RNase L activating 2′–5′ oligoadenylates bind ABCF1, -3 and Decr-1

A notable signaling mechanism employed by mammalian innate immune signaling pathways uses nucleotide based second messengers such as 2′–3′-cGAMP and 2′–5′-oligoadenylates (2′–5′ OA), which bind and activate STING and RNase L, respectively. Interestingly, the involvement of nucleotide second messengers to activate antiviral responses is evolutionary conserved, evidenced by the identification of an antiviral cGAMP-dependent pathway in Drosophila . Using a mass spectrometry approach, we identified several members of the ABCF family in human, mouse, and Drosophila cell lysates as 2′–5′ OA binding proteins, suggesting an evolutionary conserved function. Biochemical characterization of these interactions demonstrates high-affinity binding of 2′–5′ OA to ABCF1, which depended on phosphorylated 2′–5′ OA and an intact Walker A/B motif of the ABC cassette of ABCF1. As further support for species-specific interactions with 2′–5′ OA, we additionally identified that the metabolism enzyme Decr1 from mouse, but not human or Drosophila cells forms a high-affinity complex with 2′–5′ OA. A 1.4 Å co-crystal structure of the mouse Decr1–2′–5′ OA complex explains high-affinity recognition of 2′–5′ OA and the mechanism of species-specificity. Despite clear evidence of physical interactions, we could not identify profound antiviral functions of ABCF1, ABCF3 or Decr1 or 2′–5′ OA-dependent regulation of cellular translation rates as suggested by the engagement of ABCF proteins. Thus, although the biological consequences of the here identified interactions need to be identified, our data suggests that 2′–5′ OA can serve as signaling hub to distribute a signal to different recipient proteins.