Characterization and application of carbohydrate-binding modules of beta-1,3-xylanase XYL4

Identification and Characterization of a Novel Thermostable and Salt-Tolerant β-1,3 Xylanase from Flammeovirga pacifica Strain WPAGA1

β-1,3 xylanase is an important enzyme in the biorefinery process for some algae. The discovery and characterization of new β-1,3 xylanase is a hot research topic. In this paper, a novel β-1,3 xylanase (Xyl88) is revealed from the annotated genome of Flammeovirga pacifica strain WPAGA1. Bioinformatic analysis shows that Xyl88 belongs to the glycoside hydrolase 26 (GH26) with a suspected CBM (carbohydrate-binding module) sequence. The activity of rXyl88 is 75% of the highest enzyme activity (1.5 mol/L NaCl) in 3 mol/L NaCl buffer, which suggests good salt tolerance of rXy188. The optimum reaction temperature in the buffer without NaCl and with 1.5 mol/L NaCl is 45 °C and 55 °C, respectively. Notably, the catalytic efficiency of rXyl88 (k_cat/K_m) is approximately 20 higher than that of the thermophilic β-1,3 xylanase that has the highest catalytic efficiency. Xyl88 in this study becomes the most efficient enzyme ever found, and it is also the first reported moderately thermophilic and salt-tolerant β-1,3 xylanase. Results of molecular dynamics simulation further prove the excellent thermal stability of Xyl88. Moreover, according to the predicted 3D structure of the Xyl88, the surface of the enzyme is distributed with more negative charges, which is related to its salt tolerance, and significantly more hydrogen bonds and Van der Waals force between the intramolecular residues, which is related to its thermal stability.

Synergistic effect of the enzyme complexes comprising agarase, carrageenase and neoagarobiose hydrolase on degradation of the red algae

In the practice of converting red algae biomass into biofuel or valuable biomaterials, the critical step is the decomposition process of the agarose to give fermentable monomeric sugars. In this study, we selected three enzymes such as agarase, carrageenase and neoagarobiose hydrolase to inducible the simultaneous hydrolysis of the major substrates such as agar and carrageenan constituting the pretreated red algae, and expressed the chimeric enzymes and formed a complexes through optimization of addition ratio. As a result, hydrolysis by enzyme complexes showed a maximum sugar release of 679 mg L^-1 with 67.9% saccharification yield from G. verrucosa natural substrate. The difference in the reducing sugar by the enzyme complexes was 3.6-fold higher than that of the monomer enzyme (cAgaB yield 188.6 mg L^-1). The synergistic effect of producing sugars from red algae biomass through these enzyme complexes can be a very important biological tools aimed at bioenergy production.

Efficient enzymatic degradation process for hydrolysis activity of the Carrageenan from red algae in marine biomass

Carrageenan is a generic name for a family of polysaccharides obtained from certain species of red algae. New methods to produce useful cost-efficiently materials from red algae are needed to convert enzymatic processes into fermentable sugars. In this study, we constructed chimeric genes cCgkA and cCglA containing the catalytic domain of κ-carrageenase CgkA and λ-carrageenase CglA from Pseudoalteromonas carrageenovora fused with a dockerin domain. Recombinant strains expressing the chimeric carrageenase resulted in a halo formation on the carrageenan plate by alcian blue staining. The recombinant cCgkA and cCglA were assembled with scaffoldin miniCbpA via cohesin and dockerin interaction. Carbohydrate binding module (CBM) in scaffoldin was used as a tag for cellulose affinity purification using cellulose as a support. The hydrolysis process was monitored by the amount of reducing sugar released from carrageenan. Interestingly, these results indicated that miniCbpA, cCgkA and cCglA assembled into a complex and that the dockerin-fused enzymes on the scaffoldin had synergistic activity in the degradation of carrageenan. The observed enhancement of activity by carrageenolytic complex was 3.1-fold-higher compared with the corresponding enzymes alone. Thus, the assemblies of advancement of active enzyme complexes will facilitate the commercial production of useful products from red algae biomass which represents inexpensive and sustainable feed-stocks.

Mechanistic insights into the 1,3-xylanases: useful enzymes for manipulation of algal biomass

Xylanases capable of degrading the crystalline microfibrils of 1,3-xylan that reinforce the cell walls of some red and siphonous green algae have not been well studied, yet they could prove to be of great utility in algaculture for the production of food and renewable chemical feedstocks. To gain a better mechanistic understanding of these enzymes, a suite of reagents was synthesized and evaluated as substrates and inhibitors of an endo-1,3-xylanase. With these reagents, a retaining mechanism was confirmed for the xylanase, its catalytic nucleophile identified, and the existence of -3 to +2 substrate-binding subsites demonstrated. Protein crystal X-ray diffraction methods provided a high resolution structure of a trapped covalent glycosyl-enzyme intermediate, indicating that the 1,3-xylanases likely utilize the (1)S(3) → (4)H(3) → (4)C(1) conformational itinerary to effect catalysis.