Rational design of a thermophilic β-mannanase fromBacillus subtilis TJ-102 to improve its thermostability

Application of an alchemical free energy method for the prediction of thermostable DuraPETase variants

Non-equilibrium (NEQ) alchemical free energy calculations are an emerging tool for accurately predicting changes in protein folding free energy resulting from amino acid mutations. In this study, this method in combination with the Rosetta ddg monomer tool was applied to predict more thermostable variants of the polyethylene terephthalate (PET) degrading enzyme DuraPETase. The Rosetta ddg monomer tool efficiently enriched promising mutations prior to more accurate prediction by NEQ alchemical free energy calculations. The relative change in folding free energy of 96 single amino acid mutations was calculated by NEQ alchemical free energy calculation. Experimental validation of ten of the highest scoring variants identified two mutations (DuraPETaseS61M and DuraPETaseS223Y) that increased the melting temperature (Tm) of the enzyme by up to 1 °C. The calculated relative change in folding free energy showed an excellent correlation with experimentally determined Tm resulting in a Pearson's correlation coefficient of r =  - 0.84. Limitations in the prediction of strongly stabilizing mutations were, however, encountered and are discussed. Despite these challenges, this study demonstrates the practical applicability of NEQ alchemical free energy calculations in prospective enzyme engineering projects. KEY POINTS: • Rosetta ddg monomer enriches stabilizing mutations in a library of DuraPETase variants • NEQ free energy calculations accurately predict changes in Tm of DuraPETase • The DuraPETase variants S223Y, S42M, and S61M have increased Tm.

Thermophilic β-mannanases from bacteria: production, resources, structural features and bioengineering strategies

β-mannanases are pivotal enzymes that cleave the mannan backbone to release short chain mannooligosaccharides, which have tremendous biotechnological applications including food/feed, prebiotics and biofuel production. Due to the high temperature conditions in many industrial applications, thermophilic mannanases seem to have great potential to overcome the thermal impediments. Thus, structural analysis of thermostable β-mannanases is extremely important, as it could open up new avenues for genetic engineering, and protein engineering of these enzymes with enhanced properties and catalytic efficiencies. Under this scope, the present review provides a state-of-the-art discussion on the thermophilic β-mannanases from bacterial origin, their production, engineering and structural characterization. It covers broad insights into various molecular biology techniques such as gene mutagenesis, heterologous gene expression, and protein engineering, that are employed to improve the catalytic efficiency and thermostability of bacterial mannanases for potential industrial applications. Further, the bottlenecks associated with mannanase production and process optimization are also discussed. Finally, future research related to bioengineering of mannanases with novel protein expression systems for commercial applications are also elaborated.

Thermostability modification of β-mannanase from Aspergillus niger via flexibility modification engineering

Introduction

β-Mannanases can hydrolyze mannans, which are widely available in nature. However, the optimum temperature of most β-mannanases is too low to be directly utilized in industry.

Methods

To further improve the thermostability of Anman (mannanase from Aspergillus niger CBS513.88), B-factor and Gibbs unfolding free energy change were used to modify the flexible of Anman, and then combined with multiple sequence alignment and consensus mutation to generate an excellent mutant. At last, we analyzed the intermolecular forces between Anman and the mutant by molecular dynamics simulation.

Results

The thermostability of combined mutant mut5 (E15C/S65P/A84P/A195P/T298P) was increased by 70% than the wild-type Amman at 70°C, and the melting temperature (Tm) and half-life (t1/2) values were increased by 2°C and 7.8-folds, respectively. Molecular dynamics simulation showed reduced flexibility and additional chemical bonds in the region near the mutation site.

Discussion

These results indicate that we obtained a Anman mutant that is more suitable for industrial application, and they also confirm that a combination of rational and semi-rational techniques is helpful for screening mutant sites.

Enhancement of the polyethylene terephthalate and mono-(2-hydroxyethyl) terephthalate degradation activity of Ideonella sakaiensis PETase by an electrostatic interaction-based strategy

The serious environmental pollution that came up with the continuously growing demand for polyethylene terephthalate (PET) has attracted global concern. The IsPETase which has shown the highest PET degradation activity under ambient temperature is a promising enzyme for PET biodegradation, while poor thermostability limited its practical application. Herein, an electrostatic interaction-based strategy was applied for rational design of IsPETase towards enhanced thermostability. The IsPETaseI139R variant displayed the highest Tm value of 56.4 °C and 3.6-times higher PET degradation activity. Molecular simulations demonstrated that the introduction of salt bridges stabilized the local structures, resulting in robust thermostability. Meanwhile, the IsPETaseS92K/D157E/R251A not only exhibited higher thermostability but also showed a 1.74-fold kcat increase towards mono-(2-hydroxyethyl) terephthalate, which ultimately achieved PET depolymerization to complete monomer TPA. Collectively, the electrostatic interaction-based strategy, together with the derived IsPETase variants, could help promote the bio-recycle of PET, reducing the severe global burden of PET waste.

Production and characterization of thermostable acidophilic β-mannanase from Aureobasidium pullulans NRRL 58524 and its potential in mannooligosaccharide production from spent coffee ground galactomannan

The maximum yield of the crude mannanase from Aureobasidium pullulans NRRL 58524 was 8.42 ± 0.18 U mL-1 when cultured for 72 h in the optimized medium containing 3% (w v-1) defatted spent coffee grounds (SCG) and 0.67% (w v-1) ammonium sulphate. Two forms of mannanase were observed in the crude enzyme and the principal mannanase was enriched to apparent homogeneity via sequential filtration and anion exchange chromatography. The molecular mass of the enzyme was approximately 63 kDa as determined by SDS-PAGE. The enriched mannanase was active at high temperatures (45-75 °C) and a pH range from 3 to 6 with the maximum activity at 55 °C and pH 4.0. The enzyme was relatively thermostable with more than 75% of its initial activity remained after a 12 h incubation at 55 °C. The half-lives of the enriched mannanase were over 8 and 6 h at 60 and 65 °C, respectively. The enzyme was not adversely affected by chelator and most ions tested. This enzyme could hydrolyze both glucomannan and galactomannan and exhibited limited catalytic activity on beta-glucan. When the crude mannanase was used to hydrolyze galactomannan extracted from SCG, the maximum yield of reducing sugars mainly comprising of mannobiose (16.27 ± 0.84 mg 100 mg-1), and mannotriose (2.85 ± 0.20 mg 100 mg-1) was obtained at 58.22 ± 2.04 mg 100 mg-1 dry weight, under optimized condition (84.87 U g-1 mannanase, 41 h 34 min incubation at 55 °C and pH 4.0). These results suggested the prospect of the enzyme in mannan hydrolysis and mannooligosaccharide production at a larger scale.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03301-4.

Thermostability engineering of industrial enzymes through structure modification

Thermostability is an essential requirement of enzymes in the industrial processes to catalyze the reactions at high temperatures; thus, enzyme engineering through directed evolution, semi-rational design and rational design are commonly employed to construct desired thermostable mutants. Several strategies are implemented to fulfill enzymes' thermostability demand including decreasing the entropy of the unfolded state through substitutions Gly → Xxx or Xxx → Pro, hydrogen bond, salt bridge, introducing two different simultaneous interactions through single mutant, hydrophobic interaction, filling the hydrophobic cavity core, decreasing surface hydrophobicity, truncating loop, aromatic-aromatic interaction and introducing positively charged residues to enzyme surface. In the current review, horizons about compatibility between secondary structures and substitutions at preferable structural positions to generate the most desirable thermostability in industrial enzymes are broadened. KEY POINTS: • Protein engineering is a powerful tool for generating thermostable industrial enzymes. • Directed evolution and rational design are practical approaches in enzyme engineering. • Substitutions in preferable structural positions can increase thermostability.

A Review of Advanced Molecular Engineering Approaches to Enhance the Thermostability of Enzyme Breakers: From Prospective of Upstream Oil and Gas Industry

During the fracture stimulation of oil and gas wells, fracturing fluids are used to create fractures and transport the proppant into the fractured reservoirs. The fracturing fluid viscosity is responsible for proppant suspension, the viscosity can be increased through the incorporation of guar polymer and cross-linkers. After the fracturing operation, the fluid viscosity is decreased by breakers for efficient oil and gas recovery. Different types of enzyme breakers have been engineered and employed to reduce the fracturing fluid′s viscosity, but thermal stability remains the major constraint for the use of enzymes. The latest enzyme engineering approaches such as direct evolution and rational design, have great potential to increase the enzyme breakers’ thermostability against high temperatures of reservoirs. In this review article, we have reviewed recently advanced enzyme molecular engineering technologies and how these strategies could be used to enhance the thermostability of enzyme breakers in the upstream oil and gas industry.

Thermostable Cellulases / Xylanases From Thermophilic and Hyperthermophilic Microorganisms: Current Perspective

The bioconversion of lignocellulose into monosaccharides is critical for ensuring the continual manufacturing of biofuels and value-added bioproducts. Enzymatic degradation, which has a high yield, low energy consumption, and enhanced selectivity, could be the most efficient and environmentally friendly technique for converting complex lignocellulose polymers to fermentable monosaccharides, and it is expected to make cellulases and xylanases the most demanded industrial enzymes. The widespread nature of thermophilic microorganisms allows them to proliferate on a variety of substrates and release substantial quantities of cellulases and xylanases, which makes them a great source of thermostable enzymes. The most significant breakthrough of lignocellulolytic enzymes lies in lignocellulose-deconstruction by enzymatic depolymerization of holocellulose into simple monosaccharides. However, commercially valuable thermostable cellulases and xylanases are challenging to produce in high enough quantities. Thus, the present review aims at giving an overview of the most recent thermostable cellulases and xylanases isolated from thermophilic and hyperthermophilic microbes. The emphasis is on recent advancements in manufacturing these enzymes in other mesophilic host and enhancement of catalytic activity as well as thermostability of thermophilic cellulases and xylanases, using genetic engineering as a promising and efficient technology for its economic production. Additionally, the biotechnological applications of thermostable cellulases and xylanases of thermophiles were also discussed.

Rational design of 17β-hydroxysteroid dehydrogenase type3 for improving testosterone production with an engineered Pichia pastoris

Testosterone (TS) is a critical androgenic steroid that regulates human metabolism and maintains secondary sexual characteristics. The biotransformation from 4-androstene-3,17-done (4-AD) to TS is limited by the poor catalytic activity of 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3). Herein, we explored the structural characteristics and catalytic mechanism of 17β-HSD3 and adopted the rational design strategy to improve its catalytic activity. Molecular docking and molecular dynamics simulations revealed the substrate-binding pocket and the binding mode of 4-AD to 17β-HSD3. We located the pivotal residues and regulated their hydrophobicity and polarity. The obtained G186R/Y195W variant formed additional electrostatic interaction and hydrogen bond with 4-AD, increasing the binding affinity between the variant and 4-AD. Therefore, the G186R/Y195W variant produced 3.98 g/L of TS, which increased to 297%. The combination of structural and mechanism resolution drives the implementation of the rational design strategy, which provides guidance for bioproduction of TS catalyzed by 17β-HSD3.

High surfactant-tolerant β-mannanase isolated from Dynastes hercules larvae excrement, and identification of its hotspot using site-directed mutagenesis and molecular dynamics simulations

The β-mannanase from Bacillus subtilis HM7 (Man26HM7) isolated from Dynastes hercules larvae excrement was cloned and expressed in Escherichia coli. Biochemical characterization shows that optimal pH and temperature for catalysis are 6.0 and 50 °C, respectively. Man26HM7 displayed excellent surfactant stability by retaining 70% of initial activity in 1%(w/v) SDS, and more than 90% of initial activity in 1%(w/v) Triton X-100 and Tween 80. Results from amino acid sequence alignment and molecular modeling suggest residue 238 of β-mannanase as a hotspot of SDS-tolerance. Mutagenesis at the equivalent residue of another homolog, β-mannanase from Bacillus subtilis CAe24 (Man26CAe24), significantly enhanced the SDS stability of this enzyme. Comparative computational analysis, including molecular docking and molecular dynamics simulation, were then performed to compute the binding free energy of SDS to Man26HM7, Man26CAe24, and variant enzymes. The results suggest that residue 238 of Man26HM7 is involved in SDS binding to the hydrophobic surface of β-mannanase. This study provides not only the promising application of Man26HM7 in detergent and cleaning products but also valuable information for enhancing the surfactant stability of β-mannanase by enzyme engineering.

The Impact of Air Pollution on Neurodegenerative Diseases

BACKGROUND

With the development of industrialization in human society, ambient pollutants are becoming more harmful to human health. Epidemiological and toxicological studies indicate that a close relationship exists between particulate matter with a diameter ≤2.5 µm (PM2.5) and neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). To further confirm the relationship, we focus on possible relevant mechanisms of oxidative stress and neuroinflammation underlying the association between PM2.5 and neurodegenerative diseases in the review.

METHODS

A literature search was performed on the studies about PM2.5 and neurodegenerative diseases via PubMed. A total of 113 articles published were selected, and 31 studies were included.

RESULTS

PM2.5 can enter the central nervous system through 2 main pathways, the blood-brain barrier and olfactory neurons. The inflammatory response and oxidative stress are 2 primary mechanisms via which PM2.5 leads to toxicity in the brain. PM2.5 abnormally activates microglia, inducing the neuroinflammatory process. Inflammatory markers such as IL-1β play an essential role in neurodegenerative diseases such as AD and PD. Moreover, the association between lipid mechanism disorders related to PM2.5 and neurodegenerative diseases has been gaining momentum.

CONCLUSIONS

In conclusion, PM2.5 could significantly increase the risk of neurological disorders, such as AD and PD. Furthermore, any policy aimed at reducing air-polluting emissions and increasing air quality would be protective in human beings.

Applications of Microbial β-Mannanases

Mannans are main components of hemicellulosic fraction of softwoods and they are present widely in plant tissues. β-mannanases are the major mannan-degrading enzymes and are produced by different plants, animals, actinomycetes, fungi, and bacteria. These enzymes can function under conditions of wide range of pH and temperature. Applications of β-mannanases have therefore, been found in different industries such as animal feed, food, biorefinery, textile, detergent, and paper and pulp. This review summarizes the most recent studies reported on potential applications of β-mannanases and bioengineering of β-mannanases to modify and optimize their key catalytic properties to cater to growing demands of commercial sectors.

Molecular advancements on over-expression, stability and catalytic aspects of endo-β-mannanases

The hydrolysis of mannans by endo-β-mannanases continues to gather significance as exemplified by its commercial applications in food, feed, and a rekindled interest in biorefineries. The present review provides a comprehensive account of fundamental research and fascinating insights in the field of endo-β-mannanase engineering in order to improve over-expression and to decipher molecular determinants governing activity-stability during harsh conditions, substrate recognition, polysaccharide specificity, endo/exo mode of action and multi-functional activities in the modular polypeptide. In-depth analysis of the available literature has also been made on rational and directed evolution approaches, which have translated native endo-β-mannanases into superior biocatalysts for satisfying industrial requirements.

Characterization of Thermostable and Chimeric Enzymes via Isopeptide Bond-Mediated Molecular Cyclization

Mannooligosaccharides are released by mannan-degrading endo-β-1,4-mannanase and are known as functional additives in human and animal diets. To satisfy demands for biocatalysis and bioprocessing in crowed environments, in this study, we employed a recently developed enzyme-engineering system, isopeptide bond-mediated molecular cyclization, to modify a mesophilic mannanase from Bacillus subtilis. The results revealed that the cyclized enzymes showed enhanced thermostability and ion stability and resilience to aggregation and freeze-thaw treatment by maintaining their conformational structures. Additionally, by using the SpyTag/SpyCatcher system, we generated a mannanase-xylanase bifunctional enzyme that exhibited a synergistic activity in substrate deconstruction without compromising substrate affinity. Interestingly, the dual-enzyme ring conformation was observed to be more robust than the linear enzyme but inferior to the single-enzyme ring conformation. Taken together, these findings provided new insights into the mechanisms of molecular cyclization on stability improvement and will be useful in the production of new functional oligosaccharides and feed additives.