Efficient Secretory Production of Lytic Polysaccharide Monooxygenase BaLPMO10 and Its Application in Plant Biomass Conversion.

Lytic polysaccharide monooxygenases (LPMOs) can oxidatively break the glycosidic bonds of crystalline cellulose, providing more actionable sites for cellulase to facilitate the conversion of cellulose to cello-oligosaccharides, cellobiose and glucose. In this work, a bioinformatics analysis of BaLPMO10 revealed that it is a hydrophobic, stable and secreted protein. By optimizing the fermentation conditions, the highest protein secretion level was found at a IPTG concentration of 0.5 mM and 20 h of fermentation at 37 °C, with a yield of 20 mg/L and purity > 95%. The effect of metal ions on the enzyme activity of BaLPMO10 was measured, and it was found that 10 mM Ca2+ and Na+ increased the enzyme activity by 47.8% and 98.0%, respectively. However, DTT, EDTA and five organic reagents inhibited the enzyme activity of BaLPMO10. Finally, BaLPMO10 was applied in biomass conversion. The degradation of corn stover pretreated with different steam explosions was performed. BaLPMO10 and cellulase had the best synergistic degradation effect on corn stover pretreated at 200 °C for 12 min, improving reducing sugars by 9.2% compared to cellulase alone. BaLPMO10 was found to be the most efficient for ethylenediamine-pretreated Caragana korshinskii by degrading three different biomasses, increasing the content of reducing sugars by 40.5% compared to cellulase alone following co-degradation with cellulase for 48 h. The results of scanning electron microscopy revealed that BaLPMO10 disrupted the structure of Caragana korshinskii, making its surface coarse and poriferous, which increased the accessibility of other enzymes and thus promoted the process of conversion. These findings provide guidance for improving the efficiency of enzymatic digestion of lignocellulosic biomass.

Construction and Catalytic Study of Affinity Peptide Orientation and Light Crosslinking Immobilized Sucrose Isomerase.

A novel affinity peptide orientation and light-controlled covalent immobilized method was developed. Sucrose isomerase (SI) was selected as the model enzyme. Molecular simulation was first performed to select the targeted immobilization region. Subsequently, a short peptide (H2N-VNIGGX-COOH, VG) with high affinity to this region was rationally designed. Thereafter, 4-benzoyl-l-phenylalanine with the photosensitive group of benzophenone was introduced. Then, the affinity between the ligand and the SI was validated using molecular dynamics simulation. Thereafter, the SI was directionally immobilized onto the surface of the epoxy resin (EP) guided by VG via photo-crosslinking, and thus the oriented photo-crosslinking enzymes were obtained. The enzymatic activity, thermostability, and reusability of the affinity directional photo-crosslinked immobilized sucrose isomerase (hv-EP-VG-SI) were systematically studied. The oriented immobilization enzymes were significantly improved in recycling and heat resistance. Moreover, hv-EP-VG-SI retained more than 90% of the original activity and 50% of the activity after 11 cycles.

[Engineering the plastic degradation enzyme Ple629 from marine consortium to improve its thermal stability].

Petrochemical-derived polyester plastics such as polyethylene terephthalate (PET) and polybutylene adipate terephthalate (PBAT) have been widely used. However, the difficulty to be degraded in nature (PET) or the long biodegradation cycle (PBAT) resulted in serious environmental pollution. In this connection, treating these plastic wastes properly becomes one of the challenges of environment protection. From the perspective of circular economy, biologically depolymerizing the waste of polyester plastics and reusing the depolymerized products is one of the most promising directions. Recent years have seen many reports on polyester plastics degrading organisms and enzymes. Highly efficient degrading enzymes, especially those with better thermal stability, will be conducive to their application. The mesophilic plastic-degrading enzyme Ple629 from the marine microbial metagenome is capable of degrading PET and PBAT at room temperature, but it cannot tolerate high temperature, which hampers its potential application. On the basis of the three-dimensional structure of Ple629 obtained from our previous study, we identified some sites which might be important for its thermal stability by structural comparison and mutation energy analysis. We carried out transformation design, and performed expression, purification and thermal stability determination of the mutants. The melting temperature (Tm) values of mutants V80C and D226C/S281C were increased by 5.2 ℃ and 6.9 ℃, respectively, and the activity of mutant D226C/S281C was also increased by 1.5 times compared with that of the wild-type enzyme. These results provide useful information for future engineering and application of Ple629 in polyester plastic degradation.

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.

Design of carboxylated single-walled carbon nanotubes as highly efficient inhibitors against Aß40 fibrillation based on the HyBER mechanism.

Misfolding and the subsequent self-assembly of amyloid-ß protein (Aß) is very important in the occurrence of Alzheimer's disease (AD). Thus, inhibition of Aß aggregation is currently an effective method to alleviate and treat AD. Herein, a carboxylated single-walled carbon nanotube (SWCNT-COOH) was rationally designed based on the hydrophobic binding-electrostatic repulsion (HyBER) mechanism. The inhibitory effect of SWCNT-COOH on Aß fibrillogenesis was first studied. Based on the results of thioflavin T fluorescence and atomic force microscopy imaging assays, it was shown that SWCNT-COOH can not only effectively inhibit Aß aggregation, but also depolymerize the mature fibrils of Aß. In addition, its inhibitory action will be affected by the content of carboxyl groups. Moreover, the influence of SWCNT-COOH on cytotoxicity induced by Aß was investigated by the MTT method. It was found that SWCNT-COOH can produce an anti-Aß neuroprotective effect in vitro. Molecular dynamics simulations showed that SWCNT-COOH significantly destroyed the overall and internal structural stability of an Aß40 trimer. Moreover, SWCNT-COOH interacted strongly with the N-terminal region, turn region and C-terminal region of the Aß40 trimer via hydrogen bonds, salt bridges and π-π interactions, which triggered a large structural disturbance of the Aß40 trimer, reduced the ß-sheet content of the Aß40 trimer and led to more disorder in these regions. All the above data not only reveal the suppressive effect of SWCNT-COOH on Aß aggregation, but also reveal its inhibitory mechanism, which provides a useful clue to exploit anti-Aß drugs in the future.

Molecular basis for polyol-induced protein stability revealed by molecular dynamics simulations.

Molecular dynamics simulations of chymotrypsin inhibitor 2 in different polyols (glycerol, xylitol, sorbitol, trehalose, and sucrose) at 363 K were performed to probe the molecular basis of the stabilizing effect, and the data in water, ethanol, and glycol were compared. It is found that protein protection by polyols is positively correlated with both the molecular volume and the fractional polar surface area, and the former contributes more significantly to the protein's stability. Polyol molecules have only a few direct hydrogen bonds with the protein, and the number of hydrogen bonds between a polyol and the protein is similar for different polyols. Thus, it is concluded that the direct interactions contribute little to the stabilizing effect. It is clarified that the preferential exclusion of the polyols is the origin of their protective effects, and it increases with increasing polyol size. Namely, there is preferential hydration on the protein surface (2 A), and polyol molecules cluster around the protein at a distance of about 4 A. The preferential exclusion of polyols leads to indirect interactions that prevent the protein from thermal unfolding. The water structure becomes more ordered with increasing the polyol size. So, the entropy of water in the first hydration shell decreases, and a larger extent of decrease is observed with increasing polyol size, leading to larger transfer free energy. The findings suggest that polyols protect the protein from thermal unfolding via indirect interactions. The work has thus elucidated the molecular mechanism of structural stability of the protein in polyol solutions.

Construction of the R17L mutant of MtC1LPMO for improved lignocellulosic biomass conversion by rational point mutation and investigation of the mechanism by molecular dynamics simulations.

To enhance the biomass conversion efficiency, the R17L mutant of the lytic polysaccharide monooxygenase (LPMO) MtC1LPMO with improved catalytic efficiency was constructed via rational point mutation based on the HotSpot Wizard 3.0 and dezyme web servers. Compared with the wild-type (WT) MtC1LPMO, R17L exhibited a 1.8-fold increase of specific activity and 1.92-fold increase of catalytic efficiency (kcat/Km). The degree of increase of the reducing sugar yield from microcrystalline cellulose and three plant biomass materials during synergistic hydrolysis using cellulase in combination with R17L was about 2 times higher than with the WT. Molecular dynamics simulations revealed that the R17L mutation reduced the stability of the region R18-I36, which then weakened the direct interactions between region N24-V31 and the substrate cellohexaose. Consequently, the deflection time of the cellohexaose conformation in R17L was prolonged compared to the WT, which enhanced its catalytic efficiency.

Molecular insight into the inhibition effect of trehalose on the nucleation and elongation of amyloid beta-peptide oligomers.

Soluble amyloid oligomers are a cytotoxic species in Alzheimer's disease, and the recent discovery that trehalose can prohibit aggregation of amyloid beta-peptide (Abeta) has received great attention. However, its inhibition mechanism remains unclear. In order to investigate the molecular mechanism of the inhibition effect, molecular dynamics simulations of Abeta(16-22) and Abeta(40) peptides at different trehalose concentrations (0-0.18 mol/L) are performed using an all-atom model. The simulations confirmed that Abeta(16-22) aggregation is prevented by trehalose in a dose-dependent manner, and it is found that the preferential exclusion effect of trehalose is the origin of its inhibition effects. Namely, there is preferential hydration on the peptide surface (3 A), and trehalose molecules cluster around the peptides at a distance of 4-5 A. At high trehalose concentrations, the preferential exclusion of trehalose leads to three sequential effects that prevent the nucleation and elongation of Abeta(16-22) oligomers. First, the secondary structures of Abeta(16-22) monomers are stabilized in the turn, bend, or coil, so the beta-sheet-rich structure that is prone to forming peptide oligomers is prevented. Second, the thin hydration layer and trehalose clusters can weaken hydrophobic interactions that lead to Abeta(16-22) aggregation. Third, more direct and indirect H-bonds form between trehalose and Abeta(16-22), which suppress the interpeptide hydrogen bonding. Analyses of the simulation data for a single Abeta(40) peptide indicate that trehalose can inhibit the nucleation and elongation of Abeta(40) by a similar mechanism with that on Abeta(16-22) oligomerization. The work has thus elucidated the molecular mechanism of trehalose on the inhibition of Abeta oligomeric aggregation.

Design of LVFFARK and LVFFARK-functionalized nanoparticles for inhibiting amyloid ß-protein fibrillation and cytotoxicity.

Aggregation of amyloid ß-protein (Aß) into amyloid oligomers and fibrils is pathologically linked to Alzheimer's disease (AD). Hence, the inhibition of Aß aggregation is essential for the prevention and treatment of AD, but the development of potent agents capable of inhibiting Aß fibrillogenesis has posed significant challenges. Herein, we designed Ac-LVFFARK-NH2 (LK7) by incorporating two positively charged residues, R and K, into the central hydrophobic fragment of Aß17-21 (LVFFA) and examined its inhibitory effect on Aß42 aggregation and cytotoxicity by extensive physical, biophysical, and biological analyses. LK7 was observed to inhibit Aß42 fibrillogenesis in a dose-dependent manner, but its strong self-assembly characteristic also resulted in high cytotoxicity. In order to prevent the cytotoxicity that resulted from the self-assembly of LK7, the peptide was then conjugated to the surface of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) to fabricate a nanosized inhibitor, LK7@PLGA-NPs. It was found that LK7@PLGA-NPs had little cytotoxicity because the self-assembly of the LK7 conjugated on the NPs was completely inhibited. Moreover, the NPs-based inhibitor showed remarkable inhibitory capability against Aß42 aggregation and significantly alleviated its cytotoxicity at a low LK7@PLGA-NPs concentration of 20 µg/mL. At the same peptide concentration, free LK7 showed little inhibitory effect. It is considered that several synergetic effects contributed to the strong inhibitory ability of LK7@PLGA-NPs, including the enhanced interactions between Aß42 and LK7@PLGA-NPs brought on by inhibiting LK7 self-assembly, restricting conformational changes of Aß42, and thus redirecting Aß42 aggregation into unstructured, off-pathway aggregates. The working mechanisms of the inhibitory effects of LK7 and LK7@PLGA-NPs on Aß42 aggregation were proposed based on experimental observations. This work provides new insights into the design and development of potent NPs-based inhibitors against Aß aggregation and cytotoxicity.