Biochemical Characterization of a Pectate Lyase AnPL9 from Aspergillus nidulans

Pectinolytic enzymes have diverse industrial applications. Among these, pectate lyases act on the internal α-1,4-linkage of the pectate backbone, playing a critical role in pectin degradation. While most pectate lyases characterized thus far are of bacterial origin, fungi can also be excellent sources of pectinolytic enzymes. In this study, we performed biochemical characterization of the pectate lyase AnPL9 belonging to the polysaccharide lyase family 9 (PL9) from the filamentous fungus Aspergillus nidulans. Recombinant AnPL9 was produced using a Pichia pastoris expression system and purified. AnPL9 exhibited high activity on homogalacturonan (HG), pectin from citrus peel, pectin from apple, and the HG region in rhamnogalacturonan-I. Although digalacturonic acid and trigalacturonic acid were not degraded by AnPL9, tetragalacturonic acid was converted to 4,5-unsaturated digalacturonic acid and digalacturonic acid. These results indicate that AnPL9 degrades HG oligosaccharides with a degree of polymerization > 4. Furthermore, AnPL9 was stable within a neutral-to-alkaline pH range (pH 6.0-11.0). Our findings suggest that AnPL9 is a candidate pectate lyase for biotechnological applications in the food, paper, and textile industries. This is the first report on a fungal pectate lyase belonging to the PL9 family.

Biochemical Properties of a New Polysaccharide Lyase Family 25 Ulvan Lyase TsUly25B from Marine Bacterium Thalassomonas sp. LD5

Marine macroalgae, contributing much to the bioeconomy, have inspired tremendous attention as sustainable raw materials. Ulvan, as one of the main structural components of green algae cell walls, can be degraded by ulvan lyase through the β-elimination mechanism to obtain oligosaccharides exhibiting several good physiological activities. Only a few ulvan lyases have been characterized until now. This thesis explores the properties of a new polysaccharide lyase family 25 ulvan lyase TsUly25B from the marine bacterium Thalassomonas sp. LD5. Its protein molecular weight was 54.54 KDa, and it was most active under the conditions of 60 °C and pH 9.0. The K_m and k_cat values were 1.01 ± 0.05 mg/mL and 10.52 ± 0.28 s⁻¹, respectively. TsUly25B was salt-tolerant and NaCl can significantly improve its thermal stability. Over 80% of activity can be preserved after being incubated at 30 °C for two days when the concentration of NaCl in the solution is above 1 M, while 60% can be preserved after incubation at 40 °C for 10 h with 2 M NaCl. TsUly25B adopted an endolytic manner to degrade ulvan polysaccharides, and the main end-products were unsaturated ulvan disaccharides and tetrasaccharides. In conclusion, our research enriches the ulvan lyase library and advances the utilization of ulvan lyases in further fundamental research as well as ulvan oligosaccharides production.

A Novel Alginate Lyase: Identification, Characterization, and Potential Application in Alginate Trisaccharide Preparation

Alginate oligosaccharides (AOS) have many biological activities and significant applications in prebiotics, nutritional supplements, and plant growth development. Alginate lyases have unique advantages in the preparation of AOS. However, only a limited number of alginate lyases have been so far reported to have potentials in the preparation of AOS with specific degrees of polymerization. Here, an alginate-degrading strain Pseudoalteromonasarctica M9 was isolated from Sargassum, and five alginate lyases were predicted in its genome. These putative alginate lyases were expressed and their degradation products towards sodium alginate were analyzed. Among them, AlyM2 mainly generated trisaccharides, which accounted for 79.9% in the products. AlyM2 is a PL6 lyase with low sequence identity (≤28.3%) to the characterized alginate lyases and may adopt a distinct catalytic mechanism from the other PL6 alginate lyases based on sequence alignment. AlyM2 is a bifunctional endotype lyase, exhibiting the highest activity at 30 °C, pH 8.0, and 0.5 M NaCl. AlyM2 predominantly produces trisaccharides from homopolymeric M block (PM), homopolymeric G block (PG), or sodium alginate, with a trisaccharide production of 588.4 mg/g from sodium alginate, indicating its promising potential in preparing trisaccharides from these polysaccharides.

Comparison of Biochemical Characteristics, Action Models, and Enzymatic Mechanisms of a Novel Exolytic and Two Endolytic Lyases with Mannuronate Preference

Recent explorations of tool-like alginate lyases have been focused on their oligosaccharide-yielding properties and corresponding mechanisms, whereas most were reported as endo-type with α-L-guluronate (G) preference. Less is known about the β-D-mannuronate (M) preference, whose commercial production and enzyme application is limited. In this study, we elucidated Aly6 of Flammeovirga sp. strain MY04 as a novel M-preferred exolytic bifunctional lyase and compared it with AlgLs of Pseudomonas aeruginosa (Pae-AlgL) and Azotobacter vinelandii (Avi-AlgL), two typical M-specific endolytic lyases. This study demonstrated that the AlgL and heparinase_II_III modules play indispensable roles in determining the characteristics of the recombinant exo-type enzyme rAly6, which is preferred to degrade M-enriched substrates by continuously cleaving various monosaccharide units from the nonreducing end, thus yielding various size-defined ΔG-terminated oligosaccharides as intermediate products. By contrast, the endolytic enzymes Pae-rAlgL and Avi-rAlgL varied their action modes specifically against M-enriched substrates and finally degraded associated substrate chains into various size-defined oligosaccharides with a succession rule, changing from ΔM to ΔG-terminus when the product size increased. Furthermore, site-directed mutations and further protein structure tests indicated that H¹⁹⁵NHSTW is an active, half-conserved, and essential enzyme motif. This study provided new insights into M-preferring lyases for novel resource discoveries, oligosaccharide preparations, and sequence determinations.

Characterization and enhanced extracellular overexpression of a new salt-activated alginate lyase

BACKGROUND

Alginate lyases (EC 4.4.2.3/4.4.2.11) have been applied to produce alginate oligosaccharides, which have physiological advantages such as prebiotic and antidiabetic effects, and are of benefit in the food and pharmaceutical industries. Extracellular production of recombinant proteins in Escherichia coli presents advantages including simplified downstream processing and high productivity; however, the presence of certain signal peptides does not always ensure successful secretion, which make the extracellular production of alginate lyase in E. coli rarely reported but of great significance.

RESULTS

A PL7 family alginate lyase, Aly01, with its native signal peptide from Vibrio natriegens SK42.001, was identified, characterized, and extracellularly expressed in E. coli. The enzyme specifically released trisaccharide from alginate and was strictly NaCl activated. Green fluorescent protein (GFP) was fused with the Aly01 signal peptide and successfully secreted in E. coli to expand the feasibility of using this signal peptide to produce other heterologous proteins extracellularly. Through a synergistic strategy of utilizing Terrific Broth (TB) medium supplemented with 120 mmol L^-1 glycine and 10 mmol L^-1 calcium, the lag phase of protein secretion was reduced to 3 h from 12 h; meanwhile calcium remedied glycine-related cell growth impairment, leading to further enhancement of overall enzyme productivity, reaching a maximum of 4.55 U mL^-1 .

CONCLUSION

A new salt-activated alginate lyase, Aly01, was identified and characterized. E. coli employed its signal peptide and extracellularly expressed both Aly01 and a GFP, which indicated the signal peptide of Aly01 could be a powerful tool for extracellular production of other heterologous proteins in E. coli. © 2021 Society of Chemical Industry.

Degradation and Utilization of Alginate by Marine Pseudoalteromonas: a Review

Alginate, which is mainly produced by brown algae and decomposed by heterotrophic bacteria, is an important marine organic carbon source. The genus Pseudoalteromonas contains diverse forms of heterotrophic bacteria that are widely distributed in marine environments and are an important group in alginate degradation. In this review, the diversity of alginate-degrading Pseudoalteromonas is introduced, and the characteristics of Pseudoalteromonas alginate lyases, including their sequences, enzymatic properties, structures, and catalytic mechanisms, and the synergistic effect of Pseudoalteromonas alginate lyases on alginate degradation are introduced. The acquisition of the alginate degradation capacity and the alginate utilization pathways of Pseudoalteromonas are also introduced. This paper provides a comprehensive overview of alginate degradation by Pseudoalteromonas, which will contribute to the understanding of the degradation and recycling of marine algal polysaccharides driven by marine bacteria.

Mechanistic Insights into Substrate Recognition and Catalysis of a New Ulvan Lyase of Polysaccharide Lyase Family 24

Ulvan is an important marine polysaccharide. Bacterial ulvan lyases play important roles in ulvan degradation and marine carbon cycling. Until now, only a small number of ulvan lyases have been characterized. Here, a new ulvan lyase, Uly1, belonging to polysaccharide lyase family 24 (PL24) from the marine bacterium Catenovulum maritimum, is characterized. The optimal temperature and pH for Uly1 to degrade ulvan are 40°C and pH 9.0, respectively. Uly1 degrades ulvan polysaccharides in the endolytic manner, mainly producing ΔRha3S, consisting of an unsaturated 4-deoxy-l-threo-hex-4-enopyranosiduronic acid and a 3-O-sulfated α-l-rhamnose. The structure of Uly1 was resolved at a 2.10-Å resolution. Uly1 adopts a seven-bladed β-propeller architecture. Structural and site-directed mutagenesis analyses indicate that four highly conserved residues, H128, H149, Y223, and R239, are essential for catalysis. H128 functions as both the catalytic acid and base, H149 and R239 function as the neutralizers, and Y223 plays a supporting role in catalysis. Structural comparison and sequence alignment suggest that Uly1 and many other PL24 enzymes may directly bind the substrate near the catalytic residues for catalysis, different from the PL24 ulvan lyase LOR_107, which adopts a two-stage substrate binding process. This study provides new insights into ulvan lyases and ulvan degradation. IMPORTANCE Ulvan is a major cell wall component of green algae of the genus Ulva. Many marine heterotrophic bacteria can produce extracellular ulvan lyases to degrade ulvan for a carbon nutrient. In addition, ulvan has a range of physiological bioactivities based on its specific chemical structure. Ulvan lyase thus plays an important role in marine carbon cycling and has great potential in biotechnological applications. However, only a small number of ulvan lyases have been characterized over the past 10 years. Here, based on biochemical and structural analyses, a new ulvan lyase of polysaccharide lyase family 24 is characterized, and its substrate recognition and catalytic mechanisms are revealed. Moreover, a new substrate binding process adopted by PL24 ulvan lyases is proposed. This study offers a better understanding of bacterial ulvan lyases and is helpful for studying the application potentials of ulvan lyases.

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.

Structural and molecular basis for the substrate positioning mechanism of a new PL7 subfamily alginate lyase from the arctic

Alginate lyases play important roles in alginate degradation in the ocean. Although a large number of alginate lyases have been characterized, little is yet known about those in extremely cold polar environments, which may have unique mechanisms for environmental adaptation and for alginate degradation. Here, we report the characterization of a novel PL7 alginate lyase AlyC3 from Psychromonas sp. C-3 isolated from the Arctic brown alga Laminaria, including its phylogenetic classification, catalytic properties, and structure. We propose the establishment of a new PM-specific subfamily of PL7 (subfamily 6) represented by AlyC3 based on phylogenetic analysis and enzymatic properties. Structural and biochemical analyses showed that AlyC3 is a dimer, representing the first dimeric endo-alginate lyase structure. AlyC3 is activated by NaCl and adopts a novel salt-activated mechanism; that is, salinity adjusts the enzymatic activity by affecting its aggregation states. We further solved the structure of an inactive mutant H127A/Y244A in complex with a dimannuronate molecule and proposed the catalytic process of AlyC3 based on structural and biochemical analyses. We show that Arg82 and Tyr190 at the two ends of the catalytic canyon help the positioning of the repeated units of the substrate and that His127, Tyr244, Arg78, and Gln125 mediate the catalytic reaction. Our study uncovers, for the first time, the amino acid residues for alginate positioning in an alginate lyase and demonstrates that such residues involved in alginate positioning are conserved in other alginate lyases. This study provides a better understanding of the mechanisms of alginate degradation by alginate lyases.

Construction and biochemical characterization of a novel hybrid alginate lyase with high activity by module recombination to prepare alginate oligosaccharides

Alginate lyases are essential tools to prepare alginate oligosaccharides with various biological activities. However, alginate lyases with excellent properties such as high activity and good thermal stability are still in shortage. Therefore, it is crucial to exploit new alginate lyases with high activity and polysaccharide-degrading efficiency for alginate oligosaccharide preparation. Herein, we proposed to construct a novel hybrid alginate lyase with improved property by module recombination. The hybrid alginate lyase, designated as Aly7C, was successfully constructed by recombining the carbohydrate binding module (CBM) of Aly7A with the catalytic module of Aly7B. Interestingly, the hybrid enzyme Aly7C exhibited higher activity than the catalytic domain. Moreover, it could degrade sodium alginate, polyM and polyG into oligosaccharides with degrees of polymerization (Dps) 2-5, which exhibit perfect product specificity. This work provides a new insight into well-defined generation of alginate oligosaccharides with associated CBMs and enhances the understanding of functions of the modules.

Biochemical characterization of a thermophilic hyaluronate lyase TcHly8C from Thermasporomyces composti DSM22891

Hyaluronic acid (HA) is an anionic linear polysaccharide abundantly distributed in the extracellular matrix of mammalian connective, growing, and tumor tissues. Hyaluronidase is used as an important drug diffusion promoter and a tool enzyme to produce HA oligosaccharides. However, there is no thermostable hyaluronidase suitable for application to date. In this study, a thermophilic hyaluronate lyase, TcHly8C, from Thermasporomyces composti DSM22891 was expressed in Escherichia coli. The recombinant TcHly8C was most active at 70 °C, and it retained about 30% of initial activity after incubation at 60 °C for 28 days. The half-lives of TcHly8C at 60 °C and 70 °C were 16.1 d and 2.3 h, respectively. The optimum pH of TcHly8C is 5.93, and it was stable at pH 6.15-10.90. The presence of Mg²⁺ could enhance its enzymatic activity significantly. K_m, k_cat, and k_cat/K_m of TcHly8C towards HA were 3.69 mg∙ml^-1, 17.82 s^-1, and 4.82 ml∙mg^-1∙s^-1, respectively. TcHly8C degraded HA in an exolytic mode, and the end product was unsaturated HA disaccharide (ΔUA-GlcNAc). Overall, our results show that TcHly8C is the first reported PL8 exo-type hyaluronate lyase with high thermostability, which provides a potential enzyme used in medicine and production of HA oligosaccharides.

Engineered small metal-binding protein tag improves the production of recombinant human growth hormone in the periplasm of Escherichia coli

Fusion proteins play an important role in the production of recombinant proteins in Escherichia coli. They are mostly used for cytoplasmic expression since they can be designed to increase the solubility of the target protein, which then can be easily purified via affinity chromatography. In contrast, fusion proteins are not usually included in construct designs for periplasmic production. Instead, a signal sequence is inserted for protein transport into the periplasm and a C-terminal his-tag added for subsequent purification. Our research group has proposed the small metal-binding protein (SmbP) isolated from the periplasm of Nitrosomonas europaea as a new fusion protein to express recombinant proteins in the cytoplasm or periplasm of E. coli. SmbP also allows purification via immobilized metal affinity chromatography using Ni(II) ions. Recently, we have optimized the periplasmic production of proteins tagged with SmbP by exchanging its native signal peptide with one taken from pectate lyase B (PelB), substantially increasing the amount of protein produced. In this work, we have expressed and purified soluble bioactive human growth hormone (hGH) tagged with PelB-SmbP and obtained the highest periplasmic production reported for this protein so far. Its activity, tested on Nb2-11 cells, was equivalent to commercial growth hormone at 50 ng·mL-1 . Therefore, we strongly recommend the use of PelB-SmbP as a protein tag for the expression and purification of hGH or other possible target proteins in the periplasm of E. coli.

Cloning, Secretory Expression and Characterization of a Unique pH-Stable and Cold-Adapted Alginate Lyase

Cold-adapted alginate lyases have unique advantages for alginate oligosaccharide (AOS) preparation and brown seaweed processing. Robust and cold-adapted alginate lyases are urgently needed for industrial applications. In this study, a cold-adapted alginate lyase-producing strain Vibrio sp. W2 was screened. Then, the gene ALYW201 was cloned from Vibrio sp. W2 and expressed in a food-grade host, Yarrowia lipolytica. The secreted Alyw201 showed the activity of 64.2 U/mL, with a molecular weight of approximate 38.0 kDa, and a specific activity of 876.4 U/mg. Alyw201 performed the highest activity at 30 °C, and more than 80% activity at 25-40 °C. Furthermore, more than 70% of the activity was obtained in a broad pH range of 5.0-10.0. Alyw201 was also NaCl-independent and salt-tolerant. The degraded product was that of the oligosaccharides of DP (Degree of polymerization) 2-6. Due to its robustness and its unique pH-stable property, Alyw201 can be an efficient tool for industrial production.

Alginate Lyase Guided Silver Nanocomposites for Eradicating Pseudomonas aeruginosa from Lungs

Pseudomonas aeruginosa (P. aeruginosa) infections lead to a high mortality rate for cystic fibrosis or immunocompromised patients. The alginate of the biofilm was believed to be the key factor disabling immune therapy and antibiotic treatments. A silver nanocomposite consisting of silver nanoparticles and a mesoporous organosilica layer was created to deliver two pharmaceutical compounds (alginate lyase and ceftazidime) to degrade the alginate and eradicate P. aeruginosa from the lungs. The introduction of thioether-bridged mesoporous organosilica into the nanocomposites greatly benefited the conjunction of foreign functional molecules such as alginate lyase and increased their hemocompatibility and drug-loading capacity. Silver nanocomposites with a uniform diameter (∼39 nm) exhibited a high dispersity, good biocompatibility, and high ceftazidime-loading capacity (380.96 mg/g). Notably, the silver nanocomposites displayed a low pH-dependent drug release and degradation profiles (pH 6.4), guaranteeing the targeted release of the drugs in the acidic niches of the P. aeruginosa biofilm. Indeed, particles loaded with alginate lyase and ceftazidime exhibited high inhibitory and degradation effects on the biofilm of P. aeruginosa PAO1 based on the specific catalytic activity of the enzyme to the alginate and antibacterial function of their loaded ceftazidime and silver ions. It should be noted that the enzyme-decorated nanocomposites succeeded in eradicating P. aeruginosa PAO1 from the mouse lungs and decreasing the lung injuries. No deaths or serious side effects were observed during the experiments. We believe that the silver nanocomposites with high biocompatibility and organic group-incorporated framework have the potential to be used to deliver multiple functional molecules for antibacterial therapy in clinical application.

Two New Alginate Lyases of PL7 and PL6 Families from Polysaccharide-Degrading Bacterium Formosa algae KMM 3553T: Structure, Properties, and Products Analysis

A bifunctional alginate lyase (ALFA3) and mannuronate-specific alginate lyase (ALFA4) genes were found in the genome of polysaccharide-degrading marine bacterium Formosa algae KMM 3553^T. They were classified to PL7 and PL6 polysaccharide lyases families and expressed in E. coli. The recombinant ALFA3 appeared to be active both on mannuronate- and guluronate-enriched alginates, as well as pure sodium mannuronate. For all substrates, optimum conditions were pH 6.0 and 35 °C; Km was 0.12 ± 0.01 mg/ml, and half-inactivation time was 30 min at 42 °C. Recombinant ALFA4 was active predominately on pure sodium mannuronate, with optimum pH 8.0 and temperature 30 °C, Km was 3.01 ± 0.05 mg/ml. It was stable up to 30 °C; half-inactivation time was 1h 40 min at 37 °C. ¹H NMR analysis showed that ALFA3 degraded mannuronate and mannuronate-guluronate blocks, while ALFA4 degraded only mannuronate blocks, producing mainly disaccharides. Products of digestion of pure sodium mannuronate by ALFA3 at 200 µg/ml inhibited anchorage-independent colony formation of human melanoma cells SK-MEL-5, SK-MEL-28, and RPMI-7951 up to 17% stronger compared to native polymannuronate. This fact supports previous data and suggests that mannuronate oligosaccharides may be useful for synergic tumor therapy.

Characterization and Application of an Alginate Lyase, Aly1281 from Marine Bacterium Pseudoalteromonas carrageenovora ASY5

Alginate extracted from widely cultured brown seaweed can be hydrolyzed by alginate lyase to produce alginate oligosaccharides (AOS) with intriguing biological activities. Herein, a novel alginate lyase Aly1281 was cloned from marine bacterium Pseudoalteromonas carrageenovora ASY5 isolated from mangrove soil and found to belong to polysaccharide lyase family 7. Aly1281 exhibited maximum activity at pH 8.0 and 50 °C and have broad substrate specificity for polyguluronate and polymannuronate. Compared with other alginate lyases, Aly1281 exhibited high degradation specificity and mainly produced di-alginate oligosaccharides which displayed good antioxidant function to reduce ferric and scavenge radicals such as hydroxyl, ABTS+ and DPPH. Moreover, the catalytic activity and kinetic performance of Aly1281 were highly improved with the addition of salt, demonstrating a salt-activation property. A putative conformational structural feature of Aly1281 was found by MD simulation analysis for understanding the salt-activation effect.

Functional Characterization of Carbohydrate-Binding Modules in a New Alginate Lyase, TsAly7B, from Thalassomonas sp. LD5

Alginate lyases degrade alginate into oligosaccharides, of which the biological activities have vital roles in various fields. Some alginate lyases contain one or more carbohydrate-binding modules (CBMs), which assist the function of the catalytic modules. However, the precise function of CBMs in alginate lyases has yet to be fully elucidated. We have identified a new multi-domain alginate lyase, TsAly7B, in the marine bacterium Thalassomonas sp. LD5. This novel lyase contains an N-terminal CBM9, an internal CBM32, and a C-terminal polysaccharide lyase family 7 (PL7) catalytic module. To investigate the specific function of each of these CBMs, we expressed and characterized the full-length TsAly7B and three truncated mutants: TM1 (CBM32-PL7), TM2 (CBM9-PL7), and TM3 (PL7 catalytic module). CBM9 and CBM32 could enhance the degradation of alginate. Notably, the specific activity of TM2 was 7.6-fold higher than that of TM3. CBM32 enhanced the resistance of the catalytic module to high temperatures. In addition, a combination of CBM9 and CBM32 showed enhanced thermostability when incubated at 80 °C for 1 h. This is the first report that finds CBM9 can significantly improve the ability of enzyme degradation. Our findings provide new insight into the interrelationships of tandem CBMs and alginate lyases and other polysaccharide-degrading enzymes, which may inspire CBM fusion strategies.

Cloning, Expression, and Characterization of a New Glycosaminoglycan Lyase from Microbacterium sp. H14

Glycosaminoglycan (GAG) lyase is an effective tool for the structural and functional studies of glycosaminoglycans and preparation of functional oligosaccharides. A new GAG lyase from Microbacterium sp. H14 was cloned, expressed, purified, and characterized, with a molecular weight of approximately 85.9 kDa. The deduced lyase HCLaseM belonged to the polysaccharide lyase (PL) family 8. Based on the phylogenetic tree, HCLaseM could not be classified into the existing three subfamilies of this family. HCLaseM showed almost the same enzyme activity towards hyaluronan (HA), chondroitin sulfate A (CS-A), CS-B, CS-C, and CS-D, which was different from reported GAG lyases. HCLaseM exhibited the highest activities to both HA and CS-A at its optimal temperature (35 °C) and pH (pH 7.0). HCLaseM was stable in the range of pH 5.0–8.0 and temperature below 30 °C. The enzyme activity was independent of divalent metal ions and was not obviously affected by most metal ions. HCLaseM is an endo-type enzyme yielding unsaturated disaccharides as the end products. The facilitated diffusion effect of HCLaseM is dose-dependent in animal experiments. These properties make it a candidate for further basic research and application.

Flax rhamnogalacturonan lyases: phylogeny, differential expression and modeling of protein structure

Rhamnogalacturonan lyases (RGLs; EC 4.2.2.23) degrade the rhamnogalacturonan I (RG-I) backbone of pectins present in the plant cell wall. These enzymes belong to polysaccharide lyase family 4, members of which are mainly from plants and plant pathogens. RGLs are investigated, as a rule, as pathogen 'weapons' for plant cell wall degradation and subsequent infection. Despite the presence of genes annotated as RGLs in plant genomes and the presence of substrates for enzyme activity in plant cells, evidence supporting the involvement of this enzyme in certain processes is limited. The differential expression of some RGL genes in flax (Linum usitatissimum L.) tissues, revealed in our previous work, prompted us to carry out a total revision (phylogenetic analysis, analysis of expression and protein structure modeling) of all the sequences of flax predicted as coding for RGLs. Comparison of the expressions of LusRGL in various tissues of flax stem revealed that LusRGLs belong to distinct phylogenetic clades, which correspond to two co-expression groups. One of these groups comprised LusRGL6-A and LusRGL6-B genes and was specifically upregulated in flax fibers during deposition of the tertiary cell wall, which has complex RG-I as a key noncellulosic component. The results of homology modeling and docking demonstrated that the topology of the LusRGL6-A catalytic site allowed binding to the RG-I ligand. These findings lead us to suggest the presence of RGL activity in planta and the involvement of special isoforms of RGLs in the modification of RG-I of the tertiary cell wall in plant fibers.

Characterization of a bifunctional alginate lyase as a new member of the polysaccharide lyase family 17 from a marine strain BP-2

OBJECTIVES

Bifunctional alginate lyase can efficiently saccharify alginate biomass and prepare functional oligosaccharides of alginate.

RESULTS

A new BP-2 strain that produces alginate lyase was screened and identified from rotted Sargassum. A new alginate lyase, Alg17B, belonging to the polysaccharide lyase family 17, was isolated and purified from BP-2 fermentation broth by freeze-drying, dialysis, and ion exchange chromatography. The enzymatic properties of the purified lyase were investigated. The molecular weight of Alg17B was approximately 77 kDa, its optimum reaction temperature was 40-45 °C, and its optimum reaction pH was 7.5-8.0. The enzyme was relatively stable at pH 7.0-8.0, with a temperature range of 25-35 °C, and the specific activity of the purified enzyme reached 4036 U/mg. A low Na+ concentration stimulated Alg17B enzyme activity, but Ca2+, Zn2+, and other metal ions inhibited it. Substrate specificity analysis, thin-layer chromatography, and mass spectrometry showed that Alg17B is an alginate lyase that catalyses the hydrolysis of sodium alginate, polymannuronic acid (polyM) and polyguluronic acid to produce monosaccharides and low molecular weight oligosaccharides. Alg17B is also bifunctional, exhibiting both endolytic and exolytic activities toward alginate, and has a wide substrate utilization range with a preference for polyM.

CONCLUSIONS

Alg17B can be used to saccharify the main carbohydrate, alginate, in the ethanolic production of brown algae fuel as well as in preparing and researching oligosaccharides.

A bacterial endo-β-1,4-glucuronan lyase, CUL-I from Brevundimonas sp. SH203, belonging to a novel polysaccharide lyase family

Cellouronate is a (1,4)-β-D-glucuronan prepared by TEMPO-mediated oxidation from regenerated cellulose. We have previously isolated a cellouronate-degrading bacterial strain, Brevundimonas sp. SH203, that produces a cellouronate lyase (β-1,4-glucuronan lyase, CUL-I). In this study, the gene encoding CUL-I was cloned, and the recombinant enzyme was heterologously expressed in Escherichia coli. The predicted CUL-I protein is composed of 426 amino acid residues and includes a putative 21-amino acid signal peptide. The recombinant CUL-I specifically depolymerized β-1,4-glycoside linkages of cellouronate, and its mode of action was endo-type, like the native CUL-I. Sequence analysis showed CUL-I has no similarity to previously known polysaccharide lyases (PLs), indicating that CUL-I should be classified into a novel PL family.

A surrogate structural platform informed by ancestral reconstruction and resurrection of a putative carbohydrate binding module hybrid illuminates the neofunctionalization of a pectate lyase

Yersinia enterocolitica is a pectinolytic zoonotic foodborne pathogen, the genome of which contains pectin-binding proteins and several different classes of pectinases, including polysaccharide lyases (PLs) and an exopolygalacturonase. These proteins operate within a coordinated pathway to completely saccharify homogalacturonan (HG). Polysaccharide lyase family 2 (PL2) is divided into two major subfamilies that are broadly-associated with contrasting 'endolytic' (PL2A) or 'exolytic' (PL2B) activities on HG. In the Y. enterocolitica genome, the PL2A gene is adjacent to an independent carbohydrate binding module from family 32 (YeCBM32), which possesses a N-terminal secretion tag and is known to specifically bind HG. Independent CBMs are rare in nature and, most commonly, are fused to enzymes in order to potentiate catalysis. The unconventional gene architecture of YePL2A and YeCBM32, therefore, may represent an ancestral relic of a fission event that decoupled PL2A from its cognate CBM. To provide further insight into the evolution of this pectinolytic locus and the molecular basis of HG depolymerisation within Y. enterocolitica, we have resurrected a YePL2A-YeCBM32 chimera and demonstrated that the extant PL2A digests HG more efficiently. In addition, we have engineered a tryptophan from the active site of the exolytic YePL2B into YePL2A (YePL2A-K291W) and demonstrated, using X-ray crystallography of substrate complexes, that it is a structural determinant of exo-activity within the PL2 family. In this manner, surrogate structural platforms may assist in the study of phylogenetic relationships informed by extant and resurrected sequences, and can be used to overcome challenging structural problems within carbohydrate active enzyme families.

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.

Biochemical Characterization and Elucidation of Action Pattern of a Novel Polysaccharide Lyase 6 Family Alginate Lyase from Marine Bacterium Flammeovirga sp. NJ-04

Alginate lyases have been widely used to prepare alginate oligosaccharides in food, agricultural, and medical industries. Therefore, discovering and characterizing novel alginate lyases with excellent properties has drawn increasing attention. Herein, a novel alginate lyase FsAlyPL6 of Polysaccharide Lyase (PL) 6 family is identified and biochemically characterized from Flammeovirga sp. NJ-04. It shows highest activity at 45 °C and could retain 50% of activity after being incubated at 45 °C for 1 h. The Thin-Layer Chromatography (TLC) and Electrospray Ionization Mass Spectrometry (ESI-MS) analysis indicates that FsAlyPL6 endolytically degrades alginate polysaccharide into oligosaccharides ranging from monosaccharides to pentasaccharides. In addition, the action pattern of the enzyme is also elucidated and the result suggests that FsAlyPL6 could recognize tetrasaccharide as the minimal substrate and cleave the glycosidic bonds between the subsites of −1 and +3. The research provides extended insights into the substrate recognition and degradation pattern of PL6 alginate lyases, which may further expand the application of alginate lyases.

Characterization of an Alkaline Alginate Lyase with pH-Stable and Thermo-Tolerance Property

Alginate oligosaccharides (AOS) show versatile bioactivities. Although various alginate lyases have been characterized, enzymes with special characteristics are still rare. In this study, a polysaccharide lyase family 7 (PL7) alginate lyase-encoding gene, aly08, was cloned from the marine bacterium Vibrio sp. SY01 and expressed in Escherichia coli. The purified alginate lyase Aly08, with a molecular weight of 35 kDa, showed a specific activity of 841 U/mg at its optimal pH (pH 8.35) and temperature (45 °C). Aly08 showed good pH-stability, as it remained more than 80% of its initial activity in a wide pH range (4.0–10.0). Aly08 was also a thermo-tolerant enzyme that recovered 70.8% of its initial activity following heat shock treatment for 5 min. This study also demonstrated that Aly08 is a polyG-preferred enzyme. Furthermore, Aly08 degraded alginates into disaccharides and trisaccharides in an endo-manner. Its thermo-tolerance and pH-stable properties make Aly08 a good candidate for further applications.