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

TitleStructure and mechanism of the rebeccamycin sugar 4'-O-methyltransferase RebM.
Publication TypeJournal Article
Year of Publication2008
AuthorsSingh S, McCoy JG, Zhang C, Bingman CA, Phillips GN, Thorson JS
JournalJ Biol Chem
Volume283
Issue33
Pagination22628-36
Date Published2008 Aug 15
ISSN0021-9258
KeywordsCarbazoles, Crystallization, Crystallography, X-Ray, Escherichia coli, Methyltransferases, Models, Molecular, Molecular Conformation, Protein Conformation, Recombinant Proteins, S-Adenosylhomocysteine, Staurosporine
Abstract

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.

DOI10.1074/jbc.M800503200
Alternate JournalJ. Biol. Chem.
PubMed ID18502766
PubMed Central IDPMC2504894
Grant ListAI52218 / AI / NIAID NIH HHS / United States
CA84374 / CA / NCI NIH HHS / United States
U19 CA113297 / CA / NCI NIH HHS / United States