Bacterial tannases: classification and biochemical properties

Abstract

Tannin acyl hydrolases, also known as tannases, are a group of enzymes 22 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 24 nowadays become relevant in microbial enzymology research due to their relevant role in 25 food tannin transformation. 26 Microorganisms, particularly bacteria, are major sources of tannase. Cloning and 27 heterologous expression of bacterial tannase genes and structural studies have been 28 performed in the last few years. However, a systematic compilation of the information 29 related to all recombinant tannases, their classification and characteristics is missing. In 30 this review, we explore the diversity of heterologously produced bacterial tannases, 31 describing their substrate specificity and biochemical characterization. Moreover, a new 32 classification based on sequence similarity analysis is proposed. Finally, putative tannases 33 have been identified in silico for each group of tannases taking advantage of the use of the 34 "tannase" distinctive features previously proposed. 35 36 37 Keywords Tannase • Feruloyl esterase • Esterase • Hydrolysable tannins • Gallic acid 38 39 The majority of industrial enzymes are classified as "hydrolases", and "tannases" 64 belong to this class. Since their discovery more than a century ago, tannases have been 65 used in the food, feed, beverage, pharmaceutical and chemical industries. Among the 66 commercial applications of tannases, the most relevant are the production of gallic acid, 67 instant tea, and coffee-flavored refreshing drinks. Moreover, these enzymes are used for the clarification of beer and fruits juices, the improvement of flavor of grape wine, and the 69 manufacture of animal feeds (Jana et al. 2014). 70 Tannase production can be achieved from microbial, animal and vegetal sources, 71 but microorganisms are commonly used for its commercial production. Microorganisms 72 are the main source of industrial enzymes due to their biochemical diversity and their 73 amenability to genetic modifications. To date, commercially available tannases are mainly 74 produced by the fermentation of fungi, especially the Aspergillus species, from which only 75 crude enzymes are readily produced (Aguilar et al. 2007). Recombinant expression 76 appears to be an appealing alternative to produce pure enzymes, however, the attempt to 77 clone fungal tannase genes has proven difficult and inefficient, probably due to the 78 complexity of fungal enzymes (Aguilar et al. 2007, Hatamoto et al. 1996, Zhong et al. 79 2004). Therefore, bacterial tannases might constitute an adequate alternative to fungal 80 enzymes. Research on bacterial tannases has been primarily focused on the screening of 81 new tannase-producing bacterial strains with the desired properties. The selected tannase-82 producer strains are often employed either directly or using their crude cellular extracts, 83 without enzyme isolation. Surprisingly, little knowledge is...

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“…The interaction and binding between phenolic compounds and proteins, e.g., digestive enzymes and dietary proteins, depends not only on the structures of both the phenolics and proteins, but also on some environmental parameters, such as pH and temperature [58]. Condensed tannins, i.e., proanthocyanidins, are a subgroup of tannins with potential toxic effects on many organisms and relatively high tendency to precipitate protein molecules [60,61]. Microbial tannase enzymes have been evolved for biodegradation of tannins for energy production and toxicity reduction and are often expressed during fermentation processes of bacteria and fungi [60].…”

“…Condensed tannins, i.e., proanthocyanidins, are a subgroup of tannins with potential toxic effects on many organisms and relatively high tendency to precipitate protein molecules [60,61]. Microbial tannase enzymes have been evolved for biodegradation of tannins for energy production and toxicity reduction and are often expressed during fermentation processes of bacteria and fungi [60]. For example, Lactobacillus plantarum strains are commonly isolated from fermented plant materials, and many of them express tannase enzymes capable of tannin compound degradation [62].…”

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“…MO13 and CIAN4 are representatives of ABhydrolase superfamily SSF53474 and belong to the group C of the tannase/feruloyl_esterase family [38,39]. Feruloyl esterases (E.C.…”

“…3.1.1.1) that are able to hydrolyse the ester bond between hydroxycinnamic acids and sugars present in the plant cell walls [39][40][41]. Tannase (E.C.3.1.1.20) is an inducible microbial enzyme that hydrolyses ester and depside bonds in hydrolysable tannins to produce gallic acid and glucose [38]. This family includes fungal tannase and feruloyl esterase [42,43], several bacterial homologues of unknown function, and polyethylene terephthalate (PET) hydrolysing enzymes, e.g., the mono(2-hydroxyethyl) terephthalate hydrolase from the bacterium Ideonella sakaiensis [44,45].…”

“…The comparison of YqfB and D8_RL amino acid sequences showed merely 17 identical residues between these two proteins, and only 2 of the 4 YqfB catalytic amino acids were among them, although the aspartic acid residue in position 72 of the D8_RL and the catalytic glutamic acid residue in position 74 of the YqfB enzyme can also be considered conservative ones (Figure 3 and Figure S2). produce gallic acid and glucose [38]. This family includes fungal tannase and feruloyl esterase [42,43], several bacterial homologues of unknown function, and polyethylene terephthalate (PET) hydrolysing enzymes, e.g., the mono(2-hydroxyethyl) terephthalate hydrolase from the bacterium Ideonella sakaiensis [44,45].…”