Isolation and characterization of a ferulic acid esterase (Fae1A) from the rumen fungus Anaeromyces mucronatus

Structural insights into the molecular mechanisms of substrate recognition and hydrolysis by feruloyl esterase from Aspergillus sydowii

The depolymerization of lignocellulosic biomass is facilitated by feruloyl esterases (FAEs), which hydrolyze ester bonds between lignin and polysaccharides. Fungal FAEs belonging to subfamily (SF) 6 release precursors such as ferulic acid derivatives, attractive for biochemical production. Among these, Aspergillus sydowii FAE (AsFaeE), an SF6 FAE, exhibits remarkable activity across various substrates. In this study, we conducted X-ray crystallography and kinetic analysis to unravel the molecular mechanisms governing substrate recognition and catalysis by AsFaeE. AsFaeE exhibits a typical α/β-hydrolase fold, characterized by a catalytic triad of serine, aspartate, and histidine. Comparative analysis of substrate-free, ferulic acid-bound, and sinapic acid-bound forms of AsFaeE suggests a conformational change in the loop covering the substrate-binding pocket upon binding. Notably, Pro158 and Phe159 within this loop cover the phenolic part of the substrate, forming three layers of planar rings. Our structure-based functional mutagenesis clarifies the roles of the residues involved in substrate binding and catalytic activity. Furthermore, distinct substrate-binding mechanisms between AsFaeE and other studied FAEs are identified. This investigation offers the initial structural insights into substrate recognition by SF6 FAEs, equipping us with structural knowledge that might facilitate the design of FAE variants capable of efficiently processing a wider range of substrate sizes.

Lignin deconstruction by anaerobic fungi

Lignocellulose forms plant cell walls, and its three constituent polymers, cellulose, hemicellulose and lignin, represent the largest renewable organic carbon pool in the terrestrial biosphere. Insights into biological lignocellulose deconstruction inform understandings of global carbon sequestration dynamics and provide inspiration for biotechnologies seeking to address the current climate crisis by producing renewable chemicals from plant biomass. Organisms in diverse environments disassemble lignocellulose, and carbohydrate degradation processes are well defined, but biological lignin deconstruction is described only in aerobic systems. It is currently unclear whether anaerobic lignin deconstruction is impossible because of biochemical constraints or, alternatively, has not yet been measured. We applied whole cell-wall nuclear magnetic resonance, gel-permeation chromatography and transcriptome sequencing to interrogate the apparent paradox that anaerobic fungi (Neocallimastigomycetes), well-documented lignocellulose degradation specialists, are unable to modify lignin. We find that Neocallimastigomycetes anaerobically break chemical bonds in grass and hardwood lignins, and we further associate upregulated gene products with the observed lignocellulose deconstruction. These findings alter perceptions of lignin deconstruction by anaerobes and provide opportunities to advance decarbonization biotechnologies that depend on depolymerizing lignocellulose.

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.

Carbohydrate active enzyme system in rumen fungi: a review

Hydrolysis and dehydration reactions of carbohydrates, which are used as energy raw materials by all living things in nature, are controlled by Carbohydrate Active Enzyme (CAZy) systems. These enzymes are also used in different industrial areas today. There are different types of microorganisms that have the CAZy system and are used in the industrial sector. Apart from current organisms, there are also rumen fungi within the group of candidate microorganisms with the CAZy system. It has been reported that xylanase (EC3.2.1.8 and EC3.2.1.37) enzyme, a member of the glycoside hydrolase enzyme family obtained from Trichoderma sp. and used especially in areas such as bread, paper, and feed industry, is more synthesized in rumen fungi such as Orpinomyces sp. and Neocallimastix sp. Therefore, this study reviews Neocallimastixsp., Orpinomyces sp., Caecomyces sp., Piromyces sp., and Anaeromyces sp., registered in the CAZy and Mycocosm database for rumen fungi to have both CAZy enzyme activity and to be an alternative microorganism in the industry. Furthermore the CAZy enzyme activities of the strains are investigated. The review shows thatNeocallimax sp. and Orpinomyces sp. areconsidered as candidate microorganisms.

The release and catabolism of ferulic acid in plant cell wall by rumen microbes: A review

Ferulic acid (FA) is one of the most abundant hydroxycinnamic acids in the plant world, especially in the cell wall of grain bran, in comparison with forage and crop residues. Previous studies noted that FA was mainly linked with arabinoxylans and lignin in plant cell walls in ester and ether covalent forms. After forages were ingested by ruminant animals or encountered rumen microbial fermentation in vitro, these cross-linkages form physical and chemical barriers to protect cell-wall carbohydrates from microbial attack and enzymatic hydrolysis. Additionally, increasing studies noted that FA presented some toxic effect on microbial growth in the rumen. In recent decades, many studies have addressed the relationships of ester and/or ether-linked FA with rumen nutrient digestibility, and there is still some controversy whether these linkages could be used as a predicator of forage digestibility in ruminants. The authors in this review summarized the possible relationships between ester and/or ether-linked FA and fiber digestion in ruminants. Rumen microbes, especially bacteria and fungi, were found capable of breaking down the ester linkages within plant cell walls by secreting feruloyl and p-coumaroyl esterase, resulting in the release of free FA and improvement of cell wall digestibility. The increasing evidence noted that these esterases secreted by rumen microbes presented synergistic effects with xylanase and cellulase to effectively hydrolyze forage cell walls. Some released FA were absorbed through the rumen wall directly and entered into blood circulation and presented antioxidant effects on host animals. The others were partially catabolized into volatile fatty acids by rumen microbes, and the possible catabolic pathways discussed. To better understand plant cell wall degradation in the rumen, the metabolic fate of FA along with lignin decomposition mechanisms are needed to be explored via future microbial isolation and incubation studies with aims to maximize dietary fiber intake and enhance fiber digestion in ruminant animals.

Decoding the roles of extremophilic microbes in the anaerobic environments: Past, Present, and Future

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The inaccessible extreme environments harbor a large majority of anaerobic microbes which remain unknown.

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Anaerobic microbes are used in a variety of industrial applications.

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In the future, metagenomic-assisted techniques can be used to identify novel anaerobic microbes from the unexplored extreme environments.

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Genetic engineering can be used to enhance the efficiency of anaerobic microbes for various processes.

The genome of an organism is directly or indirectly correlated with its environment. Consequently, different microbes have evolved to survive and sustain themselves in a variety of environments, including unusual anaerobic environments. It is believed that their genetic material could have played an important role in the early evolution of their existence in the past. Presently, out of the uncountable number of microbes found in different ecosystems we have been able to discover only one percent of the total communities. A large majority of the microbial populations exists in the most unusual and extreme environments. For instance, many anaerobic bacteria are found in the gastrointestinal tract of humans, soil, and hydrothermal vents. The recent advancements in Metagenomics and Next Generation Sequencing technologies have improved the understanding of their roles in these environments. Presently, anaerobic bacteria are used in various industries associated with biofuels, fermentation, production of enzymes, vaccines, vitamins, and dairy products. This broad applicability brings focus to the significant contribution of their genomes in these functions. Although the anaerobic microbes have become an irreplaceable component of our lives, a major and important section of such anaerobic microbes still remain unexplored. Therefore, it can be said that unlocking the role of the microbial genomes of the anaerobes can be a noteworthy discovery not just for mankind but for the entire biosystem as well.

Isolation, purification and characterization of a novel esterase from camel rumen metagenome

Bacterial esterases are gaining the importance in pharmaceuticals and agrochemical industries due to their excellent biocatalytic properties and a wide range of applications. In the present study, a novel gene encoding an esterase (designated as Est-CR) was identified from shotgun metagenomic sequencing data of camel rumen (Camelus dromedarius) liquor. The open reading frame consisted of 1,224bp, which showed 84.03% sequence identity to Bacteroidales bacterium, corresponding to a protein of 407 amino acids and has a catalytic domain belonging to an esterase. Est-CR belonged to family V with GLSMG domain. The purified enzyme with a molecular mass of 62.64 kDa was checked on SDS-PAGE, and its expression was confirmed by western blotting. The enzyme was active and stable over a broad range of temperature (35-65 °C), displayed the maximum activity at 50 °C and pH 7.0. Individually all metal ions inhibited the enzyme activity, while in combination, K²⁺, Ca²⁺, Mg²⁺ and Mn²⁺ metal ions enhanced the enzyme activity. The detergents strongly inhibited the activity, while EDTA (10 mM) increased the activity of the Est-CR enzyme. The enzyme showed specificity to short-chain substrates and displayed an optimum activity against butyrate ester. This novel enzyme might serve as a promising candidate to meet some harsh industrial processes enzymatic needs.

Polysaccharide utilization loci-driven enzyme discovery reveals BD-FAE: a bifunctional feruloyl and acetyl xylan esterase active on complex natural xylans

BACKGROUND

Nowadays there is a strong trend towards a circular economy using lignocellulosic biowaste for the production of biofuels and other bio-based products. The use of enzymes at several stages of the production process (e.g., saccharification) can offer a sustainable route due to avoidance of harsh chemicals and high temperatures. For novel enzyme discovery, physically linked gene clusters targeting carbohydrate degradation in bacteria, polysaccharide utilization loci (PULs), are recognized 'treasure troves' in the era of exponentially growing numbers of sequenced genomes.

RESULTS

We determined the biochemical properties and structure of a protein of unknown function (PUF) encoded within PULs of metagenomes from beaver droppings and moose rumen enriched on poplar hydrolysate. The corresponding novel bifunctional carbohydrate esterase (CE), now named BD-FAE, displayed feruloyl esterase (FAE) and acetyl esterase activity on simple, synthetic substrates. Whereas acetyl xylan esterase (AcXE) activity was detected on acetylated glucuronoxylan from birchwood, only FAE activity was observed on acetylated and feruloylated xylooligosaccharides from corn fiber. The genomic contexts of 200 homologs of BD-FAE revealed that the 33 closest homologs appear in PULs likely involved in xylan breakdown, while the more distant homologs were found either in alginate-targeting PULs or else outside PUL contexts. Although the BD-FAE structure adopts a typical α/β-hydrolase fold with a catalytic triad (Ser-Asp-His), it is distinct from other biochemically characterized CEs.

CONCLUSIONS

The bifunctional CE, BD-FAE, represents a new candidate for biomass processing given its capacity to remove ferulic acid and acetic acid from natural corn and birchwood xylan substrates, respectively. Its detailed biochemical characterization and solved crystal structure add to the toolbox of enzymes for biomass valorization as well as structural information to inform the classification of new CEs.

A novel esterase from a soil metagenomic library displaying a broad substrate range

A novel esterase gene was isolated from a soil metagenomic library. The gene encoded a protein of 520 amino acids which contained a 21 aa signal peptide. Primary structure analysis of the protein sequence revealed that it contained a conserved active site motif (SxSxG) and a structural motif (CS-D-HC). Then the esterase gene was cloned and expressed in Escherichia coli BL21(DE3). SDS-PAGE analysis of the purified esterase showed that it was expressed in a highly soluble form and its molecular mass was estimated to be 55 kDa. Characterization of the esterase revealed that it exhibited high activity toward p-nitrophenyl esters with short acyl chains and especially p-nitrophenyl acetate, suggesting that it was a typical carboxylesterase rather than a lipase. With p-nitrophenyl acetate as substrate, the enzyme showed its optimal activity at pH 7.0 and 30 °C, and it was stable at a broad pH range from 4.5 to 10.0 and temperature not higher than 50 °C. Furthermore, the enzyme showed different substrate specificity from known esterase, it was not only hydrolyzing against p-nitrophenyl esters, but also hydrolyzing all hydroxybenzoic esters and hydroxycinnamic ester assayed. As it was an enzyme active on a broad range of phenolic esters, simultaneously possessing feruloyl esterase, chlorogenate esterase and tannase activities, it could serve as a valuable candidate for applications in biotechnology.

Nucleotide and protein researches on anaerobic fungi during four decades

Anaerobic fungi habitat in the gastrointestinal tract of foregut fermenters or hindgut fermenters and degrade fibrous plant biomass through the hydrolysis reactions with a wide variety of cellulolytic enzymes and physical penetration through fiber matrix with their rhizoids. To date, seventeen genera have been described in family Neocallimasticaceae, class Neocallimastigomycetes, phylum Neocallimastigomycota and one genus has been described in phylum Neocallimastigomycota. In National Center for Biotechnology Information (NCBI) database (DB), 23,830 nucleotide sequences and 59,512 protein sequences have been deposited and most of them were originated from Piromyces, Neocallimastix and Anaeromyces. Most of protein sequences (44,025) were acquired with PacBio next generation sequencing system. The whole genome sequences of Anaeromyces robustus, Neocallimastix californiae, Pecoramyces ruminantium, Piromyces finnis and Piromyces sp. E2 are available in Joint Genome Institute (JGI) database. According to the results of protein prediction, average Isoelectric points (pIs) were ranged from 5.88 (Anaeromyces) to 6.57 (Piromyces) and average molecular weights were ranged from 38.7 kDa (Orpinomyces) to 56.6 kDa (Piromyces). In Carbohydrate-Active enZYmes (CAZY) database, glycoside hydrolases (36), carbohydrate binding module (11), carbohydrate esterases (8), glycosyltransferase (5) and polysaccharide lyases (3) from anaerobic fungi were registered. During four decades, 1,031 research articles about anaerobic fungi were published and 444 and 719 articles were available in PubMed (PM) and PubMed Central (PMC) DB.

Efficient ferulic acid and xylo-oligosaccharides production by a novel multi-modular bifunctional xylanase/feruloyl esterase using agricultural residues as substrates

Liberating high value-added compounds ferulic acid (FA) and xylo-oligosaccharides (XOSs) from agricultural residues is a promising strategy for the utilization of lignocellulose. In this study, a bifunctional xylanase/feruloyl esterase from bacterial consortium EMSD5 was heterogeneously expressed in Escherichia coli. Depending on the inter-domain synergism of the recombinant enzyme rXyn10A/Fae1A, high yields of FA (2.78, 1.82, 1.15 and 7.31 mg/g substrate, respectively) were obtained from 20 mg in-soluble wheat arabinoxylan, de-starched wheat bran, ultrafine-grinding corn stover and steam-exploded corncob. Meanwhile, 3.210, 1.235, 1.215 and 0.823 mg xylose/XOSs were also released. For cost-saving enzyme production, we firstly constructed a recombinant E. coli, which could secrete the bifunctional xylanase/feruloyl esterase out of cells. When the recombinant E. coli was cultured in medium containing 200 mg de-starched wheat bran, 474 μg FA and 18.2 mg xylose/XOSs were also detected. Hence, rXyn10A/Fae1A and the recombinant strain showed great applied potential for FA and XOSs production.

Characterization of feruloyl esterases in maize pollen

Ferulic acid esterases have been identified and partially purified from maize pollen. Results suggest that maize pollen FAEs may play an important role in pollen fertilization. A critical step in maize (Zea mays) seed production involves fertilization of the ovule by pollen, a process that relies on ability of the pollen tube to grow through the highly structured and feruloylated arabinoxylan/cellulose-rich tissue of the silk and stigma. It is known that different cell wall hydrolases are present on the surface of pollen. An important hydrolase reported to date is an endo-xylanase (ZmXYN1). We report presence and characterization of another hydrolase, ferulic acid esterase (FAE), in maize pollen. Using a combination of biochemical approaches, these FAEs were partially purified and characterized with respect to their biochemical properties and putative sequences. Maize pollen FAEs were shown to be expressed early during pollen development, to release significant amounts of both monomeric and dimeric ferulates esterified from maize silks and other grass cell walls, and to synergize with an externally applied fungal endo-1,4-β-xylanase on the release of cell wall ferulates and diferulates. Preliminary analysis of maize silk cell walls following pollination, showed a significant reduction of esterified ferulates up to 96 h following pollination, compared to unpollinated silks. These results suggest that maize pollen FAEs may play an important biological role in pollen fertilization and possibly in seed production.

Characterization of Acetylxylan Esterase from White-Rot Fungus Irpex lacteus

The carbohydrate esterase family 1 (CE1) in CAZy contains acetylxylan esterases (AXEs) and feruloyl esterases (FAEs). Here we cloned a gene coding for an AXE belonging to CE1 from Irpex lacteus (IlAXE1). IlAXE1 was heterologously expressed in Pichia pastoris, and the recombinant enzyme was purified and characterized. IlAXE1 hydrolyzed p-nitrophenyl acetate, α-naphthyl acetate and 4-methylumbelliferyl acetate, however, it did not show any activity on ethyl ferulate and methyl p-coumarate. We also examined the activity on partially acetylated and feruloylated xylan extracted from corncob by hydrothermal reaction. Similarly, ferulic and p-coumaric acids were not liberated, and acetic acid was only detected in the reaction mixture. The results indicated that IlAXE1 is an acetylxylan esterase actually reacted to acetyl xylan. However, since IlAXE1 was unable to completely release acetic acid esterifying xylopyranosyl residues, it is assumed that acetyl groups exhibiting resistance to deacetylation by IlAXE1 are present in corn cob xylan.

Metatranscriptomics reveals mycoviral populations in the ovine rumen

The rumen is known to contain DNA-based viruses, although it is not known whether RNA-based viruses that infect fungi (mycoviruses) are also present. Analysis of publicly available rumen metatranscriptome sequence data from sheep rumen samples (n = 20) was used to assess whether RNA-based viruses exist within the ovine rumen. A total of 2466 unique RNA viral contigs were identified that had homology to nine viral families. The Partitiviridae was the most consistently observed mycoviral family. High variation in the abundance of each detected mycovirus suggests that rumen mycoviral populations vary greatly between individual sheep. Functional analysis of the genes within the assembled mycoviral contigs suggests that the mycoviruses detected had simple genomes, often only carrying the machinery required for replication. The fungal population of the ovine rumen was also assessed using metagenomics data from the same samples, and was consistently dominated by the phyla Ascomycota and Basidomycota. The strictly anaerobic phyla Neocallimastigomycota were also present in all samples but at a low abundance. This preliminary investigation has provided clear evidence that mycoviruses with RNA genomes exist in the rumen, with further in-depth studies now required to characterise this mycoviral community and determine its role in the rumen.

Carbohydrate Esterases: An Overview

Carbohydrate esterases are a group of enzymes which release acyl or alkyl groups attached by ester linkage to carbohydrates. The CAZy database, which classifies enzymes that assemble, modify, and break down carbohydrates and glycoconjugates, classifies all carbohydrate esterases into 16 families. This chapter is an overview of the research for nearly 50 years around the main groups of carbohydrate esterases dealing with the degradation of polysaccharides, their main biochemical and molecular traits, as well as its application for the synthesis of high added value esters.

Thermotolerant hemicellulolytic and cellulolytic enzymes from Eupenicillium parvum 4-14 display high efficiency upon release of ferulic acid from wheat bran

AIMS

To characterize the hemicellulolytic and cellulolytic enzymes from novel fungi, and evaluate the potential of novel enzyme system in releasing ferulic acid (FA) from biomass resource.

METHODS AND RESULTS

A hemicellulolytic and cellulolytic enzyme-producing fungus 4-14 was isolated from soil by Congo red staining method, and identified as Eupenicillium parvum based on the morphologic and molecular phylogenetic analysis. The optimum temperature of fungal growth was 37°C. Hemicellulolytic and cellulolytic enzymes were produced by this fungus in solid-state fermentation (SSF), and their maximum activities were 554, 385, 218, 2·62 and 5·25 U g(-1) for CMCase, xylanase, β-glucosidase, FPase and FAE respectively. These enzymes displayed the best catalytic ability at low pH values (pH 4·5-5·0). The optimum temperatures were 70°C, 70°C, 75°C and 55°C for CMCase, β-glucosidase, xylanase and FAE respectively. CMCase, xylanase and FAE were stable at different pHs or high temperature (60°C). Enzymatic hydrolysis experiment indicated that the maximum (76·8 ± 4)% of total alkali-extractable FA was released from de-starched wheat bran by the fungal enzyme system.

CONCLUSIONS

High activities of thermotolerant CMCase, β-glucosidase, xylanase and FAE were produced by the newly isolated fungus E. parvum 4-14 in SSF. The fungal enzyme system displayed high efficiency at releasing FA from wheat bran.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides a new fungal strain for researches of novel hemicellulolytic and cellulolytic enzymes and will improve the bioconversion and utilization of agricultural by-products.

Contributions of a unique β-clamp to substrate recognition illuminates the molecular basis of exolysis in ferulic acid esterases

Lignocellulosic biomass is a promising renewable resource; however, deconstruction of this material is still the rate-limiting step. Major obstacles in the biocatalytic turnover of lignocellulose are ester-linked decorations that prevent access to primary structural polysaccharides. Enzymes targeting these esters represent promising biotools for increasing bioconversion efficiency. Ruminant livestock are unique in their ability to degrade lignocellulose through the action of their gut microbiome. The anaerobic fungi (phylum Neocallimastigomycota) are key members of this ecosystem that express a large repertoire of carbohydrate-active enzymes (CAZymes) with little sequence identity with characterized CAZymes [Lombard, Golaconda, Drula, Coutinho and Henrissat (2014) Nucleic Acids Res. 42: , D490-D495]. We have identified a carbohydrate esterase family 1 (CE1) ferulic acid esterase (FAE) belonging to Anaeromyces mucronatus(AmCE1/Fae1a), and determined its X-ray structure in both the presence [1.55 Å (1 Å=0.1 nm)] and absence (1.60 Å) of ferulic acid. AmCE1 adopts an α/β-hydrolase fold that is structurally conserved with bacterial FAEs, and possesses a unique loop, termed the β-clamp, that encloses the ligand. Isothermal titration calorimetry reveals that substrate binding is driven by enthalpic contributions, which overcomes a large entropic penalty. A comparative analysis of AmCE1 with related enzymes has uncovered the apparent structural basis for differential FAE activities targeting cross-linking ferulic acid conjugates compared with terminal decorations. Based on comparisons to structurally characterized FAEs, we propose that the β-clamp may define the structural basis of exolytic activities in FAEs. This provides a structure-based tool for predicting exolysis and endolysis in CE1. These insights hold promise for rationally identifying enzymes tailored for bioconversion of biomass with variations in cell wall composition.

Diversity of fungal feruloyl esterases: updated phylogenetic classification, properties, and industrial applications

Feruloyl esterases (FAEs) represent a diverse group of carboxyl esterases that specifically catalyze the hydrolysis of ester bonds between ferulic (hydroxycinnamic) acid and plant cell wall polysaccharides. Therefore, FAEs act as accessory enzymes to assist xylanolytic and pectinolytic enzymes in gaining access to their site of action during biomass conversion. Their ability to release ferulic acid and other hydroxycinnamic acids from plant biomass makes FAEs potential biocatalysts in a wide variety of applications such as in biofuel, food and feed, pulp and paper, cosmetics, and pharmaceutical industries. This review provides an updated overview of the knowledge on fungal FAEs, in particular describing their role in plant biomass degradation, diversity of their biochemical properties and substrate specificities, their regulation and conditions needed for their induction. Furthermore, the discovery of new FAEs using genome mining and phylogenetic analysis of current publicly accessible fungal genomes will also be presented. This has led to a new subfamily classification of fungal FAEs that takes into account both phylogeny and substrate specificity.

Review on technological and scientific aspects of feruloyl esterases: A versatile enzyme for biorefining of biomass

With increasing focus on sustainable energy, bio-refining from lignocellulosic biomass has become a thrust area of research. With most of the works being focused on biofuels, significant efforts are also being directed towards other value added products. Feruloyl esterases (EC. 3.1.1.73) can be used as a tool for bio-refining of lignocellulosic material for the recovery and purification of ferulic acid and related hydroxycinnamic acids ubiquitously found in the plant cell wall. More and more genes coding for feruloyl esterases have been mined out from various sources to allow efficient enzymatic release of ferulic acid and allied hydroxycinnamic acids (HCAs) from plant-based biomass. A sum up on enzymatic extraction of HCAs and its recovery from less explored agro residual by-products is still a missing link and this review brushes up the achieved landmarks so far in this direction and also covers a detailed patent search on this biomass refining enzyme.

A chlorogenic acid esterase with a unique substrate specificity from Ustilago maydis

An extracellular chlorogenic acid esterase from Ustilago maydis (UmChlE) was purified to homogeneity by using three separation steps, including anion-exchange chromatography on a Q Sepharose FF column, preparative isoelectric focusing (IEF), and, finally, a combination of affinity chromatography and hydrophobic interaction chromatography on polyamide. SDS-PAGE analysis suggested a monomeric protein of ∼71 kDa. The purified enzyme showed maximal activity at pH 7.5 and at 37°C and was active over a wide pH range (3.5 to 9.5). Previously described chlorogenic acid esterases exhibited a comparable affinity for chlorogenic acid, but the enzyme from Ustilago was also active on typical feruloyl esterase substrates. Kinetic constants for chlorogenic acid, methyl p-coumarate, methyl caffeate, and methyl ferulate were as follows: Km values of 19.6 μM, 64.1 μM, 72.5 μM, and 101.8 μM, respectively, and kcat/Km values of 25.83 mM(-1) s(-1), 7.63 mM(-1) s(-1), 3.83 mM(-1) s(-1) and 3.75 mM(-1) s(-1), respectively. UmChlE released ferulic, p-coumaric, and caffeic acids from natural substrates such as destarched wheat bran (DSWB) and coffee pulp (CP), confirming activity on complex plant biomass. The full-length gene encoding UmChlE consisted of 1,758 bp, corresponding to a protein of 585 amino acids, and was functionally produced in Pichia pastoris GS115. Sequence alignments with annotated chlorogenic acid and feruloyl esterases underlined the uniqueness of this enzyme.

Formulation of enzyme blends to maximize the hydrolysis of alkaline peroxide pretreated alfalfa hay and barley straw by rumen enzymes and commercial cellulases

BACKGROUND

Efficient conversion of lignocellulosic biomass to fermentable sugars requires the synergistic action of multiple enzymes; consequently enzyme mixtures must be properly formulated for effective hydrolysis. The nature of an optimal enzyme blends depends on the type of pretreatment employed as well the characteristics of the substrate. In this study, statistical experimental design was used to develop mixtures of recombinant glycosyl hydrolases from thermophilic and anaerobic fungi that enhanced the digestion of alkaline peroxide treated alfalfa hay and barley straw by mixed rumen enzymes as well as commercial cellulases (Accelerase 1500, A1500; Accelerase XC, AXC).

RESULTS

Combinations of feruloyl and acetyl xylan esterases (FAE1a; AXE16A_ASPNG), endoglucanase GH7 (EGL7A_THITE) and polygalacturonase (PGA28A_ASPNG) with rumen enzymes improved straw digestion. Inclusion of pectinase (PGA28A_ASPNG), endoxylanase (XYN11A_THITE), feruloyl esterase (FAE1a) and β-glucosidase (E-BGLUC) with A1500 or endoglucanase GH7 (EGL7A_THITE) and β-xylosidase (E-BXSRB) with AXC increased glucose release from alfalfa hay. Glucose yield from straw was improved when FAE1a and endoglucanase GH7 (EGL7A_THITE) were added to A1500, while FAE1a and AXE16A_ASPNG enhanced the activity of AXC on straw. Xylose release from alfalfa hay was augmented by supplementing A1500 with E-BGLUC, or AXC with EGL7A_THITE and XYN11A_THITE. Adding arabinofuranosidase (ABF54B_ASPNG) and esterases (AXE16A_ASPNG; AXE16B_ASPNG) to A1500, or FAE1a and AXE16A_ASPNG to AXC enhanced xylose release from barley straw, a response confirmed in a scaled up assay.

CONCLUSION

The efficacy of commercial enzyme mixtures as well as mixed enzymes from the rumen was improved through formulation with synergetic recombinant enzymes. This approach reliably identified supplemental enzymes that enhanced sugar release from alkaline pretreated alfalfa hay and barley straw.

A halotolerant type A feruloyl esterase from Pleurotus eryngii

An extracellular feruloyl esterase (PeFaeA) from the culture supernatant of Pleurotus eryngii was purified to homogeneity using cation exchange, hydrophobic interaction, and size exclusion chromatography. The length of the complete coding sequence of PeFaeA was determined to 1668 bp corresponding to a protein of 555 amino acids. The catalytic triad of Ser-Glu-His demonstrated the uniqueness of the enzyme compared to previously published FAEs. The purified PeFaeA was a monomer with an estimated molecular mass of 67 kDa. Maximum feruloyl esterase (FAE) activity was observed at pH 5.0 and 50 °C, respectively. Metal ions (5 mM), except Hg(2+), had no significant influence on the enzyme activity. Substrate specificity profiling characterized the enzyme as a type A FAE preferring bulky natural substrates, such as feruloylated saccharides, rather than small synthetic ones. Km and kcat of the purified enzyme for methyl ferulate were 0.15 mM and 0.85 s(-1). In the presence of 3 M NaCl activity of the enzyme increased by 28 %. PeFaeA alone released only little ferulic acid from destarched wheat bran (DSWB), whereas after addition of Trichoderma viride xylanase the concentration increased more than 20 fold.

The production and characterization of a new active lipase from Acremonium alcalophilum using a plant bioreactor

BACKGROUND

Microorganisms are the most proficient decomposers in nature, using secreted enzymes in the hydrolysis of lignocellulose. As such, they present the most abundant source for discovery of new enzymes. Acremonium alcalophilum is the only known cellulolytic fungus that thrives in alkaline conditions and can be cultured readily in the laboratory. Its optimal conditions for growth are 30°C and pH 9.0-9.2. The genome sequence of Acremonium alcalophilum has revealed a large number of genes encoding biomass-degrading enzymes. Among these enzymes, lipases are interesting because of several industrial applications including biofuels, detergent, food processing and textile industries.

RESULTS

We identified a lipA gene in the genome sequence of Acremonium alcalophilum, encoding a protein with a predicted lipase domain with weak sequence identity to characterized enzymes. Unusually, the predicted lipase displays ≈ 30% amino acid sequence identity to both feruloyl esterase and lipase of Aspergillus niger. LipA, when transiently produced in Nicotiana benthamiana, accumulated to over 9% of total soluble protein. Plant-produced recombinant LipA is active towards p-nitrophenol esters of various carbon chain lengths with peak activity on medium-chain fatty acid (C8). The enzyme is also highly active on xylose tetra-acetate and oat spelt xylan. These results suggests that LipA is a novel lipolytic enzyme that possesses both lipase and acetylxylan esterase activity. We determined that LipA is a glycoprotein with pH and temperature optima at 8.0 and 40°C, respectively.

CONCLUSION

Besides being the first heterologous expression and characterization of a gene coding for a lipase from A. alcalophilum, this report shows that LipA is very versatile exhibiting both acetylxylan esterase and lipase activities potentially useful for diverse industry sectors, and that tobacco is a suitable bioreactor for producing fungal proteins.