3rfa
X-ray structure of RlmN from Escherichia coli in complex with S-adenosylmethionine
Structural highlights
FunctionRLMN_ECOLI Specifically methylates position 2 of adenine 2503 in 23S rRNA and position 2 of adenine 37 in tRNAs. m2A2503 modification seems to play a crucial role in the proofreading step occurring at the peptidyl transferase center and thus would serve to optimize ribosomal fidelity. Unmodified tRNA is not a suitable substrate for RlmN, which suggests that RlmN works in a late step during tRNA maturation.[1] [2] [3] Publication Abstract from PubMedThe radical SAM (RS) 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 that SAM 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. Structural Basis for Methyl Transfer by a Radical SAM Enzyme.,Boal AK, Grove TL, McLaughlin MI, Yennawar NH, Booker SJ, Rosenzweig AC Science. 2011 Apr 28. PMID:21527678[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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