2eg5
The structure of xanthosine methyltransferase
OverviewOverview
Caffeine (1,3,7-trimethylxanthine) is a secondary metabolite produced by certain plant species and an important component of coffee (Coffea arabica and Coffea canephora) and tea (Camellia sinensis). Here we describe the structures of two S-adenosyl-l-methionine-dependent N-methyltransferases that mediate caffeine biosynthesis in C. canephora 'robusta', xanthosine (XR) methyltransferase (XMT), and 1,7-dimethylxanthine methyltransferase (DXMT). Both were cocrystallized with the demethylated cofactor, S-adenosyl-L-cysteine, and substrate, either xanthosine or theobromine. Our structures reveal several elements that appear critical for substrate selectivity. Serine-316 in XMT appears central to the recognition of XR. Likewise, a change from glutamine-161 in XMT to histidine-160 in DXMT is likely to have catalytic consequences. A phenylalanine-266 to isoleucine-266 change in DXMT is also likely to be crucial for the discrimination between mono and dimethyl transferases in coffee. These key residues are probably functionally important and will guide future studies with implications for the biosynthesis of caffeine and its derivatives in plants.
About this StructureAbout this Structure
2EG5 is a Single protein structure of sequence from Coffea canephora. Full crystallographic information is available from OCA.
ReferenceReference
The structure of two N-methyltransferases from the caffeine biosynthetic pathway., McCarthy AA, McCarthy JG, Plant Physiol. 2007 Jun;144(2):879-89. Epub 2007 Apr 13. PMID:17434991 Page seeded by OCA on Sun May 4 02:30:03 2008