2eg5
From Proteopedia
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The structure of xanthosine methyltransferase
Overview
Caffeine (1,3,7-trimethylxanthine) is a secondary metabolite produced by, certain plant species and an important component of coffee and tea. Here, we describe the structures of two S-adenosyl-L-methione (SAM) dependant, N-methyltransferases that mediate caffeine biosynthesis in Coffea, canephora (robusta), xanthosine methyltransferase (XMT) and 1,7, dimethylxanthine methyltransferase (DXMT). Both were co-crystallized with, the demethylated cofactor, S-adenosyl-L-cysteine (SAH), and substrate, either xanthosine (XMT) or theobromine (DXMT). Our structures reveal, several elements that appear critical for substrate selectivity. S316 in, XMT appears central to the recognition of xanthosine. Likewise, a change, from Q161 in XMT to H160 in DXMT is likely to have catalytic consequences., A F266 to I266 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. Finally, we propose an enzymatic mechanism whereby XMT could, potentially generate 7-methylxanthine from xanthosine.
About this Structure
2EG5 is a Single protein structure of sequence from Coffea canephora with and as ligands. Full crystallographic information is available from OCA.
Reference
The Structure of Two N-methyltransferases from the Caffeine Biosynthetic Pathway., McCarthy AA, McCarthy JG, Plant Physiol. 2007 Apr 13;. PMID:17434991
Page seeded by OCA on Wed Jan 23 14:47:17 2008
