Mechanisms of substrate recognition and N6-methyladenosine demethylation revealed by crystal structures of ALKBH5-RNA complexes.Kaur, S., Tam, N.Y., McDonough, M.A., Schofield, C.J., Aik, W.S.
(2022) Nucleic Acids Res 50: 4148-4160
- PubMed: 35333330
- DOI: https://doi.org/10.1093/nar/gkac195
- Primary Citation of Related Structures:
7V4G, 7WKV, 7WL0
- PubMed Abstract:
AlkB homologue 5 (ALKBH5) is a ferrous iron and 2-oxoglutarate dependent oxygenase that demethylates RNA N6-methyladenosine (m6A), a post-transcriptional RNA modification with an emerging set of regulatory roles. Along with the fat mass and obesity-associated protein (FTO), ALKBH5 is one of only two identified human m6A RNA oxidizing enzymes and is a potential target for cancer treatment. Unlike FTO, ALKBH5 efficiently catalyzes fragmentation of its proposed nascent hemiaminal intermediate to give formaldehyde and a demethylated nucleoside. A detailed analysis of the molecular mechanisms used by ALKBH5 for substrate recognition and m6A demethylation is lacking. We report three crystal structures of ALKBH5 in complex with an m6A-ssRNA 8-mer substrate and supporting biochemical analyses. Strikingly, the single-stranded RNA substrate binds to the active site of ALKBH5 in a 5'-3' orientation that is opposite to single-stranded or double-stranded DNA substrates observed for other AlkB subfamily members, including single-stranded DNA bound to FTO. The combined structural and biochemical results provide insight into the preference of ALKBH5 for substrates containing a (A/G)m6AC consensus sequence motif. The results support a mechanism involving formation of an m6A hemiaminal intermediate, followed by efficient ALKBH5 catalyzed demethylation, enabled by a proton shuttle network involving Lys132 and Tyr139.
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China.