IMR Press / FBL / Volume 9 / Issue 2 / DOI: 10.2741/1364

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Article
Caffeine synthase and related methyltransferases in plants
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1 Graduate School of Humanities and Sciences, Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo112-8610, Japan
2 Faculty of Bioresource Sciences, Akita Prefectural University, Akita City, Akita 010-0195, Japan
Front. Biosci. (Landmark Ed) 2004, 9(2), 1833–1842; https://doi.org/10.2741/1364
Published: 1 May 2004
Abstract

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 carboxyl 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.

Keywords
Caffeine
Caffeine synthase
Camellia sinensis
Coffea arabica
N-methyltransferase
S-adenosylL-methionine
Review
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