Metabolically capped RNAs contain nicotinamide adenine dinucleotide (NAD) groups or flavin adenine (FAD) groups at their 5' ends. DXO hydrolyzes NAD from the 5' ends of RNAs (an activity termed deNADding), yielding NAD+ and an uncapped, 5'-monophosphorylated RNA (inferred from the mouse homolog). DXO is then able to degrade the 5'-monophosphorylated RNA by 5'-3' exonucleolytic activity (inferred from the mouse homolog).
Metabolite caps also include dephospho-CoA (dpCoA), UDP-glucose, and others (Sharma et al. 2025, reviewed in Doamekpor et al. 2022). DXO can remove NAD (deNADding), FAD (deFADding), dpCoA (deCoAping), and UDP-glucose caps (Doamekpor et al. 2020). Separately, Nudix enzymes and XRNs can also have deNADding and/or deFADding activities (Grudzien-Nogalska et al. 2019, Sharma et al. 2020, Sharma et al. 2022).