Characterization of a tannin acyl hydrolase from Streptomyces sviceus with substrate preference for digalloyl ester bonds

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.

Structural diversity and substrate preferences of three tannase enzymes encoded by the anaerobic bacterium Clostridium butyricum

Tannins are secondary metabolites that are enriched in the bark, roots, and knots in trees and are known to hinder microbial attack. The biological degradation of water-soluble gallotannins, such as tannic acid, is initiated by tannase enzymes (EC 3.1.1.20), which are esterases able to liberate gallic acid from aromatic-sugar complexes. However, only few tannases have previously been studied in detail. Here, for the first time, we biochemically and structurally characterize three tannases from a single organism, the anaerobic bacterium Clostridium butyricum, which inhabits both soil and gut environments. The enzymes were named CbTan1-3, and we show that each one exhibits a unique substrate preference on a range of galloyl ester model substrates; CbTan1 and 3 demonstrated preference toward galloyl esters linked to glucose, while CbTan2 was more promiscuous. All enzymes were also active on oak bark extractives. Furthermore, we solved the crystal structure of CbTan2 and produced homology models for CbTan1 and 3. In each structure, the catalytic triad and gallate-binding regions in the core domain were found in very similar positions in the active site compared with other bacterial tannases, suggesting a similar mechanism of action among these enzymes, though large inserts in each enzyme showcase overall structural diversity. In conclusion, the varied structural features and substrate specificities of the C. butyricum tannases indicate that they have different biological roles and could further be used in development of new valorization strategies for renewable plant biomass.

Characterization and Secretory Expression of a Thermostable Tannase from Aureobasidium melanogenum T9: Potential Candidate for Food and Agricultural Industries

Being a key industrial enzyme, tannase is extensively applied in various fields. Despite the characterizations of a large number of tannases, there are hardly a few tannases with exceptional thermostability. In this detailed study, a tannase-encoding gene named tanA was identified from Aureobasidium melanogenum T9 and heterologously expressed in Yarrowia lipolytica host of food grade. The purified tannase TanA with a molecular weight of above 63.0 kDa displayed a specific activity of 941.4 U/mg. Moreover, TanA showed optimum activity at 60°C and pH 6.0. Interestingly, TanA exhibited up to 61.3% activity after incubation for 12 h at 55°C, signifying its thermophilic property and distinguished thermostability. Additionally, TanA was a multifunctional tannase with high specific activities to catalyze the degradation of various gallic acid esters. Therefore, this study presents a novel tannase, TanA, with remarkable properties, posing as a potential candidate for food and agricultural processing.

Biochemical and Structural Characterization of a Novel Bacterial Tannase From Lachnospiraceae bacterium in Ruminant Gastrointestinal Tract

Tannases are a family of esterases that catalyze the hydrolysis of ester and depside bonds present in hydrolyzable tannins to release gallic acid. Here, a novel tannase from Lachnospiraceae bacterium (TanA_Lb) was characterized. The recombinant TanA_Lb exhibited maximal activity at pH 7.0 and 50°C, and it maintained more than 70% relative activity from 30°C to 55°C. The activity of TanA_Lb was enhanced by Mg²⁺ and Ca²⁺, and was dramatically reduced by Cu²⁺ and Mn²⁺. TanA_Lb is capable of degrading esters of phenolic acids with long-chain alcohols, such as lauryl gallate as well as tannic acid. The Km value and catalytic efficiency (k_cat /Km) of TanA_Lb toward five substrates showed that tannic acid (TA) was the favorite substrate. Homology modeling and structural analysis indicated that TanA_Lb contains an insertion loop (residues 341–450). Based on the moleculer docking and molecular dynamics (MD) simulation, this loop was observed as a flap-like lid to interact with bulk substrates such as tannic acid. TanA_Lb is a novel bacterial tannase, and the characteristics of this enzyme make it potentially interesting for industrial use.

Heterologous expression and biophysical characterization of a mesophilic tannase following manganese nanoparticle immobilization

In the current study, we analyzed the efficacy of manganese oxide nanoparticle (MnNP)-water dispersion as an immobilization matrix for bacterial tannase. The tannase-secreting Bacillus subtilis strain NJKL.tan.2 obtained from tannery effluent soil was subsequently purified and cloned in pET20b vector. The activity of MnNP-tan (tannase activated by manganese nanoparticles) was 1.51- and 3.5-fold higher at 20 °C and 80 °C, respectively, compared with the free enzyme. MnNP-tan decreased K_m by 41.66 % and 3-fold, whereas free tannase showed two-fold and six-fold improvement in K_cat at 37 °C and 80 °C, respectively. MnNP-tan showed an increase in (half-life)t_1/2and E_d by 13-fold and 50.05 units, respectively, at 80 °C, in contrast to the native enzyme. MnNP-tan retained its residual activity by 78.2 % at 37 °C and 34.24 % at 80 °C after 180 min of incubation when compared with untreated set. MnNP-tan retained 51 % of its activity after 120 days with the native enzyme losing ∼50 % functionality following 40 days of incubation. The MnNP-mediated tannase immobilization technique is being reported for the first time. The technique has numerous advantages due to the use of MnNP as a potential matrix for biomolecule immobilization, which can be further extended to immobilize other biocatalysts used in agro-industrial and lab-based applications.

Crystal structure of fungal tannase from Aspergillus niger

Tannases are serine esterases that were first discovered in fungi more than one and half centuries ago. They catalyze the hydrolysis of the gallolyl ester bonds in gallotannins to release gallic acid, which is an important intermediate in the chemical and pharmaceutical industries. Since their discovery, fungal tannases have found wide industrial applications, although there is scarce knowledge about these enzymes at the molecular level, including their catalytic and substrate-binding sites. While this lack of knowledge hinders engineering efforts to modify the enzymes, many tannases have been isolated from various fungal strains in a search for the desired enzymatic properties. Here, the first crystal structure of a fungal tannase, that from Aspergillus niger, is reported. The enzyme possesses a typical α/β-hydrolase-fold domain with a large inserted cap domain, which together form a bowl-shaped hemispherical shape with a surface concavity surrounded by N-linked glycans. Gallic acid is bound at the junction of the two domains within the concavity by forming two hydrogen-bonding networks with neighbouring residues. One is formed around the carboxyl group of the gallic acid and involves residues from the hydrolase-fold domain, including those from the catalytic triad, which consists of Ser206, His485 and Asp439. The other is formed around the three hydroxyl groups of the compound, with the involvement of residues mainly from the cap domain, including Gln238, Gln239, His242 and Ser441. Gallic acid is bound in a sandwich-like mode by forming a hydrophobic contact with Ile442. All of these residues are found to be highly conserved among fungal and yeast tannases.

Bacterial tannases: classification and biochemical properties

Tannin acyl hydrolases, also known as tannases, are a group of enzymes critical for the transformation of tannins. The study of these enzymes, which initially evolved in different organisms to detoxify and/or use these plant metabolites, has nowadays become relevant in microbial enzymology research due to their relevant role in food tannin transformation. Microorganisms, particularly bacteria, are major sources of tannase. Cloning and heterologous expression of bacterial tannase genes and structural studies have been performed in the last few years. However, a systematic compilation of the information related to all recombinant tannases, their classification, and characteristics is missing. In this review, we explore the diversity of heterologously produced bacterial tannases, describing their substrate specificity and biochemical characterization. Moreover, a new classification based on sequence similarity analysis is proposed. Finally, putative tannases have been identified in silico for each group of tannases taking advantage of the use of the "tannase" distinctive features previously proposed.

Substrates specificity of tannase from Streptomyces sviceus and Lactobacillus plantarum

Tannases can catalyze the hydrolysis of galloyl ester and depside bonds of hydrolysable tannins to release gallic acid and glucose, but tannases from different species have different substrate specificities. Our prior studies found that tannase from Lactobacillus plantarum (LP-tan) performed a higher esterase activity, while the tannase from Streptomyces sviceus (SS-tan) performed a higher depsidase activity; but the molecular mechanism is not elucidated. Based on the crystal structure of LP-tan and the amino acid sequences alignment between LP-tan and SS-tan, we found that the sandwich structure formed by Ile206-substrate-Pro356 in LP-tan was replaced with Ile253-substrate-Gly384 in SS-tan, and the flap domain (amino acids: 225–247) formed in LP-tan was missed in SS-tan, while a flap-like domain (amino acids: 93–143) was found in SS-tan. In this study, we investigated the functional role of sandwich structure and the flap (flap-like) domain in the substrate specificity of tannase. Site-directed mutagenesis was used to disrupt the sandwich structure in LP-tan (P356G) and rebuilt it in SS-tan (G384P). The flap in LP-tan and the flap-like domain in SS-tan were deleted to construct the new variants. The activity assay results showed that the sandwich and the flap domain can help to catalytic the ester bonds, while the flap-like domain in SS-tan mainly worked on the depside bonds. Enzymatic characterization and kinetics data showed that the sandwich and the flap domain can help to catalytic the ester bonds, while the flap-like domain in SS-tan may worked on the depside bonds.

Identification of a highly active tannase enzyme from the oral pathogen Fusobacterium nucleatum subsp. polymorphum

BACKGROUND

Tannases are tannin-degrading enzymes that have been described in fungi and bacteria as an adaptative mechanism to overcome the stress conditions associated with the presence of these phenolic compounds.

RESULTS

We have identified and expressed in E. coli a tannase from the oral microbiota member Fusobacterium nucleatum subs. polymorphum (TanB_Fnp). TanB_Fnp is the first tannase identified in an oral pathogen. Sequence analyses revealed that it is closely related to other bacterial tannases. The enzyme exhibits biochemical properties that make it an interesting target for industrial use. TanB_Fnp has one of the highest specific activities of all bacterial tannases described to date and shows optimal biochemical properties such as a high thermal stability: the enzyme keeps 100% of its activity after prolonged incubations at different temperatures up to 45 °C. TanB_Fnp also shows a wide temperature range of activity, maintaining above 80% of its maximum activity between 22 and 55 °C. The use of a panel of 27 esters of phenolic acids demonstrated activity of TanB_Fnp only against esters of gallic and protocatechuic acid, including tannic acid, gallocatechin gallate and epigallocatechin gallate. Overall, TanB_Fnp possesses biochemical properties that make the enzyme potentially useful in biotechnological applications.

CONCLUSIONS

We have identified and characterized a metabolic enzyme from the oral pathogen Fusobacterium nucleatum subsp. polymorphum. The biochemical properties of TanB_Fnp suggest that it has a major role in the breakdown of complex food tannins during oral processing. Our results also provide some clues regarding its possible participation on bacterial survival in the oral cavity. Furthermore, the characteristics of this enzyme make it of potential interest for industrial use.

Occurrence of a novel tannase (tan BLP ) in endophytic Streptomyces sp. AL1L from the leaf of Ailanthus excelsa Roxb

The tannase production ability by endophytic actinobacteria and the genetic identity of responsible tannase gene were determined. The studied strains were isolated from surface-sterilized leaf discs of Ailanthus excelsa Roxb. Four strains were found to hydrolyze tannic acid on solid media containing 0.4% tannic acid. The strain AL1L was found as tanB_LP indicating production of tannase with diverse of substrate affinity. The tannase production from the potential strain AL1L was performed in liquid tannic acid broth (0.4%, w/v). The strain was later identified as Streptomyces sp. AL1L on the basis of 16S rDNA homology. Highest enzyme activity was observed at 48 h of incubation at the exponential growth phase. The enzyme was purified by ammonium sulfate precipitation followed by dialysis (15 kD cut off). This enzyme, with molecular weight 180 kD shows highest catalytic activity at 35 °C, pH 6 with substrate concentration 0.1 g%. The purified enzyme possesses 1.4 × 10^-3 K_m and 11.15 U/ml as V_max. The above study indicates high industrial prospective of endophytic actinobacteria as source of tannase of potential biotechnological applications.

Development of nitrilase promoter-derived inducible vectors for Streptomyces

An inducible expression vector, pSH19, which harbors regulatory expression system PnitA-NitR, for streptomycetes was constructed previously. Here, we have modified pSH19 to obtain shuttle vectors for Streptomyces-E. coli by introducing the replication origin of a plasmid for E. coli (ColE1) and an antibiotic-resistant gene. Six inducible shuttle vectors, pESH19cF, pESH19cR, pESH19kF, pESH19kR, pESH19aF, and pESH19aR, for Streptomyces-E. coli, were successfully developed. The stability of these vectors was examined in five different E. coli strains and Streptomyces lividans TK24. The stability test showed that the pSH19-derived shuttle vectors were stable in E. coli Stbl2 and S. lividans TK24. Heterologous expression experiments involving each of the catechol 2,3-dioxygenase, nitrilase, and N-substituted formamide deformylase genes as a reporter gene showed that pESH19cF, pESH19kF, and pESH19aF possess inducible expression ability in S. lividans TK24. Thus, these vectors were found to be useful expression tools for experiments on both Gram-negative and Gram-positive bacterial genes.