Caffeine synthase and related methyltransferases in plants
Caffeine synthase and related methyltransferases in plants
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DOI：
10.2741/1364
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发表时间：
2004-05-01
影响因子：
3.1
通讯作者：
Mizuno, K
中科院分区：
文献类型：
--
作者：
Kato, M;Mizuno, K
咖啡因（1，3，7-三甲基黄嘌呤）是一种嘌呤生物碱，在茶和咖啡中浓度很高，也存在于许多饮料中，如可口可乐。阐明咖啡因的生物合成途径，克隆与咖啡因产生相关的基因，不仅对研究嘌呤生物碱的代谢，而且对控制茶叶和咖啡中咖啡因的含量都是十分必要的。现有的数据支持黄嘌呤的操作？7-甲基黄嘌呤？7-甲基黄嘌呤？可可碱？咖啡因途径是咖啡因的主要途径。由于咖啡因生物合成途径包含三个S-腺苷-L-甲硫氨酸（SAM）依赖的甲基化步骤，N-甲基转移酶发挥重要作用。本文就嘌呤环甲基化的相关酶和基因作一综述。咖啡因合成酶是一种SAM依赖的甲基转移酶，参与咖啡因生物合成的最后两个步骤，最初是从茶树幼叶中纯化的。分离的cDNA称为TCS 1，由1，483个碱基对组成，编码369个氨基酸的蛋白质。随后，从咖啡中分离出编码咖啡因生物合成酶的同源基因。重组蛋白根据其底物特异性分为3类，即7-甲基黄嘌呤合酶、可可碱合酶和咖啡因合酶。预测了C. arabica的同源性在80%以上，而与C. sinensis。此外，它们与属于基序B'甲基转移酶家族的水杨酸羧甲基转移酶、苯甲酸羧甲基转移酶和茉莉酸羧甲基转移酶的氨基酸序列有40%的同源性，这些甲基转移酶是以基序B'取代基序B作为保守区的新型植物甲基转移酶。
Caffeine (1,3,7-trimethylxanthine) is a purine alkaloid present in high concentrations in tea and coffee and it is also found in a number of beverages such as coca cola. It is necessary to elucidate the caffeine biosynthetic pathway and to clone the genes related to the production of caffeine not only to determine the metabolism of the purine alkaloid but also to control the content of caffeine in tea and coffee. The available data support the operation of a xanthosine ? 7-methylxanthosine? 7-methylxanthine ? theobromine ? caffeine pathway as the major route to caffeine. Since the caffeine biosynthetic pathway contains three S-adenosyl-L-methionine (SAM) dependent methylation steps, N-methyltransferases play important roles. This review focuses on the enzymes and genes involved in the methylation of purine ring. Caffeine synthase, the SAM-dependent methyltransferase involved in the last two steps of caffeine biosynthesis, was originally purified from young tea leaves (Camellia sinensis). The isolated cDNA, termed TCS1, consists of 1,483 base pairs and encodes a protein of 369 amino acids. Subsequently, the homologous genes that encode caffeine biosynthetic enzymes from coffee ( Coffea arabica) were isolated. The recombinant proteins are classified into the three types on the basis of their substrate specificity i.e. 7-methylxanthosine synthase, theobromine synthase and caffeine synthase. The predicted amino acid sequences of caffeine biosynthetic enzymes derived from C. arabica exhibit more than 80% homology with those of the clones and but show only 40% homology with TCS1 derived from C. sinensis. In addition, they share 40% homology with the amino acid sequences of salicylic carboxyl methyltransferase, benzoic acid carboxy l methyltransferase and jasmonic acid carboxyl methyltransferase which belong to a family of motif B' methyltransferases which are novel plant methyltransferases with motif B' instead of motif B as the conserved region.