If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Phenylpropanoid Derivatives Biosynthesis → Hydrolyzable Tannins Biosynthesis|
Expected Taxonomic Range: Viridiplantae
Hydrolyzable tannins (HT), divided in the two subclasses gallotannins (see gallotannin biosynthesis) and ellagitannins (see cornusiin E biosynthesis) are derivatives of pentagalloylglucose (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose) [Niemetz00]. The category 'hydrolyzable tannins' is based on the classical definition of Freudenberg [Freudenberg20] who distinguished condensed tannins (also referred to as proanthocyanins; flavonoid origin) and hydrolysable tannins (esters of gallic acid with typically β-D-glucose). That class of compounds belongs to the more general 'plant polyphenols' (synonym vegetable tannins) which have been intensively studied in the last few decades (reviewed in [Haslam89] [Haslam94] [Haslam98].
The name 'tannin' derived from the pronounced property of these compounds to precipitate proteins which has been used over the centuries for the tannery procedure to produce endurable leather from raw hides. Beside that, hydrolyzable tannins have many antimicrobial, antioxidant and antitumor properties used in human health care [Haslam96] and apply the varying amount of astringency as food components/phytonutrients [Beecher03]. Hydrolyzable tannins are widely distributed among plants but differ with regard to gallotannins (more restricted occurence) and ellagitannins (broad occurence) [Haddock82].
The mono- to penta-substituted esters being generated on the biogenetic way towards pentagalloylglucose are also referred to as 'simple' galloylglucoses in contrast to the 'complex' galloylglucoses produced as the result of further galloylation of pentagalloylglucose [Niemetz05]. However, that categorization does not indicate the tanning potential of the associated compounds.
About This Pathway
The biosynthesis towards pentagalloylglucose displays a high specificity with a defined metabolic sequence. The first step is the formation of β-glucogallin (1-O-galloyl-β-D-glucopyranose) from gallic acid catalyzed by the UDPG-dependent gallate-1-β-glucosyltransferase [Gross82, Gross83]. This compound does not only function as the common acyl acceptor throughout the pentagalloylglucose biosynthetic pathway but exerts in addition a dual role as acyl donor indicating the characteristic of an energy-rich 'activated' compound [Gross83a].
The further galloylation follows the metabolic sequence 1,6-digalloylglucose [Schmidt87b], 1,2,6-trigalloylglucose [Gross91], 1,2,3,6-tetragalloylglucose [Hagenah93] and finally 1,2,3,4,6-pentagalloylglucose [Cammann89]. The formation of 1,2,6-trigalloylglucose may also occur using an alternative route [Denzel91].
The oxidative steps from pentagalloylglucose to the dimeric cornusiin E via the monomeric ellagiotannin tellimagrandin II are catalyzed by two enzymes that belong to the group of p-diphenol: O2-oxidoreductases (EC 18.104.22.168) also known as 'laccases' [Niemetz01a] [Niemetz03] [Niemetz03b]. The enzymes catalyzes the sterespecific phenolic coupling to produce the (S)-stereoconfiguration as observed in tellimagrandin II and cornusiin E, respectively.
The experimental data clearly indicate that the impressive number of gallotannins is produced following one general reaction type. Five enzymes catalyze the progressive galloylation of pentagalloylglucose towards penta-, hexa- and heptagalloylglucoses and even higher substituted galloylglucoses [Niemetz00, Hofmann90]. Although the enzymes are not very specific towards their substrates it was found on the basis of calculated catalytic efficiency that each of them had a preferred substrate (and major product) and therefore operates along a mainstream metabolic sequence [Niemetz05]. Those five galloyltransferases identified in sumac (also called galloyltransferase A to E) have been demonstrated to catalyze the various heptagalloylglucoses in this plant [Niemetz99, Niemetz98, Niemetz01, Frohlich02].
Cammann89: Cammann J, Denzel K, Schilling G, Gross GG (1989). "Biosynthesis of gallotannins: β-glucogallin-dependent formation of 1,2,3,4,6-pentagalloylglucose by enzymatic galloylation of 1,2,3,6-tetragalloylglucose." Arch Biochem Biophys 273(1);58-63. PMID: 2757399
Denzel91: Denzel K, Gross GG (1991). "Biosynthesis of gallotannins. Enzymatic 'disproportionation' of 1,6-digalloylglucose to 1,2,6-trigalloylglucose and 6-galloylglucose by an acyltransferase from leaves of Rhus typhina L." Planta, 184, 185-289.
Frohlich02: Frohlich B, Niemetz R, Gross GG (2002). "Gallotannin biosynthesis: two new galloyltransferases from Rhus typhina leaves preferentially acylating hexa- and heptagalloylglucoses." Planta 216(1);168-72. PMID: 12430027
Haddock82: Haddock EA, Gupta RK, Al-Shafi SM, Layden K, Haslam E, Magnolato D (1982). "The metabolism of gallic acid and hexahydroxydiphenic acid in plants: biogenetic and molecular taxonomic considerations." Phytochemistry, 21(5), 1049-1062.
Hofmann90: Hofmann AS, Gross GG (1990). "Biosynthesis of gallotannins: formation of polygalloylglucoses by enzymatic acylation of 1,2,3,4,6-penta-O-galloylglucose." Arch Biochem Biophys 283(2);530-2. PMID: 2148866
Niemetz00: Niemetz R, Niehaus JU, Gross GG (2000). "Biosynthesis and biodegradation of complex gallotannins." In: Gross, GG., Hemingway, RW. and Yoshida, T. (eds.) Plant Polyphenols 2: Chemistry and Biology, 63-83. Kluwer Academic/Plenum Publishing Corporation, New York, Boston, Dordrecht, London, Moscow.
Niemetz01a: Niemetz R, Schilling G, Gross GG (2001). "Ellagitannin biosynthesis: oxidation of pentagalloylglucose to tellimagrandin II by an enzyme from Tellima grandiflora leaves." Chem. Commun., 1, 35-36.
Niemetz03: Niemetz R, Gross GG (2003). "Oxidation of pentagalloylglucose to the ellagitannin, tellimagrandin II, by a phenol oxidase from Tellima grandiflora leaves." Phytochemistry 62(3);301-6. PMID: 12620341
Niemetz03b: Niemetz R, Gross GG (2003). "Ellagitannin biosynthesis: laccase-catalyzed dimerization of tellimagrandin II to cornusiin E in Tellima grandiflora." Phytochemistry 64(7);1197-201. PMID: 14599517
Niemetz98: Niemetz R, Gross GG (1998). "Gallotannin biosynthesis: Purification of β-glucogallin: 1,2,3,4,6-pentagalloyl-β-D-glucose galloyltransferase from Sumac leaves." Phytochemistry, 49(2), 327-332.
Niemetz99: Niemetz R, Gross GG (1999). "Gallotannin biosynthesis: A new beta-glucogallin-dependent galloyltransferase from Sumac leaves acylating gallotannins at positions 2 and 4." J Plant Physiol, 155, 441-446.
Schmidt87b: Schmidt SW, Denzel K, Schilling G, Gross GG (1987). "Enzymatic synthesis of 1,6-digalloylglucose from β-glucogallin by β-glucogallin: β-glucogallin 6-O-galloyltransferase from Oak leaves." Z. Naturforsch., 42c, 87-92.
Feldman99: Feldman KS, Sahasrabudhe K, Smith RS, Scheuchenzuber WJ (1999). "Immunostimulation by plant polyphenols: a relationship between tumor necrosis factor-α production and tannin structure." Bioorg Med Chem Lett 9(7);985-90. PMID: 10230625
Hadi00: Hadi SM, Asad SF, Singh S, Ahmad A (2000). "Putative mechanism for anticancer and apoptosis-inducing properties of plant-derived polyphenolic compounds." IUBMB Life 50(3);167-71. PMID: 11142343
Mittasch14: Mittasch J, Bottcher C, Frolova N, Bonn M, Milkowski C (2014). "Identification of UGT84A13 as a candidate enzyme for the first committed step of gallotannin biosynthesis in pedunculate oak (Quercus robur)." Phytochemistry. PMID: 24412325
Nishizawa83: Nishizawa M, Yamagishi T, Nonaka G, Nishioka I, Nagasawa T, Oura H (1983). "Tannins and related compounds. XII. Isolation and characterization of galloylglucoses from Paeoniae Radix and their effects on urea-nitrogen concentration in rat serum." Chem Pharm Bull (Tokyo) 31(8);2593-600. PMID: 6652813
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