Structure and mechanism of the rebeccamycin sugar 4'-O-methyltransferase RebM

J Biol Chem. 2008 Aug 15;283(33):22628-36. doi: 10.1074/jbc.M800503200. Epub 2008 May 23.


The 2.65-angstroms crystal structure of the rebeccamycin 4'-O-methyltransferase RebM in complex with S-adenosyl-l-homocysteine revealed RebM to adopt a typical S-adenosylmethionine-binding fold of small molecule O-methyltransferases (O-MTases) and display a weak dimerization domain unique to MTases. Using this structure as a basis, the RebM substrate binding model implicated a predominance of nonspecific hydrophobic interactions consistent with the reported ability of RebM to methylate a wide range of indolocarbazole surrogates. This model also illuminated the three putative RebM catalytic residues (His140/141 and Asp166) subsequently found to be highly conserved among sequence-related natural product O-MTases from GC-rich bacteria. Interrogation of these residues via site-directed mutagenesis in RebM demonstrated His140 and Asp166 to be most important for catalysis. This study reveals RebM to be a member of the general acid/base-dependent O-MTases and, as the first crystal structure for a sugar O-MTase, may also present a template toward the future engineering of natural product MTases for combinatorial applications.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Carbazoles / chemistry
  • Carbazoles / metabolism*
  • Crystallization
  • Crystallography, X-Ray
  • Escherichia coli / enzymology
  • Methyltransferases / chemistry*
  • Methyltransferases / genetics*
  • Methyltransferases / isolation & purification
  • Methyltransferases / metabolism
  • Models, Molecular
  • Molecular Conformation
  • Protein Conformation
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • S-Adenosylhomocysteine / metabolism
  • Staurosporine / chemistry
  • Staurosporine / metabolism


  • Carbazoles
  • Recombinant Proteins
  • rebeccamycin
  • S-Adenosylhomocysteine
  • Methyltransferases
  • rebeccamycin 4'-O-methyltransferase, Lechevalieria aerocolonigenes
  • Staurosporine

Associated data

  • PDB/3BUS