Action of poly (alpha-L-guluronate)lyase from Corynebacterium sp. ALY-1 strain on saturated oligoguluronates

Directed preparation of algal oligosaccharides with specific structures by algal polysaccharide degrading enzymes

Seaweed polysaccharides have a wide range of sources and rich content, with various biological activities such as anti-inflammatory, anti-tumor, anticoagulant, and blood pressure lowering. They can be applied in fields such as food, agriculture, and medicine. However, the poor solubility of macromolecular seaweed polysaccharides limits their further application. Reports have shown that some biological activities of seaweed oligosaccharides are more extensive and superior to that of seaweed polysaccharides. Therefore, reducing the degree of polymerization of polysaccharides will be the key to the high value utilization of seaweed polysaccharide resources. There are three main methods for degrading algal polysaccharides into algal oligosaccharides, physical, chemical and enzymatic degradation. Among them, enzymatic degradation has been a hot research topic in recent years. Various types of algal polysaccharide hydrolases and related glycosidases are powerful tools for the preparation of algal oligosaccharides, including α-agarases, β-agaroses, α-neoagarose hydrolases and β-galactosidases that are related to agar, κ-carrageenases, ι-carrageenases and λ-carrageenases that are related to carrageenan, β-porphyranases that are related to porphyran, funoran hydrolases that are related to funoran, alginate lyases that are related to alginate and ulvan lyases related to ulvan. This paper describes the bioactivities of agar oligosaccharide, carrageenan oligosaccharide, porphyran oligosaccharide, funoran oligosaccharide, alginate oligosaccharide and ulvan oligosaccharide and provides a detailed review of the progress of research on the enzymatic preparation of these six oligosaccharides. At the same time, the problems and challenges faced are presented to guide and improve the preparation and application of algal oligosaccharides in the future.

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.

Action Pattern of a Novel G-Specific Alginate Lyase: Determination of Subsite Specificity by HPAEC-PAD/MS

G-specific alginate lyases are important tools for alginate fragment biodegradation and oligosaccharide production, which have great potential in alginate refining research. In this research, a novel G-specific alginate lyase Aly7Ce was cloned, expressed, and characterized, with the optimal reaction conditions at 30 °C and pH 8.0. By employing the UPSEC-VWD-MS method, Aly7Ce was confirmed as a random endoacting alginate lyase. Its minimum substrate was tetrasaccharide, and the final product majorly consisted of disaccharide to tetrasaccharide. HPAEC-PAD/MS method was employed to investigate the structurally different unsaturated alginate oligosaccharides. The substrate recognition and subsite specificity of Aly7Ce were revealed by detecting the oligosaccharide pattern in the enzymatic products with oligosaccharides or polysaccharides as substrates. Aly7Ce mainly attacked the second glycosidic linkage from the nonreducing end of oligosaccharide substrates. The subsite specificity of Aly7Ce was revealed as -2 (M/G), - 1 (G), + 1 (M/G), and +2 (M/G). The regular oligosaccharide products of Aly7Ce could be applied for the efficient preparation of ΔG, ΔGG, and ΔGGG with high purity. The G-specific alginate lyase Aly7Ce with a well-defined product composition and action pattern provided a novel tool for the modification and structural elucidation of alginate, as well as for the targeted preparation of oligosaccharides.

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.

Characterization of a Novel Alginate Lyase with Two Alginate Lyase Domains from the Marine Bacterium Vibrio sp. C42

Alginate is abundant in the cell walls of brown algae. Alginate lyases can degrade alginate, and thus play an important role in the marine carbon cycle and industrial production. Currently, most reported alginate lyases contain only one functional alginate lyase domain. AlyC8 is a putative alginate lyase with two alginate lyase domains (CD1 and CD2) from the marine alginate-degrading strain Vibrio sp. C42. To characterize AlyC8 and its two catalytic domains, AlyC8 and its two catalytic domain-deleted mutants, AlyC8-CD1 and AlyC8-CD2, were expressed in Escherichia coli. All three proteins have noticeable activity toward sodium alginate and exhibit optimal activities at pH 8.0-9.0 and at 30-40 °C, demonstrating that both CD1 and CD2 are functional. However, CD1 and CD2 showed opposite substrate specificity. The differences in substrate specificity and degradation products of alginate between the mutants and AlyC8 demonstrate that CD1 and CD2 can act synergistically to enable AlyC8 to degrade various alginate substrates into smaller oligomeric products. Moreover, kinetic analysis indicated that AlyC8-CD1 plays a major role in the degradation of alginate by AlyC8. These results demonstrate that AlyC8 is a novel alginate lyase with two functional catalytic domains that are synergistic in alginate degradation, which is helpful for a better understanding of alginate lyases and alginate degradation.

Alginate Lyases from Marine Bacteria: An Enzyme Ocean for Sustainable Future

The cell wall of brown algae contains alginate as a major constituent. This anionic polymer is a composite of β-d-mannuronate (M) and α-l-guluronate (G). Alginate can be degraded into oligosaccharides; both the polymer and its products exhibit antioxidative, antimicrobial, and immunomodulatory activities and, hence, find many commercial applications. Alginate is attacked by various enzymes, collectively termed alginate lyases, that degrade glycosidic bonds through β-elimination. Considering the abundance of brown algae in marine ecosystems, alginate is an important source of nutrients for marine organisms, and therefore, alginate lyases play a significant role in marine carbon recycling. Various marine microorganisms, particularly those that thrive in association with brown algae, have been reported as producers of alginate lyases. Conceivably, the marine-derived alginate lyases demonstrate salt tolerance, and many are activated in the presence of salts and, therefore, find applications in the food industry. Therefore, this review summarizes the structural and biochemical features of marine bacterial alginate lyases along with their applications. This comprehensive information can aid in the expansion of future prospects of alginate lyases.

Discovery of a Novel Glucuronan Lyase System in Trichoderma parareesei

Glucuronan lyases (EC 4.2.2.14) catalyze depolymerization of linear β-(1,4)-polyglucuronic acid (glucuronan). Only a few glucuronan lyases have been characterized until now, most of them originating from bacteria. Here we report the discovery, recombinant production, and functional characterization of the full complement of six glucuronan specific polysaccharide lyases in the necrotic mycoparasite Trichoderma parareesei. The enzymes belong to four different polysaccharide lyase families and have different reaction optima and glucuronan degradation profiles. Four of them showed endo-lytic action and two, TpPL8A and TpPL38A, displayed exo-lytic action. Nuclear magnetic resonance revealed that the monomeric end product from TpPL8A and TpPL38A underwent spontaneous rearrangements to tautomeric forms. Proteomic analysis of the secretomes from T. parareesei growing on pure glucuronan and lyophilized A. bisporus fruiting bodies, respectively, showed secretion of five of the glucuronan lyases and high-performance anion-exchange chromatography with pulsed amperometric detection analysis confirmed the presence of glucuronic acid in the A. bisporus fruiting bodies. By systematic genome annotation of more than 100 fungal genomes and subsequent phylogenetic analysis of the putative glucuronan lyases, we show that glucuronan lyases occur in several ecological and taxonomic groups in the fungal kingdom. Our findings suggest that a diverse repertoire of glucuronan lyases is a common trait among Hypocreales species with mycoparasitic and entomopathogenic lifestyles. IMPORTANCE This paper reports the discovery of a set of six complementary glucuronan lyase enzymes in the mycoparasite Trichoderma parareseei. Apart from the novelty of the discovery of these enzymes in T. parareesei, the key importance of the study is the finding that the majority of these lyases are induced when T. parareesei is inoculated on Basidiomycete cell walls that contain glucuronan. The study also reveals putative glucuronan lyase encoding genes in a wealth of other fungi that furthermore points at fungal cell wall glucuronan being a target C-source for many types of fungi. In a technical context, the findings may lead to controlled production of glucuronan oligomers for advanced pharmaceutical applications and pave the way for development of new fungal biocontrol agents.

Identification and characterization of cellouronate (β-1,4-linked polyglucuronic acid) lyase from the scallop Mizuhopecten yessoensis

The semisynthetic polysaccharide cellouronate is a β-1,4-linked polyglucuronic acid prepared from regenerated cellulose by chemical oxidation. Here, we isolated a novel enzyme, MyAly, as a cellouronate lyase from a scallop Mizuhopecten yessoensis. Its optimum temperature, pH, and NaCl concentration for cellouronate degradation were determined to be 30 °C, 6.9, and 200-500 mM, respectively. MyAly endolytically degraded cellouronate into unsaturated di-, tri-, and tetrasaccharides with k_cat of 31.1 s^-1. MyAly also showed an alginate-degradation activity with a k_cat value of 0.58 s^-1. However, there was no significant difference in K_m values between cellouronate and alginate. MyAly consisted of 280 amino acids and shared 36.5-44.1 % identity with known marine gastropod alginate lyases belonging to the polysaccharide lyase family 14. This is the first study to identify and characterize a cellouronate-degrading lyase from a marine organism, providing a better understanding of the biodegradability of the industrially important polysaccharide, cellouronate, in marine environments.

Specificities and Synergistic Actions of Novel PL8 and PL7 Alginate Lyases from the Marine Fungus Paradendryphiella salina

Alginate is an anionic polysaccharide abundantly present in the cell walls of brown macroalgae. The enzymatic depolymerization is performed solely by alginate lyases (EC 4.2.2.x), categorized as polysaccharide lyases (PLs) belonging to 12 different PL families. Until now, the vast majority of the alginate lyases have been found in bacteria. We report here the first extensive characterization of four alginate lyases from a marine fungus, the ascomycete Paradendryphiella salina, a known saprophyte of seaweeds. We have identified four polysaccharide lyase encoding genes bioinformatically in P. salina, one PL8 (PsMan8A), and three PL7 alginate lyases (PsAlg7A, -B, and -C). PsMan8A was demonstrated to exert exo-action on polymannuronic acid, and no action on alginate, indicating that this enzyme is most likely an exo-acting polymannuronic acid specific lyase. This enzyme is the first alginate lyase assigned to PL8 and polymannuronic acid thus represents a new substrate specificity in this family. The PL7 lyases (PsAlg7A, -B, and -C) were found to be endo-acting alginate lyases with different activity optima, substrate affinities, and product profiles. PsAlg7A and PsMan8A showed a clear synergistic action for the complete depolymerization of polyM at pH 5. PsAlg7A depolymerized polyM to mainly DP5 and DP3 oligomers and PsMan8A to dimers and monosaccharides. PsAlg7B and PsAlg7C showed substrate affinities towards both polyM and polyG at pH 8, depolymerizing both substrates to DP9-DP2 oligomers. The findings elucidate how P. salina accomplishes alginate depolymerization and provide insight into an efficient synergistic cooperation that may provide a new foundation for enzyme selection for alginate degradation in seaweed bioprocessing.

Proteomic enzyme analysis of the marine fungus Paradendryphiella salina reveals alginate lyase as a minimal adaptation strategy for brown algae degradation

We set out to investigate the genetic adaptations of the marine fungus Paradendryphiella salina CBS112865 for degradation of brown macroalgae. We performed whole genome and transcriptome sequencing and shotgun proteomic analysis of the secretome of P. salina grown on three species of brown algae and under carbon limitation. Genome comparison with closely related terrestrial fungi revealed that P. salina had a similar but reduced CAZyme profile relative to the terrestrial fungi except for the presence of three putative alginate lyases from Polysaccharide Lyase (PL) family 7 and a putative PL8 with similarity to ascomycete chondroitin AC lyases. Phylogenetic and homology analyses place the PL7 sequences amongst mannuronic acid specific PL7 proteins from marine bacteria. Recombinant expression, purification and characterization of one of the PL7 genes confirmed the specificity. Proteomic analysis of the P. salina secretome when growing on brown algae, revealed the PL7 and PL8 enzymes abundantly secreted together with enzymes necessary for degradation of laminarin, cellulose, lipids and peptides. Our findings indicate that the basic CAZyme repertoire of saprobic and plant pathogenic ascomycetes, with the addition of PL7 alginate lyases, provide P. salina with sufficient enzymatic capabilities to degrade several types of brown algae polysaccharides.

Elucidation of degrading pattern and substrate recognition of a novel bifunctional alginate lyase from Flammeovirga sp. NJ-04 and its use for preparation alginate oligosaccharides

BACKGROUND

The alginate oligosaccharides have been widely used in agriculture, medicine, and food industries due to their versatile physiological functions such as antioxidant, anticoagulant, and antineoplastic activities. The bifunctional alginate lyases can degrade the alginate polysaccharide more efficiently into alginate oligosaccharides. Therefore, it is crucial to discover new bifunctional alginate lyase for alginate oligosaccharide production.

RESULTS

Herein, a novel bifunctional alginate lyase FsAlgB was cloned and identified from deep-sea bacterium Flammeovirga sp. NJ-04, which exhibited broad substrate specificity and the highest activity (1760.8 U/mg) at pH 8.0 and 40 °C. Furthermore, the K _m values of FsAlgB towards polyG (0.69 mM) and polyMG (0.92 mM) were lower than that towards sodium alginate (1.28 mM) and polyM (2.06 mM). Recombinant FsAlgB was further characterized as an endolytic alginate lyase, and it can recognize the tetrasaccharide as the minimal substrate and cleave the glycosidic bonds between the subsites of - 3 and + 1.

CONCLUSION

This study provided extended insights into the substrate recognition and degrading pattern of alginate lyases with broad substrate specificity.

AlgM4: A New Salt-Activated Alginate Lyase of the PL7 Family with Endolytic Activity

Alginate lyases are a group of enzymes that catalyze the depolymerization of alginates into oligosaccharides or monosaccharides. These enzymes have been widely used for a variety of purposes, such as producing bioactive oligosaccharides, controlling the rheological properties of polysaccharides, and performing structural analyses of polysaccharides. The algM4 gene of the marine bacterium Vibrio weizhoudaoensis M0101 encodes an alginate lyase that belongs to the polysaccharide lyase family 7 (PL7). In this study, the kinetic constants V_max (maximum reaction rate) and K_m (Michaelis constant) of AlgM4 activity were determined as 2.75 nmol/s and 2.72 mg/mL, respectively. The optimum temperature for AlgM4 activity was 30 °C, and at 70 °C, AlgM4 activity dropped to 11% of the maximum observed activity. The optimum pH for AlgM4 activity was 8.5, and AlgM4 was completely inactive at pH 11. The addition of 1 mol/L NaCl resulted in a more than sevenfold increase in the relative activity of AlgM4. The secondary structure of AlgM4 was altered in the presence of NaCl, which caused the α-helical content to decrease from 12.4 to 10.8% and the β-sheet content to decrease by 1.7%. In addition, NaCl enhanced the thermal stability of AlgM4 and increased the midpoint of thermal denaturation (Tm) by 4.9 °C. AlgM4 exhibited an ability to degrade sodium alginate, poly-mannuronic acid (polyM), and poly-guluronic acid (polyG), resulting in the production of oligosaccharides with a degree of polymerization (DP) of 2–9. AlgM4 possessed broader substrate, indicating that it is a bifunctional alginate lyase. Thus, AlgM4 is a novel salt-activated and bifunctional alginate lyase of the PL7 family with endolytic activity.

Characterization of PL-7 Family Alginate Lyases From Marine Organisms and Their Applications

Alginate, an anionic heteropolysaccharide extracted from natural brown algae, has useful properties for the food, chemical, medical, and agricultural industries. Degradation of alginate by alginate lyase is a key process to produce unsaturated oligoalginate and unsaturated monosaccharide 4-deoxy-l-erythro-5-hexoseulose uronic acid. Alginate lyases belonging to the polysaccharide lyase family 7 have been found in, and isolated from, organisms thriving in various environments. Furthermore, research on their function and structure has also progressed well. Here, the preparation of native and recombinant PL-7 alginate lyases and the methods for evaluation of enzymatic activity are summarized. Examples of PL-7 alginate lyase applications are also described.

A Novel Bifunctional Endolytic Alginate Lyase with Variable Alginate-Degrading Modes and Versatile Monosaccharide-Producing Properties

Endo-type alginate lyases usually degrade alginate completely into various size-defined unsaturated oligosaccharide products (≥disaccharides), while exoenzymes primarily produce monosaccharide products including saturated mannuronate (M) and guluronate (G) units and particularly unsaturated Δ units. Recently, two bifunctional alginate lyases have been identified as endolytic but M- and G-producing with variable action modes. However, endolytic Δ-producing alginate lyases remain undiscovered. Herein, a new Flammeovirga protein, Aly2, was classified into the polysaccharide lyase 7 superfamily. The recombinant enzyme and its truncated protein showed similar stable biochemical characteristics. Using different sugar chains as testing substrates, we demonstrated that the two enzymes are bifunctional while G-preferring, endolytic whereas monosaccharide-producing. Furthermore, the catalytic module of Aly2 can vary the action modes depending on the terminus type, molecular size, and M/G content of the substrate, thereby yielding different levels of M, G, and Δ units. Notably, the enzymes preferentially produce Δ units when digesting small size-defined oligosaccharide substrates, particularly the smallest substrate (unsaturated tetrasaccharide fractions). Deletion of the non-catalytic region of Aly2 caused weak changes in the action modes and biochemical characteristics. This study provided extended insights into alginate lyase groups with variable action modes for accurate enzyme use.

Discovery of a Novel Alginate Lyase from Nitratiruptor sp. SB155-2 Thriving at Deep-sea Hydrothermal Vents and Identification of the Residues Responsible for Its Heat Stability

Extremophiles are expected to represent a source of enzymes having unique functional properties. The hypothetical protein NIS_0185, termed NitAly in this study, was identified as an alginate lyase-homolog protein in the genomic database of ϵ-Proteobacteria Nitratiruptor sp. SB155-2, which was isolated from deep-sea hydrothermal vents at a water depth of 1,000 m. Among the characterized alginate lyases in the polysaccharide lyase family 7 (PL-7), the amino acid sequence of NitAly showed the highest identity (39%) with that of red alga Pyropia yezoensis alginate lyase PyAly. Recombinant NitAly (rNitAly) was successfully expressed in Escherichia coli Purified rNitAly degraded alginate in an endolytic manner. Among alginate block types, polyM was preferable to polyG and polyMG as a substrate, and its end degradation products were mainly tri-, tetra-, and penta-saccharides. The optimum temperature and pH values were 70 °C and around 6, respectively. A high concentration of NaCl (0.8-1.4 m) was required for maximum activity. In addition, a 50% loss of activity was observed after incubation at 67 °C for 30 min. Heat stability was decreased in the presence of 5 mm DTT, and Cys-80 and Cys-232 were identified as the residues responsible for heat stability but not lyase activity. Introducing two cysteines into PyAly based on homology modeling using Pseudomonas aeruginosa alginate lyase PA1167 as the template enhanced its heat stability. Thus, NitAly is a functional alginate lyase, with its unique optimum conditions adapted to its environment. These insights into the heat stability of NitAly could be applied to improve that of other PL-7 alginate lyases.

Characterization of AlgMsp, an alginate lyase from Microbulbifer sp. 6532A

Alginate is a polysaccharide produced by certain seaweeds and bacteria that consists of mannuronic acid and guluronic acid residues. Seaweed alginate is used in food and industrial chemical processes, while the biosynthesis of bacterial alginate is associated with pathogenic Pseudomonas aeruginosa. Alginate lyases cleave this polysaccharide into short oligo-uronates and thus have the potential to be utilized for both industrial and medicinal applications. An alginate lyase gene, algMsp, from Microbulbifer sp. 6532A, was synthesized as an E.coli codon-optimized clone. The resulting 37 kDa recombinant protein, AlgMsp, was expressed, purified and characterized. The alginate lyase displayed highest activity at pH 8 and 0.2 M NaCl. Activity of the alginate lyase was greatest at 50°C; however the enzyme was not stable over time when incubated at 50°C. The alginate lyase was still highly active at 25°C and displayed little or no loss of activity after 24 hours at 25°C. The activity of AlgMsp was not dependent on the presence of divalent cations. Comparing activity of the lyase against polymannuronic acid and polyguluronic acid substrates showed a higher turnover rate for polymannuronic acid. However, AlgMSP exhibited greater catalytic efficiency with the polyguluronic acid substrate. Prolonged AlgMsp-mediated degradation of alginate produced dimer, trimer, tetramer, and pentamer oligo-uronates.

Biological activities of alginate

To gain insight into the structure-activity relationship of alginate, we examined the effect of alginates with varying molecular weights and M/G ratio on murine macrophage cell line, RAW264.7 cells in terms of induction of tumor necrosis factor-α (TNF-α) secretion. Among the alginates tested, alginate with the highest molecular weight (MW 38,000, M/G 2.24) showed the most potent TNF-α-inducing activity. Alginates having higher M/G ratio tended to show higher activity. These results suggest that molecular size and M/G ratio are important structural parameters influencing the TNF-α-inducing activity. Interestingly, enzymatic depolymerization of alginate with bacterial alginate lyase resulted in dramatic increase in the TNF-α-inducing activity. The higher activity of enzymatically digested alginate oligomers to induce nitric oxide production from RAW264.7 cells than alginate polymer was also observed. On the other hand, alginate polymer and oligomer showed nearly equal hydroxyl radical scavenging activities.

Characteristics of drug release from gel beads formed by hydrolysis of alginic acid into guluronic acid blocks

Alginic acid (Alg) is a natural anionic polysaccharide, which consists of α-L-guluronic acid (G) and β-D-mannuronic acid (M). G-G sequence-rich chain regions, known as G-blocks (GB), are important regions for gelation of Alg using divalent cations. In this study, calcium-induced GB gel beads were prepared, and drug release profiles and degradation properties of the GB gel beads were investigated in aqueous media. The GB gel beads swelled slightly in JP XVI 1st fluid (pH 1.2), and only slight release of sodium diclofenac (DF) from the GB gel beads was observed. Disintegration of the GB gel beads was not observed in the 1st fluid. On the other hand, the GB gel beads disintegrated in JP XVI 2nd fluid (pH 6.8), and the rate of disintegration depended on the concentration of calcium chloride used to prepare the GB gel beads. The DF release profiles of the GB gel beads in the 2nd fluid could be controlled by the concentration of CaCl2 used to prepare the GB gel beads. The initial release profile of DF from GB gel beads was not consistent with the profile of disintegration. According to the Higuchi-plot of the percentage of drug content released against the square root of time, gel disintegration did not affect the release of DF from GB gel beads. It appears that a diffusion-type mechanism was responsible for DF release. We propose that the GB gel bead gel matrix is an effective medium by which to control the release of drug within the gastrointestinal tract.

Polysaccharide Lyases: Recent Developments as Biotechnological Tools

Polysaccharide lyases, which are polysaccharide cleavage enzymes, act mainly on anionic polysaccharides. Produced by prokaryote and eukaryote organisms, these enzymes degrade (1,4) glycosidic bond by a beta elimination mechanism and have unsaturated oligosaccharides as major products. New polysaccharides are cleaved only by their specific polysaccharide lyases. From anionic polysaccharides controlled degradations, various biotechnological applications were investigated. This review catalogues the degradation of bacterial, plant and animal polysaccharides (neutral and anionic) by this family of carbohydrate acting enzymes.

Structure-activity relationship of alginate oligosaccharides in the induction of cytokine production from RAW264.7 cells

Guluronate and mannuronate oligomers with various degree of polymerization were prepared from polyguluronate (PG) and polymannuronate (PM) with an alginate lyase from a Pseudoalteromonas sp., and their activities to induce cytokine secretion from mouse macrophage cell line RAW264.7 cells were examined. Enzymatically depolymerized unsaturated alginate oligomers induced tumor necrosis factor (TNF)-alpha secretion from RAW264.7 cells in a structure-depending manner, while the activities of saturated alginate oligomers prepared by acid hydrolysis were fairly low or only trace levels. These results suggest that unsaturated end-structure of alginate oligomers was important for the TNF-alpha-inducing activity. Among the unsaturated guluronate (G3-G9) and mannuronate (M3-M9) oligomers, G8 and M7 showed the most potent activity, respectively. Bio-Plex assay revealed that interleukin (IL)-1alpha, IL-1beta, and IL-6 secretion from RAW264.7 cells were also induced by unsaturated alginate oligomers with similar structure-activity relationship profiles as seen in TNF-alpha, and the most potent activities were observed with G8 and M7. These results suggest that G8 and M7 may have the most suitable molecular size or entire structural conformation as stimulant for cytokine secretion. Since antibodies to Toll-like receptor (TLR)2 and TLR4 effectively inhibited the G8- and M7-induced production of TNF-alpha, these alginate oligomers may stimulate innate immunity through the pattern recognition receptors on macrophages similar to microbial products.

Crystallization and preliminary X-ray analysis of alginate lyases A1-II and A1-II' from Sphingomonas sp. A1

Alginate lyases depolymerize alginate, a heteropolysaccharide consisting of alpha-L-guluronate and beta-D-mannuronate, through a beta-elimination reaction. The alginate lyases A1-II (25 kDa) and A1-II' (25 kDa) from Sphingomonas sp. A1, which belong to polysaccharide lyase family PL-7, exhibit 68% homology in primary structure but have different substrate specificities. To determine clearly the structural basis for substrate recognition in the depolymerization mechanism by alginate lyases, both proteins were crystallized at 293 K using the vapour-diffusion method. A crystal of A1-II belonged to space group P2(1) and diffracted to 2.2 A resolution, with unit-cell parameters a = 51.3, b = 30.1, c = 101.6 A, beta = 100.2 degrees, while a crystal of A1-II' belonged to space group P2(1)2(1)2(1) and diffracted to 1.0 A resolution, with unit-cell parameters a = 34.6, b = 68.5, c = 80.3 A.

Crystal Structure of the Alginate (Poly α-l-guluronate) Lyase from Corynebacterium sp. at 1.2Å Resolution

The crystal structure of alginate (poly alpha-l-guluronate) lyase from Corynebacterium sp. (ALY-1) was determined at 1.2A resolution using the MAD method and bromide ions. The structure of ALY-1 is abundant in beta-strands and has a deep cleft, similar to the jellyroll beta-sandwich found in 1,3-1,4-beta-glucanase. The structure suggests that alginate molecules may penetrate into the cleft to interact with the catalytic site of ALY-1. The reported crystal structure of another type of alginate lyase, A1-III, differs from that of ALY-1 in that it consists almost entirely of alpha-helical structure. Nevertheless, the putative catalytic residues in both enzymes are positioned in space in nearly identical arrangements. This finding suggests that both alginate lyases may have evolved through convergent evolution.

Preparation and structure elucidation of alginate oligosaccharides degraded by alginate lyase from Vibro sp. 510

Alginate that was purified from the fermentation solution of marine bacteria Vibro sp. 510 under specific reaction conditions was hydrolyzed by alginate lyase. Seven oligosaccharides, including di-, tri- and tetrasaccharides, were isolated through low-pressure, gel-permeation chromatography (LP-GPC) and semipreparative strong-anion exchange (SAX) fast-protein liquid chromatography (FPLC). The oligosaccharide structures were elucidated based on ESIMS and 2D NMR spectral analysis. The hydrolytic specificity of this alginate lyase to alginate is discussed.

Primary structure and chemical modification of some amino acid residues of bifunctional alginate lyase from a marine bacterium Pseudoalteromonas sp. strain no. 272

The entire amino acid sequence of bifunctional alginate lyase from Pseudoalteromonas sp. strain No. 272 were determined by two approaches, Edman degradation of the peptides obtained from protease digestion of the enzyme protein and analysis of PCR products of the structural gene. The former resulted in incomplete amino acid sequence in the entire sequence, due to lacking of the proper peptides from the protease digestion. To compensate for this lack of sequences we applied the method of PCR of the structural gene that was initially elucidated from the primers designed from N- and C-terminal amino acid sequences of the enzyme. The results of the amino acid sequences from these two approaches showed good agreement. The enzyme consisted of 233 amino acid residues with a molecular mass of 25,549.5, including the sole W and cystine residue. The sequence homology search among the other alginate lyases from different origins indicated that they were very weakly homologous, with the exception of the sequence homology (80.3%) of Pseudoalteromonas elyakovii alginate lyase. The consensus sequence, YFKhG + Y-Q (Wong, T. Y., Preston, L. A., and Schiller, N. L. 2000. Annu. Rev. MicrobioL 54: 289-340) in the C-terminal regions was conserved. The kinetic analyses of chemical modification of some amino acid residues of the enzyme showed that W, K, and Y appeared to be important in the enzyme function.

ALGINATE LYASE: review of major sources and enzyme characteristics, structure-function analysis, biological roles, and applications

Alginate lyases, characterized as either mannuronate (EC 4.2.2.3) or guluronate lyases (EC 4.2.2.11), catalyze the degradation of alginate, a complex copolymer of alpha-L-guluronate and its C5 epimer beta-D-mannuronate. Lyases have been isolated from a wide range of organisms, including algae, marine invertebrates, and marine and terrestrial microorganisms. This review catalogs the major characteristics of these lyases, the methods for analyzing these enzymes, as well as their biological roles. Analysis of primary sequence data identifies some markedly conserved motifs that should help elucidate functional domains. Information about the three-dimensional structure of a mannuronate lyase from Sphingomonas sp., combined with various mutagenesis studies, has identified residues that are important for catalytic activity in several lyases. Characterization of alginate lyases will enhance and expand the use of these enzymes to engineer novel alginate polymers for applications in various industrial, agricultural, and medical fields. In this review, we explore both past and present applications of this important enzyme and discuss its future prospects.

Purification and characterization of bifunctional alginate lyase from Alteromonas sp. strain no. 272 and its action on saturated oligomeric substrates

A marine bacterium (strain No. 272) isolated from sea mud in Omura Bay produced an alginate lyase and was classified as an Alteromonas species. The enzyme was purified from the culture medium of the bacterium by DEAE-Cellulofine, Sephadex G-100 gel chromatography to an electrophoretically homogeneous state in the presence and absence of SDS. The molecular mass of the enzyme was 23 and 33.9 kDa on Sephadex G-100 column chromatography and SDS-polyacrylamide gel electrophoresis, respectively, with an isoelectric point of 3.8. The predominant secondary structure of the enzyme was found to be most likely beta-structure by circular dichroism. The enzyme was most active at pH 7.5-8.0 and stable around pH 5-11. The enzyme was more labile in Tris-HCI buffer (pH 7.0) to heat treatment, than in phosphate buffer (pH 7.0). No of metal ions significantly affected the enzyme activity. The enzyme acted on sodium alginate in an endo-type manner and on two components of alginate, poly-alpha1,4-L-guluronate and poly-beta1,4-D-mannuronate, as judged by routine ultraviolet assay (235 nm) and circular dichroic spectral changes of the substrates. However, the coexisting poly-alpha1,4-L-guluronate and poly-beta1,4-D-mannuronate apparently interacted with the enzyme in a competitive manner. Although the enzyme depolymerized alginate in an endo-type, it did not act on trimeric guluronate and mannuronate, but on the tetramers or more. The kinetic analyses showed that kcat/Km for each oligomer was larger for the guluronate oligomers than for the mannuronate ones, and that the subsite structure of the enzyme most likely consisted of six binding sites from the intrinsic reaction rate constant (kint) and intrinsic substrate binding constant (Kint).

Cloning and sequence analysis of a gene (aly PG) encoding poly(α-l-guluronate)lyase from Corynebacterium sp. strain ALY-1

The aly PG gene, coding for a poly alpha-l-guluronate lyase (PG lyase) of Corynebacterium strain ALY-1, was cloned and sequenced. The gene consists of 768 bp encoding a signal peptide of 32 amino acids and a mature protein of 224 amino acids. Two disulfide bond cross-linkages were found to be formed between Cys-4 and Cys-51 and between Cys-200 and Cys-206 in the native PG lyase molecule. The deduced amino acid sequence of the Corynebacterium sp. aly PG gene exhibited 29% homology toward that of the Klebsiella pneumoniae, subsp. aerogenes aly A gene, with two conserved regions (the amino acid sequences from Y-102 to M-110 and from Y-221 to Q-229).