Nanometer-scale RNA protein clusters (RPCs) Foster Helicase Activity of DEAD-box eIF4A

Abstract

DEAD-box RNA helicases are central regulators of RNA metabolism, employing ATP-dependent mechanisms to remodel RNA structure and RNA-protein interactions, yet how helicase catalysis is coordinated with multi-subunit interactions between RNA and protein remains unresolved. Translation initiation helicase, eukaryotic initiation factor 4A (eIF4A), which acts as an intrinsically non-processive enzyme, is essential for unwinding structured mRNAs, relies on cofactors to achieve physiological activity. Here we uncover an unexpected RNA-helicase state of eIF4A, demonstrating that eIF4A forms nanometer-scale RNA-protein clusters (RPCs) of [~]2-5 MDa in presence of its physiological cofactors eIF4B and eIF4G, RNA and ATP under near-physiological concentrations. Using a single molecule approach, we directly resolve the formation of discrete clusters that recruit multiple copies of proteins with RNA upon ATP addition and show that RPC formation correlates with helicase activity in vitro. Further, we find eIF4B as a key determinant of this multi-subunit assembly. Its intrinsically disordered regions (IDRs) together with structured RNA-recognition motifs (RRMs) drive multivalent RNA-dependent clustering, critical for efficient helicase activity. Disrupting eIF4B-RNA interactions through a targeted point mutation (F139A) in the RRM reduces both the cluster size and the helicase activity, further establishing a functional link between cluster formation and catalytic activity. Consistent with these findings, in-cell diffusion measurements reveal markedly slower diffusion of wild-type eIF4B compared with the RNA-binding-deficient mutant, indicative of RPC formation within the cellular environment. Together, our results reveal regulated helicase clustering as a previously unrecognized characteristic of the translation initiation machinery, linking ATP-dependent DEAD-box helicase activity to nanometer-scale RNA-protein clusters and translation initiation regulation.