A conserved mechanism of DEAD-box ATPase activation by nucleoporins and IP(6) in mRNA export

Superfamily 1 (SF1) and superfamily 2 (SF2) RNA helicases are ubiquitous mRNA-protein (mRNP) remodelling enzymes that play critical roles in all aspects of RNA metabolism1, 2. The SF2 DEAD-box ATPase Dbp5/Ddx19 functions in mRNA export and is thought to remodel mRNPs at the nuclear pore complex (NPC)3–8. Dbp5 is localized to the NPC via an interaction with Nup159/Nup2143–5, 8, 9 and is locally activated there by Gle1 together with the small-molecule inositol hexakisphosphate (IP(6)) 10, 11. Local activation of Dbp5 at the NPC by Gle1 is essential for mRNA export in vivo11, 12; however, the mechanistic role of Dbp5 in mRNP export is poorly understood and it is not known how Gle1(IP6) and Nup159 regulate the activity of Dbp5. Here we report structures of Dbp5 in complex with Gle1(IP6), Nup159/Gle1(IP6), and RNA. These structures reveal that IP(6) functions as a small-molecule tether for the Gle1-Dbp5 interaction. Surprisingly, the Gle1(IP6)-Dbp5 complex is structurally similar to another DEAD-box ATPase complex essential for translation initiation, eIF4G-eIF4A, and we demonstrate that Gle1(IP6) and eIF4G both activate their DEAD-box partner by stimulating RNA release. Furthermore, Gle1(IP6) relieves Dbp5 auto- regulation and cooperates with Nup159 in stabilizing an open Dbp5-intermediate that precludes RNA binding. These findings explain how Gle1(IP6), Nup159, and Dbp5 collaborate in mRNA export and provide a general mechanism for DEAD-box ATPase regulation by Gle1/eIF4G-like activators.