title: Structural basis for methyl transfer by a radical SAM enzyme.
abstract: The radical S-adenosyl-L-methionine (SAM) enzymes RlmN and Cfr methylate 23S ribosomal RNA, modifying the C2 or C8 position of adenosine 2503. The methyl groups are installed by a two-step sequence involving initial methylation of a conserved Cys residue (RlmN Cys(355)) by SAM. Methyl transfer to the substrate requires reductive cleavage of a second equivalent of SAM. Crystal structures of RlmN and RlmN with SAM show that a single molecule of SAM coordinates the [4Fe-4S] cluster. Residue Cys(355) is S-methylated and located proximal to the SAM methyl group, suggesting the SAM that is involved in the initial methyl transfer binds at the same site. Thus, RlmN accomplishes its complex reaction with structural economy, harnessing the two most important reactivities of SAM within a single site.
authors.affiliation: Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Amie K
authors.initials: AK
authors.lastname: Boal
authors.forename: Tyler L
authors.initials: TL
authors.lastname: Grove
authors.forename: Monica I
authors.initials: MI
authors.lastname: McLaughlin
authors.forename: Neela H
authors.initials: NH
authors.lastname: Yennawar
authors.forename: Squire J
authors.initials: SJ
authors.lastname: Booker
authors.forename: Amy C
authors.initials: AC
authors.lastname: Rosenzweig
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D019143:Evolution, Molecular; D006860:Hydrogen Bonding; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012329:RNA, Bacterial / Q000378:metabolism; D012338:RNA, Ribosomal, 23S / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C539943:CFR protein, Staphylococcus aureus; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012338:RNA, Ribosomal, 23S; D012436:S-Adenosylmethionine; D008780:Methyltransferases; C558134:RlmN protein, E coli; D003545:Cysteine