Flavin-Dependent Methylation of RNAs: Complex Chemistry for a Simple Modification

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• RNA methylation is a crucial and conserved post-transcriptional modification impacting RNA function and cellular fate.
• Methylation typically utilizes S-adenosyl-L-methionine, but a less common reductive pathway exists.

Purpose of the Study:

• To review the discovery and chemistry of flavoenzymes TrmFO and RlmFO, which catalyze reductive RNA methylation.
• To highlight the novel role of flavins as methyl transfer agents via a CH2=(N5)FAD iminium intermediate.
• To discuss the structural adaptations of these enzymes and the broader implications of flavin-dependent methylation.

Main Methods:

• Literature review focusing on flavoenzyme-catalyzed RNA methylation.
• Analysis of the chemical mechanism involving N5,N10-methylenetetrahydrofolate (CH2=THF) and flavin adenine dinucleotide (FAD).
• Discussion of enzyme structural dynamics during catalysis.

Main Results:

• Discovery of TrmFO and RlmFO enzymes catalyzing reductive methylation of transfer and ribosomal RNAs, respectively.
• Elucidation of a novel flavin-dependent methylation mechanism using CH2=THF and FAD, distinct from S-adenosyl-L-methionine.
• Identification of a CH2=(N5)FAD iminium intermediate and associated enzyme structural changes.

Conclusions:

• Flavins act as methyl group donors in a reductive methylation pathway, expanding the known roles of these cofactors.
• This flavin-dependent mechanism, exemplified by TrmFO and RlmFO, is more widespread than previously thought, potentially including DNA synthesis enzymes.