Identification of 8-methyladenosine as the modification catalyzed by the radical SAM methyltransferase Cfr that confers antibiotic resistance in bacteria
- 14 January 2009
- journal article
- Published by Cold Spring Harbor Laboratory in RNA
- Vol. 15 (2), 327-336
- https://doi.org/10.1261/rna.1371409
Abstract
The Cfr methyltransferase confers combined resistance to five different classes of antibiotics that bind to the peptidyl transferase center of bacterial ribosomes. The Cfr-mediated modification has previously been shown to occur on nucleotide A2503 of 23S rRNA and has a mass corresponding to an additional methyl group, but its specific identity and position remained to be elucidated. A novel tandem mass spectrometry approach has been developed to further characterize the Cfr-catalyzed modification. Comparison of nucleoside fragmentation patterns of A2503 from Escherichia coli cfr+ and cfr− strains with those of a chemically synthesized nucleoside standard shows that Cfr catalyzes formation of 8-methyladenosine. In addition, analysis of RNA derived from E. coli strains lacking the m2A2503 methyltransferase reveals that Cfr also has the ability to catalyze methylation at position 2 to form 2,8-dimethyladenosine. The mutation of single conserved cysteine residues in the radical SAM motif CxxxCxxC of Cfr abolishes its activity, lending support to the notion that the Cfr modification reaction occurs via a radical-based mechanism. Antibiotic susceptibility data confirm that the antibiotic resistance conferred by Cfr is provided by methylation at the 8 position and is independent of methylation at the 2 position of A2503. This investigation is, to our knowledge, the first instance where the 8-methyladenosine modification has been described in natural RNA molecules.Keywords
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