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Role of Serine 286 in cosubstrate binding and catalysis of a flavonol O-methyltransferase


Role of Serine 286 in cosubstrate binding and catalysis of a flavonol O-methyltransferase

Kornblatt, Jack A., Muzac, Ingrid, Lim, Yoongho, Ahn, Joong Hoon and Ibrahim, Ragai K. (2004) Role of Serine 286 in cosubstrate binding and catalysis of a flavonol O-methyltransferase. Biochemistry and Cell Biology, 82 (5). pp. 531-537. ISSN 0829-8211

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Ibrahim_BiochemCellBiol_2004.pdf - Published Version

Official URL: http://dx.doi.org/10.1139/o04-054


O-Methyltransferases catalyze the transfer of the methyl groups of S-adenosyl-L-methionine to specific hydroxyl groups of several classes of flavonoid compounds. Of the several cDNA clones isolated from a Chrysosplenium americanum library, FOMT3′ encodes the 3′/5′-O-methylation of partially methylated flavonols. The recombinant protein of another clone, FOMTx which differs from FOMT3′ by a single amino acid residue (Ser286Arg) exhibits no enzymatic activity towards any of the flavonoid substrates tested. Replacement of Ser 286 in FOMT3′ with either Ala, Leu, Lys or Thr, almost abolished O-methyltransferase activity. In contrast with FOMT3′, no photoaffinity labeling could be achieved using [14CH3]AdoMet with the mutant recombinant proteins indicating that Ser 286 is also required for cosubstrate binding. These results are corroborated by isothermal titration microcalorimetry measurements. Circular dichroism spectra ruled out any significant conformational differences in the secondary structures of both FOMT3′ and Ser286Arg. Modeling FOMT3′ on the structure of chalcone methyltransferase indicates that serine 286 is greater than 10 Å from any of the residues of the active site or the AdoMet binding site of FOMT3′. At the same time, residues 282 to 290 are conserved in most of the Chrysosplenium americanum OMTs. These residues form a large part of the subunit interface, and at least five of these residues are within 4 Å of the opposing subunit. It would appear, therefore, that mutations in Ser286 exert their influence by altering the contacts between the subunits and that these contacts are necessary for maintaining the integrety of the AdoMet binding site and active site of this group of enzymes.

Divisions:Concordia University > Faculty of Arts and Science > Biology
Item Type:Article
Authors:Kornblatt, Jack A. and Muzac, Ingrid and Lim, Yoongho and Ahn, Joong Hoon and Ibrahim, Ragai K.
Journal or Publication:Biochemistry and Cell Biology
Date:May 2004
  • Natural Sciences and Engineering Research Council
  • Korea Ministry of Science and Technology
Digital Object Identifier (DOI):10.1139/o04-054
Keywords:flavonoids, O-methyltransferase, photoaffinity labeling
ID Code:6774
Deposited On:13 Jul 2010 15:24
Last Modified:18 Jan 2018 17:29
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