Microbial production, characterization and applications of feruloyl esterases

An Exploratory Study of the Enzymatic Hydroxycinnamoylation of Sucrose and Its Derivatives

Phenylpropanoid sucrose esters are a large and important group of natural substances with significant therapeutic potential. This work describes a pilot study of the enzymatic hydroxycinnamoylation of sucrose and its derivatives which was carried out with the aim of obtaining precursors of natural phenylpropanoid sucrose esters, e.g., vanicoside B. In addition to sucrose, some chemically prepared sucrose acetonides and substituted 3'-O-cinnamates were subjected to enzymatic transesterification with vinyl esters of coumaric, ferulic and 3,4,5-trimethoxycinnamic acid. Commercial enzyme preparations of Lipozyme TL IM lipase and Pentopan 500 BG exhibiting feruloyl esterase activity were tested as biocatalysts in these reactions. The substrate specificity of the used biocatalysts for the donor and acceptor as well as the regioselectivity of the reactions were evaluated and discussed. Surprisingly, Lipozyme TL IM catalyzed the cinnamoylation of sucrose derivatives more to the 1'-OH and 4'-OH positions than to the 6'-OH when the 3'-OH was free and the 6-OH was blocked by isopropylidene. In this case, Pentopan reacted comparably to 1'-OH and 6'-OH positions. If sucrose 3'-O-coumarate was used as an acceptor, in the case of feruloylation with Lipozyme in CH3CN, 6-O-ferulate was the main product (63%). Pentopan feruloylated sucrose 3'-O-coumarate comparably well at the 6-OH and 6'-OH positions (77%). When a proton-donor solvent was used, migration of the 3'-O-cinnamoyl group from fructose to the 2-OH position of glucose was observed. The enzyme hydroxycinnamoylations studied can shorten the targeted syntheses of various phenylpropanoid sucrose esters.

Mimicking the enzymatic plant cell wall hydrolysis mechanism for the degradation of polyethylene terephthalate

Plastic pollution presents a global challenge, impacting ecosystems, wildlife, and economies. Polyethylene terephthalate (PET), widely used in products like bottles, significantly contributes to this issue due to poor waste collection. In recent years, there has been increasing interest in plant biomass-degrading enzymes for plastic breakdown, due to the structural and physicochemical similarities between natural and synthetic polymers. Filamentous fungi involved in hemicellulose degradation have developed a complex mode of action that includes not only enzymes but also biosurfactants; surface-active molecules that facilitate enzyme-substrate interactions. For this reason, this study aimed to mimic the mechanism of biomass degradation by repurposing plant cell wall degrading enzymes including a cutinase and three esterases to cooperatively contribute to PET degradation. Surfactants of different charge were also introduced in the reactions, as their role is similar to biosurfactants, altering the surface tension of the polymers and thus improving enzymes' accessibility. Notably, Fusarium oxysporum cutinase combined with anionic surfactant exhibited a 2.3- and 1.6-fold higher efficacy in hydrolyzing amorphous and semi-crystalline PET, respectively. When cutinase was combined with either of two ferulic acid esterases, it resulted in complete conversion of PET intermediate products to TPA, increasing the overall product release up to 1.9- fold in presence of surfactant. The combination of cutinase with a glucuronoyl esterase demonstrated significant potential in plastic depolymerization, increasing degradation yields in semi-crystalline PET by up to 1.4-fold. The approach of incorporating enzyme cocktails and surfactants emerge as an efficient solution for PET degradation in mild reaction conditions, with potential applications in eco-friendly plastic waste management.

Unlocking the potential of feruloyl esterase from Myceliophthora verrucosa: a key player in efficient conversion of biorefinery-relevant pretreated rice straw

The lignocellulolytic accessory enzyme, Feruloyl esterase C (FE_5DR), encoded in the genome of thermotolerant Myceliophthora verrucosa was successfully cloned and heterologously expressed in Pichia pastoris. The expressed FE_5DR was purified using UNOsphere™ Q anion exchange chromatography column, exhibiting a homogeneous band of ~ 39 kDa. Its optimum temperature was determined to be 60 °C, with an optimal pH of 6.0. Additionally, the enzyme activity of FE_5DR was significantly enhanced by preincubation in a buffer containing Mg2+, Cu2+ and Ca2 metal ions. Enzyme kinetic parameters, computed from double reciprocal Lineweaver-Burk plots, yielded observed Vmax and Km values of 0.758 U/mg and 0.439 mM, respectively. Furthermore, the potential of custom-made cocktails comprising FE_5DR and benchmark cellulase derived from the developed mutant strain of Aspergillus allahabadii MAN 40, as well as the biorefinery-relevant lignocellulolytic enzyme Cellic CTec 3, resulted in improved saccharification of unwashed acid pretreated (UWAP) rice straw slurry and mild alkali deacetylated (MAD) rice straw when compared to benchmark MAN 40 and Cellic CTec 3.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04013-7.

Volatile phenols in wine: overview of origin, formation, analysis, and sensory expression

Volatile phenols impart particular aromas to wine. Due to their distinctive aroma characteristics and low sensory thresholds, volatile phenols can easily influence and modify the aroma of wine. Since these compounds can be formed in wines in various ways, it is necessary to clarify the possible sources of each volatile phenol to achieve management during the winemaking process. The sources of volatile phenols in wine are divided into berry-derived, fermentation-derived, and oak-derived. The pathways and factors influencing the formation of volatile phenols from each source are then reviewed respectively. In addition, an overview of the sensory impact of volatile phenols is given, both in terms of the aroma these volatile phenols directly bring to the wine and their contribution through aroma interactions. Finally, as an essential basis for exploring the scientific problems of volatile phenols in wine, approaches to quantitation of volatile phenols and their precursors are discussed in detail. With the advancement of analytical techniques, more details on volatile phenols have been discovered. Further exploration is worthwhile to achieve more detailed monitoring and targeted management of volatile phenols in wine.

New Labeled PET Analogues Enable the Functional Screening and Characterization of PET-Degrading Enzymes

The discovery and engineering of novel biocatalysts capable of depolymerizing polyethylene terephthalate (PET) have gained significant attention since the need for green technologies to combat plastic pollution has become increasingly urgent. This study focuses on the development of novel substrates that can indicate enzymes with PET hydrolytic activity, streamlining the process of enzyme evaluation and selection. Four novel substrates, mimicking the structure of PET, were chemically synthesized and labeled with fluorogenic or chromogenic moieties, enabling the direct analysis of candidate enzymes without complex preparatory or analysis steps. The fluorogenic substrates, mUPET1, mUPET2, and mUPET3, not only identify enzymes capable of PET breakdown but also differentiate those with exceptional performance on the polymer, such as the benchmark PETase, LCCICCG. Among the substrates, the chromogenic p-NPhPET3 stands out as a reliable tool for screening both pure and crude enzymes, offering advantages over fluorogenic substrates such as ease of assay using UV-vis spectroscopy and compatibility with crude enzyme samples. However, ferulic acid esterases and mono-(2-hydroxyethyl) terephthalate esterases (MHETases), which exhibit remarkably high affinity for PET oligomers, also show high catalytic activity on these substrates. The substrates introduced in this study hold significant value in the function-based screening and characterization of enzymes that degrade PET, as well as the the potential to be used in screening mutant libraries derived from directed evolution experiments. Following this approach, a rapid and dependable assay method can be carried out using basic laboratory infrastructure, eliminating the necessity for intricate preparatory procedures before analysis.

Fermenting Distiller's Grains by the Domesticated Microbial Consortium To Release Ferulic Acid

The microbial consortium FA12 that can release ferulic acid (FA) by fermenting distiller's grains was screened from Daqu. Taibaiella, Comamonadaceae, and Ochrobacum were highly abundant in FA12 by 16S rRNA gene sequencing. In the process of long-term acclimation with distiller's grains as a medium, the biomass of FA12 remained stable, and the pH value of fermentation liquid was also relatively stable. Meanwhile, the activities of cellulase, xylanase, and feruloyl esterase secreted by FA12 were stable in the ranges of 0.2350-0.4470, 0.1917-0.3078, and 0.1103-0.1595 U/mL, respectively, and the release of FA could reach 133.77 μg/g. It is proven that the microbial consortium has good genetic stability. In addition, the structural changes of lignocellulose in distiller's grains before and after fermentation were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), and the changes of distiller's grains weight and lignocellulose content before and after fermentation were also detected. These results all confirmed that FA12 had the function of degrading distiller's grains. In this study, we explored a method to use microbial communities to release FA from distiller's grains and degrade lignocellulose in the waste, which opened up a new way for the application of the high value of lost waste.

Effect of Dietary and Age Changes on Ruminal Microbial Diversity in Holstein Calves

Ruminal microorganisms play a crucial role in the energy supply of ruminants and animal performance. We analyzed the variations in rumen bacteria and fungi at 45 d, 75 d, and 105 d by using 16SrRNA and ITS sequencing data and investigated their correlation with rumen fermentation. According to the results, rumen microflora tended to gradually mature with age, and bacterial and fungal establishment gradually stabilized. Upon comparing the three periods, the concentration of propionic acid increased significantly (p < 0.05) after weaning, and weaning accompanied by a transition in diet remarkably decreased (p < 0.05) rumen diversity in the short term and induced a corresponding change in the rumen microbiota composition. Bacteroidota, Actinobacteriota, and Firmicutes were the core bacterial phyla for all age periods. Ruminococcus, NK4A214_group, Sharpea, Rikenellaceae_RC9_gut_group, and norank_f__Butyricicoccaceae were the markedly abundant bacterial genera in pre-weaning. After weaning, the relative abundance of Erysipelotrichaceae_ UCG-002, Eubacterium_ruminantium_group, and Solobacterium significantly increased (p < 0.05). The relative abundance of Acetitomaculum increased with age with the greatest abundance noted at 105 d (37%). The dominant fungal phyla were Ascomycota and Basidiomycota, and Aspergillus and Xeromyces were the most abundant fungal genera after weaning. Trichomonascus, Phialosimplex, and Talaromyces were enriched at 105 d. However, the low abundance of Neocallimastigomycota was not detected throughout the study, which is worthy of further investigation. In addition, correlations were observed between age-related abundances of specific genera and microbiota functions and rumen fermentation-related parameters. This study revealed that rumen microbiota and rumen fermentation capacity are correlated, which contributed to a better understanding of the effects of age and diet on rumen microbiology and fermentation in calves.

Penicillium chrysogenum as a fungal factory for feruloyl esterases

Plant biomass is a promising substrate for biorefinery, as well as a source of bioactive compounds, platform chemicals, and precursors with multiple industrial applications. These applications depend on the hydrolysis of its recalcitrant structure. However, the effective biological degradation of plant cell walls requires several enzymatic groups acting synergistically, and novel enzymes are needed in order to achieve profitable industrial hydrolysis processes. In the present work, a feruloyl esterase (FAE) activity screening of Penicillium spp. strains revealed a promising candidate (Penicillium rubens Wisconsin 54-1255; previously Penicillium chrysogenum), where two FAE-ORFs were identified and subsequently overexpressed. Enzyme extracts were analyzed, confirming the presence of FAE activity in the respective gene products (PrFaeA and PrFaeB). PrFaeB-enriched enzyme extracts were used to determine the FAE activity optima (pH 5.0 and 50-55 °C) and perform proteome analysis by means of MALDI-TOF/TOF mass spectrometry. The studies were completed with the determination of other lignocellulolytic activities, an untargeted metabolite analysis, and upscaled FAE production in stirred tank reactors. The findings described in this work present P. rubens as a promising lignocellulolytic enzyme producer. KEY POINTS: • Two Penicillium rubens ORFs were first confirmed to have feruloyl esterase activity. • Overexpression of the ORFs produced a novel P. rubens strain with improved activity. • The first in-depth proteomic study of a P. rubens lignocellulolytic extract is shown.

Microbial xylanolytic carbohydrate esterases

This article reviews microbial esterases participating in the degradation of the major plant hemicellulose, xylan. The main chain of this polysaccharide built of β-1,4-glycosidically linked xylopyranosyl residues is substituted by other sugars and also partially acetylated. Besides esters of acetic acid, there are two other types of ester linkages in plant xylans. L-Arabinofuranosyl side chains form esters with phenolic acids, predominantly with ferulic acid. The dimerization of ferulic acid residues leads to cross-links connecting the hemicellulose molecules. Ferulic acid cross-links were shown to serve as covalent linkage between lignin and hemicellulose. Another cross-linking between lignin and hemicellulose is provided by esters between the xylan side residues of glucuronic or 4-O-methyl-D-glucurononic acid and lignin alcohols. Regardless of the cross-linking, the side residues prevent xylan main chains from association that leads to crystallization similar to that of cellulose. Simultaneously, xylan decorations hamper the action of enzymes acting on the main chain. The enzymatic breakdown of plant xylan, therefore, requires a concerted action of glycanases attacking the main chain and enzymes catalyzing debranching, called accessory xylanolytic enzymes including xylanolytic esterases. While acetylxylan esterases and feruloyl esterases participate directly in xylan degradation, glucuronoyl esterases catalyze its separation from lignin. The current state of knowledge of diversity, classification and structure–function relationship of these three types of xylanolytic carbohydrate esterases is discussed with emphasis on important aspects of their future research relevant to their industrial applications.

Characterization of feruloyl esterases from Pecoramyces sp. F1 and the synergistic effect in biomass degradation

Feruloyl esterase (FAE; EC 3.1.1.73) cleaves the ester bond between ferulic acid (FA) and sugar, to assist the release of FAs and degradation of plant cell walls. In this study, two FAEs (Fae13961 and Fae16537) from the anaerobic fungus Pecoramyces sp. F1 were heterologously expressed in Pichia pastoris (P. pastoris). Compared with Fae16537, Fae13961 had higher catalytic efficiency. The optimum temperature and pH of both the FAEs were 45 ℃ and 7.0, respectively. They showed good stability-Fae16537 retained up to 80% activity after incubation at 37 ℃ for 24 h. The FAEs activity was enhanced by Ca²⁺ and reduced by Zn²⁺, Mn²⁺, Fe²⁺ and Fe³⁺. Additionally, the effect of FAEs on the hydrolytic efficiency of xylanase and cellulase was also determined. The FAE Fae13961 had synergistic effect with xylanase and it promoted the degradation of xylan substrates by xylanase, but it did not affect the degradation of cellulose substrates by cellulase. When Fae13961 was added in a mixture of xylanase and cellulase to degrade complex agricultural biomass, it significantly enhanced the mixture's ability to disintegrate complex substrates. These FAEs could serve as superior auxiliary enzymes for other lignocellulosic enzymes in the process of degradation of agricultural residues for industrial applications.

Feruloyl Esterases Protein Engineering to Enhance Their Performance as Biocatalysts: A Review

Feruloyl esterases (FAEs) are versatile enzymes able to release hydroxycinnamic acids or synthesize their ester derivatives, both molecules with interesting biological activities such as: antioxidants, antifungals, antivirals, antifibrotic, anti-inflammatory, among others. The importance of these molecules in medicine, food or cosmetic industries provides FAEs with several biotechnological applications as key industrial biocatalysts. However, FAEs have some operational limitations that must be overcome, which can be addressed through different protein engineering approaches to enhance their thermal stability, catalytic efficiencies, and selectivity. This review aims to present a brief historical tour through the mutagenesis strategies employed to improve enzymes performance and analyze the current protein engineering strategies applied to FAEs as interesting biocatalysts. Finally, an outlook of the future of FAEs protein engineering approaches to achieve successful industrial biocatalysts is given.

Enhancing the secretion of a feruloyl esterase in Bacillus subtilis by signal peptide screening and rational design

Feruloyl esterase is a subclass of α/β hydrolase, which could release ferulic acid from biomass residues for use as an efficient additive in food or pharmaceutical industries. In the present study, a feruloyl esterase with broad substrate specificity was characterised and secreted by Bacillus subtilis WB600. After codon usage optimisation and signal peptide library screening, the secretion amount of feruloyl esterase was enhanced by up to 10.2-fold in comparison with the base strain. The site-specific amino acid substitutions that facilitate protein folding further improved the secretion by about 1.5-fold. The purified rationally designed enzyme exhibited maximal activity against methyl ferulate at pH 6.5 and 65 °C. In the solid-state fermentation, the genetically engineered B. subtilis released about 37% of the total alkali-extractable ferulic acid in maize bran. This study provides a promising candidate for ferulic acid production and demonstrates that the secretion of a heterologous enzyme from B. subtilis can be cumulatively improved by changes in protein sequence features.

Ferulic Acid From Plant Biomass: A Phytochemical With Promising Antiviral Properties

Plant biomass is a magnificent renewable resource for phytochemicals that carry bioactive properties. Ferulic acid (FA) is a hydroxycinnamic acid that is found widespread in plant cell walls, mainly esterified to polysaccharides. It is well known of its strong antioxidant activity, together with numerous properties, such as antimicrobial, anti-inflammatory and neuroprotective effects. This review article provides insights into the potential for valorization of FA as a potent antiviral agent. Its pharmacokinetic properties (absorption, metabolism, distribution and excretion) and the proposed mechanisms that are purported to provide antiviral activity are presented. Novel strategies on extraction and derivatization routes, for enhancing even further the antiviral activity of FA and potentially favor its metabolism, distribution and residence time in the human body, are discussed. These routes may lead to novel high-added value biorefinery pathways to utilize plant biomass toward the production of nutraceuticals as functional foods with attractive bioactive properties, such as enhancing immunity toward viral infections.

Biochemical characterization of a novel feruloyl esterase from Burkholderia pyrrocinia B1213 and its application for hydrolyzing wheat bran

In this study, a novel feruloyl esterase (BpFae) from Burkholderia pyrrocinia B1213 was purified, biochemically characterized, and applied in releasing ferulic acid from wheat bran. The molecular mass of BpFae was approximately 60 kDa by SDS-PAGE, and the enzyme was a homomultimer in solution. BpFae displayed maximum activity at pH 4.5-5.0 and was stable at pH 3.0-7.0. The optimal temperature for BpFae was 50 °C. BpFae activity was not affected by most metal ions tested and was significantly increased by Tween-20 and Triton-100. Purified BpFae exhibited a preference for methyl ferulate (41.78 U mg^-1) over methyl p-coumarate (38.51 U mg^-1) and methyl caffeate (35.36 U mg^-1) and had the lowest activity on methyl sinapate (1.79 U mg^-1). Under the optimum conditions, the K _m and V _max for methyl ferulate were 0.53 mM and 86.74 U mg^-1, respectively. Residues Ser209, His492, and Glu245 in the catalytic pocket of BpFae could form hydrogen bonds with the substrate and were crucial for catalytic activity and substrate specificity. When G11 xylanase XynA and BpFae were used separately for hydrolyzing de-starched wheat bran (DSWB), the ferulic acid released was undetectable and 1.78%, respectively, whereas it was increased to 59.26% using the mixture of the two enzymes. Thus, BpFae is considered an attractive candidate for the production of ferulic acid from agricultural by-products.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03066-2.

Economizing the lignocellulosic hydrolysis process using heterologously expressed auxiliary enzymes feruloyl esterase D (CE1) and β-xylosidase (GH43) derived from thermophilic fungi Scytalidium thermophilum

Two lignocellulolytic accessory enzymes, feruloyl esterase D (FAED_SCYTH) and β-xylosidase (XYL43B_SCYTH) were cloned and produced in the Pichia pastoris X33 as host. The molecular weight of recombinant enzymes FAED_SCYTH and XYL43B_SCYTH were ~ 31 and 40 kDa, respectively. FAED_SCYTH showed optimal activity at pH 6.0, 60 °C; and XYL43B_SCYTH at pH 7.0, 50 °C. FAED_SCYTH and XYL43B_SCYTH exhibited t_1/2: 4 and 0.5 h, respectively (50 °C, pH 5.0). The β-xylosidase was bi-functional with pronounced activity against pNP-α-arabinofuranoside besides being highly xylose tolerant (retaining ~ 97% activity in the presence of 700 mM xylose). Cocktails prepared using these enzymes along with AA9 protein (PMO9D_SCYTH) and commercial cellulase CellicCTec2, showed improved hydrolysis of the pre-treated lignocellulosic biomass. Priming of pre-treated lignocellulosic biomass with these accessory enzymes was found to further enhance the hydrolytic potential of CellicCTec2 promising to reduce the enzyme load and cost required for obtaining sugars from biorefinery relevant pre-treated substrates.

Bioconversion of Lignocellulosic Materials with the Contribution of a Multifunctional GH78 Glycoside Hydrolase from Xylaria polymorpha to Release Aromatic Fragments and Carbohydrates

A bifunctional glycoside hydrolase GH78 from the ascomycete Xylaria polymorpha (XpoGH78) possesses catalytic versatility towards both glycosides and esters, which may be advantageous for the efficient degradation of the plant cell-wall complex that contains both diverse sugar residues and esterified structures. The contribution of XpoGH78 to the conversion of lignocellulosic materials without any chemical pretreatment to release the water-soluble aromatic fragments, carbohydrates, and methanol was studied. The disintegrating effect of enzymatic lignocellulose treatment can be significantly improved by using different kinds of hydrolases and phenoloxidases. The considerable changes in low (3 kDa), medium (30 kDa), and high (> 200 kDa) aromatic fragments were observed after the treatment with XpoGH78 alone or with this potent cocktail. Synergistic conversion of rape straw also resulted in a release of 17.3 mg of total carbohydrates (e.g., arabinose, galactose, glucose, mannose, xylose) per gram of substrate after incubating for 72 h. Moreover, the treatment of rape straw with XpoGH78 led to a marginal methanol release of approximately 17 μg/g and improved to 270 μg/g by cooperation with the above accessory enzymes. In the case of beech wood conversion, the combined catalysis by XpoGH78 and laccase caused an effect comparable with that of fungal strain X. polymorpha in woody cultures concerning the liberation of aromatic lignocellulose fragments.

Screening of Recombinant Lignocellulolytic Enzymes Through Rapid Plate Assays

In the search for novel biomass-degrading enzymes through mining microbial genomes, it is necessary to apply functional tests during high-throughput screenings, which are capable of detecting enzymatic activities directly by way of plate assay. Using the most efficient expression systems of Escherichia coli and Pichia pastoris, the production of a high amount of His-tagged recombinant proteins could be thrived, allowing the one-step isolation by affinity chromatography. Here, we describe simple and efficient assay techniques for the detection of various biomass-degrading enzymatic activities on agar plates, such as cellulolytic, hemicellulolytic, and ligninolytic activities and their isolation using immobilized-metal affinity chromatography.

Functional Validation of Two Fungal Subfamilies in Carbohydrate Esterase Family 1 by Biochemical Characterization of Esterases From Uncharacterized Branches

The fungal members of Carbohydrate Esterase family 1 (CE1) from the CAZy database include both acetyl xylan esterases (AXEs) and feruloyl esterases (FAEs). AXEs and FAEs are essential auxiliary enzymes to unlock the full potential of feedstock. They are being used in many biotechnology applications including food and feed, pulp and paper, and biomass valorization. AXEs catalyze the hydrolysis of acetyl group from xylan, while FAEs release ferulic and other hydroxycinnamic acids from xylan and pectin. Previously, we reported a phylogenetic analysis for the fungal members of CE1, establishing five subfamilies (CE1_SF1–SF5). Currently, the characterized AXEs are in the subfamily CE1_SF1, whereas CE1_SF2 contains mainly characterized FAEs. These two subfamilies are more related to each other than to the other subfamilies and are predicted to have evolved from a common ancestor, but target substrates with a different molecular structure. In this study, four ascomycete enzymes from CE1_SF1 and SF2 were heterologously produced in Pichia pastoris and characterized with respect to their biochemical properties and substrate preference toward different model and plant biomass substrates. The selected enzymes from CE1_SF1 only exhibited AXE activity, whereas the one from CE1_SF2 possessed dual FAE/AXE activity. This dual activity enzyme also showed broad substrate specificity toward model substrates for FAE activity and efficiently released both acetic acid and ferulic acid (∼50%) from wheat arabinoxylan and wheat bran which was pre-treated with a commercial xylanase. These fungal AXEs and FAEs also showed promising biochemical properties, e.g., high stability over a wide pH range and retaining more than 80% of their residual activity at pH 6.0–9.0. These newly characterized fungal AXEs and FAEs from CE1 have high potential for biotechnological applications. In particular as an additional ingredient for enzyme cocktails to remove the ester-linked decorations which enables access for the backbone degrading enzymes. Among these novel enzymes, the dual FAE/AXE activity enzyme also supports the evolutionary relationship of CE1_SF1 and SF2.

Extracellular alpha/beta-hydrolase from Paenibacillus species shares structural and functional homology to tobacco salicylic acid binding protein 2

An alpha/ beta hydrolase annotated as a putative salicylate esterase within the genome of a species of Paenibacillus previously identified from differential and selective growth on Kraft lignin was structurally and functionally characterised. Feruloyl esterases are key to the degradation of lignin in several bacterial species and although this activity was investigated, no such activity was observed. The crystal structure of the Paenibacillus esterase, here denoted as PnbE, was determined at 1.32 Å resolution, showing high similarity to Nicotiana tabacum salicylic acid binding protein 2 from the protein database. Structural similarities between these two structures across the core domains and key catalytic residues were observed, with superposition of catalytic residues giving an RMSD of 0.5 Å across equivalent Cα atoms. Conversely, the cap domains of PnbE and Nicotiana tabacum SABP2 showed greater divergence with decreased flexibility in the PnbE cap structure. Activity of PnbE as a putative methyl salicylate esterase was supported with binding studies showing affinity for salicylic acid and functional studies showing methyl salicylate esterase activity. We hypothesise that this activity could enrich Paenibacillus sp. within the rhizosphere by increasing salicylic acid concentrations within the soil.

Factors affecting intake, metabolism and health benefits of phenolic acids: do we understand individual variability?

INTRODUCTION

Phenolic acids are important phenolic compounds widespread in foods, contributing to nutritional and organoleptic properties.

FACTORS AFFCETING INDIVIDUAL VARIABILITY

The bioavailability of these compounds depends on their free or conjugated presence in food matrices, which is also affected by food processing. Phenolic acids undergo metabolism by the host and residing intestinal microbiota, which causes conjugations and structural modifications of the compounds. Human responses, metabolite profiles and health responses of phenolics, show considerable individual variation, which is affected by absorption, metabolism and genetic variations of subjects.

OPINION

A better understanding of the gut-host interplay and microbiome biochemistry is becoming highly relevant in understanding the impact of diet and its constituents. It is common to study metabolism and health benefits separately, with some exceptions; however, it should be preferred that health responders and non-responders are studied in combination with explanatory metabolite profiles and gene variants. This approach could turn interindividual variation from a problem in human research to an asset for research on personalized nutrition.

Optimization of fermentation conditions for the production of recombinant feruloyl esterase from Burkholderia pyrrocinia B1213

Statistical experimental designs were used to optimize conditions for recombinant Burkholderia pyrrocinia feruloyl esterase (BpFae) production in bacteria under lactose induction. After optimization by single factor design, Plackett-Burman design, steepest ascent design and the response surface method, the optimal conditions for BpFae production were: 6 g/L lactose, pH 5.5, pre-induced period 5 h, 23 °C, shaker rotational speed of 240 rpm, medium volume of 50 mL/250 mL, inoculum size 0.2% (v/v), and a post-induced period of 32 h in a Luria-Bertani culture. The produced BpFae activity was 7.43 U/mL, which is 2.92 times higher than that obtained under optimal conditions using IPTG as the inducer. BpFae activity was 4.82 U/mL in a 5 L fermenter under the abovementioned optimal conditions. BpFae produced a small amount of ethyl acetate but had no effect on the synthesis of other important esters in Baijiu. The results underpin further investigations into BpFae characterization and potential applications.

Feruloyl Esterases for Biorefineries: Subfamily Classified Specificity for Natural Substrates

Feruloyl esterases (FAEs) have an important role in the enzymatic conversion of lignocellulosic biomass by decoupling plant cell wall polysaccharides and lignin. Moreover, FAEs release anti-oxidative hydroxycinnamic acids (HCAs) from biomass. As a plethora of FAE candidates were found in fungal genomes, FAE classification related to substrate specificity is an indispensability for selection of most suitable candidates. Hence, linking distinct substrate specificities to a FAE classification, such as the recently classified FAE subfamilies (SF), is a promising approach to improve the application of these enzymes for a variety of industrial applications. In total, 14 FAEs that are classified members of SF1, 5, 6, 7, 9, and 13 were tested in this research. All FAEs were investigated for their activity toward a variety of substrates: synthetic model substrates, plant cell wall-derived substrates, including lignin, and natural substrates. Released HCAs were determined using reverse phase-ultra high performance liquid chromatography coupled to UV detection and mass spectrometry. Based on this study, FAEs of SF5 and SF7 showed the highest release of FA, pCA, and diFAs over the range of substrates, while FAEs of SF6 were comparable but less pronounced for diFAs release. These results suggest that SF5 and SF7 FAEs are promising enzymes for biorefinery applications, like the production of biofuels, where a complete degradation of the plant cell wall is desired. In contrast, SF6 FAEs might be of interest for industrial applications that require a high release of only FA and pCA, which are needed as precursors for the production of biochemicals. In contrast, FAEs of SF1, 9 and 13 showed an overall low release of HCAs from plant cell wall-derived and natural substrates. The obtained results substantiate the previous SF classification as a useful tool to predict the substrate specificity of FAEs, which eases the selection of FAE candidates for industrial applications.

The crystal structure of a Fusarium oxysporum feruloyl esterase that belongs to the tannase family

Feruloyl esterases are enzymes of industrial interest that catalyse the hydrolysis of the ester bond between hydroxycinnamic acids such as ferulic acid and sugars present in the plant cell wall. Although there are several structures of biochemically characterized feruloyl esterases available, the structural determinants of their substrate specificity are not yet fully understood. Here, we present the crystal structure of a feruloyl esterase from Fusarium oxysporum (FoFaeC) at 2.3 Å resolution. Similar to the two other tannase-like feruloyl esterases, FoFaeC features a large lid domain covering the active site with potential regulatory role and a disulphide bond that brings together the serine and histidine of the catalytic triad. Differences are mainly observed in the metal coordination site and the substrate binding pocket. ENZYMES: E.C.3.1.1.73. DATABASES: The sequence of FoFaeC has been deposited with UniProt with accession code A0A1D3S5H0_FUSOX and the atomic coordinates of the three-dimensional structure with Protein Data Bank, with PDB code: 6FAT.

Optimization of enzyme-assisted extraction of ferulic acid from sweet corn cob by response surface methodology

BACKGROUND

Sweet corn cob (SCC), an agricultural by-product of the corn-processing industry, contains more than 80% insoluble bound ferulic acid (FA). Extraction of these bound phenolics can be achieved through chemical or enzymatic hydrolysis; however, the shift towards greener chemistry has raised awareness about the use of enzymatic hydrolysis. In the present study, the ability of ferulic acid esterase (FAE) and xylanase (XY) to catalyze the hydrolysis of FA from SCC was investigated. Response surface methodology (RSM), based on a five-level, four-factor central composite rotatable design (CCRD), was used to establish the optimum conditions for enzymatic hydrolysis of FA from SCC. Sweet corn cob was treated with a combination of FAE and XY at various concentrations (FAE: 0.00 to 0.04 U/g; XY: 0.00 to 18 093.5 U/g), temperatures (45 to 65 °C), and pH levels (pH 4.5 to 6.5).

RESULTS

The optimum extraction conditions predicted by the model were: FAE concentration of 0.02 U/g, XY concentration of 3475.3 U/g, extraction pH of 4.5, and an extraction temperature of 45 °C.

CONCLUSION

Under these conditions, the experimental yield of FA was 1.69 ± 0.02 g kg^-1 of SCC, which is in agreement with the value predicted by the model. © 2019 Society of Chemical Industry.

Highly Efficient Extraction of Ferulic Acid from Cereal Brans by a New Type A Feruloyl Esterase from Eupenicillium parvum in Combination with Dilute Phosphoric Acid Pretreatment

Feruloyl esterase (FAE) is a critical enzyme in bio-extraction of ferulic acid (FA) from plant cell wall. A new FAE (EpFAE1) encoding gene was isolated from Eupenicillium parvum and heterologously expressed in Pichia pastoris cells. Based on phylogenetic tree analysis, the protein EpFAE1 belongs to type A of the seventh FAE subfamily. Using methyl ferulate as substrate, the optimum temperature and pH for the catalytic activity of EpFAE1 were 50 °C and 5.5, respectively. The enzyme exhibited high stability at 50 °C, in a wide pH range (3.0-11.0), or in the presence of 2 M of NaCl. Together with the endo-xylanase EpXYN1, EpFAE1 released 72.32% and 4.00% of the alkali-extractable FA from de-starched wheat bran (DSWB) or de-starched corn bran (DSCB), respectively. Meanwhile, the substrates were pretreated with 1.75% (for DSWB) or 1.0% (for DSCB) of phosphoric acid (PA) at 90 °C for 12 h, followed by enzymatic hydrolysis of the soluble and insoluble fractions. The release efficiencies of FA were up to 84.64% for DSWB and 66.73% for DSCB. Combined dilute PA pretreatment with enzymatic hydrolysis is a low-cost and highly efficient method for the extraction of FA from cereal brans.

Immobilization of bacterial feruloyl esterase on mesoporous silica particles and enhancement of synthetic activity by hydrophobic-modified surface

Here, we demonstrated the immobilization of bacterial feruloyl esterase (FAE) from Butyrivibrio sp. XPD2006, Lactobacillus crispatus, Butyrivibrio sp. AE2015, Ruminococcus albus, Cellulosilyticum ruminicola and Clostridium cellulovorans on SBA-15 and their ability to synthesize butyl ferulate (BFA). The BFae2 from Butyrivibrio sp. XPD2006 showed the best catalytic efficiency. High BFA yield was produced when the immobilization of BFae2 took place with a high protein loading and narrow pore sized SBA-15, suggesting alteration of enzyme behavior due to the crowding environment in SBA-15. Grafting of SBA-15 with octyl moieties led to shrinking pore size and resulted in 2.5-fold increment of BFA activity compared to the free enzyme and 70%mol BFA was achieved. The BFae2 encapsulated in hydrophobic-modified SBA-15 endured up to seven reaction cycles while the BFA activity remained above 60%. This is the first report showing the superior performance of hydrophobic-modified surface to entrap FAE to produce fatty phenolic esters.

A Novel VIII Carboxylesterase with High Hydrolytic Activity Against Ampicillin from a Soil Metagenomic Library

A novel carboxylesterase gene, named dlfae4, was discovered and sequenced from a soil metagenomic library. The dlfae4 gene was composed of 1017 base pairs encoding 338 amino acid residues with a predicted molecular mass of 37.2 kDa. DLFae4 exhibited strong hydrolytic activity towards methyl ferulate under optimum pH and temperature conditions (pH 8.6, 50 °C) and displayed remarkable thermostability, with residual activity as high as 50% after incubation for 3 h at 60 °C. A family VIII esterase DLFae4 was found to contain a typical serine residue within the S-X-X-K motif, which serves as a catalytic nucleophile in class C β-lactamases and family VIII esterases. As a consequence of its high sequence similarity with β-lactamases, DLFae4 exhibited significant hydrolytic activity towards ampicillin. In addition, DLFae4 was found to be the first known member of family VIII carboxylesterases with phthalate-degrading ability. Site-directed mutagenesis studies revealed that Ser11, Lys14, and Tyr121 residues play an essential catalytic role in DLFae4. These new findings, which are of great importance for further in-depth research and engineering development of carboxylesterases, should advance the implementation of biotechnological applications.

Production, characteristics, and biotechnological applications of microbial xylanases

Microbial xylanases have gathered great attention due to their biotechnological potential at industrial scale for many processes. A variety of lignocellulosic materials, such as sugarcane bagasse, rice straw, rice bran, wheat straw, wheat bran, corn cob, and ragi bran, are used for xylanase production which also solved the great issue of solid waste management. Both solid-state and submerged fermentation have been used for xylanase production controlled by various physical and nutritional parameters. Majority of xylanases have optimum pH in the range of 4.0-9.0 with optimum temperature at 30-60 °C. For biochemical, molecular studies and also for successful application in industries, purification and characterization of xylanase have been carried out using various appropriate techniques. Cloning and genetic engineering are used for commercial-level production of xylanase, to meet specific economic viability and industrial needs. Microbial xylanases are used in various biotechnological applications like biofuel production, pulp and paper industry, baking and brewing industry, food and feed industry, and deinking of waste paper. This review describes production, characteristics, and biotechnological applications of microbial xylanases.

Inhibitory effect of fermented selected barley extracts with Lactobacillus plantarum dy-1 on the proliferation of human HT-29 Cells

The objective of this study was to understand the changes of nutrition constituents in extracts of four varieties of barley fermented with Lactobacillus plantarum dy-1 (LFBEs) and to uncover the potential apoptosis-related mechanism induced by LFBE to inhibit the proliferation of HT-29 cells. The contents of total polysaccharide, polyphenol, and protein in the four LFBEs significantly changed as the fermentation time went by and exerted different inhibitory effects on the proliferation of HT-29 cells. Results indicated that LFBE (YangSi No.3) inhibited proliferation of HT-29 cells in a time- and dose-dependent manners. The scanning electron micrograph illustrated that LFBE caused representative apoptotic trait and flow cytometric analysis suggested that LFBE brought about apoptosis by ceasing cell cycle at S phase. Western-blotting results indicated that LFBE promoted apoptosis was relevant to the regulation of apoptosis-related proteins, such as B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), and the release of Cytochrome-C from mitochondria. PRACTICAL APPLICATIONS: Abundant studies have reported that extracts of fermented barley held the activities of anti-obesity, antitumor, and so on. However, little information about the comparison in the chemical profile and antiproliferation property among different barley varieties (namely, YangSi barley No.1, YangSi barley No.3, DaZhong 88-91, XiYin No.2) was observed. Results indicated that LFBE (YangSi No.3 barley) exhibited the best inhibitory property by inducing the apoptosis of HT-29 cells. These findings may be beneficial to select a higher nutritional value barley and optimize the fermentation conditions to maximize the bioactive concentration expected in foods for the human.

Directed evolution of the type C feruloyl esterase from Fusarium oxysporum FoFaeC and molecular docking analysis of its improved variants

The need to develop competitive and eco-friendly processes in the cosmetic industry leads to the search for new enzymes with improved properties for industrial bioconversions in this sector. In the present study, a complete methodology to generate, express and screen diversity for the type C feruloyl esterase from Fusarium oxysporium FoFaeC was set up in a high-throughput fashion. A library of around 30,000 random mutants of FoFaeC was generated by error prone PCR of fofaec cDNA and expressed in Yarrowia lipolytica. Screening for enzymatic activity towards the substrates 5-bromo-4-chloroindol-3-yl and 4-nitrocatechol-1-yl ferulates allowed the selection of 96 enzyme variants endowed with improved enzymatic activity that were then characterized for thermo- and solvent- tolerance. The five best mutants in terms of higher activity, thermo- and solvent- tolerance were selected for analysis of substrate specificity. Variant L432I was shown to be able to hydrolyze all the tested substrates, except methyl sinapate, with higher activity than wild type FoFaeC towards methyl p-coumarate, methyl ferulate and methyl caffeate. Moreover, the E455D variant was found to maintain completely its hydrolytic activity after two hour incubation at 55 °C, whereas the L284Q/V405I variant showed both higher thermo- and solvent- tolerance than wild type FoFaeC. Small molecule docking simulations were applied to the five novel selected variants in order to examine the binding pattern of substrates used for enzyme characterization of wild type FoFaeC and the evolved variants.

Thermophilic enzyme systems for efficient conversion of lignocellulose to valuable products: Structural insights and future perspectives for esterases and oxidative catalysts

Thermophilic enzyme systems are of major importance nowadays in all industrial processes due to their great performance at elevated temperatures. In the present review, an overview of the current knowledge on the properties of thermophilic and thermotolerant carbohydrate esterases and oxidative enzymes with great thermostability is provided, with respect to their potential use in biotechnological applications. A special focus is given to the lytic polysaccharide monooxygenases that are able to oxidatively cleave lignocellulose through the use of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. Structural characteristics of the enzymes, including active site conformation and surface properties are discussed and correlated with their substrate specificity and thermostability properties.

Changes in carotenoids, phenolic acids and antioxidant capacity in bread wheat doughs fermented with different lactic acid bacteria strains

Amongst the processing technologies able to improve the functional features of cereal-based foods, sourdough fermentation using Lactic Acid Bacteria (LAB) has been recently rediscovered for its beneficial effects. Wheat (Triticum aestivum L.) bread doughs were prepared using LAB strains belonging to different Lactobacillus species and changes in phenolic acid, carotenoid content and antioxidant capacity were evaluated. Two L. plantarum strains out of six were able to significantly increase carotenoid content in the dough, suggesting that a higher mobilization/solubilisation of these antioxidant compounds occurs. Within different fractions (free, soluble-conjugated, insoluble-bound), the relative distribution of ferulic acid and antioxidant activity changes depending on the specific strain. Overall, results indicate that some LAB strains cause in situ changes, significantly increasing the content of functional compounds in doughs during fermentation. This, in turn, could improve the functional features of bakery foods characterised by a high content in carotenoids and other bioactive compounds.

Optimized Enzymatic Synthesis of Feruloyl Derivatives Catalyzed by Three Novel Feruloyl Esterases from Talaromyces wortmannii in Detergentless Microemulsions

Three novel feruloyl esterases (Fae125, Fae7262 and Fae68) from Talaromyces wortmannii overexpressed in the C1 platform were evaluated for the transesterification of vinyl ferulate with two acceptors of different size and lipophilicity (prenol and L-arabinose) in detergentless microemulsions. The effect of reaction conditions such as the microemulsion composition, the substrate concentration, the enzyme load, the pH, the temperature and the agitation were investigated. The type A Fae125 belonging to the subfamily 5 (SF5) of phylogenetic classification showed highest yields for the synthesis of both products after optimization of reaction conditions: 81.8% for prenyl ferulate and 33.0% for L-arabinose ferulate. After optimization, an 8-fold increase in the yield and a 12-fold increase in selectivity were achieved for the synthesis of prenyl ferulate.

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Three feruloyl esterases from Talaromyces wortmannii were tested for their synthetic and hydrolytic activity.

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Reaction conditions were optimized for the synthesis two feruloyl derivatives, prenyl ferulate and L-arabinose ferulate.

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Fae125 offered highest yield for both products (81.8% and 33%, respectively).

Optimization of Transesterification Reactions with CLEA-Immobilized Feruloyl Esterases from Thermothelomyces thermophila and Talaromyces wortmannii

Feruloyl esterases (FAEs, E.C. 3.1.1.73) are biotechnologically important enzymes with several applications in ferulic acid production from biomass, but also in synthesis of hydroxycinnamic acid derivatives. The use of such biocatalysts in commercial processes can become feasible by their immobilization, providing the advantages of isolation and recycling. In this work, eight feruloyl esterases, immobilized in cross-linked enzyme aggregates (CLEAs) were tested in regard to their transesterification performance, towards the production of prenyl ferulate (PFA) and arabinose ferulate (AFA). After solvent screening, comparison with the activity of respective soluble enzymes, and operational stability tests, FAE125 was selected as the most promising biocatalyst. A central composite design revealed the optimum conditions for each transesterification product, in terms of water content, time, and substrate ratio for both products, and temperature and enzyme load additionally for prenyl ferulate. The optimum product yields obtained were 83.7% for PFA and 58.1% for AFA. FAE125 CLEAs are stable in the optimum conditions of transesterification reactions, maintaining 70% residual activity after five consecutive reactions. Overall, FAE125 CLEAs seem to be able to perform as a robust biocatalyst, offering satisfactory yields and stability, and thus showing significant potential for industrial applications.

The feruloyl esterase genes are required for full pathogenicity of the apple tree canker pathogen Valsa mali

Apple Valsa canker, caused by the fungus Valsa mali, is one of the most destructive diseases of apple trees in East Asia. Feruloyl esterases (ferulic acid esterases, FAEs), which belong to a subclass of carboxylic esterases, can cleave ester bonds that crosslink hydroxycinnamic acids and arabinoxylans or certain pectins in plant cell walls. However, a pathogenic role of FAE has not been demonstrated in plant-pathogenic fungi. In this study, the FAE gene family, including one type A, one type B, three type C and two type D FAE genes, was identified in V. mali. Five of the seven FAE genes had highly elevated transcript levels in V. mali-apple tree bark interactions compared with mycelia grown in axenic culture. Signal peptides of the VmFAEs were confirmed using yeast signal sequence trap assays. To examine whether FAEs are required for the pathogenicity of V. mali, seven single- and six double-gene deletion mutants were generated. Compared with the wild-type, three of the seven FAE single-deletion mutants showed significantly reduced pathogenicity and three of the six FAE double-deletion mutants exhibited greater reductions in pathogenicity, suggesting the joint action of FAEs in the V. mali-apple tree interaction. Most of the FAE mutants that exhibited a significant reduction in pathogenicity had significantly lower FAE activity than the wild-type fungus. These results indicate that secreted FAEs are required for the full pathogenicity of the phytopathogenic fungus V. mali.

Tailoring the specificity of the type C feruloyl esterase FoFaeC from Fusarium oxysporum towards methyl sinapate by rational redesign based on small molecule docking simulations

The type C feruloyl esterase FoFaeC from Fusarium oxysporum is a newly discovered enzyme with high potential for use in the hydrolysis of lignocellulosic biomass but it shows low activity towards sinapates. In this work, small molecule docking simulations were employed in order to identify important residues for the binding of the four model methyl esters of hydroxycinnamic acids, methyl ferulate/caffeate/sinapate/p-coumarate, to the predicted structure of FoFaeC. Subsequently rational redesign was applied to the enzyme’ active site in order to improve its specificity towards methyl sinapate. A double mutation (F230H/T202V) was considered to provide hydrophobic environment for stabilization of the methoxy substitution on sinapate and a larger binding pocket. Five mutant clones and the wild type were produced in Pichia pastoris and biochemically characterized. All clones showed improved activity, substrate affinity, catalytic efficiency and turnover rate compared to the wild type against methyl sinapate, with clone P13 showing a 5-fold improvement in catalytic efficiency. Although the affinity of all mutant clones was improved against the four model substrates, the catalytic efficiency and turnover rate decreased for the substrates containing a hydroxyl substitution.