Electrospray ionization mass spectrometric analysis of κ-carrageenan oligosaccharides obtained by degradation with κ-carrageenase from Pedobacter hainanensis

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

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

Improving the thermostability of Pseudoalteromonas Porphyrae κ-carrageenase by rational design and MD simulation

The industrial applications of the κ-carrageenases have been restricted by their poor thermostability. In this study, based on the folding free energy change (ΔΔG) and the flexibility analysis using molecular dynamics (MD) simulation for the alkaline κ-carrageenase KCgCD from Pseudoalteromonas porphyrae (WT), the mutant S190R was identified with improved thermostability. After incubation at 50 °C for 30 min, the residual activity of S190R was 63.7%, 25.7% higher than that of WT. The Tm values determined by differential scanning calorimetry were 66.2 °C and 64.4 °C for S190R and WT, respectively. The optimal temperature of S190R was 10 °C higher than that of WT. The κ-carrageenan hydrolysates produced by S190R showed higher xanthine oxidase inhibitory activity compared with the untreated κ-carrageenan. MD simulation analysis of S190R showed that the residues (V186-M194 and P196-G197) in F5 and the key residue R150 in F3 displayed the decreased flexibility, and residues of T169-N173 near the catalytic center displayed the increased flexibility. These changed flexibilities might be the reasons for the improved thermostability of mutant S190R. This study provides a useful rational design strategy of combination of ΔΔG calculation and MD simulation to improve the κ-carrageenase's thermostability for its better industrial applications.

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.

Biochemical characterization and elucidation of the action mode of a GH16 family κ-carrageenase for efficient preparation of carrageenan oligosaccharides

κ-Carrageenan oligosaccharides have a variety of biological activities. Degradation of κ-carrageenan by κ-carrageenase leads to degradation products with different degrees of polymerization (DPs). A novel gene (CecgkA) encoding a new κ-carrageenase was cloned from Colwellia echini and heterologously expressed in Escherichia coli BL21 (DE3). The enzyme is 1104 bp in length, encodes 367 amino acid residues and has a molecular weight of 41.30 kDa. Multiple alignment analysis showed that CeCgkA belongs to the glycoside hydrolase (GH16) family and has the highest homology with the κ-carrageenase of Rhodopirellula maiorica SM1, with 58% homology. The CeCgkA showed maximum activity (453.15 U/mg) at pH 8.0 and 35 °C. Determination of biochemical properties showed that CeCgkA was a thermal recovery enzyme, and 51.6% of the initial enzyme activity was recovered by immediately placing the sample at 35 °C for 60 min after enzymatic inactivation by boiling for 10 min. K⁺, Na⁺, and EDTA had an activating effect on the enzyme activity, while Ni²⁺, Cu²⁺, and Zn²⁺ inhibited the activity of the enzyme. In addition, TLC and ESI-MS analysis showed that the maximum recognition unit of CecgkA was decasaccharide and that the main degradation products were disaccharides, tetrasaccharides and hexasaccharides, indicating that the enzyme is an endo-type carrageenase.

κ-Selenocarrageenan Oligosaccharides Prepared by Deep-Sea Enzyme Alleviate Inflammatory Responses and Modulate Gut Microbiota in Ulcerative Colitis Mice

κ-Selenocarrageenan (KSC) is an organic selenium (Se) polysaccharide. There has been no report of an enzyme that can degrade κ-selenocarrageenan to κ-selenocarrageenan oligosaccharides (KSCOs). This study explored an enzyme, κ-selenocarrageenase (SeCar), from deep-sea bacteria and produced heterologously in Escherichia coli, which degraded KSC to KSCOs. Chemical and spectroscopic analyses demonstrated that purified KSCOs in hydrolysates were composed mainly of selenium-galactobiose. Organic selenium foods through dietary supplementation could help regulate inflammatory bowel diseases (IBD). This study discussed the effects of KSCOs on dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) in C57BL/6 mice. The results showed that KSCOs alleviated the symptoms of UC and suppressed colonic inflammation by reducing the activity of myeloperoxidase (MPO) and regulating the unbalanced secretion of inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10). Furthermore, KSCOs treatment regulated the composition of gut microbiota, enriched the genera Bifidobacterium, Lachnospiraceae_NK4A136_group and Ruminococcus and inhibited Dubosiella, Turicibacter and Romboutsia. These findings proved that KSCOs obtained by enzymatic degradation could be utilized to prevent or treat UC.

Characterization and Gel Properties of Low-Molecular-Weight Carrageenans Prepared by Photocatalytic Degradation

Low-molecular-weight carrageenan has attracted great interest because it shows advantages in solubility, absorption efficiency, and bioavailability compared to original carrageenan. However more environment-friendly and efficient methods to prepare low-molecular-weight carrageenan are still in great need. In the present study, a photocatalytic degradation method with only TiO₂ has been developed and it could decrease the average molecular weight of κ-carrageenan to 4 kDa within 6 h. The comparison of the chemical compositions of the degradation products with those of carrageenan by FT-IR, NMR, etc., indicates no obvious removement of sulfate group, which is essential for bioactivities. Then 20 carrageenan oligosaccharides in the degradation products were identified by HPLC-MSⁿ, and 75% of them possessed AnGal or its decarbonylated derivative at their reducing end, indicating that photocatalysis is preferential to break the glycosidic bond of AnGal. Moreover, the analysis results rheology and Cryo-SEM demonstrated that the gel property decreased gradually. Therefore, the present study demonstrated that the photocatalytic method with TiO₂ as the only catalyst has the potential to prepare low-molecular-weight carrageenan with high sulfation degree and low viscosity, and it also proposed the degradation rules after characterizing the degradation products. Thus, the present study provides an effective green method for the degradation of carrageenan.

Characterization of degradation products of carrageenan by LC-QTOF/MS with a hypothetical database

Carrageenan (CGN) belongs to the sulfated polysaccharides family that is commonly used in the food industry. For oligosaccharide analysis, a liquid chromatography quadrupole time-of-flight/mass spectrometry strategy was developed using a hypothetical database. There are 2100 structures in the developed hypothetical κ-CGN database. To eliminate false-positive results, three approaches were used, including size exclusion chromatography with mass spectrometry, which differentiates the loss of sulfated groups caused by the hydrolysis process or the ionization process. Profiling of acidic hydrolysis products of κ-CGN was found that after 12 h of HCl cultivation, the κ-CGN was hydrolyzed to oligosaccharides lower than the degree of polymerization 10, breaking the α-1,3-glycoside linkage and producing even-numbered oligosaccharides. Another finding was that the pH at which acidic hydrolysis is terminated affects the generation of even and odd oligosaccharides. Peeling reaction occurs at the reduction end 4-linked-3,6-anhydrous-d-galactose when adjusted to alkaline conditions, thus generating odd oligosaccharides.

Ultra-high-performance liquid chromatography charge transfer dissociation mass spectrometry (UHPLC-CTD-MS) as a tool for analyzing the structural heterogeneity in carrageenan oligosaccharides

Ultra-high-performance liquid chromatography (UHPLC) with charge transfer dissociation mass spectrometry (CTD-MS) is presented for the analysis of a mixture of complex sulfated oligosaccharides. The mixture contained kappa (κ), iota (ι), and lambda (λ) carrageenans that contain anhydro bridges, different degrees of sulfation ranging from one to three per dimer, different positioning of the sulfate groups along the backbone, and varying degrees of polymerization (DP) between 4 and 12. Optimization studies using standard mixtures of carrageenans helped establish the optimal conditions for online UHPLC-CTD-MS/MS analysis. Optimization included (1) UHPLC conditions; (2) ion source conditions, such as the capillary voltage, drying gas and nebulizing gas temperature, and flow rate; and (3) CTD-MS conditions, including data-dependent CTD-MS. The UHPLC-CTD results were contrasted with UHPLC-CID results of the same mixture on the same instrument. Whereas CID tends to produce B/Y and C/Z ions with many neutral losses, CTD produced more abundant A/X ions and less abundant neutral losses, which enabled more confident structural detail. The results demonstrate that He-CTD is compatible with the timescale of UHPLC and provides more structural information about carrageenans compared to state-of-the-art methods like UHPLC-CID analysis.

Health effects of dietary sulfated polysaccharides from seafoods and their interaction with gut microbiota

Various dietary sulfated polysaccharides (SPs) have been isolated from seafoods, including edible seaweeds and marine animals, and their health effects such as antiobesity and anti-inflammatory activities have attracted remarkable interest. Sulfate groups have been shown to play important roles in the bioactivities of these polysaccharides. Recent in vitro and in vivo studies have suggested that the biological effects of dietary SPs are associated with the modulation of the gut microbiota. Dietary SPs could regulate the gut microbiota structure and, accordingly, affect the production of bioactive microbial metabolites. Because of their differential chemical structures, dietary SPs may specifically affect the growth of certain gut microbiota and associated metabolite production, which may contribute to variable health effects. This review summarizes the latest findings on the types and structural characteristics of SPs, the effects of different processing techniques on the structural characteristics and health effects of SPs, and the current understanding of the role of gut microbiota in the health effects of SPs. These findings might help in better understanding the mechanism of the health effects of SPs and provide a scientific basis for their application as functional food.

Purification and characterization of a cold-adapted κ-carrageenase from Pseudoalteromonas sp. ZDY3

κ-Carrageenase (EC3.2.1.83) is a class of glycoside hydrolase, which can be used for hydrolysis of κ-carrageenan to κ-carrageenan oligosaccharides. In this study, a bacterium, identified as Pseudoalteromonas sp. ZDY3 isolated from rotten algae, was capable to degrade κ-carrageenan. The κ-carrageenase produced by Pseudoalteromonas sp. ZDY3 was purified to homogeneity and named as CgkZDY3. The accurate molecular mass of CgkZDY3 was determined through LC-HRMS, and a posttranslational removal of C-terminal end of the protein was discovered. CgkZDY3 had strict hydrolysis specificity to κ-carrageenan, the values of K_m and k_cat/K_m of CgkZDY3 were 3.67 mg mL^-1 and 53.0 mL mg^-1 s^-1, respectively. CgkZDY3 was a cold-adapted κ-carrageenase with excellent storage stability of both the temperature below 35 °C and a wide pH range, and was an endo-type κ-carrageenase with high hydrolysis rate, oligosaccharides with different degrees of polymerization can be obtained by controlling the hydrolysis time, and the final products were κ-neocarrabiose and κ-neocarratetraose. These properties are of great significance for production of κ-carrageenan oligosaccharides with different polymerization degrees under process control.

Characterization of a thermostable κ-carrageenase from a hot spring bacterium and plant protection activity of the oligosaccharide enzymolysis product

BACKGROUND

Seaweed oligosaccharides are environmentally-friendly natural products and their use for disease control in sustainable agriculture is extremely promising. Enzymatic digestion to prepare seaweed oligosaccharides has drawn considerable interest. However, the study of enzymatically degraded products of carrageenan is still in its infancy compared with that of other hydrocolloids such as agar and alginate. To prepare degraded carrageenan on a commercial scale, it is necessary to select superior producer bacterial strains to improve the yield and thermostability of carrageenases.

RESULTS

The carrageenan-degrading bacterium Bacillus sp. HT19 was isolated from sediment of a hot spring in Indonesia, and a κ-carrageenase with high activity was purified from the culture supernatant. The purified enzyme, named Car19, had maximum activity (538 U mg^-1 ) at 60 °C and pH 7.0. Notably, the enzyme retained >90% of its initial activity after incubation at 60 °C for 24 h. The Ca²⁺ obviously improved the thermostability of Car19 at 70 °C. The K_m and V_max values of purified Car19 were 0.061 mg mL^-1 and 115.13 U mg^-1 , respectively, with κ-carrageenan as substrate. Thin-layer chromatography and electrospray ionization mass-spectrometry analysis of hydrolysates indicated that the enzyme exolytically depolymerized κ-carrageenan to neo-carrabiose. The hydrolysate enhanced the resistance of cucumber to cucumber mosaic virus and increased the activity of antioxidant enzymes in infected plants.

CONCLUSION

To our knowledge, Car19 is the most thermostable κ-carrageenase reported so far. Its high optimal reaction temperature and thermostability, and unitary hydrolysate constituent, makes Car19 a promising candidate for the preparation of carrageenan oligosaccharides with plant protection activity. © 2018 Society of Chemical Industry.

Oligosaccharides Derived from Red Seaweed: Production, Properties, and Potential Health and Cosmetic Applications

Because of their potential use as functional ingredients in human nutrition, oligosaccharides derived from natural sources are receiving paramount consideration. Red seaweed, a proven rich source of agar and carrageenan, is one of the most abundantly present sources of such oligosaccharides. Agaro-oligosaccharides (AOS) and carrageenan-oligosaccharides (COS) are produced from agar and carrageenan, respectively, through chemical and enzymatic hydrolyses. Enzymatic hydrolysis of agar and carrageenan into oligosaccharides is preferred in industrial production because of certain problems associated with chemical hydrolysis, including the release of high amounts of monosaccharides and undesirable toxic products, such as furfural. AOS and COS possess many biological activities, including prebiotic, immuno-modulatory, anti-oxidant, and anti-tumor activities. These activities are related to their chemical structure, molecular weight, degree of polymerization, and the flexibility of the glycosidic linkages. Therefore, the structure–function relationship and the mechanisms occurring during the specific biological applications of AOS and COS are discussed herein. Moreover, the chromatographic separation, purification, and characterization of AOS and COS are also part of this review. This piece of writing strives to create a new perspective on the potential applications of AOS and COS in the functional food and pharmaceutical industry.

High-level expression and characterization of a new κ-carrageenase from marine bacterium Pedobacter hainanensis NJ-02

A novel κ-carrageenase gene (CgkB) has been cloned from Pedobacter hainanensis NJ-02 and expressed heterologously in Escherichia coli BL21 (DE3). It consisted of 1935 bp and encoded 644 amino acid residues with a molecular weight of 71·61 kDa. The recombinant enzyme showed maximal activity of 2458 U mg^-1 at 40°C and pH 8·0. Additionally, it could retain more than 70% of its maximal activity after being incubated at pH of 5·5-10·0 below 40°C. K⁺ and a broad range of NaCl can activate the enzyme. The K_m and V_max of CgkB was 2·4 mg ml^-1 and 126 mmol mg^-1  min^-1 . The ESI-MS analysis of hydrolysates indicated that the enzyme can endolytically depolymerize the carrageenan into tetrasaccharides and hexasaccharides. The results indicated that the enzyme with high activity could be a valuable enzyme tool to produce carrageenan oligosaccharides with various activities.

SIGNIFICANCE AND IMPACT OF THE STUDY

Enzymatic preparation of carrageenan oligosaccharides has drawn increased attention due to their various physiological activities. It is urgent to explore enzyme tools with higher activity and better stability. In this work, a novel κ-carrageenase was identified and characterized from marine bacterium Pedobacter hainanensis NJ-02. The enzyme with high activity could be a valuable tool to produce carrageenan oligosaccharides with various activities.

Enhanced Production of κ-Carrageenase and κ-Carrageenan Oligosaccharides through Immobilization of Thalassospira sp. Fjfst-332 with Magnetic Fe3O4-Chitosan Microspheres

In this study, immobilized bacteria (IMB) microsphere was prepared by embedding κ-carrageenase-producing Thalassospira sp. Fjfst-332 (TF332) onto a magnetic Fe₃O₄-chitosan carrier. The performance of Fe₃O₄-chitosan carrier was optimized by comparing its bacteria immobilization capacity at different Fe₃O₄:chitosan ratios and temperatures, while the functions of IMB microspheres were characterized by examining their κ-carrageenase production at different temperatures, pH's, and reuse cycles. At the 1:1 (w:w) Fe₃O₄:chitosan ratio, the Fe₃O₄-chitosan carriers possessed sufficient anchoring capacity for bacterial immobilization without significant compromise of their magnetism for magnetic separation of IMB from culture media. The spectroscopic analysis of IMB microspheres indicated that the immobilization of TF332 might affect the amide groups in chitosan. Compared to free bacteria, IMB can produce κ-carrageenase at higher temperature, wider pH range, and faster rate. More importantly, the κ-carrageenase-producing activity was sustained for at least seven reuse cycles. The major κ-carrageenan degradation products of IMB-derived κ-carrageenase were the oligosaccharides containing two to six monosaccharide units. Overall, this Fe₃O₄-chitosan-TF-332 microsphere has the potential to become a stable and reusable platform for large-scale production of κ-carrageenan oligosaccharides.

Medium Optimization and Fermentation Kinetics for κ-Carrageenase Production by Thalassospira sp. Fjfst-332

Effective degradation of κ-carrageenan by isolated Thalassospira sp. fjfst-332 is reported for the first time in this paper. It was identified by 16S rDNA sequencing and morphological observation using Transmission Electron Microscopy (TEM). Based on a Plackett–Burman design for significant variables, Box–Behnken experimental design and response surface methodology were used to optimize the culture conditions. Through statistical optimization, the optimum medium components were determined as follows: 2.0 g/L κ-carrageenan, 1.0 g/L yeast extract, 1.0 g/L FOS, 20.0 g/L NaCl, 2.0 g/L NaNO₃, 0.5 g/L MgSO₄·7H₂O, 0.1 g/L K₂HPO₄, and 0.1 g/L CaCl₂. The highest activity exhibited by Thalassospira sp. fjfst-332 was 267 U/mL, which makes it the most vigorous wild bacterium for κ-carrageenan production. In order to guide scaled-up production, two empirical models—the logistic equation and Luedeking–Piretequation—were proposed to predict the strain growth and enzyme production, respectively. Furthermore, we report the fermentation kinetics and every empirical equation of the coefficients (α, β, X₀, X_m and μ_m) for the two models, which could be used to design and optimize industrial processes.