Tuesday, December 23, 2008

ATP hydrolysis is required for DEAD-box protein recycling but not for duplex unwinding

Liu F, Putnam A, Jankowsky E.

Department of Biochemistry and Center for RNA Molecular Biology, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.

DEAD-box proteins, the largest helicase family, catalyze ATP-dependent remodeling of RNA-protein complexes and the unwinding of RNA duplexes. Because DEAD-box proteins hydrolyze ATP in an RNA-dependent fashion, the energy provided by ATP hydrolysis is commonly assumed to drive the energetically unfavorable duplex unwinding. Here, we show efficient unwinding of stable duplexes by several DEAD-box proteins in the presence of the nonhydrolyzable ATP analog ADP-beryllium fluoride. Another ATP analog, ADP-aluminum fluoride, does not promote unwinding. The findings show that the energy from ATP hydrolysis is dispensable for strand separation. ATP binding, however, appears necessary. ATP hydrolysis is found to be required for fast enzyme release from the RNA and multiple substrate turnovers and thus for enzyme recycling.