A review about brown algal cell walls and fucose-containing sulfated polysaccharides: Cell wall context, biomedical properties and key research challenges

Subcritical water extraction as an efficient technique to isolate biologically-active fucoidans from Nizamuddinia zanardinii

A sulfated polysaccharide (fucoidan) has been isolated from Nizamuddinia zanardinii using subcritical water extraction method (SCWE), and extraction conditions were optimised using the response surface methodology. The optimum extraction conditions were found to be: extraction time of 29 min, extraction temperature of 150 °C, and raw material-to-water ratio of 21 g/mL. The fucoidan yield under these optimum conditions was 25.98%, which was considerably higher than that of conventional solvent extraction (5.2%). Extraction time and temperature were the extraction variables that most significantly affected fucoidan yield. Chemical and monosaccharide composition, molecular weight, and the antioxidant, anticancer and immunomodulatory activities of the extract have also been investigated. The monosaccharide composition of fucoidan included fucose (34.13%), mannose (30.70%), galactose (23.19%), xylose (9.35%) and glucose (2.65%). The average molecular weight of the extracted fucoidan was 694 kDa. Antioxidant results revealed that SCWE-extracted fucoidan had appreciable ABTS radical scavenging (70.35%) and reducing power (0.182 Abs). The anticancer activity of fucoidan ranged from 24.60 to 49.46% for HeLa cells and from 23.95 to 46.78% for HepG2 cells. The NO production of RAW264.7 cells was observed to be dose-dependent, while maximum NO production was found to be 34.82 μmol at a 50 μg/mL fucoidan concentration.

Xylans of Red and Green Algae: What Is Known about Their Structures and How They Are Synthesised?

Xylans with a variety of structures have been characterised in green algae, including chlorophytes (Chlorophyta) and charophytes (in the Streptophyta), and red algae (Rhodophyta). Substituted 1,4-β-d-xylans, similar to those in land plants (embryophytes), occur in the cell wall matrix of advanced orders of charophyte green algae. Small proportions of 1,4-β-d-xylans have also been found in the cell walls of some chlorophyte green algae and red algae but have not been well characterised. 1,3-β-d-Xylans occur as triple helices in microfibrils in the cell walls of chlorophyte algae in the order Bryopsidales and of red algae in the order Bangiales. 1,3;1,4-β-d-Xylans occur in the cell wall matrix of red algae in the orders Palmariales and Nemaliales. In the angiosperm Arabidopsis thaliana, the gene IRX10 encodes a xylan 1,4-β-d-xylosyltranferase (xylan synthase), and, when heterologously expressed, this protein catalysed the production of the backbone of 1,4-β-d-xylans. An orthologous gene from the charophyte green alga Klebsormidium flaccidum, when heterologously expressed, produced a similar protein that was also able to catalyse the production of the backbone of 1,4-β-d-xylans. Indeed, it is considered that land plant xylans evolved from xylans in ancestral charophyte green algae. However, nothing is known about the biosynthesis of the different xylans found in chlorophyte green algae and red algae. There is, thus, an urgent need to identify the genes and enzymes involved.

Biomolecular Composition and Revenue Explained by Interactions between Extrinsic Factors and Endogenous Rhythms of Saccharina latissima

This review provides a systematic overview of the spatial and temporal variations in the content of biomolecular constituents of Saccharina latissima on the basis of 34 currently-available scientific studies containing primary measurements. We demonstrate the potential revenue of seaweed production and biorefinery systems by compiling a product portfolio of high-value extract products. An investigation into the endogenous rhythms and extrinsic factors that impact the biomolecular composition of S. latissima is presented, and key performance factors for optimizing seaweed production are identified. Besides the provisioning ecosystem service, we highlight the contribution of green-engineered seaweed production systems to the mitigation of the ongoing and historical anthropogenic disturbances of the climate balance and nutrient flows. We conclude that there are risks of mismanagement, and we stress the importance and necessity of creating an adaptive ecosystem-based management framework within a triple-helix partnership for balancing the utilization of ecosystem services and long-term resilience of aquatic environment.

Caulerpa Cupressoides Var. Flabellata

Green seaweeds are rich sources of sulfated polysaccharides (SPs) with potential biomedical and nutraceutical applications. The aim of this work was to evaluate the immunostimulatory activity of SPs from the seaweed, Caulerpa cupressoides var. flabellata on murine RAW 264.7 macrophages. SPs were evaluated for their ability to modify cell viability and to stimulate the production of inflammatory mediators, such as nitric oxide (NO), intracellular reactive oxygen species (ROS), and cytokines. Additionally, their effect on inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) gene expression was investigated. The results showed that SPs were not cytotoxic and were able to increase in the production of NO, ROS and the cytokines, tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). It was also observed that treatment with SPs increased iNOS and COX-2 gene expression. Together, these results indicate that C. cupressoides var. flabellata SPs have strong immunostimulatory activity, with potential biomedical applications.

Gazing at Cell Wall Expansion under a Golden Light

In plants, cell growth is constrained by a stiff cell wall, at least this is the way textbooks usually present it. Accordingly, many studies have focused on the elasticity and plasticity of the cell wall as prerequisites for expansion during growth. With their specific evolutionary history, cell wall composition, and environment, brown algae present a unique configuration offering a new perspective on the involvement of the cell wall, viewed as an inert material yet with intrinsic mechanical properties, in growth. In light of recent findings, we explore here how much of the functional relationship between cell wall chemistry and intrinsic mechanics on the one hand, and growth on the other hand, has been uncovered in brown algae.

Enzymatic synthesis of l-fucose from l-fuculose using a fucose isomerase from Raoultella sp. and the biochemical and structural analyses of the enzyme

BACKGROUND

l-Fucose is a rare sugar with potential uses in the pharmaceutical, cosmetic, and food industries. The enzymatic approach using l-fucose isomerase, which interconverts l-fucose and l-fuculose, can be an efficient way of producing l-fucose for industrial applications. Here, we performed biochemical and structural analyses of l-fucose isomerase identified from a novel species of Raoultella (RdFucI).

RESULTS

RdFucI exhibited higher enzymatic activity for l-fuculose than for l-fucose, and the rate for the reverse reaction of converting l-fuculose to l-fucose was higher than that for the forward reaction of converting l-fucose to l-fuculose. In the equilibrium mixture, a much higher proportion of l-fucose (~ ninefold) was achieved at 30 °C and pH 7, indicating that the enzyme-catalyzed reaction favors the formation of l-fucose from l-fuculose. When biochemical analysis was conducted using l-fuculose as the substrate, the optimal conditions for RdFucI activity were determined to be 40 °C and pH 10. However, the equilibrium composition was not affected by reaction temperature in the range of 30 to 50 °C. Furthermore, RdFucI was found to be a metalloenzyme requiring Mn²⁺ as a cofactor. The comparative crystal structural analysis of RdFucI revealed the distinct conformation of α7-α8 loop of RdFucI. The loop is present at the entry of the substrate binding pocket and may affect the catalytic activity.

CONCLUSIONS

RdFucI-catalyzed isomerization favored the reaction from l-fuculose to l-fucose. The biochemical and structural data of RdFucI will be helpful for the better understanding of the molecular mechanism of l-FucIs and the industrial production of l-fucose.

Evolutionary Evidence of Algal Polysaccharide Degradation Acquisition by Pseudoalteromonas carrageenovora 9T to Adapt to Macroalgal Niches

About half of seaweed biomass is composed of polysaccharides. Most of these complex polymers have a marked polyanionic character. For instance, the red algal cell wall is mainly composed of sulfated galactans, agars and carrageenans, while brown algae contain alginate and fucose-containing sulfated polysaccharides (FCSP) as cell wall polysaccharides. Some marine heterotrophic bacteria have developed abilities to grow on such macroalgal polysaccharides. This is the case of Pseudoalteromonas carrageenovora 9^T (ATCC 43555^T), a marine gammaproteobacterium isolated in 1955 and which was an early model organism for studying carrageenan catabolism. We present here the genomic analysis of P. carrageenovora. Its genome is composed of two chromosomes and of a large plasmid encompassing 109 protein-coding genes. P. carrageenovora possesses a diverse repertoire of carbohydrate-active enzymes (CAZymes), notably specific for the degradation of macroalgal polysaccharides (laminarin, alginate, FCSP, carrageenans). We confirm these predicted capacities by screening the growth of P. carrageenovora with a large collection of carbohydrates. Most of these CAZyme genes constitute clusters located either in the large chromosome or in the small one. Unexpectedly, all the carrageenan catabolism-related genes are found in the plasmid, suggesting that P. carrageenovora acquired its hallmark capacity for carrageenan degradation by horizontal gene transfer (HGT). Whereas P. carrageenovora is able to use lambda-carrageenan as a sole carbon source, genomic and physiological analyses demonstrate that its catabolic pathway for kappa- and iota-carrageenan is incomplete. This is due to the absence of the recently discovered 3,6-anhydro-D-galactosidase genes (GH127 and GH129 families). A genomic comparison with 52 Pseudoalteromonas strains confirms that carrageenan catabolism has been recently acquired only in a few species. Even though the loci for cellulose biosynthesis and alginate utilization are located on the chromosomes, they were also horizontally acquired. However, these HGTs occurred earlier in the evolution of the Pseudoalteromonas genus, the cellulose- and alginate-related loci being essentially present in one large, late-diverging clade (LDC). Altogether, the capacities to degrade cell wall polysaccharides from macroalgae are not ancestral in the Pseudoalteromonas genus. Such catabolism in P. carrageenovora resulted from a succession of HGTs, likely allowing an adaptation to the life on the macroalgal surface.

Discovery and screening of novel metagenome-derived GH107 enzymes targeting sulfated fucans from brown algae

Sulfated fucans, often denoted as fucoidans, are highly variable cell wall polysaccharides of brown algae, which possess a wide range of bioactive properties with potential pharmaceutical applications. Due to their complex architecture, the structures of algal fucans have until now only been partly determined. Enzymes capable of hydrolyzing sulfated fucans may allow specific release of defined bioactive oligosaccharides and may serve as a tool for structural elucidation of algal walls. Currently, such enzymes include only a few hydrolases belonging to the glycoside hydrolase family 107 (GH107), and little is known about their mechanistics and the substrates they degrade. In this study, we report the identification and recombinant production of three novel GH107 family proteins derived from a marine metagenome. Activity screening against a large substrate collection showed that all three enzymes degraded sulfated fucans from brown algae in the order Fucales. This is in accordance with a hydrolytic activity against α-1,4-fucosidic linkages in sulfated fucans as reported for previous GH107 members. Also, the activity screening gave new indications about the structural differences in brown algal cell walls. Finally, sequence analyses allowed identification of the proposed catalytic residues of the GH107 family. The findings presented here form a new basis for understanding the GH107 family of enzymes and investigating the complex sulfated fucans from brown algae. DATABASE: The assembled metagenome and raw sequence data is available at EMBL-EBI (Study number: PRJEB28480). Sequences of the GH107 fucanases (Fp273, Fp277, and Fp279) have been deposited in GenBank under accessions MH755451-MH755453.

Algal Polysaccharides as Therapeutic Agents for Atherosclerosis

Seaweed-derived polysaccharides including agar and alginate, have found widespread applications in biomedical research and medical therapeutic applications including wound healing, drug delivery, and tissue engineering. Given the recent increases in the incidence of diabetes, obesity and hyperlipidemia, there is a pressing need for low cost therapeutics that can economically and effectively slow the progression of atherosclerosis. Marine polysaccharides have been consumed by humans for millennia and are available in large quantities at low cost. Polysaccharides such as fucoidan, laminarin sulfate and ulvan have shown promise in reducing atherosclerosis and its accompanying risk factors in animal models. However, others have been tested in very limited context in scientific studies. In this review, we explore the current state of knowledge for these promising therapeutics and discuss the potential and challenges of using seaweed derived polysaccharides as therapies for atherosclerosis.

Fucoidan Sulfatases from Marine Bacterium Wenyingzhuangia fucanilytica CZ1127T

Fucoidans belong to a structurally heterogeneous class of sulfated polysaccharides isolated from brown algae. They have a wide spectrum of biological activities. The complex structures of these polysaccharides hinder structure-activity relationships determination. Fucoidan sulfatases can make useful tools for the determination of the fine chemical structure of fucoidans. In this study, identification and preparation of two recombinant sulfatases able to catalyze the cleavage of sulfate groups from fragments of fucoidan molecules is described for the first time. Two genes of sulfatases swf1 and swf4 of the marine bacterium Wenyingzhuangia fucanilytica CZ1127^T were cloned and the proteins were produced in Escherichia coli cells. Sulfatases SWF1 and SWF4 are assigned to S1_17 and S1_25 subfamilies of formylglycine-dependent enzymes of S1 family (SulfAtlas). Some molecular and biochemical characteristics of recombinant fucoidan sulfatases have been studied. Detailed specificity and catalytic features of sulfatases were determined using various sulfated fucooligosaccharides. Structures of products produced by SWF1 and SWF4 were established by nuclear magnetic resonance (NMR) spectroscopy. Based on the obtained data, the enzymes are classified as fucoidan exo-2O-sulfatase (SWF1) and fucoidan exo-3O-sulfatase (SWF4). In addition, we demonstrated the sequential action of sulfatases on 2,3-di-O-sulfated fucooligosacchrides, which indicates an exolitic degradation pathway of fucoidan by a marine bacterium W. fucanilytica CZ1127^T.

Structure and Bioactivity Screening of a Low Molecular Weight Ulvan from the Green Alga Ulothrix flacca

A water-soluble low molecular–weight polysaccharide named UP2-1 was isolated and purified from the marine green algae Ulothrixflacca using ion-exchange and size-exclusion chromatography. Composition and characteristics analyses showed that UP2-1 was a sulfated glucuronorhamnan consisting of rhamnose and glucuronic acid in a ratio of 2:1 with 21% sulfate content and a molecular weight of 5.0 kDa. Structural properties were determined using desulfation and methylation analyses combined with infrared spectrum (IR), gas chromatography-mass spectrometer (GC-MS) and nuclear magnetic resonance (NMR). The results showed that UP2-1 was a type of ulvan composed of alternate 4-linked-α-L-rhamnose residues (→4)-α-L-Rha(1→) and 4-linked-β-D-glucouronoc acid residues. The sulfate groups were mainly present in the O-3 position of →4)-α-L-Rha(1→. Most (70%) of the rhamnose was sulfated. UP2-1 also had a small amount of →4)-α-L-Rha(1→ branch at the O-2 position of the →4)-α-L-Rha(1→. UP2-1 exhibited significant anticoagulant and immunomodulating activity in vitro. This study demonstrated that the green algae Ulothrix flacca, which is used as a food and traditional marine herb in China, could also be considered as a source of bioactive ulvan.

Biotechnology Potential of Marine Fungi Degrading Plant and Algae Polymeric Substrates

Filamentous fungi possess the metabolic capacity to degrade environment organic matter, much of which is the plant and algae material enriched with the cell wall carbohydrates and polyphenol complexes that frequently can be assimilated by only marine fungi. As the most renewable energy feedstock on the Earth, the plant or algae polymeric substrates induce an expression of microbial extracellular enzymes that catalyze their cleaving up to the component sugars. However, the question of what the marine fungi contributes to the plant and algae material biotransformation processes has yet to be highlighted sufficiently. In this review, we summarized the potential of marine fungi alternatively to terrestrial fungi to produce the biotechnologically valuable extracellular enzymes in response to the plant and macroalgae polymeric substrates as sources of carbon for their bioconversion used for industries and bioremediation.

Glucofucogalactan, a heterogeneous low-sulfated polysaccharide from Saccharina japonica and its bioactivity

Crude polysaccharide obtained from Saccharina japonica using acid hydrolysis and precipitation was separated into sulfated fuco-oligosaccharide (HDF1) and heteropolysaccharide (HDF2). To further explore the bioactive fraction, HDF2 was successfully separated using membrane filtration into HDF2A and HDF2B, which differed in chemical composition and molecular weight. The bioactivity of all the fractions was tested in vitro, including immunomodulatory activity in RAW 264.7 cells and the protective activity in aristolochic acid (AA)-induced NRK-52E cell injury. HDF1 and HDF2B (low-molecular weight sulfated fucans/fuco-oligosaccharides) did not increase the nitric oxide production in RAW 264.7 cells, whereas HDF2 and HDF2A exhibited potential immunomodulatory activity. All the tested compounds showed different degrees of protective activity in AA-induced injury; HDF2A exhibited superior protective activity. Through chemical analysis, HPLC analysis, and IR spectroscopy and MS, it was determined that HDF2A was a galactose-enriched heteropolysaccharide- glucofucogalactan with a distinctive 2:1 ratio of galactose to fucose. In addition, HDF2A also contained a high amount of glucose and minor amounts of mannose, rhamnose, and xylose, with a low content of sulfate. Thus, HDF2A, a complex heterogeneous polysaccharide mixture with a unique monosaccharide composition, could be studied for further structural characterization and pharmaceutical applications.

Update on Marine Carbohydrate Hydrolyzing Enzymes: Biotechnological Applications

After generating much interest in the past as an aid in solving structural problems for complex molecules such as polysaccharides, carbohydrate-hydrolyzing enzymes of marine origin still appear as interesting biocatalysts for a range of useful applications in strong interdisciplinary fields such as green chemistry and similar domains. The multifaceted fields in which these enzymes are of interest and the scarce number of original articles in literature prompted us to provide the specialized analysis here reported. General considerations from modern (2016-2017 interval time) review articles are at start of this manuscript; then it is subsequently organized in sections according to particular biopolymers and original research articles are discussed. Literature sources like the Science Direct database with an optimized W/in search, and the Espacenet patent database were used.

Double blind microarray-based polysaccharide profiling enables parallel identification of uncharacterized polysaccharides and carbohydrate-binding proteins with unknown specificities

Marine algae are one of the largest sources of carbon on the planet. The microbial degradation of algal polysaccharides to their constitutive sugars is a cornerstone in the global carbon cycle in oceans. Marine polysaccharides are highly complex and heterogeneous, and poorly understood. This is also true for marine microbial proteins that specifically degrade these substrates and when characterized, they are frequently ascribed to new protein families. Marine (meta)genomic datasets contain large numbers of genes with functions putatively assigned to carbohydrate processing, but for which empirical biochemical activity is lacking. There is a paucity of knowledge on both sides of this protein/carbohydrate relationship. Addressing this 'double blind' problem requires high throughput strategies that allow large scale screening of protein activities, and polysaccharide occurrence. Glycan microarrays, in particular the Comprehensive Microarray Polymer Profiling (CoMPP) method, are powerful in screening large collections of glycans and we described the integration of this technology to a medium throughput protein expression system focused on marine genes. This methodology (Double Blind CoMPP or DB-CoMPP) enables us to characterize novel polysaccharide-binding proteins and to relate their ligands to algal clades. This data further indicate the potential of the DB-CoMPP technique to accommodate samples of all biological sources.

Enzymatic Synthesis of GDP-α-l-fucofuranose by MtdL and Hyg20

Two mutases, MtdL and Hyg20, are reported. Both are able to functionally drive the biosynthesis of GDP-α-l-fucofuranose. Both enzymes catalyze similar functions, catalytically enabling the bidirectional reaction between GDP-β-l-fucopyranose and GDP-α-l-fucofuranose using only divalent cations as cofactors. This realization is but one of a number of important insights into fucofuranose biosynthesis presented herein.