Abstract of the PDB Structure's related Publication:
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.
Dual-specificity enzyme that catalyzes methylation of both rRNA and tRNA. Two acronyms have been assigned to one protein in this case and they denote the activitiy on rRNA (RlmN) or on tRNA (TrmG). RlmN carries out the AdoMet-dependent methylation of an amidine carbon of an adenine target (formation of m2A) at position 2503 of the Peptidyl Transferase Center of 23S rRNA (in single stranded region between hairpins 89 and 90 of Domain V). TrmG is responsible for the m(2)A synthesis at purine 37 in a tRNA. The enzyme can utilize protein-free 23S rRNA as a substrate, but not the fully assembled large ribosomal subunit. The key recognition elements in the 23S rRNA are helices 90-92 and the adjacent single stranded RNA that encompasses A2503.RlmN belongs to Radical SAM superfamily and contains the characteristic cysteine-rich CX(3)CX(2)C motif. It is evolutionarily related to the enzyme Cfr of the Gram-positive Staphylococcus aureus catalyzing a similar reaction (formation of m8A) on the same target in rRNA A2503.
Cfr and RlmN contain a single [4Fe-4S] cluster, which directs two distinct reactivities for S-adenosylmethionine: methyl transfer by SN2 displacement and radical generation.
Biochemical and Computational Analysis of the Substrate Specificities of Cfr and RlmN Methyltransferases
Cfr and RlmN contain a single [4Fe-4S] cluster, which directs two distinct reactivities for S-adenosylmethionine: methyl transfer by SN2 displacement and radical generation.
Covalent Intermediate in the Catalytic Mechanism of the Radical S-Adenosyl-l-methionine Methyl Synthase RlmN Trapped by Mutagenesis.
Emerging themes in radical SAM chemistry.
Radical-mediated enzymatic methylation: a tale of two SAMS.
RlmN and Cfr are radical SAM enzymes involved in methylation of ribosomal RNA
RNA methylation by radical SAM enzymes RlmN and Cfr proceeds via methylene transfer and hydride shift.
Structural basis for methyl transfer by a radical SAM enzyme.
The Escherichia coli RlmN methyltransferase is a dual-specificity enzyme that modifies both rRNA and tRNA and controls translational accuracy.
The methyltransferase YfgB/RlmN is responsible for modification of adenosine 2503 in 23S rRNA.