Unwinding cycle of DEAD-box helicases and activation of DbpA by HP92 RNA. (A) Schematic diagram of futile cycles (top) and productive unwinding cycles (bottom) of DEAD-box helicases. The helicase core (RecA_N domain blue, RecA_C domain cyan) alternates between an open conformation in the apo or ATP-bound state and a closed conformation in the presence of ATP and RNA. (B) Domain orientation of DbpA in the open (left) and closed state (right). The C-terminal RNA recognition motif (RRM) (gray) orients HP92 (red) such that the stem of HP92 forms favorable interactions with a positively charged patch (indicated by + signs) on the RecA_N domain in the closed state. This stabilizes the closed state and enables the recruitment of the substrate duplex (orange, located 5′ to HP92) to the active site of the helicase core.
