Structural and functional aspects of mannuronic acid-specific PL6 alginate lyase from the human gut microbe Bacteroides cellulosilyticus

Characterization and elucidation of a novel M-specific alginate lyase Aly7Aq with strict recognition at subsites ±2

A novel alginate lyase Aly7Aq was cloned and heterologous expressed by a combination of bioinformatics and molecular biology. Aly7Aq was an M-specific alginate lyase, exhibiting optimum reaction conditions at 50 °C and pH 10.0. Aly7Aq was determined to degrade polysaccharides in a random endo-acting manner. The minimum reaction substrate was tetrasaccharide, and Aly7Aq mainly attacked the third glycosidic linkage from the reducing end of oligosaccharide substrates. The disaccharide product of Aly7Aq was ΔM and the trisaccharide products were ΔMM and ΔMG, which differed from all previously characterized M-specific alginate lyases. The degradation products demonstrated that the ±2 subsites of Aly7Aq strictly recognized M units, while the -1 subsite accommodated both M and G units. Therefore, the substrate specificity of Aly7Aq was derived from the specificity of ±2 subsites. This is the first report on the specificity at subsite ±2 of M-specific alginate lyase. The novel M-specific Aly7Aq could serve as a potential tool in the specific degradation of alginate and targeted preparation of oligosaccharide.

Identification and characterization of a novel thermostable PL7 alginate lyase from a submarine volcanic metagenomic library

Seaweed biomass is as an abundant and renewable source of complex polysaccharides, including alginate which has a variety of applications. A sustainable method for exploiting alginate towards the production of valuable oligosaccharides is through enzymatic processing, using alginate lyases. Industrial refinement methods demand robust enzymes. Metagenomic libraries from extreme environments are a new source of unique enzymes with great industrial potential. Herein we report the identification of a new thermostable alginate lyase with only 58 % identity to known sequences, identified by mining a metagenomic library obtained from the hydrothermal vents of the volcano Kolumbo in the Aegean Sea (Kolumbo Alginate Lyase, KAlLy). Sequence analysis and biochemical characterization of KAlLy showed that this new alginate lyase is a Polysaccharide Lyase of family 7 (PL7) enzyme with endo- and exo-action on alginate and poly-mannuronic acid, with high activity at 60°C (56 ± 8 U/mg) and high thermostability (half-life time of 30 h at 50°C). The response surface methodology analysis revealed that the reaction optimum conditions with poly-mannuronic acid as substrate are 44°C, pH of 5.5 with 440 mM NaCl. This novel alginate lyase is a valuable addition to the toolbox of alginate modifying enzymes, due to its diverse sequence and its good thermal stability.

Polysaccharides and oligosaccharides originated from green algae: structure, extraction, purification, activity and applications

With the proceeding of global warming and water eutrophication, the phenomenon of green tide has garnered significant societal interest. Consequently, researchers had increasingly focused on the potential applications of green algae biomass, particularly its polysaccharides. The polysaccharide serves as the primary active constituent of green algae and has demonstrated numerous advantageous biological activities, including antioxidant, antiviral, anticoagulant, hypolipidemic and immuno-modulatory activities. The favorable bioavailability and solubility of green algae oligosaccharides are attributed to their low molecular weight. So there has been a growing interest in researching green algae polysaccharides and oligosaccharides for the utilization of marine biological resources. This review summarized the extraction, purification, chemical structure, composition, biological activity, and potential applications prospect of polysaccharides and oligosaccharides derived from green algae. The review could be helpful for expanding the applications of polysaccharides and oligosaccharides of green algae.

Action and cooperation in alginate degradation by three enzymes from the human gut bacterium Bacteroides eggerthii DSM 20697

Alginate is a polysaccharide consumed by humans in edible seaweed and different foods where it is applied as a texturizing hydrocolloid or in encapsulations of drugs and probiotics. While gut bacteria are found to utilize and ferment alginate to health-beneficial short-chain fatty acids, knowledge on the details of the molecular reactions is sparse. Alginates are composed of mannuronic acid (M) and its C-5 epimer guluronic acid (G). An alginate-related polysaccharide utilization locus (PUL) has been identified in the gut bacterium Bacteroides eggerthii DSM 20697. The PUL encodes two polysaccharide lyases (PLs) from the PL6 (BePL6) and PL17 (BePL17) families as well as a KdgF-like metalloprotein (BeKdgF) known to catalyze ring-opening of 4,5-unsaturated monouronates yielding 4-deoxy-l-erythro-5-hexoseulose uronate (DEH). B. eggerthii DSM 20697 does not grow on alginate, but readily proliferates with a lag phase of a few hours in the presence of an endo-acting alginate lyase A1-I from the marine bacterium Sphingomonas sp. A1. The B. eggerthii lyases are both exo-acting and while BePL6 is strictly G-block specific, BePL17 prefers M-blocks. BeKdgF retained 10-27% activity in the presence of 0.1-1 mM EDTA. X-ray crystallography was used to investigate the three-dimensional structure of BeKdgF, based on which a catalytic mechanism was proposed to involve Asp102, acting as acid/base having pKa of 5.9 as determined by NMR pH titration. BePL6 and BePL17 cooperate in alginate degradation with BeKdgF linearizing producing 4,5-unsaturated monouronates. Their efficiency of alginate degradation was much enhanced by the addition of the A1-I alginate lyase.

Structural basis for the minimal bifunctional alginate epimerase AlgE3 from Azotobacter chroococcum

Among the epimerases specific to alginate, some of them in Azotobacter genera convert β-d-mannuronic acid to α-l-guluronic acid but also have lyase activity to degrade alginate. The remarkable characteristics of these epimerases make it a promising enzyme for tailoring alginates to meet specific demands. Here, we determined the structure of the bifunctional mannuronan C-5 epimerase AlgE3 from Azotobacter chroococcum (AcAlgE3) in complex with several mannuronic acid oligomers as well as in apo form, which allowed us to elucidate the binding manner of each mannuronic acid oligomer, and the structural plasticity, which is dependent on calcium ions. Moreover, a comprehensive analysis of the lyase activity profiles of AcAlgE3 combined with structural characteristics explained the preference for different chain length oligomers.

Efficient preparation of alginate oligosaccharides by using alginate lyases and evaluation of the development promoting effects on Brassica napus L. in saline-alkali environment

Enzymatic degradation of alginate for the preparation of alginate oligosaccharides (AOS) is currently receiving significant attention in the field. AOS has been shown to promote crop growth and improve plant resistance to abiotic stresses. In this study, two PL6 family alginate lyases, AlyRmA and AlyRmB, were expressed and characterized. These enzymes demonstrate exceptional activity and stable thermophilicity compared to other known alginate lyases. AlyRmA (8855.34 U/mg) and AlyRmB (7879.44 U/mg) exhibited excellent degradation activity towards sodium alginate even at high temperatures (70 °C). The AlyRmA and AlyRmB were characterized and utilized to efficiently produce AOS. The study investigated the promotional effect of AOS on the growth of Brassica napus L. seedlings in a saline-alkaline environment. The results of this study demonstrate the high activity and thermal stability of AlyRmA and AlyRmB, highlighting their potential in the preparation of AOS. Moreover, the application of AOS prepared by AlyRmB could enhance the resistance of Brassica napus L. to saline-alkali environments, thereby broadening the potential applications of AOS.

Exploring potential polysaccharide utilization loci involved in the degradation of typical marine seaweed polysaccharides by Bacteroides thetaiotaomicron

Introduction

Research on the mechanism of marine polysaccharide utilization by Bacteroides thetaiotaomicron has drawn substantial attention in recent years. Derived from marine algae, the marine algae polysaccharides could serve as prebiotics to facilitate intestinal microecological balance and alleviate colonic diseases. Bacteroides thetaiotaomicron, considered the most efficient degrader of polysaccharides, relates to its capacity to degrade an extensive spectrum of complex polysaccharides. Polysaccharide utilization loci (PULs), a specialized organization of a collection of genes-encoded enzymes engaged in the breakdown and utilization of polysaccharides, make it possible for Bacteroides thetaiotaomicron to metabolize various polysaccharides. However, there is still a paucity of comprehensive studies on the procedure of polysaccharide degradation by Bacteroides thetaiotaomicron.

Methods

In the current study, the degradation of four kinds of marine algae polysaccharides, including sodium alginate, fucoidan, laminarin, and Pyropia haitanensis polysaccharides, and the underlying mechanism by Bacteroides thetaiotaomicron G4 were investigated. Pure culture of Bacteroides thetaiotaomicron G4 in a substrate supplemented with these polysaccharides were performed. The change of OD600, total carbohydrate contents, and molecular weight during this fermentation were determined. Genomic sequencing and bioinformatic analysis were further performed to elucidate the mechanisms involved. Specifically, Gene Ontology (GO) annotation, Clusters of Orthologous Groups (COG) annotation, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were utilized to identify potential target genes and pathways.

Results

Underlying target genes and pathways were recognized by employing bioinformatic analysis. Several PULs were found that are anticipated to participate in the breakdown of these four polysaccharides. These findings may help to understand the interactions between these marine seaweed polysaccharides and gut microorganisms.

Discussion

The elucidation of polysaccharide degradation mechanisms by Bacteroides thetaiotaomicron provides valuable insights into the utilization of marine polysaccharides as prebiotics and their potential impact on gut health. Further studies are warranted to explore the specific roles of individual PULs and their contributions to polysaccharide metabolism in the gut microbiota.

Advances in alginate lyases and the potential application of enzymatic prepared alginate oligosaccharides: A mini review

Alginate is mainly a linear polysaccharide composed of randomly arranged β-D-mannuronic acid and α-L-guluronic acid linked by α, β-(1,4)-glycosidic bonds. Alginate lyases degrade alginate mainly adopting a β-elimination mechanism, breaking the glycosidic bonds between the monomers and forming a double bond between the C4 and C5 sugar rings to produce alginate oligosaccharides consisting of 2-25 monomers, which have various physiological functions. Thus, it can be used for the continuous industrial production of alginate oligosaccharides with a specific degree of polymerization, in accordance with the requirements of green exploitation of marine resources. With the development of structural analysis, the quantity of characterized alginate lyase structures is progressively growing, leading to a concomitant improvement in understanding the catalytic mechanism. Additionally, the use of molecular modification methods including rational design, truncated expression of non-catalytic domains, and recombination of conserved domains can improve the catalytic properties of the original enzyme, enabling researchers to screen out the enzyme with the expected excellent performance with high success rate and less workload. This review presents the latest findings on the catalytic mechanism of alginate lyases and outlines the methods for molecular modifications. Moreover, it explores the connection between the degree of polymerization and the physiological functions of alginate oligosaccharides, providing a reference for enzymatic preparation development and utilization.

Three alginate lyases provide a new gut Bacteroides ovatus isolate with the ability to grow on alginate

Humans consume alginate in the form of seaweed, food hydrocolloids, and encapsulations, making the digestion of this mannuronic acid (M) and guluronic acid (G) polymer of key interest for human health. To increase knowledge on alginate degradation in the gut, a gene catalog from human feces was mined for potential alginate lyases (ALs). The predicted ALs were present in nine species of the Bacteroidetes phylum, of which two required supplementation of an endo-acting AL, expected to mimic cross-feeding in the gut. However, only a new isolate grew on alginate. Whole-genome sequencing of this alginate-utilizing isolate suggested that it is a new Bacteroides ovatus strain harboring a polysaccharide utilization locus (PUL) containing three ALs of families: PL6, PL17, and PL38. The BoPL6 degraded polyG to oligosaccharides of DP 1-3, and BoPL17 released 4,5-unsaturated monouronate from polyM. BoPL38 degraded both alginates, polyM, polyG, and polyMG, in endo-mode; hence, it was assumed to deliver oligosaccharide substrates for BoPL6 and BoPL17, corresponding well with synergistic action on alginate. BoPL17 and BoPL38 crystal structures, determined at 1.61 and 2.11 Å, respectively, showed (α/α)6-barrel + anti-parallel β-sheet and (α/α)7-barrel folds, distinctive for these PL families. BoPL17 had a more open active site than the two homologous structures. BoPL38 was very similar to the structure of an uncharacterized PL38, albeit with a different triad of residues possibly interacting with substrate in the presumed active site tunnel. Altogether, the study provides unique functional and structural insights into alginate-degrading lyases of a PUL in a human gut bacterium.IMPORTANCEHuman ingestion of sustainable biopolymers calls for insight into their utilization in our gut. Seaweed is one such resource with alginate, a major cell wall component, used as a food hydrocolloid and for encapsulation of pharmaceuticals and probiotics. Knowledge is sparse on the molecular basis for alginate utilization in the gut. We identified a new Bacteroides ovatus strain from human feces that grew on alginate and encoded three alginate lyases in a gene cluster. BoPL6 and BoPL17 show complementary specificity toward guluronate (G) and mannuronate (M) residues, releasing unsaturated oligosaccharides and monouronic acids. BoPL38 produces oligosaccharides degraded by BoPL6 and BoPL17 from both alginates, G-, M-, and MG-substrates. Enzymatic and structural characterization discloses the mode of action and synergistic degradation of alginate by these alginate lyases. Other bacteria were cross-feeding on alginate oligosaccharides produced by an endo-acting alginate lyase. Hence, there is an interdependent community in our guts that can utilize alginate.

Advances in oligosaccharides production from algal sources and potential applications

In recent years, algal-derived glycans and oligosaccharides have become increasingly important in health applications due to higher bioactivities than plant-derived oligosaccharides. The marine organisms have complex, and highly branched glycans and more reactive groups to elicit greater bioactivities. However, complex and large molecules have limited use in broad commercial applications due to dissolution limitations. In comparison to these, oligosaccharides show better solubility and retain their bioactivities, hence, offering better applications opportunity. Accordingly, efforts are being made to develop a cost-effective method for enzymatic extraction of oligosaccharides from algal polysaccharides and algal biomass. Yet detailed structural characterization of algal-derived glycans is required to produce and characterize the potential biomolecules for improved bioactivity and commercial applications. Some macroalgae and microalgae are being evaluated as in vivo biofactories for efficient clinical trials, which could be very helpful in understanding the therapeutic responses. This review discusses the recent advancements in the production of oligosaccharides from microalgae. It also discusses the bottlenecks of the oligosaccharides research, technological limitations, and probable solutions to these problems. Furthermore, it presents the emerging bioactivities of algal oligosaccharides and their promising potential for possible biotherapeutic application.

Improving the thermostability of a novel PL-6 family alginate lyase by rational design engineering for industrial preparation of alginate oligosaccharides

Alginate is degraded into alginate oligosaccharides with various biological activities by enzymes. However, the thermostability of the enzyme limits its industrial application. In this study, a novel PL-6 alginate lyase, AlyRm6A from Rhodothermus marinus 4252 was expressed and characterized. In addition, an efficient comprehensive strategy was proposed, including automatic design of heat-resistant mutants, multiple computer-aided ΔΔGfold value calculation, and conservative analysis of mutation sites. AlyRm6A has naturally high thermostability. Compared with the WT, T43I and Q216I kept their original activities, and their half-lives were increased from 3.68 h to 4.29 h and 4.54 h, melting point temperatures increased from 61.5 °C to 62.9 °C and 63.5 °C, respectively. The results of circular dichroism showed that both the mutants and the wild type had the characteristic peaks of β-sheet at 195 nm and 216 nm, which indicated that there was no significant effect on the secondary structure of the protein. Molecular dynamics simulation (MD) analyses suggest that the enhancement of the hydrophobic interaction network, improvement of molecular rigidity, and denser structure could improve the stability of AlyRm6A. To the best of our knowledge, our findings indicate that AlyRm6A mutants exhibit the highest thermostability among the characterized PL-6 alginate lyases, making them potential candidates for industrial production of alginate oligosaccharides.

Ulvan and Ulva oligosaccharides: a systematic review of structure, preparation, biological activities and applications

Ulva is one of the main green algae causing green tide disasters. Ulvan is the primarily component polysaccharide of the cell wall of Ulva and its complex structure and monosaccharide composition resulted in various biological activities. However, the high-value and effective utilization of extracted ulvan have been obstructed by limitations ranging from large molecular weight and low solubility to poor bioavailability. Ulva oligosaccharide obtained by degrading ulvan can not only ideally retain the various biological activities of ulvan very well but also effectively solve the problems of low solubility and poor bioavailability. The preparation and biological activity studies of ulvan and Ulva oligosaccharides have become a hot spot in the field of marine biological resources development research. At present, the comprehensive reviews of ulvan and Ulva oligosaccharides are still scarce. What are overviewed in this paper are the chemical composition, structure, extraction, and purification of ulvan and Ulva oligosaccharides, where research progress on the biological activities of ulvan and Ulva oligosaccharides is summarized and prospected. A theoretical and practical basis has been provided for further research on ulvan and Ulva oligosaccharides, as well as the high-value development and effective utilization of marine algae resources.

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.

Accurate detection of enzymatic degradation processes of gelatin-alginate microcapsule by 1H NMR spectroscopy: Probing biodegradation mechanism and kinetics

With an increase in the severity of environmental pollution caused by microbeads, the development of biodegradable microcapsules that can be applied in diverse fields has attracted significant attention. The degradation processes are directly related to biodegradable microcapsule creation with high stability and persistence. In this study, biodegradable microcapsules are synthesized via a complex coacervation approach using gelatin and alginate as the capsule main wall materials; additionally, enzyme-induced decomposition mechanisms are proposed by observing spectral changes in proton nuclear magnetic resonance (¹H NMR) analyses. Additional analytical techniques confirm the chemical structure, morphology, and size distribution of the synthesized capsules; these uniform spherical microcapsules are 20-30 μm in size and possess a smooth surface. In addition to characterization, the microcapsules were exposed to targeted enzymes to investigate enzymatic effects using short-term and long-term degradation kinetics. Close inspection reveals that determination of the degradation rate constant of the major components in the capsule is feasible, and suggests two types of 4-stage degradation mechanisms that are enzyme-specific. These investigations demonstrate that capsule degradation can be explored in detail using ¹H NMR spectroscopy to provide a viable strategy for monitoring degradation properties in the development of new biodegradable polymers.

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

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

Dissecting the essential role of N-glycosylation in catalytic performance of xanthan lyase

Modified xanthan produced by xanthan lyase has broad application prospects in the food industry. However, the catalytic performance of xanthan lyase still needs to be improved through rational design. To address this problem, in this work, the glycosylation and its influences on the catalytic performance of a xanthan lyase (EcXly), which was heterologously expressed in Escherichia coli, were reported. Liquid chromatography coupled to tandem mass spectrometry analysis revealed that the N599 site of EcXly was modified by a single N-glycan chain. Based on sequence alignment and three-dimensional structure prediction, it could be deduced that the N599 site was located in the catalytic domain of EcXly and in close proximity to the catalytic residues. After site-directed mutagenesis of N599 with alanine, aspartic acid and glycine, respectively, the EcXly and its mutants were characterized and compared. The results demonstrated that elimination of the N-glycosylation had diminished the specific activity, pH stability, and substrate affinity of EcXly. Fluorescence spectra further revealed that the glycosylation could significantly affect the overall tertiary structure of EcXly. Therefore, in prokaryotic hosts, the N-glycosylation could influence the catalytic performance of the enzyme by changing its structure. To the best of our knowledge, this is the first report about the post-translational modification of xanthan lyase in prokaryotes. Overall, our work enriched research on the role of glycan chains in the functional performance of proteins expressed in prokaryotes and should be valuable for the rational design of xanthan lyase to produce modified xanthan for industrial application.

Characterization of degradation patterns and enzymatic properties of a novel alkali-resistant alginate lyase AlyRm1 from Rubrivirga marina

Alginate lyase is essential for the production of alginate oligosaccharides (AOSs), which exhibit diverse bioactivities and have numerous applications in the food and pharmaceutical industries. The creation of recombinant alginate lyase by genetic engineering lays a crucial foundation for the commercialization of alginate lyase. This study cloned and expressed the polysaccharide lyase family 6 (PL6) alginate lyase gene alyrm1 from Rubrivirga marina.The optimum temperature and pH for recombinant AlyRm1 are 30 °C and 10.0, respectively. AlyRm1 shows good alkaline stability, for it remained over 80% of the enzyme activity after being incubated at pH 10.0 for 24 h AlyRm1 preferentially degrades PolyM into AOSs with degrees of polymerization (DP) 2-5 and monosaccharides as an endolytic bifunctional lyase. In addition, the analysis of degradation products toward oligosaccharides revealed that the minimal substrate of AlyRm1 is trisaccharide and clarified the degradation patterns.

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.

Human Gut Microbiota and Drug Metabolism

The efficacy of drugs widely varies in individuals, and the gut microbiota plays an important role in this variability. The commensal microbiota living in the human gut encodes several enzymes that chemically modify systemic and orally administered drugs, and such modifications can lead to activation, inactivation, toxification, altered stability, poor bioavailability, and rapid excretion. Our knowledge of the role of the human gut microbiome in therapeutic outcomes continues to evolve. Recent studies suggest the existence of complex interactions between microbial functions and therapeutic drugs across the human body. Therapeutic drugs or xenobiotics can influence the composition of the gut microbiome and the microbial encoded functions. Both these deviations can alter the chemical transformations of the drugs and hence treatment outcomes. In this review, we provide an overview of (i) the genetic ecology of microbially encoded functions linked with xenobiotic degradation; (ii) the effect of drugs on the composition and function of the gut microbiome; and (iii) the importance of the gut microbiota in drug metabolism.

Simulated gastrointestinal digestion of protein alginate complexes: effects of whey protein cross-linking and the composition and degradation of alginate

Alginate and whey protein are common additives in food production improving storage stability, texture and nutritional value. Alginate forms complexes with whey protein and inhibits proteolysis by pepsin and trypsin, but the influence of alginate protein complexation on digestion is poorly understood. This study shows that whey protein cross-linking by microbial transglutaminase dramatically decreased particle size (2-fold) and viscosity of alginate protein complexes. The INFOGEST in vitro simulated gastrointestinal digestion of whey protein was increased by cross-linking (16%) and suppressed by alginate, most pronounced with high mannuronic acid and least with high guluronic acid content. Sizes of alginate whey protein particles increased during gastric digestion, whereas for cross-linked whey protein complexes the size initially increased, but returned to their initial size at the end of gastric digestion. While alginate is not degraded by human enzymes, a few gut bacteria were recently found to encode lyases and other enzymes metabolizing alginate. Alginate lyase added to the intestinal phase enhanced digestion (9%) as controlled by alginate composition and enzyme specificity. Thus we provide evidence that use of hydrocolloids and processing of protein strongly influence digestion and should be considered when using food additives.

Sodium alginate and galactooligosaccharides ameliorate metabolic disorders and alter the composition of the gut microbiota in mice with high-fat diet-induced obesity

We aimed to investigate the effects of sodium alginate (SA) and galactooligosaccharides (GOS) on the metabolism and gut microbiota of high-fat diet (HFD)-fed obese mice. GOS and SA delayed high-fat diet-induced obesity, reduced the epididymal fat and liver indices, and improved the circulating lipid profile. Low- and high-dose GOS reduced weight gain by 48.8 % and 35.3 %, and low- and high-dose SA reduced it by 37.7 % and 34.4 %, respectively. GOS and SA reduced blood glucose concentration, probably by increasing the expression of glucose transporter 4. GOS and SA increased the expression of tight junction proteins (ZO-1 and occludin), reduced the D-lactic acid (D-LA) and lipopolysaccharide concentrations, and reduced the expression of toll-like receptors, consistent with improved intestinal barrier function. GOS and SA also increased the abundance of Bacteroidota, Bifidobacterium, and Lactobacillus; and reduced that of Patescibacteria in the gut. The abundance of Parabacteroides positively correlated with the circulating low-density lipoprotein-cholesterol (LDL-C) concentration; that of Lactobacillus negatively correlated with LDL-C, D-LA, and tumor necrosis factor-α concentration; and that of Bifidobacterium positively correlated with high-density lipoprotein-cholesterol concentration, according to Spearman correlation analysis. In conclusion, SA and GOS ameliorate obesity and the associated metabolic disorders in mice, and also modulate their gut microbial composition.

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

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

Preparation and potential applications of alginate oligosaccharides

Alginate, a linear polymer consisting of β-D-mannuronic acid (M) and α-L-guluronic acid (G) with 1,4-glycosidic linkages and comprising 40% of the dry weight of algae, possesses various applications in the food and nutraceutical industries. However, the potential applications of alginate are restricted in some fields because of its low water solubility and high solution viscosity. Alginate oligosaccharides (AOS) on the other hand, have low molecular weight which result in better water solubility. Hence, it becomes a more popular target to be researched in recent years for its use in foods and nutraceuticals. AOS can be obtained by multiple degradation methods, including enzymatic degradation, from alginate or alginate-derived poly G and poly M. AOS have unique bioactivity and can bring human health benefits, which render them potentials to be developed/incorporated into functional food. This review comprehensively covers methods of the preparation and analysis of AOS, and discussed the potential applications of AOS in foods and nutraceuticals.

Cloning and Characterization of a Novel Alginate Lyase from Paenibacillus sp. LJ-23

As a low molecular weight alginate, alginate oligosaccharides (AOS) exhibit improved water solubility, better bioavailability, and comprehensive health benefits. In addition, their biocompatibility, biodegradability, non-toxicity, non-immunogenicity, and gelling capability make them an excellent biomaterial with a dual curative effect when applied in a drug delivery system. In this paper, a novel alginate lyase, Algpt, was cloned and characterized from a marine bacterium, Paenibacillus sp. LJ-23. The purified enzyme was composed of 387 amino acid residues, and had a molecular weight of 42.8 kDa. The optimal pH of Algpt was 7.0 and the optimal temperature was 45 °C. The analysis of the conserved domain and the prediction of the three-dimensional structure indicated that Algpt was a novel alginate lyase. The dominant degradation products of Algpt on alginate were AOS dimer to octamer, depending on the incubation time, which demonstrated that Algpt degraded alginate in an endolytic manner. In addition, Algpt was a salt-independent and thermo-tolerant alginate lyase. Its high stability and wide adaptability endow Algpt with great application potential for the efficient preparation of AOS with different sizes and AOS-based products.

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

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

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

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

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

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

Exploring molecular determinants of polysaccharide Lyase family 6-1 enzyme activity

The Polysaccharide Lyase Family 6 (PL6) represents one of the 41 polysaccharide lyase families classified in the CAZy database with the vast majority of its members being alginate lyases grouped into three subfamilies, PL6_1-3. To decipher the mode of recognition and action of the enzymes belonging to subfamily PL6_1, we solved the crystal structures of Pedsa0632, Patl3640, Pedsa3628 and Pedsa3807, which all show different substrate specificities and mode of action (endo-/exo-lyase). Thorough exploration of the structures of Pedsa0632 and Patl3640 in complex with their substrates as well as docking experiments confirm that the conserved residues in subsites -1 to +3 of the catalytic site form a common platform which can accommodate various types of alginate in a very similar manner but with a series of original adaptations bringing them their specificities of action. From comparative studies with existing structures of PL6_1 alginate lyases, we observe that in the right-handed parallel β-helix fold shared by all these enzymes, the substrate binding site harbors the same overall conserved structures and organization. Despite this apparent similarity, it appears that members of the PL6_1 subfamily specifically accommodate and catalyze the degradation of different alginates suggesting that this common platform is actually a highly adaptable and specific tool.

Potential applications of alginate oligosaccharides for biomedicine - A mini review

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

Plant-Based Diet Index and Metabolic Risk in Men: Exploring the Role of the Gut Microbiome

BACKGROUND

Healthy plant-based diet index (hPDI) is associated with a lower risk of cardiometabolic conditions, but its association as well as interactions with microbiome have not been elucidated.

OBJECTIVES

We aimed to investigate the interrelations between hPDI, gut microbiome, and cardiometabolic risk markers.

METHODS

hPDI was derived from dietary assessments by a validated FFQ and was examined in relation to metagenomic profiles of 911 fecal samples collected from 303 men aged 71 ± 4 y with an average BMI (in kg/m2) of 25.2 ± 3.6 in the Men's Lifestyle Validation Study. Principal coordinate (PCo) analysis based on Bray-Curtis dissimilarity was conducted, and interactions between hPDI and PCo were examined by using a metabolic risk score composed of blood lipids, BMI, and glycated hemoglobin.

RESULTS

After multivariable adjustment, hPDI was significantly associated with the relative abundance of 7 species and 9 pathways. In particular, higher hPDI was significantly associated with a higher relative abundance of Bacteroides cellulosilyticus and Eubacterium eligens, amino acid biosynthesis pathways (l-isoleucine biosynthesis I and III and l-valine biosynthesis), and the pathway of pyruvate fermentation to isobutanol. A favorable association between hPDI and the metabolic risk score was more pronounced among men with a higher PCo characterized by higher abundance of Bacteroides uniformis and lower abundance of Prevotella copri. At the individual species level, a similar interaction was also observed between hPDI and P. copri, as well as with Clostridium clostridioforme or Blautia hydrogenotrophica (all P-interaction < 0.01).

CONCLUSION

A greater adherence to a healthy plant-based diet by older men was associated with a microbial profile characterized by a higher abundance of multiple species, including B. cellulosilyticus and E. eligens, as well as pathways in amino acid metabolism and pyruvate fermentation. In addition, inverse associations between healthy plant-based diet and human metabolic risk may partially depend on microbial compositions.

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

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

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

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

Overview on Microbial Enzymatic Production of Algal Oligosaccharides for Nutraceutical Applications

Global requirement for algal foods is increasing, as they are progressively consumed for its nutrition and health. Macroalgae is a proven source of metabolites, proteins, pigments, bioactive compounds, and algal polysaccharides. The unique polysaccharides such as agar, carrageenan, porphyran, alginate, fucoidan, laminarin, and ulvan are known for its wide range of bioactivities and extensively used for applications from tissue engineering to drug delivery. However, there are few limitations due to its high molecular size, low compatibility, and hydrocolloid nature. Hence, the enzymatically produced algal oligosaccharides have drawn tremendous attention due to its green synthesis, solubility, and lower molecular size. They are reported to have bioactivities including antioxidant, antiglycemic, immunostimulatory, anti-inflammatory, and prebiotic activities, which can be used in the healthcare and nutraceutical industry for the manufacture of functional foods and dietary supplements. However, identification of potential microorganisms, producing polysaccharide hydrolyzing enzymes, remains a major bottle neck for efficient utilization of bioactive algal oligosaccharides. This review summarizes the recent developments in the identification and characterization of microbial enzymes for the production of bioactive algal oligosaccharides. This can improve our understanding of bioactive algal oligosaccharides and pave way for efficient utilization of macroalgae to prevent various chronic diseases.

Structural basis for the exolytic activity of polysaccharide lyase family 6 alginate lyase BcAlyPL6 from human gut microbe Bacteroides clarus

Alginate is the structural polysaccharide of the cell wall of brown algae, which is an important carbon source for marine life. The depolymerization of alginate is dependent on alginate lyases. Recent studies showed that the alginate utilization ability had been obtained by human gut microbes. In contrast to the great number of studies on alginate lyases from marine/soil organisms, studies on alginate lyases from gut microbes are still limited. Here, the structure of a polysaccharide lyase family 6 (PL6) alginate lyase from human gut microbe Bacteroides clarus was solved by X-ray crystallography, which represents the cluster of two-domain PL6 alginate lyases from Bacteroidetes. Similar with the two-domain alginate lyase AlyGC originated from marine bacterium, both the N terminal domain (NTD) and C terminal domain (CTD) of BcAlyPL6 show right-handed parallel β-helix fold. However, unlike AlyGC, which forms a homodimer, BcAlyPL6 functions as a monomer. Biochemical analysis indicates that the substrate binding affinity is mainly contributed by the NTD while the CTD of BcAlyPL6 is involved in the formation of -1 subsite, which is essential for substrate turnover rate. Furthermore, CTD is involved in shaping a closed catalytic pocket, and deletion of it leads to increased activity towards highly polymerized substrate. Structure comparison of PL6 family alginate lyases implies that the linkers of two-domain alginate lyases might have evolutionary relationship with the N/C terminal extension of single-domain lyases.

Structural insights into the substrate-binding cleft of AlyF reveal the first long-chain alginate-binding mode

The products of alginate degradation, alginate oligosaccharides (AOS), have potential applications in many areas, including functional foods and marine drugs. Enzyme-based approaches using alginate lyases have advantages in the preparation of well defined AOS and have attracted much attention in recent years. However, a lack of structural insight into the whole substrate-binding cleft for most known alginate lyases severely hampers their application in the industrial generation of well defined AOS. To solve this issue, AlyF was co-crystallized with the long alginate oligosaccharide G6 (L-hexaguluronic acid hexasodium salt), which is the longest bound substrate in all solved alginate lyase complex structures. AlyF formed interactions with G6 from subsites -3 to +3 without additional substrate-binding site interactions, suggesting that the substrate-binding cleft of AlyF was fully occupied by six sugars, which was further confirmed by isothermal titration calorimetry and differential scanning calorimetry analyses. More importantly, a combination of structural comparisons and mutagenetic analyses determined that three key loops (loop 1, Lys215-Glu236; loop 2, Gln402-Ile416; loop 3, Arg334-Gly348) mainly function in binding long substrates (degree of polymerization of >4). The potential flexibility of loop 1 and loop 2 might enable the substrate to continue to enter the cleft after binding to subsites +1 to +3; loop 3 stabilizes and orients the substrate at subsites -2 and -3. Taken together, these results provide the first possible alginate lyase-substrate binding profile for long-chain alginates, facilitating the rational design of new enzymes for industrial purposes.

Characteristics and applications of alginate lyases: A review

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

Macroalgal dietary glycans: potential source for human gut bacteria and enhancing immune system for better health

Macroalgae are the diverse group of photosynthetic algae found at the intertidal regions of oceans. Recent advances suggest that macroalgal derived glycans have tremendous potential to maintain gut microbiome and immune system. The human gut bacteria harbor unique arsenals for utilizing a variety of macroalgal glycans, and produce a variety of oligosaccharides in vivo. Those oligosaccharides interact with immune cell receptors, and also are available for microbial fermentation, thus play magnificent roles in balancing the gut homeostasis. However, this area of research is still in infancy condition in term to understand their molecular interactions. For wooing this area, we urge to emphasize more studies on mechanistic level sympathetic of depolymerizing marine dietary glycans by gut bacteria and elucidating molecular aspect of glycans to cell receptors interactions. This will invent new nutraceutical strategies to purposefully manipulate the microbial composition to improve health. Therefore, review focuses on the recent development of mechanistic understanding of human gut bacterial communities for utilizing macroalgal derived glycans. Recent trends of application of glycans in modulating immune system at mechanistic level and their available evidences are discussed.

Biochemical characterization and degradation pattern analysis of a novel PL-6 alginate lyase from Streptomyces coelicolor A3(2)

Alginate is the main component of brown algae which contributes to a huge biomass. The alginate oligosaccharides (AOs) have been widely used in food, cosmetic and pharmaceutical industries due to their various physiological activities. In this study, we expressed and characterized a novel PL-6 alginate lyase, named OUC-ScCD6. The results indicated that OUC-ScCD6 showed highest activity at 50 °C and pH 9.0. OUC-ScCD6 prefers to degrade poly M blocks and could digest poly G blocks as well. Endolytic action mode towards polysaccharides contributes to the creation of AOs with the degrees of polymerization 2-6. Degradation towards saturated oligosaccharides showed that saturated trisaccharides (M3 and G3) were minimum identifiable substrates. Furthermore, OUC-ScCD6 shows an even-numbered glycosidic bonds preference from non-reducing end which provided clearer insights into the substrate recognition and action mode of PL-6 family alginate lyases.