Improvement in the thermostability of a type A feruloyl esterase, AuFaeA, from Aspergillus usamii by iterative saturation mutagenesis

Optimization of fermentation conditions for the production of recombinant feruloyl esterase BpFaeT132C-D143C

Feruloyl esterases (FAEs) are a crucial component of the hemicellulose-degrading enzyme family that facilitates the degradation of lignocellulose while releasing hydroxycinnamic acids such as ferulic acid with high added value. Currently, the low enzyme yield of FAEs is one of the primary factors limiting its application. Therefore, in this paper, we optimized the fermentation conditions for the expression of FAE BpFaeT132C-D143C with excellent thermal stability in Escherichia coli by experimental design. Firstly, we explored the effects of 11 factors such as medium type, isopropyl-β-D-thiogalactopyranoside (IPTG) concentration, and inoculum size on BpFaeT132C-D143C activity separately by the single factor design. Then, the significance of the effects of seven factors, such as post-induction temperature, shaker rotational speed, and inoculum size on BpFaeT132C-D143C activity, was analyzed by Plackett-Burman design. We identified the main factors affecting the fermentation conditions of E. coli expressing BpFaeT132C-D143C as post-induction temperature, pre-induction period, and post-induction period. Finally, we used the steepest ascent path design and response surface method to optimize the levels of these three factors further. Under the optimal conditions, the activity of BpFaeT132C-D143C was 3.58 U/ml, which was a significant 6.6-fold increase compared to the pre-optimization (0.47 U/ml), demonstrating the effectiveness of this optimization process. Moreover, BpFaeT132C-D143C activity was 1.52 U/ml in a 3-l fermenter under the abovementioned optimal conditions. It was determined that the expression of BpFaeT132C-D143C in E. coli was predominantly intracellular in the cytoplasm. This study lays the foundation for further research on BpFaeT132C-D143C in degrading agricultural waste transformation applications.

Thermostability and activity improvement in l-threonine aldolase through targeted mutations in V-shaped subunit

l-threonine aldolase (LTA) catalyzes the synthesis of β-hydroxy-α-amino acids, which are important chiral intermediates widely used in the fields of pharmaceuticals and pesticides. However, the limited thermostability of LTA hinders its industrial application. Furthermore, the trade-off between thermostability and activity presents a challenge in the thermostability engineering of this enzyme. This study proposes a strategy to regulate the rigidity of LTA's V-shaped subunit by modifying its opening and hinge regions, distant from the active center, aiming to mitigate the trade-off. With LTA from Bacillus nealsonii as targeted enzyme, a total of 25 residues in these two regions were investigated by directed evolution. Finally, mutant G85A/M207L/A12C was obtained, showing significantly enhanced thermostability with a 20 °C increase in T5060 to 66 °C, and specific activity elevated by 34 % at the optimum temperature. Molecular dynamics simulations showed that the newly formed hydrophobicity and hydrogen bonds improved the thermostability and boosted proton transfer efficiency. This work enhances the thermostability of LTA while preventing the loss of activity. It opens new avenues for the thermostability engineering of other industrially relevant enzymes with active center located at the interface of subunits or domains.

Empowering Protein Engineering through Recombination of Beneficial Substitutions

Directed evolution stands as a seminal technology for generating novel protein functionalities, a cornerstone in biocatalysis, metabolic engineering, and synthetic biology. Today, with the development of various mutagenesis methods and advanced analytical machines, the challenge of diversity generation and high-throughput screening platforms is largely solved, and one of the remaining challenges is: how to empower the potential of single beneficial substitutions with recombination to achieve the epistatic effect. This review overviews experimental and computer-assisted recombination methods in protein engineering campaigns. In addition, integrated and machine learning-guided strategies were highlighted to discuss how these recombination approaches contribute to generating the screening library with better diversity, coverage, and size. A decision tree was finally summarized to guide the further selection of proper recombination strategies in practice, which was beneficial for accelerating protein engineering.

Simultaneous enhancement of thermostability and catalytic activity of κ-carrageenase from Pseudoalteromonas tetraodonis by rational design

κ-Carrageenase provides an attractive enzymatic approach to preparation of κ-carrageenan oligosaccharides. Pseudoalteromonas tetraodonis κ-carrageenase is active at the alkaline conditions but displays low thermostability. To further improve its enzymatic performance, two mutants of Q42V and I51H exhibiting both improved thermostability and enzyme activity were screened by the PoPMuSiC algorithm. Compared with the wild-type κ-carrageenase (WT), Q42V and I51H increased the enzyme activity by 20.9% and 25.4%, respectively. After treatment at 50 ℃ for 40 min, Q42V and I51H enhanced the residual activity by 31.1% and 25.9%, respectively. The T_m values of Q42V, I51H, and WT determined by differential scanning calorimetry were 58.2 ℃, 54.8 ℃, and 51.2 ℃, respectively. Compared with untreated and HCl-treated κ-carrageenans, Q42V-treated κ-carrageenan exhibited higher pancreatic lipase inhibitory activity. Molecular docking analysis indicated that the additional pi-sigma force and hydrophobic interaction in the enzyme-substrate complex could account for the increased catalytic activity of Q42V and I51H, respectively. Molecular dynamics analysis indicated that the improved thermostability of mutants Q42V and I51H could be attributed to the less structural deviation and the flexible changes of enzyme conformation at high temperature. This study provides new insight into κ-carrageenase performance improvement and identifies good candidates for 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.

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.

Overview of strategies for developing high thermostability industrial enzymes: Discovery, mechanism, modification and challenges

Biocatalysts such as enzymes are environmentally friendly and have substrate specificity, which are preferred in the production of various industrial products. However, the strict reaction conditions in industry including high temperature, organic solvents, strong acids and bases and other harsh environments often destabilize enzymes, and thus substantially compromise their catalytic functions, and greatly restrict their applications in food, pharmaceutical, textile, bio-refining and feed industries. Therefore, developing industrial enzymes with high thermostability becomes very important in industry as thermozymes have more advantages under high temperature. Discovering new thermostable enzymes using genome sequencing, metagenomics and sample isolation from extreme environments, or performing molecular modification of the existing enzymes with poor thermostability using emerging protein engineering technology have become an effective means of obtaining thermozymes. Based on the thermozymes as biocatalytic chips in industry, this review systematically analyzes the ways to discover thermostable enzymes from extreme environment, clarifies various interaction forces that will affect thermal stability of enzymes, and proposes different strategies to improve enzymes' thermostability. Furthermore, latest development in the thermal stability modification of industrial enzymes through rational design strategies is comprehensively introduced from structure-activity relationship point of view. Challenges and future research perspectives are put forward as well.

Rational design and structure-based engineering of alkaline pectate lyase from Paenibacillus sp. 0602 to improve thermostability

BACKGROUND

Ramie degumming is often carried out at high temperatures; therefore, thermostable alkaline pectate lyase (PL) is beneficial for ramie degumming for industrial applications. Thermostable PLs are usually obtained by exploring new enzymes or reconstructing existing enzyme by rational design. Here, we improved the thermostability of an alkaline pectate lyase (PelN) from Paenibacillus sp. 0602 with rational design and structure-based engineering.

RESULTS

From 26 mutants, two mutants of G241A and G241V showed a higher thermostability compared with the wild-type PL. The mutant K93I showed increasing specific activity at 45 °C. Subsequently, we obtained combinational mutations (K93I/G241A) and found that their thermostability and specific activity improved simultaneously. The K93I/G241A mutant showed a half-life time of 15.9 min longer at 60 °C and a melting temperature of 1.6 °C higher than those of the wild PL. The optimum temperature decreased remarkably from 67.5 °C to 60 °C, accompanied by a 57% decrease in Km compared with the Km value of the wild-type strain. Finally, we found that the intramolecular interaction in PelN was the source in the improvements of molecular properties by comparing the model structures. Rational design of PelN was performed by stabilizing the α-helices with high conservation and increasing the stability of the overall structure of the protein. Two engineering strategies were applied by decreasing the mutation energy calculated by Discovery Studio and predicting the free energy in the process of protein folding by the PoPMuSiC algorithm.

CONCLUSIONS

The results demonstrated that the K93I/G241A mutant was more suitable for industrial production than the wild-type enzyme. Furthermore, the two forementioned strategies could be extended to reveal engineering of other kinds of industrial enzymes.

Chitosan-based CLEAs from Aspergillus niger type A feruloyl esterase: high-productivity biocatalyst for alkyl ferulate synthesis

The enzymatic synthesis of alkyl ferulates is an important reaction in cosmetic and pharmaceutical chemistries, since it may allow to expand the biorefinery concept valorizing biomass wastes enriched in ferulic acid. However, robust biocatalysts for that purpose are scarce. Herein, we have immobilized the type A feruloyl esterase from Aspergillus niger (AnFaeA) as cross-linked enzyme aggregates, employing chitosan as co-feeder (ChCLEAs). High immobilization yields and relative activity recovery were attained in all assessed conditions (> 93%). Furthermore, we enhanced the thermal stability of the soluble enzyme 32-fold. AnFaeA-ChCLEAs were capable to quantitatively perform the solvent-free direct esterification of short- to medium-chain alkyl ferulates (C4-C12) in less than 24 h. By raising the operational temperature to 50 °C, AnFaeA-ChCLEAs transformed 350 mM ferulic acid into isopentyl ferulate with a space-time yield of 46.1 g of product × L^-1 × day^-1, 73-fold higher than previously reported. The overall sustainability of this alkyl ferulate production bioprocess is supported by the high total turnover number (TTN 7 × 10⁵) and the calculated green metrics (E factor = 30). Therefore, we herein present a robust, efficient, and versatile heterogeneous biocatalyst useful for the synthesis of a wide diversity of alkyl ferulates. KEY POINTS: • CLEAs of feruloyl esterase A from A. niger using chitosan as co-feeder were obtained. • Microenvironment of the biocatalysts allowed to obtain C1 to C18 alkyl ferulates. • Biocatalyst at boundary conditions showed a high productivity of 46 g/L day. Graphical Abstract.

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.

Crystal Structure of GH49 Dextranase from Arthrobacter oxidans KQ11: Identification of Catalytic Base and Improvement of Thermostability Using Semirational Design Based on B-Factors

The crystal structure of Dextranase from the marine bacterium Arthrobacter oxidans KQ11 (Aodex) was determined at a resolution of 1.4 Å. The crystal structure of the conserved Aodex fragment (Ala52-Thr638) consisted of an N-terminal domain N and a C-terminal domain C. The N-terminal domain N was identified as a β-sandwich, connected to a right-handed parallel β-helix at the C-terminus. Sequence comparisons, cavity regions, and key residues of the catalytic domain analysis all suggested that the Aodex was an inverting enzyme, and the catalytic acid and base were Asp439 and Asp420, respectively. Asp440 was not a general base in the Aodex catalytic domain, and Asp396 in Dex49A may not be a general base in the catalytic domain. The thermostability of the S357F mutant using semirational design based on B-factors was clearly better than that of wild-type Aodex. This process may promote the aromatic-aromatic interactions that increase the thermostability of mutant Phe357.

Feruloyl esterases: Biocatalysts to overcome biomass recalcitrance and for the production of bioactive compounds

Ferulic acid and its hydroxycinnamate derivatives represent one of the most abundant forms of low molecular weight phenolic compounds in plant biomass. Feruloyl esterases are part of a microorganism's plant cell wall-degrading enzymatic arsenal responsible for cleaving insoluble wall-bound hydroxycinnamates and soluble cytosolic conjugates. Stimulated by industrial requirements, accelerating scientific discoveries and knowledge transfer, continuous improvement efforts have been made to identify, create and repurposed biocatalysts dedicated to plant biomass conversion and biosynthesis of high-added value molecules. Here we review the basic knowledge and recent advances in biotechnological characteristics and the gene content encoding for feruloyl esterases. Information about several enzymes is systematically organized according to their function, biochemical properties, substrate specificity, and biotechnological applications. This review contributes to further structural, functional, and biotechnological R&D both for obtaining hydroxycinnamates from agricultural by-products as well as for lignocellulose biomass treatments aiming for production of bioethanol and other derivatives of industrial interest.

In Silico insights on enhancing thermostability and activity of a plant Fructosyltransferase from Pachysandra terminalis via introduction of disulfide bridges

Drawbacks of industrially-used fructosyltransferases (FTs) such as low optimum temperature and low fructooligosaccharides (FOS) yield necessitates the search for engineered FTs that are highly thermostable and active. With the availability of the first plant FT crystal structure from Pachysandra terminalis (PDB ID: 3UGH), computer-aided protein engineering of plant FT is now feasible. To obtain insights on the effect of specific mutations i.e. disulfide bridge introduction, wild-type and mutant FTs were subjected to a 15 μs Martini Coarse-grained Molecular Dynamics (CGMD) simulations at 303 K and 334 K. We report here the five mutants, M31C-Q49C, L144C-S193C, P34C-W300C, S219C-L226C and V470C-S498C with enhanced thermostabilities and/or activities relative to the wild type. Interestingly, M31C-Q49C, which is located within the catalytic-carrying blade of the catalytic domain, has an activity enhancement at both temperatures. At 334 K, three mutations, L144C-S193C, P34C-W300C and V470C-S498C, achieved thermostability relative to the wild type. Intriguingly, both activity and stability enhancement exhibited only at 334 K can be achieved provided that the mutation is located either on the catalytic-carrying residue blade of the catalytic domain or on the non-catalytic domain. Our results suggest that V470C-S498C and L144C-S193C are promising mutants and that domain-specific approach may be exploited to customize enzyme properties.

Multidisciplinary involvement and potential of thermophiles

The full biotechnological exploitation of thermostable enzymes in industrial processes is necessary for their commercial interest and industrious value. The heat-tolerant and heat-resistant enzymes are a key for efficient and cost-effective translation of substrates into useful products for commercial applications. The thermophilic, hyperthermophilic, and microorganisms adapted to extreme temperatures (i.e., low-temperature lovers or psychrophiles) are a rich source of thermostable enzymes with broad-ranging thermal properties, which have structural and functional stability to underpin a variety of technologies. These enzymes are under scrutiny for their great biotechnological potential. Temperature is one of the most critical parameters that shape microorganisms and their biomolecules for stability under harsh environmental conditions. This review describes in detail the sources of thermophiles and thermostable enzymes from prokaryotes and eukaryotes (microbial cell factories). Furthermore, the review critically examines perspectives to improve modern biocatalysts, its production and performance aiming to increase their value for biotechnology through higher standards, specificity, resistance, lowing costs, etc. These thermostable and thermally adapted extremophilic enzymes have been used in a wide range of industries that span all six enzyme classes. Thus, in particular, target of this review paper is to show the possibility of both high-value-low-volume (e.g., fine-chemical synthesis) and low-value-high-volume by-products (e.g., fuels) by minimizing changes to current industrial processes.

Improving the temperature characteristics and catalytic efficiency of a mesophilic xylanase from Aspergillus oryzae, AoXyn11A, by iterative mutagenesis based on in silico design

To improve the temperature characteristics and catalytic efficiency of a glycoside hydrolase family (GHF) 11 xylanase from Aspergillus oryzae (AoXyn11A), its variants were predicted based on in silico design. Firstly, Gly²¹ with the maximum B-factor value, which was confirmed by molecular dynamics (MD) simulation on the three-dimensional structure of AoXyn11A, was subjected to site-saturation mutagenesis. Thus, one variant with the highest thermostability, AoXyn11A^G21I, was selected from the mutagenesis library, E. coli/Aoxyn11A^G21X (X: any one of 20 amino acids). Secondly, based on the primary structure multiple alignment of AoXyn11A with seven thermophilic GHF11 xylanases, AoXyn11A^Y13F or AoXyn11A^G21I–Y13F, was designed by replacing Tyr¹³ in AoXyn11A or AoXyn11A^G21I with Phe. Finally, three variant-encoding genes, Aoxyn11A^G21I, Aoxyn11A^Y13F and Aoxyn11A^G21I–Y13F, were constructed by two-stage whole-plasmid PCR method, and expressed in Pichia pastoris GS115, respectively. The temperature optimum (T_opt) of recombinant (re) AoXyn11A^G21I–Y13F was 60 °C, being 5 °C higher than that of reAoXyn11A^G21I or reAoXyn11A^Y13F, and 10 °C higher than that of reAoXyn11A. The thermal inactivation half-life (t_1/2) of reAoXyn11A^G21I–Y13F at 50 °C was 240 min, being 40-, 3.4- and 2.5-fold longer than those of reAoXyn11A, reAoXyn11A^G21I and reAoXyn11A^Y13F. The melting temperature (T_m) values of reAoXyn11A, reAoXyn11A^G21I, reAoXyn11A^Y13F and reAoXyn11A^G21I–Y13F were 52.3, 56.5, 58.6 and 61.3 °C, respectively. These findings indicated that the iterative mutagenesis of both Gly21Ile and Tyr13Phe improved the temperature characteristics of AoXyn11A in a synergistic mode. Besides those, the catalytic efficiency (k_cat/K_m) of reAoXyn11A^G21I–Y13F was 473.1 mL mg⁻¹ s⁻¹, which was 1.65-fold higher than that of reAoXyn11A.

Improvement thermostability of Pseudoalteromonas carrageenovora arylsulfatase by rational design

This study aimed to improve the thermostability of arylsulfatase from Pseudoalteromonas carrageenovora. A total of 10 single-site mutants were chosen using the PoPMuSiC program, and two mutants of K253N and P314T showed enhanced thermal stability. By saturation mutagenesis and thermostability analysis, K253H and P314T were the best mutants at the two sites. Combinational mutations of K253H, P314T and H260L were subsequently introduced, and the best mutant of K253H/H260L was selected. Thermal inactivation analysis showed the half-life (t_1/2) value at 55°C for K253H/H260L was 7.7-fold that of the wild-type enzyme (WT), meanwhile this mutant maintained the specific enzyme activity. Structure modeling demonstrated that the additional hydrogen bonds, optimization of surface charge-charge interactions, and increasing of hydrophobic interaction could account for the improved thermostability imparted by K253H/H260L.

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.