Directed evolution of feruloyl esterase from Lactobacillus acidophilus and its application for ferulic acid production

Characterization of a novel multifunctional β-glucosidase/xylanase/feruloyl esterase and its effects on improving the quality of Longjing tea

Herein, a novel multifunctional enzyme β-glucosidase/xylanase/feruloyl esterase (GXF) was constructed by fusion of β-glucosidase and bifunctional xylanase/feruloyl esterase. The activities of β-glucosidase, xylanase, feruloyl esterase and acetyl xylan esterase displayed by GXF were 67.18 %, 49.54 %, 38.92 % and 23.54 %, respectively, higher than that of the corresponding single functional enzymes. Moreover, the GXF performed better in enhancing aroma and quality of Longjing tea than the single functional enzymes and their mixtures. After treatment with GXF, the grassy and floral odors of tea infusion were significantly improved. Moreover, GXF treatment could improve concentrations of flavonoid aglycones of myricetin, kaempferol and quercetin by 68.1-, 81.42- and 77.39-fold, respectively. In addition, GXF could accelerate the release of reducing sugars, ferulic acid and xylo-oligosaccharides by 9.48-, 8.25- and 4.11-fold, respectively. This multifunctional enzyme may have potential applications in other fields such as food production and biomass degradation.

Multiple strategies to improve extracellular secretion and activity of feruloyl esterase

Feruloyl esterase has a wide range of applications, but there are still problems with low enzyme yield and activity, and complex purification steps. Our previous research found Lactobacillus amylovorus feruloyl esterase could be secreted extracellular in Escherichia coli. In this study, multiple strategies were implemented to maximize the extracellular production of feruloyl esterase with improved activity in E. coli. Firstly, codon-optimized feruloyl esterase was obtained based on the preference of E. coli, resulting in 41.97 % increase in extracellular secretion. Furthermore, by cascading T7 promoters, replacing the 5' UTR, randomly mutating the N-terminal sequence, and co-expressing secretory cofactors, the extracellular secretion was increased by 36.46 %, 31.25 %, 20.66 % and 25.75 %, respectively. Moreover, the feruloyl esterase were mutated to improve the substrate affinity and activity. The catalytic efficiency of Fae-Q134T and Fae-Q198A increased by 4.62-fold and 5.42-fold. Combining above strategies, extracellular feruloyl esterase activity was increased from 2013.70 U/L to 10,349.04 U/L. These results indicated that the activity and yield of feruloyl esterase secreted by E. coli were significantly increased, which laid a foundation for its industrial application.

Simple phenylpropanoids: recent advances in biological activities, biosynthetic pathways, and microbial production

Covering: 2000 to 2023Simple phenylpropanoids are a large group of natural products with primary C6-C3 skeletons. They are not only important biomolecules for plant growth but also crucial chemicals for high-value industries, including fragrances, nutraceuticals, biomaterials, and pharmaceuticals. However, with the growing global demand for simple phenylpropanoids, direct plant extraction or chemical synthesis often struggles to meet current needs in terms of yield, titre, cost, and environmental impact. Benefiting from the rapid development of metabolic engineering and synthetic biology, microbial production of natural products from inexpensive and renewable sources provides a feasible solution for sustainable supply. This review outlines the biological activities of simple phenylpropanoids, compares their biosynthetic pathways in different species (plants, bacteria, and fungi), and summarises key research on the microbial production of simple phenylpropanoids over the last decade, with a focus on engineering strategies that seem to hold most potential for further development. Moreover, constructive solutions to the current challenges and future perspectives for industrial production of phenylpropanoids are presented.

Structural insights into the oligomeric effects on catalytic activity of a decameric feruloyl esterase and its application in ferulic acid production

Oligomeric feruloyl esterase (FAE) has great application prospect in industry due to its potentially high stability and fine-tuned activity. However, the relationship between catalytic capability and oligomeric structure remains undetermined. Here we identified and characterized a novel, cold-adapted FAE (BtFae) derived from Bacteroides thetaiotaomicron. Structural studies unraveled that BtFae adopts a barrel-like decameric architecture unique in esterase families. By disrupting the interface, the monomeric variant exhibited significantly reduced catalytic activity and stability toward methyl ferulate, potentially due to its impact on the flexibility of the catalytic triad. Additionally, our results also showed that the monomerization of BtFae severely decreased the ferulic acid release from de-starched wheat bran and insoluble wheat arabinoxylan by 75 % and 80 %, respectively. Collectively, this study revealed novel connections between oligomerization and FAE catalytic function, which will benefit for further protein engineering of FAEs at the quaternary structure level for improved industrial applications.

Effects of Fermentation on Bioactivity and the Composition of Polyphenols Contained in Polyphenol-Rich Foods: A Review

Polyphenols, as common components with various functional activities in plants, have become a research hotspot. However, researchers have found that the bioavailability and bioactivity of plant polyphenols is generally low because they are usually in the form of tannins, anthocyanins and glycosides. Polyphenol-rich fermented foods (PFFs) are reported to have better bioavailability and bioactivity than polyphenol-rich foods, because polyphenols are used as substrates during food fermentation and are hydrolyzed into smaller phenolic compounds (such as quercetin, kaempferol, gallic acid, ellagic acid, etc.) with higher bioactivity and bioavailability by polyphenol-associated enzymes (PAEs, e.g., tannases, esterases, phenolic acid decarboxylases and glycosidases). Biotransformation pathways of different polyphenols by PAEs secreted by different microorganisms are different. Meanwhile, polyphenols could also promote the growth of beneficial bacteria during the fermentation process while inhibiting the growth of pathogenic bacteria. Therefore, during the fermentation of PFFs, there must be an interactive relationship between polyphenols and microorganisms. The present study is an integration and analysis of the interaction mechanism between PFFs and microorganisms and is systematically elaborated. The present study will provide some new insights to explore the bioavailability and bioactivity of polyphenol-rich foods and greater exploitation of the availability of functional components (such as polyphenols) in plant-derived foods.

Feruloyl Esterase (LaFae) from Lactobacillus acidophilus: Structural Insights and Functional Characterization for Application in Ferulic Acid Production

Ferulic acid and related hydroxycinnamic acids, used as antioxidants and preservatives in the food, cosmetic, pharmaceutical and biotechnology industries, are among the most abundant phenolic compounds present in plant biomass. Identification of novel compounds that can produce ferulic acid and hydroxycinnamic acids, that are safe and can be mass-produced, is critical for the sustainability of these industries. In this study, we aimed to obtain and characterize a feruloyl esterase (LaFae) from Lactobacillus acidophilus. Our results demonstrated that LaFae reacts with ethyl ferulate and can be used to effectively produce ferulic acid from wheat bran, rice bran and corn stalks. In addition, xylanase supplementation was found to enhance LaFae enzymatic hydrolysis, thereby augmenting ferulic acid production. To further investigate the active site configuration of LaFae, crystal structures of unliganded and ethyl ferulate-bound LaFae were determined at 2.3 and 2.19 Å resolutions, respectively. Structural analysis shows that a Phe34 residue, located at the active site entrance, acts as a gatekeeper residue and controls substrate binding. Mutating this Phe34 to Ala produced an approximately 1.6-fold increase in LaFae activity against p-nitrophenyl butyrate. Our results highlight the considerable application potential of LaFae to produce ferulic acid from plant biomass and agricultural by-products.

A feruloyl esterase/cellulase integrated biological system for high-efficiency and toxic-chemical free isolation of tobacco based cellulose nanofibers

Tobacco based cellulose nanofiber (TCNF) is a novel nanocellulose that has recently been used to replace undesirable wood pulp fibers in the preparation of reconstructed tobacco sheets (RTS). However, given the strict requirements for controlling toxic chemical content in tobacco products, there is a global interest in developing a green, efficient, and toxic-chemical free approach to isolate TCNF from tobacco stem as a bioresource. In this study, we propose a creative and environmentally friendly method to efficiently and safely isolate TCNF from tobacco stem pulp, which involves integrated biological pretreatment followed by a facile mechanical defibrillation process. Feruloyl esterase is used to pretreat the stem pulp by disrupting the ether and ester bonds between lignin and polysaccharide carbohydrates within the fiber wall, which effectively facilitates cellulase hydrolysis and swelling of the stem pulp fiber, as well as the following mechanical shearing treatment for TCNF isolation. The results demonstrate that TCNF obtained by the comprehensive feruloyl esterase/cellulase/mechanical process exhibit uniform and well-dispersed nanofiber morphology, higher crystallinity, and stronger mechanical properties than those of the control. The addition of 0.5 % TCNF can replace wood pulp by 18 wt% ~ 25 wt% in the production of RTS samples while maintaining their reasonable strength properties.

Lactic acid bacteria as a tool for biovanillin production: A review

Vanilla is the most commonly used natural flavoring agent in industries like food, flavoring, medicine, and fragrance. Vanillin can be obtained naturally, chemically, or through a biotechnological process. However, the yield from vanilla pods is low and does not meet market demand, and the use of vanillin produced by chemical synthesis is restricted in the food and pharmaceutical industries. As a result, the biotechnological process is the most efficient and cost-effective method for producing vanillin with consumer-demanding properties while also supporting industrial applications. Toxin-free biovanillin production, based on renewable sources such as industrial wastes or by-products, is a promising approach. In addition, only natural-labeled vanillin is approved for use in the food industry. Accordingly, this review focuses on biovanillin production from lactic acid bacteria (LAB), which is generally recognized as safe (GRAS), and the cost-cutting efforts that are utilized to improve the efficiency of biotransformation of inexpensive and readily available sources. LABs can utilize agro-wastes rich in ferulic acid to produce ferulic acid, which is then employed in vanillin production via fermentation, and various efforts have been applied to enhance the vanillin titer. However, different designs, such as response surface methods, using immobilized cells or pure enzymes for the spontaneous release of vanillin, are strongly advised.

Fungal feruloyl esterases can catalyze release of diferulic acids from complex arabinoxylan

Feruloyl esterases (FAEs, EC 3.1.1.73) catalyze the hydrolytic cleavage of ester bonds between feruloyl and arabinosyl moieties in arabinoxylans. Recently, we discovered that two bacterial FAEs could catalyze release of diferulic acids (diFAs) from highly substituted, cross-linked corn bran arabinoxylan. Here, we show that several fungal FAEs, notably AnFae1 (Aspergillus niger), AoFae1 (A. oryzae), and MgFae1 (Magnaporthe oryzae (also known as M. grisae)) also catalyze liberation of diFAs from complex arabinoxylan. By comparing the enzyme kinetics of diFA release to feruloyl esterase activity of the enzymes on methyl- and arabinosyl-ferulate substrates we demonstrate that the diFA release activity cannot be predicted from the activity of the enzymes on these synthetic substrates. A detailed structure-function analysis, based on AlphaFold2 modeled enzyme structures and docking with the relevant di-feruloyl ligands, reveal how distinct differences in the active site topology and surroundings may explain the diFA releasing action of the enzymes. Interestingly, the analysis also unveils that the carbohydrate binding module of the MgFae1 may play a key role in the diFA releasing ability of this enzyme. The findings contribute further understanding of the function of FAEs in the deconstruction of complex arabinoxylans and provide new opportunities for enzyme assisted upgrading of complex bran arabinoxylans.

Enhancing the Hydrolysis and Acyl Transfer Activity of Carboxylesterase DLFae4 by a Combinational Mutagenesis and In-Silico Method

In the present study, a feruloyl esterase DLFae4 identified in our previous research was modified by error-prone PCR and site-directed saturation mutation to enhance the catalytic efficiency and acyltransferase activity further. Five mutants with 6.9–118.9% enhanced catalytic activity toward methyl ferulate (MFA) were characterized under the optimum conditions. Double variant DLFae4-m5 exhibited the highest hydrolytic activity (270.97 U/mg), the Km value decreased by 83.91%, and the Kcat/Km value increased by 6.08-fold toward MFA. Molecular docking indicated that a complex hydrogen bond network in DLFae4-m5 was formed, with four of five bond lengths being shortened compared with DLFae4, which might account for the increase in catalytic activity. Acyl transfer activity assay revealed that the activity of DLFae4 was as high as 1550.796 U/mg and enhanced by 375.49% (5823.172 U/mg) toward 4-nitrophenyl acetate when residue Ala-341 was mutated to glycine (A341G), and the corresponding acyl transfer efficiency was increased by 7.7 times, representing the highest acyltransferase activity to date, and demonstrating that the WGG motif was pivotal for the acyltransferase activity in family VIII carboxylesterases. Further experiments indicated that DLFae4 and variant DLFae4 (A341G) could acylate cyanidin-3-O-glucoside effectively in aqueous solution. Taken together, our study suggested the effectiveness of error-prone PCR and site-directed saturation mutation to increase the specific activity of enzymes and may facilitate the practical application of this critical feruloyl esterase.

Bio-separation of value-added products from Kraft lignin: A promising two-stage lignin biorefinery via microbial electrochemical technology

The most ubiquitous aromatic biopolymer in nature, lignin offers a promising foundation for the development of bio-based chemicals with wide-ranging industrial uses attributable to its aromatic structure. Lignin must first be depolymerized into smaller oligomeric and monomeric units at the initial stage of lignin bioconversion, followed by separation to recover valuable products. This study demonstrates an integrative biorefinery idea based on in-situ depolymerization of the lignin via microbial electro-Fenton reaction in a microbial peroxide-producing cell and recovery of the identified products i.e., phenolic or aromatic monomers by one step high throughput chromatography. The yield percentage of acetovanillone, ethylvanillin, and ferulic acid recovered from the depolymerized lignin using the integrative biorefinery strategy were 2.1 %, 9.1 %, and 9.04 %, respectively. These products have diverse industrial usage and can be employed as platform chemicals. The development of a novel system for efficient simultaneous lignin depolymerization and subsequent quality separation are demonstrated in this study.

Crystal structure of the feruloyl esterase from Lentilactobacillus buchneri reveals a novel homodimeric state

Ferulic acid is a common constituent of the plant cell-wall matrix where it decorates and can crosslink mainly arabinoxylans to provide structural reinforcement. Microbial feruloyl esterases (FAEs) specialize in catalyzing hydrolysis of the ester bonds between phenolic acids and sugar residues in plant cell-wall polysaccharides such as arabinoxylan to release cinnamoyl compounds. Feruloyl esterases from lactic acid bacteria (LAB) have been highlighted as interesting enzymes for their potential applications in the food and pharmaceutical industries; however, there are few studies on the activity and structure of FAEs of LAB origin. Here, we report the crystal structure and biochemical characterization of a feruloyl esterase (LbFAE) from Lentilactobacillus buchneri, a LAB strain that has been used as a silage additive. The LbFAE structure was determined in the absence and presence of product (FA) and reveals a new type of homodimer association not previously observed for fungal or bacterial FAEs. The two subunits associate to restrict access to the active site such that only single FA chains attached to arabinoxylan can be accommodated, an arrangement that excludes access to FA cross-links between arabinoxylan chains. This narrow specificity is further corroborated by the observation that no FA dimers are produced, only FA, when feruloylated arabinoxylan is used as substrate. Docking of arabinofuranosyl-ferulate in the LbFAE structure highlights the restricted active site and lends further support to our hypothesis that LbFAE is specific for single FA side chains in arabinoxylan.

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.

Valorization of agro-food wastes: Ease of concomitant-enzymes production with application in food and biofuel industries

The novel and greener approach toward the co-production of hydrolytic enzymes in a single-cultivation medium with inexpensive substrates can bring down the production costs. Likewise, the natural and industrial organic biomass/solid are all nutritionally rich substrates waiting for free use in industries such as food, biofuel, etc. Valorization must broaden its applications in industries and households with a step towards a sustainable environment. The biofuel approach can be projected as one of the most promising deputations to meet future energy demands, in reduction of the environmental pollution due to excessive fossil fuel consumption. The present review highlights the multifaceted stature of microbial enzymes in this direction and possible implications mainly in the food industry and biofuel with the global impact of similar bio-based industries. In this review, design scale-up, fermentation cost, energy needs,and agro-food waste management have been meticulously delineated.

Biochemical characterization of an engineered bifunctional xylanase/feruloyl esterase and its synergistic effects with cellulase on lignocellulose hydrolysis

Herein, the xylanase and feruloyl esterase domains of the xylanase/feruloyl esterase bifunctional enzyme (Xyn-Fae) from Prevotella ruminicola 23 were identified using N- and C-terminal truncation mutagenesis. In addition, a novel and more efficient xylanase/feruloyl esterase bifunctional enzyme XynII-Fae was constructed, and its synergistic action with a commercial cellulase for lignocellulose hydrolysis was studied. When 40% cellulase was replaced by XynII-Fae, the production of reducing sugars increased by 65% than that with the cellulase alone, and the conversions of xylan and glucan were increased by 125.1% and 54.3%, respectively. When 80% cellulase was substituted by XynII-Fae, up to 43.5 μg/mL ferulic acid and 418.7 μg/mL acetic acid were obtained. The XynII-Fae could also accelerate the hydrolysis of wheat straw and sugarcane bagasse with commercial cellulase. These results indicated that the synergistic action of XynII-Fae with cellulase could dramatically improve the hydrolysis efficiency of lignocellulose, showing the great potential for industrial applications.

Engineering the Active Site Pocket to Enhance the Catalytic Efficiency of a Novel Feruloyl Esterase Derived From Human Intestinal Bacteria Dorea formicigenerans

The human gut microbiota play essential roles in metabolism and human health, especially by enzymatically utilizing dietary fiber that the host cannot directly digest and releasing functional components including short-chain fatty acids (SCFAs) and hydroxycinnamic acids (e.g., ferulic acid). In our previous study, seven potential feruloyl esterase (FAE) genes were identified from the gut microbiota. In the current work, one of the genes encoding a novel FAE (DfFAE) from Dorea formicigenerans of Firmicutes was bacterially expressed, purified and characterized. The 30.5 kDa type-A DfFAE has an optimum pH and temperature of 8.4 and 40 °C, respectively, exhibiting a higher substrate specificity toward short-chain acyl-ester substrate (pNPA). The AlphaFold2 based ab initio structural modeling revealed a five α-helices cap domain that shaped an unusually narrow and deep active site pocket containing a specific substrate access tunnel in DfFAE. Furthermore, rational design strategy was subjected to the active site pocket in an aim of improving its enzymatic activities. The mutants V252A, N156A, W255A, P149A, and P186A showed 1.8 to 5.7-fold increase in catalytic efficiency toward pNPA, while W255A also exhibited altered substrate preference toward long-chain substrate pNPO (45.5-fold). This study highlighted an unusual active site architecture in DfFAE that influenced its substrate selectivity and illustrated the applicability of rational design for enhanced enzymatic properties.

Phthalate hydrolase: distribution, diversity and molecular evolution

The alpha/beta-fold superfamily of hydrolases is rapidly becoming one of the largest groups of structurally related enzymes with diverse catalytic functions. In this superfamily of enzymes, esterase deserves special attention because of their wide distribution in biological systems and importance towards environmental and industrial applications. Among various esterases, phthalate hydrolases are the key alpha/beta enzymes involved in the metabolism of structurally diverse estrogenic phthalic acid esters, ubiquitously distributed synthetic chemicals, used as plasticizer in plastic manufacturing processes. Although they vary both at the sequence and functional levels, these hydrolases use a similar acid-base-nucleophile catalytic mechanism to catalyse reactions on structurally different substrates. The current review attempts to present insights on phthalate hydrolases, describing their sources, structural diversities, phylogenetic affiliations and catalytically different types or classes of enzymes, categorized as diesterase, monoesterase and diesterase-monoesterase, capable of hydrolysing phthalate diester, phthalate monoester and both respectively. Furthermore, available information on in silico analyses and site-directed mutagenesis studies revealing structure-function integrity and altered enzyme kinetics have been highlighted along with the possible scenario of their evolution at the molecular level.

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.

Characteration of a novel arylesterase from probiotics Lacticaseibacillus rhamnosus GG with the preference for medium- and long-chain p-Nitrophenyl esters

We prospected a novel arylesterase LggEst from the probiotics Lacticaseibacillus rhamnosus GG by genome mining strategy, and characterized the enzymatic properties in detail. Biochemical characterization revealed that arylesterase LggEst presented high activity at a wide range of temperatures from 25 to 65 °C with maximum activity at 50 °C. LggEst maintained high activity in the pH range from 5.5 to 7.5 with optimum pH of 6.5. LggEst might efficiently hydrolyze a series of aryl substrates p-nitrophenyl esters with different acyl chain lengths. LggEst displayed the V_max from 2.8 to 77.3 μmol min^-1 mg^-1 protein and the k _cat from 1.8 to 48.8 s^-1 with the highest catalytic activity on pNPC6. The K _M of LggEst on different substrates varied significantly from 4.9 μM to 5.6 mM with the highest affinity on pNPC10. LggEst exhibited the preference for medium- and long-chain p-nitrophenyl esters. LggEst showed remarkable thermostability at 45 °C. LggEst could be tolerant of several organic solvents at the concentration of 10% and DMSO and methanol at the concentration of 20%. Catalytic activity of LggEst was improved by 12% in the presence of 20% ethylene glycol. LggEst was resistant to high concentrations of sodium citrate and sodium chloride. Notably, enzymatic activity of LggEst was significantly enhanced in the presence of 0.1% sodium deoxycholate at high temperatures.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03053-7.

Rational Design for Broadened Substrate Specificity and Enhanced Activity of a Novel Acetyl Xylan Esterase from Bacteroides thetaiotaomicron

Gut bacteria-derived enzymes play important roles in the metabolism of dietary fiber through enabling the hydrolysis of polysaccharides. In this study, we identified and characterized a 29 kDa novel acetyl xylan esterase, BTAxe1, from Bacteroides thetaiotaomicron VPI5482. Then, we solved the structure of BTAxe1 and performed the rational design. Mutants N65S and N65A increased the activities toward short-chain (pNPA, pNPB) to near four-fold, and gained the activities toward longer-chain substrate (pNPO). Molecular docking analysis showed that the mutant N65S had a larger substrate binding pocket than the wild type. Hydrolysis studies using natural substrates showed that either N65S or N65A showed higher activity of that of wild-type, yielding 131.31 and 136.09 mM of acetic acid from xylan. This is the first study on the rational design of gut bacteria-derived Axes with broadened substrate specificity and enhanced activity, which can be referenced by other acetyl esterases or gut-derived enzymes.