Analysis of the galactomannan binding ability of β-mannosidases, BtMan2A and CmMan5A, regarding their activity and synergism with a β-mannanase

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BtMan2A preferred short manno-oligomers, while CmMan5A preferred longer ones; DP >2.

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BtMan2A displayed stronger irreversible binding to galactomannan than CmMan5A.

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BtMan2A binding to galactomannan did not affect its activity, while CmMan5A lost activity.

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BtMan2A binding was pH-dependent, with increased binding ability at lower pH.

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CmMan5A synergised with CcManA, while BtMan2A did not – even though the enzyme was active.

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High loadings of BtMan2A abolished CcManA activity; at protein ratios ≥ 5:1.

Both β-mannanases and β-mannosidases are required for mannan-backbone degradation into mannose. In this study, two β-mannosidases of glycoside hydrolase (GH) families 2 (BtMan2A) and 5 (CmMan5A) were evaluated for their substrate specificities and galactomannan binding ability. BtMan2A preferred short manno-oligomers, while CmMan5A preferred longer ones; DP >2, and galactomannans. BtMan2A displayed irreversible galactomannan binding, which was pH-dependent, with higher binding observed at low pH, while CmMan5A had limited binding. Docking and molecular dynamics (MD) simulations showed that BtMan2A galactomannan binding was stronger under acidic conditions (-8.4 kcal/mol) than in a neutral environment (-7.6 kcal/mol), and the galactomannan ligand was more unstable under neutral conditions than acidic conditions. Qualitative surface plasmon resonance (SPR) experimentally confirmed the reduced binding capacity of BtMan2A at pH 7. Finally, synergistic β-mannanase to β-mannosidase (BtMan2A or CmMan5A) ratios required for maximal galactomannan hydrolysis were determined. All CcManA to CmMan5A combinations were synergistic (≈1.2-fold), while combinations of CcManA with BtMan2A (≈1.0-fold) yielded no hydrolysis improvement. In conclusion, the low specific activity of BtMan2A towards long and galactose-containing oligomers and its non-catalytic galactomannan binding ability led to no synergy with the mannanase, making GH2 mannosidases ineffective for use in cocktails for mannan degradation.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Development of sequential and simultaneous bacterial cultures to hydrolyse and detoxify wood pre-hydrolysate for enhanced acetone-butanol-ethanol (ABE) production

The use of microorganisms is a promising option for an eco-efficient and successful conversion of hardwood hemicelluloses to biofuels. The focus of this work is the treatment of hemicellulosic pre-hydrolysate by flocculation, followed by simultaneous or separate detoxification with Ureibacillus thermosphaericus and Cupriavidus taiwanensis co-culture, and hydrolysis with Paenibacillus campinasensis. A reduction of phenolic compounds was achieved mainly after flocculation, applied as a first detoxification step, but no increase in sugars concentration was observed. The ABE fermentation of the hydrolysate obtained from the simultaneous hydrolysis and detoxification produced 6.8 g L^-1 of butanol after 116 h, which was higher than that generated with xylose synthetic medium. The higher biofuel concentration in the hydrolysate is attributed to the existence of carbon sources, other than xylose.

Robust Surface Plasmon Resonance Chips for Repetitive and Accurate Analysis of Lignin-Peptide Interactions

We have developed novel surface plasmon resonance (SPR) sensor chips whose surfaces bear newly synthesized functional self-assembled monolayer (SAM) anchoring lignin through covalent chemical bonds. The SPR sensor chips are remarkably robust and suitable for repetitive and accurate measurement of noncovalent lignin-peptide interactions, which is of significant interest in the chemical or biochemical conversion of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored SAMs were prepared for the first time by click chemistry based on an azide-alkyne Huisgen cycloaddition: mixed SAMs are fabricated on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene oxide) disulfides and then reacted with azidated milled wood lignins to furnish the functional SAMs anchoring lignins covalently. The resulting SAMs were characterized using infrared reflection-absorption, Raman, and X-ray photoelectron spectroscopies to confirm covalent immobilization of the lignins to the SAMs via triazole linkages and also to reveal that the SAM formation induces a helical conformation of the ethylene oxide chains. Further, SPR measurements of the noncovalent lignin-peptide interactions using lignin-binding peptides have demonstrated high reproducibility and durability of the prepared lignin-anchored sensor chips.

Discovery of 12-mer peptides that bind to wood lignin

Lignin, an abundant terrestrial polymer, is the only large-volume renewable feedstock composed of an aromatic skeleton. Lignin has been used mostly as an energy source during paper production; however, recent interest in replacing fossil fuels with renewable resources has highlighted its potential value in providing aromatic chemicals. Highly selective degradation of lignin is pivotal for industrial production of paper, biofuels, chemicals, and materials. However, few studies have examined natural and synthetic molecular components recognizing the heterogeneous aromatic polymer. Here, we report the first identification of lignin-binding peptides possessing characteristic sequences using a phage display technique. The consensus sequence HFPSP was found in several lignin-binding peptides, and the outer amino acid sequence affected the binding affinity of the peptides. Substitution of phenylalanine7 with Ile in the lignin-binding peptide C416 (HFPSPIFQRHSH) decreased the affinity of the peptide for softwood lignin without changing its affinity for hardwood lignin, indicating that C416 recognised structural differences between the lignins. Circular dichroism spectroscopy demonstrated that this peptide adopted a highly flexible random coil structure, allowing key residues to be appropriately arranged in relation to the binding site in lignin. These results provide a useful platform for designing synthetic and biological catalysts selectively bind to lignin.

High specific detection of osteopontin using a three-dimensional copolymer layer support based on electrochemical impedance spectroscopy

Tumor marker detection is essential for the therapy efficiency of early stage tumors and the evaluation of disease progression. Osteopontin (OPN) is supposed to be closely related to several kinds of tumors. In the present study, we describe a label-free electrochemical detection of OPN based on a specific reaction between OPN and its relevant antibody. An artificial three-dimensional (3D) scaffold structure consisting of 11-mercaptoundecanoic acid/6-mercapto-1-hexanol, dextran amino and synthetic peptides was designed as a substrate for the immobilization of the antibody. This substrate was characterized using cyclic voltammetry, atomic force microscopy and Fourier transform infrared reflection spectroscopy. Antibody immobilization and OPN detection were conducted using electrochemical impedance spectroscopy (EIS). The low limit of detection was 0.17 nM. The concentration of cancer risk (5.77 nM) can be selectively detected with a high EIS signal. The fabricated 3D OPN sensor is proposed for application in clinical analysis.

Lignin nanotubes as vehicles for gene delivery into human cells

Lignin nanotubes (LNTs) synthesized from the aromatic plant cell wall polymer lignin in a sacrificial alumina membrane template have as useful features their flexibility, ease of functionalization due to the availability of many functional groups, label-free detection by autofluorescence, and customizable optical properties. In this report we show that the physicochemical properties of LNTs can be varied over a wide range to match requirements for specific applications by using lignin with different subunit composition, a function of plant species and genotype, and by choosing the lignin isolation method (thioglycolic acid, phosphoric acid, sulfuric acid (Klason), sodium hydroxide lignin), which influences the size and reactivity of the lignin fragments. Cytotoxicity studies with human HeLa cells showed that concentrations of up to 90 mg/mL are tolerated, which is a 10-fold higher concentration than observed for single- or multiwalled carbon nanotubes (CNTs). Confocal microscopy imaging revealed that all LNT formulations enter HeLa cells without auxiliary agents and that LNTs made from NaOH-lignin penetrate the cell nucleus. We further show that DNA can adsorb to LNTs. Consequently, exposure of HeLa cells to LNTs coated with DNA encoding the green fluorescent protein (GFP) leads to transfection and expression of GFP. The highest transfection efficiency was obtained with LNTs made from NaOH-lignin due to a combination of high DNA binding capacity and DNA delivery directly into the nucleus. These combined features of LNTs make LNTs attractive as smart delivery vehicles of DNA without the cytotoxicity associated with CNTs or the immunogenicity of viral vectors.