Enzymatic liquefaction of agarose above the sol–gel transition temperature using a thermostable endo-type β-agarase, Aga16B

Identification of the enantiomeric nature of 2-keto-3-deoxy-galactonate in the catabolic pathway of 3,6-anhydro-L-galactose

A novel metabolic pathway of 3,6-anhydro-L-galactose (L-AHG), the main sugar component in red macroalgae, was first discovered in the marine bacterium Vibrio sp. EJY3. L-AHG is converted to 2-keto-3-deoxy-galactonate (KDGal) in two metabolic steps. Here, we identified the enantiomeric nature of KDGal in the L-AHG catabolic pathway via stereospecific enzymatic reactions accompanying the biosynthesis of enantiopure L-KDGal and D-KDGal. Enantiopure L-KDGal and D-KDGal were synthesized by enzymatic reactions derived from the fungal galacturonate and bacterial oxidative galactose pathways, respectively. KDGal, which is involved in the L-AHG pathway, was also prepared. The results obtained from the reactions with an L-KDGal aldolase, specifically acting on L-KDGal, showed that KDGal in the L-AHG pathway exists in an L-enantiomeric form. Notably, we demonstrated the utilization of L-KDGal by Escherichia coli for the first time. E. coli cannot utilize L-KDGal as the sole carbon source. However, when a mixture of L-KDGal and D-galacturonate was used, E. coli utilized both. Our study suggests a stereoselective method to determine the absolute configuration of a compound. In addition, our results can be used to explore the novel L-KDGal catabolic pathway in E. coli and to construct an engineered microbial platform that assimilates L-AHG or L-KDGal as substrates. KEY POINTS: • Stereospecific enzyme reactions were used to identify enantiomeric nature of KDGal • KDGal in the L-AHG catabolic pathway exists in an L-enantiomeric form • E. coli can utilize L-KDGal as a carbon source when supplied with D-galacturonate.

Nature-Derived Polysaccharide-Based Composite Hydrogels for Promoting Wound Healing

Numerous innovative advancements in dressing technology for wound healing have emerged. Among the various types of wound dressings available, hydrogel dressings, structured with a three-dimensional network and composed of predominantly hydrophilic components, are widely used for wound care due to their remarkable capacity to absorb abundant wound exudate, maintain a moisture environment, provide soothing and cooling effects, and mimic the extracellular matrix. Composite hydrogel dressings, one of the evolved dressings, address the limitations of traditional hydrogel dressings by incorporating additional components, including particles, fibers, fabrics, or foams, within the hydrogels, effectively promoting wound treatment and healing. The added elements enhance the features or add specific functionalities of the dressings, such as sensitivity to external factors, adhesiveness, mechanical strength, control over the release of therapeutic agents, antioxidant and antimicrobial properties, and tissue regeneration behavior. They can be categorized as natural or synthetic based on the origin of the main components of the hydrogel network. This review focuses on recent research on developing natural polysaccharide-based composite hydrogel wound dressings. It explores their preparation and composition, the reinforcement materials integrated into hydrogels, and therapeutic agents. Furthermore, it discusses their features and the specific types of wounds where applied.

Controllable and complete conversion of agarose into oligosaccharides and monosaccharides by microwave-assisted hydrothermal and enzymatic hydrolysis and antibacterial activity of agaro-oligosaccharides

Hydrolysis of agar or agarose can yield two types of oligosaccharides: agaro-oligosaccharides (AOS) and neoagaro-oligosaccharides (NAOS). These oligosaccharides have various biological activities and promising applications in the future food industry and pharmaceuticals. In this study, we prepared AOS from agarose by microwave-assisted hydrothermal hydrolysis and then used a commercial β-galactosidase to treat AOS for producing NAOS. A complete conversion from agarose to AOS or NAOS can be achieved by microwave hydrothermal treatment and one-step enzyme reaction, and the production process was completely green. In addition, we combined β-galactosidase and α-neoagarobiose hydrolase from Saccharophagus degradans 2-40 (SdNABH) to treat AOS, and AOS was completely converted into monosaccharides. Then the results of the inhibitory activity of AOS on the growth of Streptococcus mutans showed that AOS might be a good potential sugar substitute for dental caries prevention. This study provides an efficient approach for the production of multiple mixed degrees of polymerization (DP) of pure AOS and NAOS without requiring acid catalyst and agarases while simplifying the production processes and reducing costs.

Production of Ethyl-agarobioside, a Novel Skin Moisturizer, by Mimicking the Alcoholysis from the Japanese Sake-Brewing Process

Agarobiose (AB; d-galactose-β-1,4-AHG), produced by one-step acid hydrolysis of agarose of red seaweed, is considered a promising cosmetic ingredient due to its skin-moisturizing activity. In this study, the use of AB as a cosmetic ingredient was found to be hampered due to its instability at high temperature and alkaline pH. Therefore, to increase the chemical stability of AB, we devised a novel process to synthesize ethyl-agarobioside (ethyl-AB) from the acid-catalyzed alcoholysis of agarose. This process mimics the generation of ethyl α-glucoside and glyceryl α-glucoside by alcoholysis in the presence of ethanol and glycerol during the traditional Japanese sake-brewing process. Ethyl-AB also showed in vitro skin-moisturizing activity similar to that of AB, but showed higher thermal and pH stability than AB. This is the first report of ethyl-AB, a novel compound produced from red seaweed, as a functional cosmetic ingredient with high chemical stability.

Extracellular production of a thermostable Cellvibrio endolytic β-agarase in Escherichia coli for agarose liquefaction

Four GH16 family β-agarases (GH16A, GH16B, GH16C, and GH16D), originated from an agarolytic bacterium Cellvibrio sp. KY-GH-1, were expressed in an Escherichia coli system and their activities were compared. Only GH16B (597 amino acids, 63.8 kDa), with N-terminal 22-amino acid signal sequence, was secreted into the culture supernatant and demonstrated a robust endolytic agarose hydrolyzing activity for producing neoagarotetraose (NA4) and neoagarohexaose (NA6) as end products. The optimal temperature and pH for the enzyme activity were 50 °C and 7.0, respectively. The enzyme was stable up to 50 °C and over a pH range of 5.0-8.0. The kinetic parameters, including Km, Vmax, kcat, and kcat/Km, of GH16B β-agarases for agarose were 14.40 mg/mL, 542.0 U/mg, 576.3 s^-1, and 4.80 × 10⁶ s^-1 M^-1, respectively. The addition of 1 mM MnCl₂ and 15 mM tris(2-carboxyethyl)phosphine enhanced the enzymatic activity. When agarose or neoagaro-oligosaccharides were used as substrates, the end products of enzymatic catalysis were NA4 and NA6, whereas agaropentaose was produced along with NA4 and NA6 when agaro-oligosaccharides were used as substrates. Treatment of 9%[w/v] melted agarose with the enzyme (1.6 µg/mL) under continuous magnetic stirring at 50 °C for 14 h resulted in efficient agarose liquefaction into NA4 and NA6. Purification of NA4 and NA6 from the enzymatic hydrolysate (9%[w/v] agarose, 20 mL) via Sephadex G-15 column chromatography yielded ~ 650 mg NA4/~ 900 mg NA6 (i.e., ~ 85.3% of the theoretical maximum yield). These findings suggest that the recombinant thermostable GH16B β-agarase is useful for agarose liquefaction to produce NA4 and NA6.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Enzymatic preparation and potential applications of agar oligosaccharides: a review

Oligosaccharides derived from agar, that is, agarooligosaccharides and neoagarooligosaccharides, have demonstrated various kinds of bioactivities which have been utilized in a variety of fields. Enzymatic hydrolysis is a feasible approach that principally allows for obtaining specific agar oligosaccharides in a sustainable way at an industrial scale. This review summarizes recent technologies employed to improve the properties of agarase. Additionally, the relationship between the degree of polymerization, bioactivities, and potential applications of agar-derived oligosaccharides for pharmaceutical, food, cosmetic, and agricultural industries are discussed. Engineered agarase exhibited general improvement of enzymatic performance, which is mostly achieved by truncation. Rational and semi-rational design assisted by computational methods present the latest strategy for agarase improvement with greatest potential to satisfy future industrial needs. Agarase immobilized on magnetic Fe3O4 nanoparticles via covalent bond formation showed characteristics well suited for industry. Additionally, albeit with the relationship between the degree of polymerization and versatile bioactivities like anti-oxidants, anti-inflammatory, anti-microbial agents, prebiotics and in skin care of agar-derived oligosaccharides are discussed here, further researches are still needed to unravel the complicated relationship between bioactivity and structure of the different oligosaccharides.

Multi-Step Enzymatic Production and Purification of 2-Keto-3-Deoxy-Galactonate from Red-Macroalgae-Derived Agarose

2-keto-3-deoxy sugar acids, which have potential as precursors in medicinal compound production, have gained attention in various fields. Among these acids, 2-keto-3-deoxy-l-galactonate (KDGal) has been biologically produced from D-galacturonate originating from plant-derived pectin. KDGal is also found in the catabolic pathway of 3,6-anhydro-l-galactose (AHG), the main component of red-algae-derived agarose. AHG is converted to 3,6-anhydrogalactonate by AHG dehydrogenase and subsequently isomerized to KDGal by 3,6-anhydrogalactonate cycloisomerase. Therefore, we used the above-described pathway to produce KDGal from agarose. Agarose was depolymerized to AHG and to agarotriose (AgaDP3) and agaropentaose (AgaDP5), both of which have significantly higher molecular weights than AHG. When only AHG was converted to KDGal, AgaDP3 and AgaDP5 remained unreacted. Finally, KDGal was effectively purified from the enzymatic products by size-exclusion chromatography based on the differences in molecular weights. These results show that KDGal can be enzymatically produced and purified from agarose for use as a precursor to high-value products.

Recent Advances in Bioutilization of Marine Macroalgae Carbohydrates: Degradation, Metabolism, and Fermentation

Marine macroalgae are considered renewable natural resources due to their high carbohydrate content, which gives better utilization value in biorefineries and higher value conversion than first- and second-generation biomass. However, due to the diverse composition, complex structure, and rare metabolic pathways of macroalgae polysaccharides, their bioavailability needs to be improved. In recent years, enzymes and pathways related to the degradation and metabolism of macroalgae polysaccharides have been continuously developed, and new microbial fermentation platforms have emerged. Aiming at the bioutilization and transformation of macroalgae resources, this review describes the latest research results from the direction of green degradation, biorefining, and metabolic pathway design, including summarizing the the latest biorefining technology and the fermentation platform design of agarose, alginate, and other polysaccharides. This information will provide new research directions and solutions for the biotransformation and utilization of marine macroalgae.

Enhanced production of neoagarobiose from agar with Corynebacterium glutamicum producing exo-type and endo-type β-agarases

Neoagarobiose (NA2) derived from agar marine biomass is a rare reagent that acts as an anti-melanogenesis reagent and moisturizer. Here, for the economical manufacturing of NA2, we developed the co-secretory production system of endo-type β-agarases (DagA) and exo-type β-agarases (EXB3) in Corynebacterium glutamicum. For this purpose, we first developed a secretory system of DagA via Tat pathway. To improve the secretion efficiency, we coexpressed two Tat pathway components (TatA and TatC), and to improve the purity of secreted DagA in the culture supernatant, two endogenous protein genes (Cg2052 and Cg1514) were removed. Using the engineered strain (C. glutamicum SP002), we confirmed that DagA as high as 1.53 g l^-1 was successfully produced in the culture media with high purity (72.7% in the supernatant protein fraction). Next, we constructed the expression system (pHCP-CgR-DagA-EXB3) for the simultaneous secretion of EXB3 via Sec-pathway together with DagA, and it was clearly confirmed that DagA and EXB3 were successfully secreted as high as 54% and 24.5%, respectively. Finally, using culture medium containing DagA and EXB3, we successfully demonstrated the conversion of high-concentration agar (40 g l^-1 ) into NA2 via a two-stage hydrolysis process.

In Vitro Prebiotic and Anti-Colon Cancer Activities of Agar-Derived Sugars from Red Seaweeds

Numerous health benefits of diets containing red seaweeds or agar-derived sugar mixtures produced by enzymatic or acid hydrolysis of agar have been reported. However, among various agar-derived sugars, the key components that confer health-beneficial effects, such as prebiotic and anti-colon cancer activities, remain unclear. Here, we prepared various agar-derived sugars by multiple enzymatic reactions using an endo-type and an exo-type of β-agarase and a neoagarobiose hydrolase and tested their in vitro prebiotic and anti-colon cancer activities. Among various agar-derived sugars, agarotriose exhibited prebiotic activity that was verified based on the fermentability of agarotriose by probiotic bifidobacteria. Furthermore, we demonstrated the anti-colon cancer activity of 3,6-anhydro-l-galactose, which significantly inhibited the proliferation of human colon cancer cells and induced their apoptosis. Our results provide crucial information regarding the key compounds derived from red seaweeds that confer beneficial health effects, including prebiotic and anti-colon cancer activities, to the host.

Characterization of BpGH16A of Bacteroides plebeius, a key enzyme initiating the depolymerization of agarose in the human gut

Seaweeds have received considerable attention as sources of dietary fiber and biomass for manufacturing valuable products. The major polysaccharides of red seaweeds include agar and porphyran. In a marine environment, marine bacteria utilize agar and porphyran through the agarase and porphyranase genes encoded in their genomes. Most of these enzymes identified and characterized so far originate from marine bacteria. Recently, Bacteroides plebeius, a human gut bacterium isolated from seaweed-eating Japanese individuals, was revealed to contain a polysaccharide utilization locus (PUL) targeting the porphyran and agarose of red seaweeds. For example, B. plebeius contains an endo-type β-agarase, BpGH16A, belonging to glycoside hydrolase family 16. BpGH16A cleaves the β-1,4-glycosidic linkages of agarose and produces neoagarooligosccharides from agarose. Since it is crucial to study the characteristics of BpGH16A to understand the depolymerization pathway of red seaweed polysaccharides by B. plebeius in the human gut and to industrially apply the enzyme for the depolymerization of agar, we characterized BpGH16A for the first time. According to our results, BpGH16A is an extracellular endo-type β-agarase with an optimal temperature of 40 °C and an optimal pH of 7.0, which correspond to the temperature and pH of the human colon. BpGH16A depolymerizes agarose into neoagarotetraose (as the main product) and neoagarobiose (as the minor product). Thus, BpGH16A is suggested to be an important enzyme that initiates the depolymerization of red seaweed agarose or agar in the human gut by B. plebeius. KEY POINTS: • Bacteroides plebeius is a human gut bacterium isolated from seaweed-eating humans. • BpGH16A is an extracellular endo-type β-agarase with optimal conditions of 40 °C and pH 7.0. • BpGH16A depolymerizes agarose into neoagarotetraose and neoagarobiose.

Dual Agarolytic Pathways in a Marine Bacterium, Vibrio sp. Strain EJY3: Molecular and Enzymatic Verification

Vibrio sp. strain EJY3 is an agarolytic marine bacterium that catabolizes 3,6-anhydro-l-galactose (AHG), a monomeric sugar unit of agarose. While the AHG catabolic pathway in EJY3 has been discovered recently, the complete agarolytic system of EJY3 remains unclear. We have identified five enzymes, namely, the β-agarases VejGH50A, VejGH50B, VejGH50C, and VejGH50D and the α-neoagarooligosaccharide (NAOS) hydrolase VejGH117, involved in the agarolytic system of EJY3. Based on the characterization of recombinant enzymes and intracellular metabolite analysis, we found that EJY3 catabolizes agarose via two different agarolytic pathways. Among the four β-agarases of EJY3, VejGH50A, VejGH50B, and VejGH50C were found to be extracellular agarases, producing mainly neoagarotetraose (NeoDP4) and neoagarobiose. By detecting intracellular NeoDP4 in EJY3 grown on agarose, NeoDP4 was observed being taken up by cells. Intriguingly, intracellular NeoDP4 acted as a branching point for the two different downstream agarolytic pathways. First, via the well-known agarolytic pathway, NeoDP4 was depolymerized into monomeric sugars by the exo-type β-agarase VejGH50D and the α-NAOS hydrolase VejGH117. Second, via the newly found alternative agarolytic pathway, NeoDP4 was depolymerized into AHG and agarotriose (AgaDP3) by VejGH117, and AgaDP3 then was completely depolymerized into monomeric sugars by sequential reactions of the agarolytic β-galactosidases (ABG) VejABG and VejGH117. Therefore, by experimentally verifying agarolytic enzymatic activity and transport of NeoDP4 into EJY3 cells, we revealed that EJY3 possesses both the known pathway and the newly discovered alternative pathway that involves α-NAOS hydrolase and ABG.IMPORTANCE Agarose is the main polysaccharide of red macroalgae and is composed of galactose and 3,6-anhydro-l-galactose. Many marine bacteria possess enzymes capable of depolymerizing agarose into oligomers and then depolymerizing the oligomers into monomers. Here, we experimentally verified that both a well-known agarolytic pathway and a novel agarolytic pathway exist in a marine bacterium, Vibrio sp. strain EJY3. In agarolytic pathways, agarose is depolymerized mainly into 4-sugar-unit oligomers by extracellular enzymes, which are then transported into cells. The imported oligomers are intracellularly depolymerized into galactose and 3,6-anhydro-l-galactose by two different agarolytic pathways, using different combinations of intracellular enzymes. These results elucidate the depolymerization routes of red macroalgal biomass in the ocean by marine bacteria and provide clues for developing industrial processes for efficiently producing sugars from red macroalgae.

A Novel Route for Agarooligosaccharide Production with the Neoagarooligosaccharide-Producing β-Agarase as Catalyst

Enzymes are catalysts with high specificity. Different compounds could be produced by different enzymes. In case of agaro-oligosaccharides, agarooligosaccharide (AOS) can be produced by α-agarase through cleaving the α-1,3-glycosidic linkages of agarose, while neoagarooligosaccharide (NAOS) can be produced by β-agarase through cleaving the β-1,4-glycosidic linkages of agarose. However, in this study, we showed that β-agarase could also be used to produce AOSs with high purity and yield. The feasibility of our route was confirmed by agarotriose (A3) and agaropentaose (A5) formation from agaroheptaose (A7) and agarononoses (A9) catalyzed by β-agarase. Agarose was firstly liquesced by citric acid into a mixture of AOSs. The AOSs mixture was further catalyzed by β-agarase. When using the neoagarotetraose-forming β-agarase AgWH50B, agarotriose could be produced with the yield of 48%. When using neoagarotetraose, neoagarohexaose-forming β-agarase DagA, both agarotriose and agaropentaose could be produced with the yield of 14% and 13%, respectively. Our method can be used to produce other value-added agaro-oligosaccharides from agarose by different agarolytic enzymes.

Implications of agar and agarase in industrial applications of sustainable marine biomass

Agar, a major component of the cell wall of red algae, is an interesting heteropolysaccharide containing an unusual sugar, 3,6-anhydro-L-galactose. It is widely used as a valuable material in various industrial and experimental applications due to its characteristic gelling and stabilizing properties. Agar-derived oligosaccharides or mono-sugars produced by various agarases have become a promising subject for research owing to their unique biological activities, including anti-obesity, anti-diabetic, immunomodulatory, anti-tumor, antioxidant, skin-whitening, skin-moisturizing, anti-fatigue, and anti-cariogenic activities. Agar is also considered as an alternative sustainable source of biomass for chemical feedstock and biofuel production to substitute for the fossil resource. In this review, we summarize various biochemically characterized agarases, which are useful for industrial applications, such as neoagarooligosaccharide or agarooligosaccharide production and saccharification of agar. Additionally, we succinctly discuss various recent studies that have been conducted to investigate the versatile biological activities of agar-derived saccharides and biofuel production from agar biomass. This review provides a basic framework for understanding the importance of agarases and agar-derived saccharides with broad applications in pharmaceutical, cosmetic, food, and bioenergy industries.

Anticariogenic Activity of Agarobiose and Agarooligosaccharides Derived from Red Macroalgae

3,6-Anhydro-l-galactose (AHG) produced from agarose in red macroalgae was recently suggested as an anticariogenic sugar to replace widely used xylitol. However, the multi-step process for obtaining monomeric sugar AHG from agarose may be expensive. Generally, it is easier to obtain oligosaccharides than monosaccharides from polysaccharides. Therefore, a one-step process to obtain agarobiose (AB) from agarose was recently developed, and here, we suggest AB as a new anticariogenic agent, owing to its anticariogenic activity against Streptococcus mutans. Among AHG-containing oligosaccharides, AB, neoagarobiose (NAB), agarooligosaccharides (AOSs), and neoagarooligosaccharides (NAOSs), AB showed higher inhibitory activity than AOSs against the growth and lactic acid production of S. mutans; no such inhibitory activity was observed for NAB and NAOSs. This inhibitory effect of AB was comparable to the previously reported inhibitory activity of AHG against S. mutans. These results suggest that AB, which can be more economically and simply produced than AHG, may serve as an anticariogenic sugar.

Biochemical Characterization of a New β-Agarase from Cellulophaga Algicola

Cellulophaga algicola DSM 14237, isolated from the Eastern Antarctic coastal zone, was found to be able to hydrolyze several types of polysaccharide materials. In this study, a predicted β-agarase (CaAga1) from C. algicola was heterologously expressed in Escherichia coli. The purified recombinant CaAga1 showed specific activities of 29.39, 20.20, 14.12, and 8.99 U/mg toward agarose, pure agar, and crude agars from Gracilaria lemaneiformis and Porphyra haitanensis, respectively. CaAga1 exhibited an optimal temperature and pH of 40 °C and 7, respectively. CaAga1 was stable over a wide pH range from 4 to 11. The recombinant enzyme showed an unusual thermostability, that is, it was stable at temperature below or equal to 40 °C and around 70 °C, but was thermolabile at about 50 °C. With the agarose as the substrate, the K_m and V_max values for CaAga1 were 1.19 mg/mL and 36.21 U/mg, respectively. The reducing reagent (dithiothreitol) enhanced the activity of CaAga1 by more than one fold. In addition, CaAga1 was salt-tolerant given that it retained approximately 70% of the maximum activity in the presence of 2 M NaCl. The thin layer chromatography results indicated that CaAga1 is an endo-type β-agarase and efficiently hydrolyzed agarose into neoagarotetraose (NA4) and neoagarohexaose (NA6). A structural model of CaAga1 in complex with neoagarooctaose (NA8) was built by homology modeling and explained the hydrolysis pattern of CaAga1.

One-Step Process for Environment-Friendly Preparation of Agar Oligosaccharides From Gracilaria lemaneiformis by the Action of Flammeovirga sp. OC4

Oligosaccharides extracted from agar Gracilaria lemaneiformis (G. lemaneiformis) have stronger physiological activities and a higher value than agar itself, but the pollution caused by the extraction process greatly restricts the sustainable use of agar. In this study, four bacterial strains with a high ability to degrade G. lemaneiformis were isolated from seawater by in situ enrichment in the deep sea. Among them, Flammeovirga sp. OC4, identified by morphological observation and its 16S rRNA sequencing (98.07% similarity to type strain JL-4 of Flammeovirga aprica), was selected. The optimum temperature and pH of crude enzyme produced by Flammeovirga sp. OC4 were 50°C and 8, respectively. More than 60% of the maximum enzyme activity remained after storage at pH 5.0-10.0 for 60 min. Both Mn²⁺ and Ba²⁺ could enhance the enzyme activity. A "one-step process" for preparation of oligosaccharides from G. lemaneiformis was established using Flammeovirga sp. OC4. After optimization of the Plackett-Burman (PB) design and response surface methodology (RSM), the yield of oligosaccharides was increased by 36.1% from 2.71 to 3.09 g L^-1 in a 250-mL fermenter with optimized parameters: 30 g L^-1 G. lemaneiformis powder, 4.84 g L^-1 (NH4)₂SO₄, 44.8-mL working medium volume at 36.7°C, and a shaking speed of 200 × g for 42 h. The extracted oligosaccharides were identified by thin layer chromatography (TLC) and ion chromatography, which consisted of neoagarobiose, agarotriose, neoagarotetraose, agaropentaose, and neoagarohexaose. These results provided an alternative approach for environment-friendly and sustainable utilization of algae.

Mutagenesis on the surface of a β-agarase from Vibrio sp. ZC-1 increased its thermo-stability

The recombinant rAgaZC-1 was a family GH50 β-agarase from Vibrio sp. ZC-1 (CICC 24670). In this paper, the mutant D622G (i.e., mutate the aspartic acid at position 622 to glycine) had better thermo-stability than rAgaZC-1, showing 1.5℃ higher T₅₀¹⁰ (the temperature at which the half-time is 10 min) and 4-folds of half-time at 41℃, while they had almost same optimum temperature (38.5℃), optimum pH (pH6.0) and catalytic efficiency. Thermal deactivation kinetical analysis showed that D622G had higher activation energy for deactivation, enthalpy and Gibbs free energy than rAgaZC-1, indicating that more energy is required by D622G for deactivation. Substrate can protect agarase against thermal inactivation, especially D622G. Hence the yield of agarose hydrolysis catalyzed by D622G was higher than that by rAgaZC-1. The models of D622G and rAgaZC-1 predicted by homology modeling were compared to find that it is the improved distribution of surface electrostatic potential, great symmetric positive potential and more hydrophobic interactions of D622G that enhance the thermo-stability.

Novel Two-Step Process Utilizing a Single Enzyme for the Production of High-Titer 3,6-Anhydro-l-galactose from Agarose Derived from Red Macroalgae

3,6-Anhydro-l-galactose (l-AHG), a major component of agarose derived from red macroalgae, has excellent potential for industrial applications based on its physiological activities such as skin whitening, moisturizing, anticariogenicity, and anti-inflammation. However, l-AHG is not yet commercially available due to the complexity, inefficiency, and high cost of the current processes for producing l-AHG. Currently, l-AHG production depends on a multistep process requiring several enzymes. Here, we designed and tested a novel two-step process for obtaining high-titer l-AHG by using a single enzyme. First, to depolymerize agarose preferentially into agarobiose (AB) at a high titer, the agarose prehydrolysis using phosphoric acid as a catalyst was optimized at a 30.7% (w/v) agarose loading, which is the highest agarose or agar loading reported so far. Then AB produced by the prehydrolysis was hydrolyzed into l-AHG and d-galactose (d-Gal) by using a recently discovered enzyme, Bgl1B. We suggest that this simple and efficient process could be a feasible solution for the commercialization and mass production of l-AHG.

Recombinant β-agarases: insights into molecular, biochemical, and physiochemical characteristics

Agarases (agarose 4-glycanohydrolase; EC 3.2.1.81) are class of enzymes that belong to glycoside hydrolase (GH) family capable of hydrolyzing agar. Their classification depends on hydrolysis pattern and product formation. Among all the agarases, β-agarases and the oligosaccharides formed by its action have fascinated quite a lot of industries. Ample of β-agarase genes have been endowed from marine sources such as algae, sea water, and marine sediments, and the expression of these genes into suitable host gives rise to recombinant β-agarases. These recombinant β-agarases have wide range of industrial applications due to its improved catalytic efficiency and stability in tough environments with ease of production on large scale. In this review, we have perused different types of recombinant β-agarases in consort with their molecular, physiochemical, and kinetic properties in detail and the significant features of those agarases are spotlighted. From the literature reviewed after 2010, we have found that the recombinant β-agarases belonged to the families GH16, GH39, GH50, GH86, and GH118. Among that, GH39, GH50, and GH86 belonged to clan GH-A, while the GH16 family belonged to clan GH-B. It was observed that GH16 is the largest polyspecific glycoside hydrolase family with ample number of β-agarases and the families GH50 and GH118 were found to be monospecific with only β-agarase activity. And, out of 84 non-catalytic carbohydrate-binding modules (CBMs), only CBM6 and CBM13 were professed in β-agarases. We witnessed a larger heterogeneity in molecular, physiochemical, and catalytic characteristics of the recombinant β-agarases including molecular mass: 32-132 kDa, optimum pH: 4.5-9, optimum temperature 16-60 °C, K _M: 0.68-59.8 mg/ml, and V _max: 0.781-11,400 U/mg. Owing to this extensive range of heterogeneity, they have lion's share in the multibillion dollar enzyme market. This review provides a holistic insight to a few aspects of recombinant β-agarases which can be referred by the upcoming explorers to this area.

Effect of 3,6-anhydro-l-galactose on α-melanocyte stimulating hormone-induced melanogenesis in human melanocytes and a skin-equivalent model

3,6‐Anhydro‐l‐galactose (l‐AHG) is a bioactive sugar that is a major component of agarose. Recently, l‐AHG was reported to have anti‐melanogenic potential in human epidermal melanocytes (HEMs) and B16F10 melanoma cells; however, its underlying molecular mechanisms remain unknown. At noncytotoxic concentrations, l‐AHG has been shown to inhibit alpha‐melanocyte‐stimulating hormone‐induced melanin synthesis in various cell models, including HEMs, melan‐a cells, and B16F10 cells. Although l‐AHG did not inhibit tyrosinase activity in vitro, reverse transcription‐polymerase chain reaction results demonstrated that the anti‐melanogenic effect of l‐AHG was mediated by transcriptional repression of melanogenesis‐related genes, including tyrosinase, tyrosinase‐related protein‐1 (TRP‐1), tyrosinase‐related protein‐2 (TRP‐2), and microphthalmia‐associated transcription factor (MITF) in HEMs. Western blot analysis showed that l‐AHG effectively attenuated α‐melanocyte‐stimulating hormone‐induced melanogenic proteins by inhibiting cyclic adenosine monophosphate/cyclic adenosine monophosphate–dependent protein kinase, mitogen‐activated protein kinase, and Akt signaling pathways in HEMs. Topical application of l‐AHG significantly ameliorated melanin production in a 3D pigmented human skin model. Collectively, these results suggest that l‐AHG could be utilized as novel cosmetic compounds with skin‐whitening efficacy.

Different Levels of Skin Whitening Activity among 3,6-Anhydro-l-galactose, Agarooligosaccharides, and Neoagarooligosaccharides

3,6-Anhydro-l-galactose (AHG), a major monomeric constituent of red macroalgae (Rhodophyta), was recently reported to possess skin whitening activity. Moreover, AHG-containing oligosaccharides, such as agarooligosaccharides (AOSs) and neoagarooligosaccharides (NAOSs), have various physiological activities, including anti-inflammatory, antioxidant, and skin moisturizing effects. In this study, AHG and NAOSs were produced from agarose by enzymatic reactions catalyzed by an endo-type β-agarase, an exo-type β-agarase, and a neoagarobiose hydrolase. In a cell proliferation assay, AHG, AOSs, and NAOSs at 12.5, 25, and 50 μg/mL concentrations did not exhibit cytotoxicity toward murine B16 melanoma cells or human epidermal melanocytes. In an in vitro skin whitening activity assay of AHG, AOSs, and NAOSs at 50 μg/mL, AHG showed the highest skin whitening activity in both murine B16 melanoma cells and human epidermal melanocytes; this activity was mediated by the inhibition of melanogenesis. Neoagarotetraose and neoagarohexaose also exhibited in vitro skin whitening activity, whereas neoagarobiose and AOSs with degrees of polymerization of 3 (agarotriose), 5 (agaropentaose), and 7 (agaroheptaose) did not. Therefore, AHG is responsible for the skin whitening activity of agar-derived sugars, and the structural differences among the AHG-containing oligosaccharides may be responsible for their different skin whitening activities.

Identification and characterization of a thermostable endolytic β-agarase Aga2 from a newly isolated marine agarolytic bacteria Cellulophaga omnivescoria W5C

Research on the enzymatic breakdown of seaweed-derived agar has recently gained attention due to the progress in green technologies for marine biomass utilization. The enzymes known as agarases catalyze the cleavage of glycosidic bonds within the polysaccharide. In this study, a new β-agarase, Aga2, was identified from Cellulophaga omnivescoria W5C. Aga2 is one of four putative agarases from the W5C genome, and it belongs to the glycoside hydrolase 16 family. It was shown to be exclusive to the Cellulophaga genus. Agarase activity assays showed that Aga2 is an endolytic-type β-agarase that produces tetrameric and hexameric neoagaro-oligosaccharides, with optimum activity at 45°C and pH 8.0. Zinc ions slightly enhanced its activity while manganese ions had inhibitory effects even at very low concentrations. Aga2 has a K_m of 2.59mgmL^-1 and V_max of 275.48Umg^-1. The K_cat is 1.73×10²s^-1, while the K_cat/K_m is 8.04×10⁶s^-1M^-1. Aga2 also showed good thermostability at 45°C and above, and retained >90% of its activity after repeated freeze-thaw cycles. Bioinformatic analysis of its amino acid sequence revealed that intrinsic properties of the protein (e.g. presence of certain dipeptides and the relative volume occupied by aliphatic amino acids) and tertiary structural elements (e.g. presence of salt bridges, hydrophobic interactions and H-bonding) contributed to its thermostability.

Complete genome sequence and analysis of three kinds of β-agarase of Cellulophaga lytica DAU203 isolated from marine sediment

Cellulophaga lytica DAU203 (KACC 19187), isolated from the marine sediment in Korea, has a strong ability to degrade agar. The genome of C. lytica DAU203 contains a single chromosome that is 3,952,957bp in length, with 32.02% G+C contents. The genomic information predicted that the DAU203 has the potential to be utilized in various enzymatic industries.