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ACS Chem Biol. 2013 Jul 19;8(7):1632-9. doi: 10.1021/cb400068k. Epub 2013 May 23.

Structural and functional characterization of CalS11, a TDP-rhamnose 3'-O-methyltransferase involved in calicheamicin biosynthesis.

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Center for Pharmaceutical Research and Innovation, University of Kentucky College of Pharmacy , Lexington, Kentucky 40536, United States.


Sugar methyltransferases (MTs) are an important class of tailoring enzymes that catalyze the transfer of a methyl group from S-adenosyl-l-methionine to sugar-based N-, C- and O-nucleophiles. While sugar N- and C-MTs involved in natural product biosynthesis have been found to act on sugar nucleotide substrates prior to a subsequent glycosyltransferase reaction, corresponding sugar O-methylation reactions studied thus far occur after the glycosyltransfer reaction. Herein we report the first in vitro characterization using (1)H-(13)C-gHSQC with isotopically labeled substrates and the X-ray structure determination at 1.55 Å resolution of the TDP-3'-O-rhamnose-methyltransferase CalS11 from Micromonospora echinospora. This study highlights a unique NMR-based methyltransferase assay, implicates CalS11 to be a metal- and general acid/base-dependent O-methyltransferase, and as a first crystal structure for a TDP-hexose-O-methyltransferase, presents a new template for mechanistic studies and/or engineering.

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