The first committed step reaction of caffeine biosynthesis: 7-methylxanthosine synthase is closely homologous to caffeine synthases in coffee (Coffea arabica L.).
In coffee and tea plants, caffeine is synthesized from xanthosine via a pathway that has three methylation steps. We identified and characterized the gene encoding the enzyme for the first methylation step of caffeine biosynthesis. The full-length cDNA of coffee tentative caffeine synthase 1, CtCS1, previously isolated by the rapid amplification of cDNA ends was translated with an Escherichia coli expression system and the resultant recombinant protein was purified using Ni-NTA column. The protein renamed CmXRS1 has 7-methylxanthine synthase (xanthosine:S-adenosyl-L-methionine methyltransferase) activity. CmXRS1 was specific for xanthosine and xanthosine 5'-monophosphate (XMP) could not be used as a substrate. The K(m) value for xanthosine was 73.7 microM. CmXRS1 is homologous to coffee genes encoding enzymes for the second and third methylation steps of caffeine biosynthesis.
Mizuno
Kouichi
K
Faculty of Bioresource Sciences, Akita Prefectural University, Akita City, 010-0195, Akita, Japan. koumno@akita-pu.ac.jp <koumno@akita-pu.ac.jp>
Kato
Misako
M
Irino
Fumi
F
Yoneyama
Naho
N
Fujimura
Tatsuhito
T
Ashihara
Hiroshi
H
D002110:Caffeine / Q000096:biosynthesis*; D003069:Coffee / Q000201:enzymology*; D007700:Kinetics; D008780:Methyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D003069:Coffee; D011994:Recombinant Proteins; D002110:Caffeine; C477002:7-methylxanthosine synthase; D008780:Methyltransferases; C120479:caffeine synthase