A Simple Method for Enzymatic Synthesis of Unlabeled and Radiolabeled Hydroxycinnamate-CoA

Hydroxycinnamate coenzyme A (CoA) thioesters are substrates for biosynthesis of lignin and hydroxycinnamate esters of polysaccharides and other polymers. Hence, a supply of these substrates is essential for investigation of cell wall biosynthesis. In this study, three recombinant enzymes, caffeic acid 3-O-methyltransferase, 4-coumarate-CoA ligase 1, and 4-coumarate-CoA ligase 5, were cloned from wheat, tobacco, and Arabidopsis, respectively, and were used to synthesize ¹⁴C-feruloyl-CoA, caffeoyl-CoA, p-coumaroyl-CoA, feruloyl-CoA, and sinapoyl-CoA. The corresponding hydroxycinnamoyl-CoA thioesters were high-performance liquid chromatography purified, the only extraction/purification step necessary, with total yields between 88–95%. Radiolabeled ¹⁴C-feruloyl-CoA was generated from caffeic acid and S-adenosyl-¹⁴C-methionine under the combined action of caffeic acid 3-O-methyltransferase and 4-coumarate-CoA ligase 1. About 70% of ¹⁴C-methyl groups from S-adenosyl methionine were incorporated into the final product. The methods presented are simple, fast, and efficient for the preparation of the hydroxycinnamate thioesters.     

S-adenosyl-L-methionine:trans-caffeoyl-coenzyme A 3-O-methyltransferase from elicitor-treated parsley cell suspension cultures

An S-adenosyl-L-methionine:caffeoyl-CoA 3-O-methyltransferase was purified 82-fold from elicitor-induced parsley cell suspension cultures by ammonium sulfate fractionation, anionic exchange and hydrophobic interaction chromatographies, and chromatofocusing. The enzyme has an apparent pI of 5.7 and a molecular weight of approx 48,000 determined by gel filtration chromatography. Maximal activity was observed at pH 7.5 in 50 mM phosphate or Tris-HCl buffers and the additional presence of 0.5 M NaCl. The methyltransferase activity was dependent on Mg2+, whereas EDTA, Mn2+, and Ca2+ inhibited the reaction. The partially purified enzyme efficiently catalyzed the methylation of caffeoyl-CoA, but also accepted with low affinity various other caffeic esters as substrates. Dark-grown parsley cells contained considerable methyltransferase activity which was nevertheless increased approx threefold within 12 h following the addition of a crude fungal elicitor to the cell suspensions. We propose that the O-methyltransferase activity is an important component in the rapid resistance response of the cells, which depends on the formation of cell wall-bound ferulic polymers.     

The enzymic conversion of hydroxycinnamic acids to p-coumarylquinic and chlorogenic acids in tomato fruits

Two enzymes thought to be involved in the biosynthesis of chlorogenic acid have been separated and purified by ion exchange chromatography and their properties studied. These two enzymes, p-coumarate CoA ligase and hydroxycinnamyl CoA: quinate hydroxycinnamyl transferase, acting together catalyse the conversion of p-coumaric acid to 5′-p-coumarylquinic acid and of caffeic acid to chlorogenic acid. The ligase has a higher affinity for p-coumaric than for caffeic acid and will in addition activate a number of other cinnamic acids such as ferulic, isoferulic and m-coumaric acids but not cinnamic acid. The transferase shows higher activity and affinity with p-coumaryl CoA than caffeyl CoA. It also acts with ferulyl CoA but only very slowly. The enzyme shows high specificity for quinic acid; shikimic acid is esterified at only 2% of the rate with quinic acid and glucose is not a substrate. The transferase activity is reversible and both chlorogenic acid and 5′-p-coumarylquinic acids are cleaved in the presence of CoA to form quinic acid and the corresponding hydroxycinnamyl CoA thioester.     

羟基肉桂酰基转移酶的结构、功能与应用

羟基肉桂酰基转移酶（hydroxycinnamoyl transferase,HCT）属于植物酰基转移酶家族的一个重要分支,具有“HXXXD”和“DFGWG”两个保守序列,以多种酰基辅酶A（肉桂酰辅酶A、对香豆酰辅酶A、咖啡酰辅酶A、阿魏酰辅酶A和芥子酰辅酶A等）作为酰基供体,催化多种底物（莽草酸、奎尼酸、4 羟基苯乳酸、龙胆酸和4 羟基苯乙胺等）形成酯类或酰胺化合物。其酰基化产物可改善植物次生代谢产物的理化性质和生物活性,因此HCT被广泛应用于开发生物质能源、改良作物品种和研制抗炎药物,对植物次生代谢产物的合成与后修饰具有重要意义。本文系统介绍了HCT的序列特点、蛋白质结构特征、酰基化反应机制和其在工业、农业及医药行业的应用,并对HCT的未来发展前景进行了展望。     

Properties and Activity Changes of Chlorogenic Acid:Glucaric Acid Caffeoyltransferase From Tomato (Lycopersicon esculentum)

A novel acyltransferase from cotyledons of tomato (Lycopersicon esculentum Mill.), which catalyzes the transfer of caffeic acid from chlorogenic acid (5-O-caffeoylquinic acid) to glucaric and galactaric acids, was purified with a 2400-fold enrichment and a 4% recovery. The enzyme showed specific activities (theoretical V_max per milligram of protein) of 625 nanokatals (caffeoylglucaric acid formation) and 310 nanokatals (caffeoylgalactaric acid formation). On sodium dodecyl sulfate-polyacrylamide gel electrophoresis it gave an apparent M_r of 40,000, identical to the value obtained by gel filtration column chromatography. Highest activity was found at pH 5.7, which was constant over a range of 20 to 120 millimolar K-phosphate. The isoelectric point of the enzyme was at pH 5.75. The reaction temperature optimum was at 38°C and the apparent energy of activation was calculated to be 57 kilojoules per mole. The apparent K_m values were 0.4 millimolar for glucaric acid, 1.7 millimolar for galactaric acid, and with both acceptors as second substrates 20 millimolar for chlorogenic acid. The relative ratio of the V_max/K_m values for glucaric acid and galactaric acid was found to be 100:12. Substrate-competition experiments support the conclusion that one single enzyme is responsible for both the glucaric and galactaric acid ester formation with marked preference for glucaric acid. It is proposed that the enzyme be called chlorogenic acid:glucaric acid O-caffeoyltransferase (EC 2.3.1.-). The three caffeic acid-dependent enzyme activities involved in the formation of the glucaric and galactaric acid esters, the chlorogenic acid:glucaric acid caffeoyltransferase as the key activity as well as the caffeic acid:CoA ligase and the caffeoyl-CoA:quinic acid caffeoyltransferase as the preceding activities, were determined. The time course of changes in these activities were followed during development of the seedling in the cotyledons and growth of the young plant in the first and second leaf. The results from tomato seedlings suggest a sequential appearance of these enzymes.     

Purification and properties of S-adenosyl-L-methionine: caffeic acid O-methyltransferase from leaves of spinach beet (Beta vulgaris L).

1. An enzyme catalysing the methylation of caffeic acid to ferulic acid, using S-adenosyl-L-methionine as methyl donor, has been extracted from leaves of spinach beet and purified 75-fold to obtain a stable preparation. 2. The enzyme showed optimum activity at pH 6.5, and did not require the addition of Mg2+ for maximum activity. 3. It was most active with caffeic acid, but showed some activity with catechol, protocatechuic acid and 3,4-dihydroxybenzaldehyde. The Km for caffeic acid was 68 muM. 4. 4. The Km for S-adenosyl-L-methionine was 12.5 muM. S-Adenosyl-L-homocystein (Ki = 4.4 muM) was a competitive inhibitor of S-adenosyl-L-methionine. 5. The synthesis of S-adenosyl-L-homocysteine from adenosine and L-homocysteine and its consequent effect on caffeic acid methylation were demonstrated with a partially-purified preparation from spinach-beet leaves, which possessed both S-adenosyl-L-homocysteine hydrolase (EC 3.3.1.1) and adenosine nucleosidase (EC 3.2.2.7) activities. This preparation was also able to catalyse the rapid breakdown of S-adenosyl-L-homocysteine to adenosine and adenine; the possible significance of this reaction in relieving the inhibition of caffeic acid methylation by S-adenosyl-L-homocystein is discussed.     

Enzymatic synthesis and purification of aromatic coenzyme a esters

Two recombinant His-tagged proteins, a plant 4-coumarate:coenzyme A ligase (EC 6.2.1.12) and a bacterial benzoate:coenzyme A ligase (EC 6.2.1.25), were expressed in Escherichia coli and purified in a single step using Ni-chelating chromatography. Purified enzymes were used to synthesize cinnamoyl-coenzyme A (CoA), p-coumaroyl-CoA, feruloyl-CoA, caffeoyl-CoA, and benzoyl-CoA. Conversions up to 95% were achieved. Using a rapid solid-phase extraction procedure, the target CoA esters were isolated with yields of up to 80%. Structures were confirmed by analytical comparison with chemically synthesized reference compounds and electrospray ionization-mass spectrometry. The recombinant enzymes were stable for several months at -80 degrees C, thus providing a reliable and facile method to produce these delicate biological intermediates.     

Purification and substrate specifities of hydroxycinnamate: CoA ligase from anthocyanin-containing and anthocyanin-free carrot cells

Callus cells of Daucus carota L. have different phenylpropanoid pathways depending on the medium composition. Cells propagated on a medium with gibberellic acid do not accumulate cyanidin but incorporate [¹⁴C]phenylalanine into chlorogenic acid at a high rate. Cells grown on a medium free of gibberellic acid accumulate cyanidin in very large amounts. We here describe partial purification of hydroxycinnamate: CoA ligase, and its properties in these two cell lines. The enzymes extracted from the two cell populations had different substrate specifities: for that from anthocyanin-containing cells, p-coumaric acid was the best substrate, and caffeic acid and ferulic acid were also activated. With enzyme from anthocyanin-free cells, the lowest K_m values were obtained for caffeic acid, while ferulic acid had higher values, and p-coumaric acid was nearly inactive. The enzyme did not separate into isoenzymes during purification. Only on polyacrylamide gels the partially purified enzyme from anthocyanin-containing cells separated into three peaks, and that from anthocyanin-free cells, into only two peaks. This difference is discussed in the context of the lack of activity with p-coumaric acid in anthocyanin-free cells.Abbreviations GA₃ gibberellic acid     

4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL)--An enzyme of phenylpropanoid chain cleavage from Pseudomonas

The enzyme 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL), which catalyzes a hydration and two-carbon cleavage step in the degradation of 4-hydroxycinnamic acids, has been purified and characterized from Pseudomonas fluorescens strain AN103. The enzyme is a homodimer and is active with three closely related substrates, 4-coumaroyl-CoA, caffeoyl-CoA, and feruloyl-CoA (Km values: 5.2, 1.6, and 2.4 microM, respectively), but not with cinnamoyl-CoA or with sinapinoyl-CoA. The abundance of the enzyme reflects a low catalytic center activity (2.3 molecules s-1 at 30 degrees C; 4-coumaroyl-CoA as substrate).     

Clarification of cinnamoyl co-enzyme A reductase catalysis in monolignol biosynthesis of Aspen

Cinnamoyl co-enzyme A reductase (CCR), one of the key enzymes involved in the biosynthesis of monolignols, has been thought to catalyze the conversion of several cinnamoyl-CoA esters to their respective cinnamaldehydes. However, it is unclear which cinnamoyl-CoA ester is metabolized for monolignol biosynthesis. A xylem-specific CCR cDNA was cloned from aspen (Populus tremuloides) developing xylem tissue. The recombinant CCR protein was produced through an Escherichia coli expression system and purified to electrophoretic homogeneity. The biochemical properties of CCR were characterized through direct structural corroboration and quantitative analysis of the reaction products using a liquid chromatography-mass spectrometry system. The enzyme kinetics demonstrated that CCR selectively catalyzed the reduction of feruloyl-CoA from a mixture of five cinnamoyl CoA esters. Furthermore, feruloyl-CoA showed a strong competitive inhibition of the CCR catalysis of other cinnamoyl CoA esters. Importantly, when CCR was coupled with caffeoyl-CoA O-methyltransferase (CCoAOMT) to catalyze the substrate caffeoyl-CoA ester, coniferaldehyde was formed, suggesting that CCoAOMT and CCR are neighboring enzymes. However, the in vitro results also revealed that the reactions mediated by these two neighboring enzymes require different pH environments, indicating that compartmentalization is probably needed for CCR and CCoAOMT to function properly in vivo. Eight CCR homologous genes were identified in the P. trichocarpa genome and their expression profiling suggests that they may function differentially.     

The biosynthesis of feruloyltyramine in Nicotiana tabacum

The biosynthesis of feruloyltyramine in Nicotiana tabacum Xanthi n.c. leaves is achieved through the action of the enzyme feruloyl-CoA tyramine N-feruloyl-CoA transferase. Its activity is increased 5- to 8-fold following infection by tobacco mosaic virus at 20°. The enzyme is soluble, its MW is 45 000, and it can synthesize a wide range of amides due to its low specificity for cinnamoyl-CoA thioesters and aromatic amines. Its affinity for feruloyl-CoA fragments is also described.     

Substrate profiles and expression of caffeoyl coenzyme A and caffeic acid O-methyltransferases in secondary xylem of aspen during seasonal development

Seasonal expression of caffeoyl-CoA O-methyltransferase (EC 2.1.1.104) was analyzed in aspen developing secondary xylem in parallel with caffeate O-methyltransferase (EC 2.1.1.68). Enzyme activity and mRNA levels for both enzymes peaked in the middle of the growing season. These results strongly suggest that both forms of O-methyltransferase were actively participating in lignin precursor biosynthesis during the growing season. To determine the role of each enzyme form, xylem extracts from two days in the growing season were assayed with four substrates: caffeoyl-CoA, 5-hydroxyferuloyl-CoA, caffeate acid and 5-hydroxyferulic acid. Recombinant forms of caffeoyl-CoA and caffeate O-methyltransferase were also assayed with these substrates. The recombinant enzymes have different substrate specificity with the caffeoyl-CoA O-methyltransferase being essentially specific for CoA ester substrates with a preference for caffeoyl-CoA, while caffeate O-methyltransferase utilized all four substrates with a preference for the free acid forms. We suggest that caffeoyl-CoA O-methyltransferase is likely to be responsible for biosynthesis of lignin precursors in the guaiacyl pathway and may represent a more primitive enzyme form leftover from very early land plant evolution. Caffeate O-methyltransferase is more likely to be responsible for lignin precursor biosynthesis in the syringyl pathway, especially since it can catalyze methylation of 5-hydroxyferuloyl-CoA quite effectively. This latter enzyme form then may be considered a more recently evolved component of the lignin biosynthetic pathways of the evolutionarily advanced plants such as angiosperms.     

Biosynthesis of curcuminoids and gingerols in turmeric (Curcuma longa) and ginger (Zingiber officinale): identification of curcuminoid synthase and hydroxycinnamoyl-CoA thioesterases

Members of the Zingiberaceae such as turmeric (Curcuma longa L.) and ginger (Zingiber officinale Rosc.) accumulate at high levels in their rhizomes important pharmacologically active metabolites that appear to be derived from the phenylpropanoid pathway. In ginger, these compounds are the gingerols; in turmeric these are the curcuminoids. Despite their importance, little is known about the biosynthesis of these compounds. This investigation describes the identification of enzymes in the biosynthetic pathway leading to the production of these bioactive natural products. Assays for enzymes in the phenylpropanoid pathway identified the corresponding enzyme activities in protein crude extracts from leaf, shoot and rhizome tissues from ginger and turmeric. These enzymes included phenylalanine ammonia lyase, polyketide synthases, p-coumaroyl shikimate transferase, p-coumaroyl quinate transferase, caffeic acid O-methyltransferase, and caffeoyl-CoA O-methyltransferase, which were evaluated because of their potential roles in controlling production of certain classes of gingerols and curcuminoids. All crude extracts possessed activity for all of these enzymes, with the exception of polyketide synthases. The results of polyketide synthase assays showed detectable curcuminoid synthase activity in the extracts from turmeric with the highest activity found in extracts from leaves. However, no gingerol synthase activity could be identified. This result was explained by the identification of thioesterase activities that cleaved phenylpropanoid pathway CoA esters, and which were found to be present at high levels in all tissues, especially in ginger tissues. These activities may shunt phenylpropanoid pathway intermediates away from the production of curcuminoids and gingerols, thereby potentially playing a regulatory role in the biosynthesis of these compounds.     

Fungal elicitor-mediated responses in pine cell cultures

A tissue culture system has been developed to examine phenylpropanoid metabolism induced in pine tissues by an ectomycorrhizal symbiont. An elicitor preparation from the ectomycorrhizal fungus Thelephora terrestris Fr. induced enhanced phenolic metabolism in suspension cultured cells of Pinus banksiana Lamb., as indicated by tissue lignification and accumulation of specific methanol-extractable compounds in the cells. Induction of lignification was observed as early as 12 h after elicitation. The activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), the entry-point enzyme into phenylpropanoid metabolism, also increased within the same time-frame in elicited cells. Significant increases in PAL activity were evident by 6 h after elicitation, and, by 12 h after elicitation, PAL activity in elicited cells was ten times greater than that in the corresponding controls. Lignification of the elicited tissue was also accompanied by an increase in the activity of other enzymes associated with lignin synthesis, including caffeic acid O-methyl transferase (EC 2.1.1.46), hydroxycinnamate:CoA ligase (EC 6.2.1.12), cinnamyl alcohol dehydrogenase (EC 1.1.1.-), coniferin glucosidase (EC 3.2.1.21) and peroxidase (EC 1.11.1.7). The increase in total peroxidase activity was associated with a change in the pattern of soluble peroxidase isoforms. The pine cell culture-ectomycorrhizal elicitor system provides a good model for molecular analysis of the process of lignification in an economically important softwood species.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 4CL hydroxycinnamate:Coenzyme A ligase (EC 6.2.1.12) - CAD cinnamyl alcohol dehydrogenase (EC 1.1.1.-) - COMT S-adenosyl-l-methionine:caffeate O-methyl transferase (EC 2.1.1.46) - HPLC high-pressure liquid chromatography - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - TGA thioglycolic acid To whom correspondence should be addressedFinancial assistance for this work was provided by the Natural Sciences and Engineering Research Council of Canada.     

Purification,cloning, and properties of an acyltransferase controlling shikimate and quinate ester intermediates in phenylpropanoid metabolism

A protein hydrolyzing hydroxycinnamoyl-CoA esters has been purified from tobacco stem extracts by a series of high pressure liquid chromatography steps. The determination of its N-terminal amino acid sequence allowed design of primers permitting the corresponding cDNA to be cloned by PCR. Sequence analysis revealed that the tobacco gene belongs to a plant acyltransferase gene family, the members of which have various functions. The tobacco cDNA was expressed in bacterial cells as a recombinant protein fused to glutathione S-transferase. The fusion protein was affinity-purified and cleaved to yield the recombinant enzyme for use in the study of catalytic properties. The enzyme catalyzed the synthesis of shikimate and quinate esters shown recently to be substrates of the cytochrome P450 3-hydroxylase involved in phenylpropanoid biosynthesis. The enzyme has been named hydroxycinnamoyl-CoA: shikimate/quinate hydroxycinnamoyltransferase. We show that p-coumaroyl-CoA and caffeoyl-CoA are the best acyl group donors and that the acyl group is transferred more efficiently to shikimate than to quinate. The enzyme also catalyzed the reverse reaction, i.e. the formation of caffeoyl-CoA from chlorogenate (5-O-caffeoyl quinate ester). Thus, hydroxycinnamoyl-CoA:shikimate/quinate hydroxycinnamoyltransferase appears to control the biosynthesis and turnover of major plant phenolic compounds such as lignin and chlorogenic acid.     

Bile acid: CoASH ligases from guinea pig and porcine liver microsomes. Purification and characterization

A procedure for the purification of the enzyme bile acid:CoA ligase from guinea pig liver microsomes was developed. Activity toward chenodeoxycholate, cholate, deoxycholate, and lithocholate co-purified suggesting that a single enzyme form catalyzes the activation of all four bile acids. Activity toward lithocholate could not be accurately assayed during the earlier stages of purification due to a protein which interfered with the assay. The purified ligase had a specific activity that was 333-fold enriched relative to the microsomal cell fraction. The purification procedure successfully removed several enzymes that could potentially interfere with assay procedures for ligase activity, i.e. ATPase, AMPase, inorganic pyrophosphatase, and bile acid-CoA thiolase. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified ligase gave a single band of approximately 63,000 Mr. A molecular size of 116,000 +/- 4,000 daltons was obtained by radiation inactivation analysis of the ligase in its native microsomal environment, suggesting that the functional unit of the ligase is a dimer. The purified enzyme was extensively delipidated by adsorption to alumina. The delipidated enzyme was extremely unstable but could be partially stabilized by the addition of phospholipid vesicles or detergent. However, such additions did not enhance enzymatic activity. Kinetic analysis revealed that chenodeoxycholate, cholate, deoxycholate, and lithocholate were all relatively good substrates for the purified enzyme. The trihydroxy bile acid cholate was the least efficient substrate due to its relatively low affinity for the enzyme. Bile acid:CoA ligase could also be solubilized from porcine liver microsomes and purified 180-fold by a modification of the above procedure. The final preparation contains three polypeptides as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The three peptides range in size from 50,000 to 59,000, somewhat smaller than the guinea pig enzyme. The functional size of the porcine enzyme in its native microsomal environment was determined by the technique of radiation inactivation analysis to be 108,000 +/- 5,000 daltons. Thus, the functional form of the porcine enzyme also appears to be a dimer.