Multiple mutations in the aglycone binding pocket to convert the substrate specificity of dalcochinase to linamarase

Facilitating secretory expression of apple seed β-glucosidase in Komagataella phaffii for the efficient preparation of salidroside

Plant-derived β-glucosidases hold promise for glycoside biosynthesis via reverse hydrolysis because of their excellent glucose tolerance and robust stability. However, their poor heterologous expression hinders the development of large-scale production and applications. In this study, we overexpressed apple seed β-glucosidase (ASG II) in Komagataella phaffii and enhanced its production from 289 to 4322 U L-1 through expression cassette engineering and protein engineering. Upon scaling up to a 5-L high cell-density fermentation, the resultant mutant ASG IIV80A achieved a maximum protein concentration and activity in the secreted supernatant of 2.3 g L-1 and 41.4 kU L-1, respectively. The preparative biosynthesis of salidroside by ASG IIV80A exhibited a high space-time yield of 33.1 g L-1 d-1, which is so far the highest level by plant-derived β-glucosidase. Our work addresses the long-standing challenge of the heterologous expression of plant-derived β-glucosidase in microorganisms and presents new avenues for the efficient production of salidroside and other natural glycosides.

Catalytic efficiency and thermal stability promotion of the cassava linamarase with multiple mutations for better cyanogenic glycoside degradation

In our previous study, we found that cassava cyanogenic glycosides had an acute health risk. Therefore, to solve this problem, the improvement of specific degradation of cyanogenic glycosides of cassava linamarase during processing is the key. In this study, the catalytic activity and thermal stability of enzymes were screened before investigating the degradation efficiency of cyanogenic glycosides with a cassava linamarase mutant K263P-T53F-S366R-V335C-F339C (CASmut) -controlled technique. The CASmut was obtained with the optimum temperature of 45 °C, which was improved by 10 °C. The specific activity of CASmut was 85.1 ± 4.6 U/mg, which was 2.02 times higher than that of the wild type. Molecular dynamics simulation analysis and flexible docking showed there were more hydrogen bonding interactions at the pocket, and the aliphatic glycoside of the linamarin was partially surrounded by hydrophobic residues. The optimum conditions of degradation reactions was screened with CASmut addition of 47 mg/L at 45 °C, pH 6.0. The CASmut combined with ultrasonication improved the degradation from 478.2 ± 10.4 mg/kg to 86.7 ± 7.4 mg/kg. Those results indicating the great potential of CASmut in applying in the cassava food or cyanogenic food. However, challenges in terms of the catalytic mechanism research is worthy of being noticed in further studies.

Structural and mutational analysis of glycoside hydrolase family 1 Br2 β-glucosidase derived from bovine rumen metagenome

Ruminant animals rely on the activities of β-glucosidases from residential microbes to convert feed fibers into glucose for further metabolic uses. In this report, we determined the structures of Br2, which is a glycoside hydrolase family 1 β-glucosidase from the bovine rumen metagenome. Br2 folds into a classical (β/α)8-TIM barrel domain but displays unique structural features at loop β5→α5 and α-helix 5, resulting in different positive subsites from those of other GH1 enzymes. Br2 exhibited the highest specificity toward laminaritriose, suggesting its involvement in β-glucan hydrolysis in digested feed. We then substituted the residues at subsites +1 and + 2 of Br2 with those of Halothermothrix orenii β-glucosidase. The C170E and C221T mutations provided favorable interactions with glucooligosaccharide substrates at subsite +2, while the A219N mutation probably improved the substrate preference for cellobiose and gentiobiose relative to laminaribiose at subsite +1. The N407Y mutation increased the affinity toward cellooligosaccharides. These results give further insights into the molecular determinants responsible for substrate specificity in GH1 β-glucosidases and may provide a basis for future enzyme engineering applications.

Synthesis of long-chain alkyl glucosides via reverse hydrolysis reactions catalyzed by an engineered β-glucosidase

Long-chain alkyl glucosides, such as octyl and decyl β-d-glucopyranosides (OG and DG, respectively), are regarded as a new generation of biodegradable, non-ionic surfactants. Previously, the mutants of Dalbergia cochinchinensis Pierre dalcochinase showed potential in the synthesis of oligosaccharides and alkyl glucosides. In this study, the N189F dalcochinase mutant gave the highest yields of OG and DG synthesis under reverse hydrolysis conditions. The optimized yield of OG (57.5 mol%) was obtained in the reactions containing 0.25 M glucose and 0.3 units of the N189 F mutant in buffer-saturated octanol at 30 °C. The identity of OG and DG products was confirmed by high resolution mass spectrometry (HRMS) and NMR. Consistent with its capability for synthesis, the reactivation kinetics and ITC analysis revealed that the aglycone binding pocket of the N189F mutant was more favorable for long-chain alkyl alcohols than the wild-type dalcochinase, while their glycone binding pockets showed similar affinity for the glucosyl moiety. STD NMR revealed higher interactions at the aglycone sites than the glycone sites. Our results demonstrated a promising potential of the N189F dalcochinase mutant in the future commercial production of long-chain alkyl glucosides via reverse hydrolysis reactions.

Improved synthesis of long-chain alkyl glucosides catalyzed by an engineered β-glucosidase in organic solvents and ionic liquids

OBJECTIVE

To synthesize octyl β-D-glucopyranoside (OG) and decyl β-D-glucopyranoside (DG) in three non-aqueous reaction systems, namely organic solvents, ionic liquids and co-solvent mixtures, via reverse hydrolysis reactions catalyzed by the N189F dalcochinase mutant.

RESULTS

The highest yield of OG (67 mol%) was obtained in the reaction containing 0.5 M glucose, 3 unit ml^-1 enzyme in 20% (v/v) octanol and 70% (v/v) [BMIm][PF₆] at 30 °C. On the other hand, the highest yield of DG (64 mol%) was obtained in the reaction containing 0.5 M glucose, 3 unit ml^-1 enzyme in 20% (v/v) decanol, 20% (v/v) acetone and 50% (v/v) [BMIm][PF₆] at 30 °C. The identities of OG and DG products were confirmed by HRMS and NMR.

CONCLUSION

This is the first report of enzymatic synthesis of OG and DG via reverse hydrolysis reactions in ionic liquids and co-solvent mixtures. The N189F dalcochinase mutant and the non-aqueous reaction systems described here show great potential for future commercial production of long-chain alkyl glucosides.

A computer-based approach for developing linamarase inhibitory agents

Cassava is a strategic crop, especially for developing countries. However, the presence of cyanogenic compounds in cassava products limits the proper nutrients utilization. Due to the poor availability of structure discovery and elucidation in the Protein Data Bank is limiting the full understanding of the enzyme, how to inhibit it and applications in different fields. There is a need to solve the three-dimensional structure (3-D) of linamarase from cassava. The structural elucidation will allow the development of a competitive inhibitor and various industrial applications of the enzyme. The goal of this review is to summarize and present the available 3-D modeling structure of linamarase enzyme using different computational strategies. This approach could help in determining the structure of linamarase and later guide the structure elucidationin silicoand experimentally.