Expression and characterization of a novel lytic polysaccharide monooxygenase, PdLPMO9A, from the edible fungus Pleurotus djamor and its synergistic interactions with cellulase in corn straw biomass saccharification

Current Advances in the Functional Genes of Edible and Medicinal Fungi: Research Techniques, Functional Analysis, and Prospects

Functional genes encode various biological functions required for the life activities of organisms. By analyzing the functional genes of edible and medicinal fungi, varieties of edible and medicinal fungi can be improved to enhance their agronomic traits, growth rates, and ability to withstand adversity, thereby increasing yield and quality and promoting industrial development. With the rapid development of functional gene research technology and the publication of many whole-genome sequences of edible and medicinal fungi, genes related to important biological traits have been mined, located, and functionally analyzed. This paper summarizes the advantages and disadvantages of different functional gene research techniques and application examples for edible and medicinal fungi; systematically reviews the research progress of functional genes of edible and medicinal fungi in biological processes such as mating type, mycelium and fruit growth and development, substrate utilization and nutrient transport, environmental response, and the synthesis and regulation of important active substances; and proposes future research directions for functional gene research for edible and medicinal fungi. The overall aim of this study was to provide a valuable reference for further promoting the molecular breeding of edible and medicinal fungi with high yield and quality and to promote the wide application of edible and medicinal fungi products in food, medicine, and industry.

Influences of the Carbohydrate-Binding Module on a Fungal Starch-Active Lytic Polysaccharide Monooxygenase

Noncatalytic carbohydrate-binding modules (CBMs) play important roles in the function of lytic polysaccharide monooxygenases (LPMOs) but have not been well demonstrated for starch-active AA13 LPMO. In this study, four new CBMs were investigated systematically for their influence on MtLPMO toward starch in terms of substrate binding, H2O2 production activity, oxidative product yields, and the degradation effect with α-amylase and glucoamylase toward different starch substrates. Among the four MtLPMO-CBM chimeras, MtLPMO-CnCBM harboring the CBM fromColletotrichum nymphaeae showed the highest substrate binding toward different types of starch compared to MtLPMO without CBM. MtLPMO-PvCBM harboring the CBM from Pseudogymnoascus verrucosus and MtLPMO-CnCBM showed dramatically enhanced H2O2 production activity of 4.6-fold and 3.6-fold, respectively, than MtLPMO without CBM. More importantly, MtLPMO-CBM generated more oxidative products from starch polysaccharides degradation than MtLPMO alone, with 6.0-fold and 4.6-fold enhancement obtained from the oxidation of amylopectin and corn starch with MtLPMO-CnCBM, and a 5.2-fold improvement obtained with MtLPMO-AcCBM for amylose. MtLPMO-AcCBM significantly boosted the yields of reducing sugar with α-amylase upon degrading amylopectin and corn starch. These findings demonstrate that CBMs greatly influence the performance of starch-active AA13 LPMOs due to their enhanced binding and H2O2 production activity.

Oxidative Machinery of basidiomycetes as potential enhancers in lignocellulosic biorefineries: A lytic polysaccharide monooxygenases approach

Basidiomycetes are renowned as highly effective decomposers of plant materials, due to their extensive array of oxidative enzymes, which enable them to efficiently break down complex lignocellulosic biomass structures. Among the oxidative machinery of industrially relevant basidiomycetes, the role of lytic polysaccharide monooxygenases (LPMO) in lignocellulosic biomass deconstruction is highlighted. So far, only a limited number of basidiomycetes LPMOs have been identified and heterologously expressed. These LPMOs have presented activity on cellulose and hemicellulose, as well as participation in the deconstruction of lignin. Expanding on this, the current review proposes both enzymatic and non-enzymatic mechanisms of LPMOs for biomass conversion, considering the significance of the Carbohydrate-Binding Modules and other C-terminal regions domains associated with their structure, which is involved in the deconstruction of lignocellulosic biomass.

Current insights of factors interfering the stability of lytic polysaccharide monooxygenases

Cellulose and chitin are two of the most abundant biopolymers in nature, but they cannot be effectively utilized in industry due to their recalcitrance. This limitation was overcome by the advent of lytic polysaccharide monooxygenases (LPMOs), which promote the disruption of biopolymers through oxidative mechanism and provide a breakthrough in the action of hydrolytic enzymes. In the application of LPMOs to biomass degradation, the key to consistent and effective functioning lies in their stability. The efficient transformation of biomass resources using LPMOs depends on factors that interfere with their stability. This review discussed three aspects that affect LPMO stability: general external factors, structural factors, and factors in the enzyme-substrate reaction. It explains how these factors impact LPMO stability, discusses the resulting effects, and finally presents relevant measures and considerations, including potential resolutions. The review also provides suggestions for the application of LPMOs in polysaccharide degradation.

Heterologous expression and characterization of novel GH12 β-glucanase and AA10 lytic polysaccharide monooxygenase from Streptomyces megaspores and their synergistic action in cellulose saccharification

BACKGROUND

The combination of cellulase and lytic polysaccharide monooxygenase (LPMO) is known to boost enzymatic saccharification of cellulose. Although the synergy between cellulases (GH5, 6 or 7) and LPMOs (AA9) has been extensively studied, the interplay between other glycoside hydrolase and LPMO families remains poorly understood.

RESULTS

In this study, two cellulolytic enzyme-encoding genes SmBglu12A and SmLpmo10A from Streptomyces megaspores were identified and heterologously expressed in Escherichia coli. The recombinant SmBglu12A is a non-typical endo-β-1,4-glucanase that preferentially hydrolyzed β-1,3-1,4-glucans and slightly hydrolyzed β-1,4-glucans and belongs to GH12 family. The recombinant SmLpmo10A belongs to a C1-oxidizing cellulose-active LPMO that catalyzed the oxidation of phosphoric acid swollen cellulose to produce celloaldonic acids. Moreover, individual SmBglu12A and SmLpmo10A were both active on barley β-1,3-1,4-glucan, lichenan, sodium carboxymethyl cellulose, phosphoric acid swollen cellulose, as well as Avicel. Furthermore, the combination of SmBglu12A and SmLpmo10A enhanced enzymatic saccharification of phosphoric acid swollen cellulose by improving the native and oxidized cello-oligosaccharides yields.

CONCLUSIONS

These results proved for the first time that the AA10 LPMO was able to boost the catalytic efficiency of GH12 glycoside hydrolases on cellulosic substrates, providing another novel combination of glycoside hydrolase and LPMO for cellulose enzymatic saccharification.

Improving cold-adaptability of mesophilic cellulase complex with a novel mushroom cellobiohydrolase for efficient low-temperature ensiling

Low ambient temperature poses a challenge for rice straw-silage processing in cold climate regions, as cold limits enzyme and microbial activity in silages. Here, a novel cold-active cellobiohydrolase (VvCBHI-I) was isolated from Volvariella volvacea, which exhibited outstanding cellobiohydrolase activity at 10-30 °C. The crude cellulase complex in the VvCBHI-I-expressing transformant T1 retained 50% relative activity at 10 °C, while the wildtype Trichoderma reesei showed <5% of the activity. VvCBHI-I greatly improved the saccharification efficiency of the cellulase complex with pretreated rice straw as substrate at 10 °C. In rice straw silage, pH (<4.5) and lactic acid content (>4.6%) remained stable after 15-day ensiling with the cellulase complex from T1 and Lactobacillus plantarum. Moreover, the proportions of cellulose and hemicellulose decreased to 29.84% ± 0.15% and 21.25% ± 0.26% of the dried material. This demonstrates the crucial potential of mushroom-derived cold-active cellobiohydrolases in successful ensiling in cold regions.

Combinatorial Enzymatic Catalysis for Bioproduction of Ginsenoside Compound K

Ginsenoside compound K (CK) is an emerging functional food or pharmaceutical product. To date, there are still challenges to exploring effective catalytic enzymes for enzyme-catalyzed manufacturing processes and establishing enzyme-catalyzed processes. Herein, we identified three ginsenoside hydrolases BG07 (glucoamylase), BG19 (β-glucosidase), and BG23 (β-glucosidase) from Aspergillus tubingensis JE0609 by transcriptome analysis and peptide mass fingerprinting. Among them, BG23 was expressed in Komagataella phaffii with a high volumetric activity of 235.73 U mL-1 (pNPG). Enzymatic property studies have shown that BG23 is an acidic (pH adaptation range of 4.5-7.0) and mesophilic (thermostable < 50 °C) enzyme. Moreover, a one-pot combinatorial enzyme-catalyzed strategy based on BG23 and BGA35 (β-galactosidase from Aspergillus oryzae) was established, with a high CK yield of 396.7 mg L-1 h-1. This study explored the ginsenoside hydrolases derived from A. tubingensis at the molecular level and provided a reference for the efficient production of CK.

Lytic polysaccharide monooxygenase - A new driving force for lignocellulosic biomass degradation

Lytic polysaccharide monooxygenases (LPMOs) can catalyze polysaccharides by oxidative cleavage of glycosidic bonds and have catalytic activity for cellulose, hemicellulose, chitin, starch and pectin, thus playing an important role in the biomass conversion of lignocellulose. The catalytic substrates of LPMOs are different and the specific catalytic mechanism has not been fully elucidated. Although there have been many studies related to LPMOs, few have actually been put into industrial biomass conversion, which poses a challenge for their expression, regulation and application. In this review, the origin, substrate specificity, structural features, and the relationship between structure and function of LPMOs are described. Additionally, the catalytic mechanism and electron donor of LPMOs and their heterologous expression and regulation are discussed. Finally, the synergistic degradation of biomass by LPMOs with other polysaccharide hydrolases is reviewed, and their current problems and future research directions are pointed out.

Lytic polysaccharide monooxygenase (LPMO)-derived saccharification of lignocellulosic biomass

Given that traditional biorefineries have been based on microbial fermentation to produce useful fuels, materials, and chemicals as metabolites, saccharification is an important step to obtain fermentable sugars from biomass. It is well-known that glycosidic hydrolases (GHs) are responsible for the saccharification of recalcitrant polysaccharides through hydrolysis, but the discovery of lytic polysaccharide monooxygenase (LPMO), which is a kind of oxidative enzyme involved in cleaving polysaccharides and boosting GH performance, has profoundly changed the understanding of enzyme-based saccharification. This review briefly introduces the classification, structural information, and catalytic mechanism of LPMOs. In addition to recombinant expression strategies, synergistic effects with GH are comprehensively discussed. Challenges and perspectives for LPMO-based saccharification on a large scale are also briefly mentioned. Ultimately, this review can provide insights for constructing an economically viable lignocellulose-based biorefinery system and a closed-carbon loop to cope with climate change.

Research Progress on Lignocellulosic Biomass Degradation Catalyzed by Enzymatic Nanomaterials

Lignocellulose biomass (LCB) has extensive applications in many fields such as bioenergy, food, medicines, and raw materials for producing value-added products. One of the keys to efficient utilization of LCB is to obtain directly available oligo- and monomers (e.g., glucose). With the characteristics of easy recovery and separation, high efficiency, economy, and environmental protection, immobilized enzymes have been developed as heterogeneous catalysts to degrade LCB effectively. In this review, applications and mechanisms of LCB-degrading enzymes are discussed, and the nanomaterials and methods used to immobilize enzymes are also discussed. Finally, the research progress of lignocellulose biodegradation catalyzed by nano-enzymes was discussed.