The methyltransferase domain of the Sudan ebolavirus L protein specifically targets internal adenosines of RNA substrates, in addition to the cap structure

Martin, Baptiste; Coutard, Bruno; Guez, Théo; Paesen, Guido C; Canard, Bruno; Debart, Françoise; Vasseur, Jean-Jacques; Grimes, Jonathan M; Decroly, Etienne

In addition to its cap-MTase activity, SUDV MTase harbors an unexpected MTase activity inducing viral epigenetic or epitranscriptomic RNA modifications on both capped and uncapped RNAs. We demonstrated that the SUDV MTase targets adenosines present within homo-and heteropolymeric RNA sequences at the 2'O position of the ribose. Unlike the n1 guanosine, internal guanosines are not methylated suggesting that substrate recognition is different for cap-dependent and cap-independent 2'O methylations. Interestingly, the structure of the closely related hMPV MTase lacks a cap-binding site such as that present in flaviviruses, coronaviruses and vaccinia virus where the cap is stacked between aromatic residues (26, 37, 41, 42) . As SUDV MTase+CTD (like its hMPV counterpart) recognizes both cap and uncapped RNAs with a similar affinity and all SUDV MTase activities are carried out by a single catalytic site, our results suggest that the domain has evolved away from the requirement of a cap-binding site.