biorefining technology and the fermentation platform design of agarose, alginate, and other polysaccharides. This information will provide new research directions and solutions for the biotransformation and utilization of marine macroalgae.

Self-assembled κ-carrageenase-inorganic hybrid nanoflowers exerting high catalytic efficiency with stable and recyclable properties

κ-Carrageenan oligosaccharides from κ-carrageenan hydrolysis are important biochemicals with more bioactivity. Enzyme engineering plays a key role in improving κ-carrageenase catalytic efficiency for production of κ-carrageenan oligosaccharides. Effect of metal ions on enzyme activity, especially stability and efficiency, is main factor in catalytic process, but metal ions addition leads to gelation of κ-carrageenan solution. In this study, molecular dynamics simulation was used to explore the interaction between κ-carrageenase CgkPZ and Ca²⁺, and Ca²⁺ bonded to D164 and E167 in the catalytic center resulting in the catalytic efficiency increase. Circular dichroism analysis indicated that the secondary structure of κ-carrageenase could change in the presence of Ca²⁺. Therefore, a novel self-assembly κ-carrageenase-inorganic hybrid nanoflowers CaNF@CgkPZ was synthesized and systematically characterized. The catalytic efficiency (k_cat/K_m) of CaNF@CgkPZ was 382.1 mL·mg^-1·s^-1, increased by 292% compared with free κ-carrageenase. Notably, the enzyme activity of CaNF@CgkPZ was not reduced significantly after 19 cycles use, and 70-100% relative activity was still retained when stored at 4-25 ℃ for 15 days. This work provides an efficient approach for κ-carrageenase immobilization with good storage stability, reusability and enhanced catalytic efficiency, which is of great significance in practical applications.

Antiviral Activity of Carrageenans and Processing Implications

Carrageenan and carrageenan oligosaccharides are red seaweed sulfated carbohydrates with well-known antiviral properties, mainly through the blocking of the viral attachment stage. They also exhibit other interesting biological properties and can be used to prepare different drug delivery systems for controlled administration. The most active forms are λ-, ι-, and κ-carrageenans, the degree and sulfation position being determined in their properties. They can be obtained from sustainable worldwide available resources and the influence of manufacturing on composition, structure, and antiviral properties should be considered. This review presents a survey of the antiviral properties of carrageenan in relation to the processing conditions, particularly those assisted by intensification technologies during the extraction stage, and discusses the possibility of further chemical modifications.

Expression and Characterization of a Novel Cold-Adapted and Stable β-Agarase Gene agaW1540 from the Deep-Sea Bacterium Shewanella sp. WPAGA9

The neoagaro-oligosaccharides, degraded from agarose by agarases, are important natural substances with many bioactivities. In this study, a novel agarase gene, agaW1540, from the genome of a deep-sea bacterium Shewanella sp. WPAGA9, was expressed, and the recombinant AgaW1540 (rAgaW1540) displayed the maximum activity under the optimal pH and temperature of 7.0 and 35 °C, respectively. rAgaW1540 retained 85.4% of its maximum activity at 0 °C and retained more than 92% of its maximum activity at the temperature range of 20-40 °C and the pH range of 4.0-9.0, respectively, indicating its extensive working temperature and pH values. The activity of rAgaW1540 was dramatically suppressed by Cu²⁺ and Zn²⁺, whereas Fe²⁺ displayed an intensification of enzymatic activity. The K_m and V_max of rAgaW1540 for agarose degradation were 15.7 mg/mL and 23.4 U/mg, respectively. rAgaW1540 retained 94.7%, 97.9%, and 42.4% of its maximum activity after incubation at 20 °C, 25 °C, and 30 °C for 60 min, respectively. Thin-layer chromatography and ion chromatography analyses verified that rAgaW1540 is an endo-acting β-agarase that degrades agarose into neoagarotetraose and neoagarohexaose as the main products. The wide variety of working conditions and stable activity at room temperatures make rAgaW1540an appropriate bio-tool for further industrial production of neoagaro-oligosaccharides.

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.

Module function analysis of a full-length κ-carrageenase from Pseudoalteromonas sp. ZDY3

κ-Carrageenan oligosaccharides with many excellent biological properties could be produced by κ-carrageenases selectively. In this study, based on the encoding gene of full length κ-carrageenase obtained from Pseudoalteromonas sp. ZDY3 and the reported mature secreted κ-carrageenase composed of 275 amino acid residues (N26-T300), CgkPZ_GH16 was expressed in E. coli, but no soluble active protein could be detected. Fortunately, the signal peptide of wild-type κ-carrageenase was recognized, and cleaved in the soluble and folding form in E. coli, the K_m and k_cat values of CgkPZ_SP_GH16 was 1.007 mg/mL and 362.8 s^-1. By molecular dynamics simulations, it was showed that YjdB domain might affect the activity of κ-carrageenase. Due to the absence of mature processing modification system in E. coli, YjdB was remained in recombinant full length κ-carrageenase, and the lost catalytic efficiency of CgkPZ was compensated by expression level and thermal stability. Interestingly, CgkPZ_GH16_YjdB was expressed soluble without the signal peptide, which indicated that YjdB could contribute to the expression and folding of κ-carrageenase. These results provide new insight into the effects of different modules of κ-carrageenase on the expression and properties of enzyme.

Enzymatic Synthesis and Characterization of Different Families of Chitooligosaccharides and Their Bioactive Properties

Chitooligosaccharides (COS) are homo- or hetero-oligomers of D-glucosamine (GlcN) and N-acetyl-D-glucosamine (GlcNAc) that can be obtained by chitosan or chitin hydrolysis. Their enzymatic production is preferred over other methodologies (physical, chemical, etc.) due to the mild conditions required, the fewer amounts of waste and its efficiency to control product composition. By properly selecting the enzyme (chitinase, chitosanase or nonspecific enzymes) and the substrate properties (degree of deacetylation, molecular weight, etc.), it is possible to direct the synthesis towards any of the three COS types: fully acetylated (faCOS), partially acetylated (paCOS) and fully deacetylated (fdCOS). In this article, we review the main strategies to steer the COS production towards a specific group. The chemical characterization of COS by advanced techniques, e.g., high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and MALDI-TOF mass spectrometry, is critical for structure–function studies. The scaling of processes to synthesize specific COS mixtures is difficult due to the low solubility of chitin/chitosan, the heterogeneity of the reaction mixtures, and high amounts of salts. Enzyme immobilization can help to minimize such hurdles. The main bioactive properties of COS are herein reviewed. Finally, the anti-inflammatory activity of three COS mixtures was assayed in murine macrophages after stimulation with lipopolysaccharides.

Phylogenetic Distribution of Polysaccharide-Degrading Enzymes in Marine Bacteria

Deconstruction is an essential step of conversion of polysaccharides, and polysaccharide-degrading enzymes play a key role in this process. Although there is recent progress in the identification of these enzymes, the diversity and phylogenetic distribution of these enzymes in marine microorganisms remain largely unknown, hindering our understanding of the ecological roles of marine microorganisms in the ocean carbon cycle. Here, we studied the phylogenetic distribution of nine types of polysaccharide-degrading enzymes in marine bacterial genomes. First, we manually compiled a reference sequence database containing 961 experimentally verified enzymes. With this reference database, we annotated 9,335 enzyme sequences from 2,182 high-quality marine bacterial genomes, revealing extended distribution for six enzymes at the phylum level and for all nine enzymes at lower taxonomic levels. Next, phylogenetic analyses revealed intra-clade diversity in the encoding potentials and phylogenetic conservation of a few enzymes at the genus level. Lastly, our analyses revealed correlations between enzymes, with alginate lyases demonstrating the most extensive correlations with others. Intriguingly, chitinases showed negative correlations with cellulases, alginate lyases, and agarases in a few genera. This result suggested that intra-genus lifestyle differentiation occurred many times in marine bacteria and that the utilization of polysaccharides may act as an important driver in the recent ecological differentiation of a few lineages. This study expanded our knowledge of the phylogenetic distribution of polysaccharide enzymes and provided insights into the ecological differentiation of marine bacteria.

Physical Properties, Chemical Analysis, and Evaluation of Antimicrobial Response of New Polylactide/Alginate/Copper Composite Materials

In recent years, due to an expansion of antibiotic-resistant microorganisms, there has been growing interest in biodegradable and antibacterial polymers that can be used in selected biomedical applications. The present work describes the synthesis of antimicrobial polylactide-copper alginate (PLA-ALG-Cu2+) composite fibers and their characterization. The composites were prepared by immersing PLA fibers in aqueous solution of sodium alginate, followed by ionic cross-linking of alginate chains within the polylactide fibers with Cu(II) ions to yield PLA-ALG-Cu2+ composite fibers. The composites, so prepared, were characterized by scanning electron microscopy (SEM), UV/VIS transmittance and attenuated total reflection Fourier-transform infrared spectroscopy ATR-FTIR, and by determination of their specific surface area (SSA), total/average pore volumes (through application of the 5-point Brunauer-Emmett-Teller method (BET)), and ability to block UV radiation (determination of the ultraviolet protection factor (UPF) of samples). The composites were also subjected to in vitro antimicrobial activity evaluation tests against colonies of Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria and antifungal susceptibility tests against Aspergillus niger and Chaetomium globosum fungal mold species. All the results obtained in this work showed that the obtained composites were promising materials to be used as an antimicrobial wound dressing.